Thinking about buying a 5 ton -- need advice please!

[G744]

Ummm...Most all the G744 drop-ins (the top loader Timkin/Rockwell units) have the same 6.44:1 ratio, as they're interchangeable between locations. Missile trucks used a gearset in the 10:1 range.

The Sprag unit runs free if everything is turning the SAME speed. They lock if the rears slip going forward in mud or some such traction-slipping event by 6% or more than the front. Vice-versa in reverse.

Sorry to rain on your parade about front gearing having different ratios.

G744

 

[msgjd]

2. Also, that's good to know on rolling back when starting on a hill. Obviously I try not to, but I'm also not perfect. As a side note, I don't have my CDL and am hoping to get away with not needing it, but I still need to call the DOT or find a trooper to talk to and make sure my understanding of the law is correct.

3. I bet that feeling the front engage and disengage as you describe is an interesting feeling.

I'm not sure how I'd know that the transfer case was engaging properly until it snows or maybe I find a mud puddle


9. One thing I like hearing about the Mack is it sounds like it does a lot better at low rpm than the Cummins does. Parts availability and price sounds like a major plus for the Cummins. I'm pretty sure I don't want a multifuel in a 5-ton though, which seems like what's in most of the M39 trucks I've seen

DougB

2: that's one of the things the hand brake is handy for .

26001# and up is the magic number regardless whether a vehicle has air brakes or not . The M39-series and M809-series are considered hydraulic brakes

although federalization was supposed to make all the rules standard in all states , they are not .. Some states are written "registered GVW", others go by the tag GVW , and as you have found, exceptions vary by state . a state's definition/interpretation of "commercial" is key

3: it is an odd feeling, it has everything to do with change of momentum... for example, at road speeds the slipping truck will all of a sudden enter supersonic forward pull as the G-force sinks you into the back of the seat .. but BS aside, OTR you can feel (barely) an increase in momentum as long as the front wheels have a good bite

for lack of a mud puddle or steep bank or gravel pile to test the sprag and transfer case, the difficult option would be to pull the driveshaft behind the transfer case and see if truck moves fwd/back ..

there is a compromise though, i will call it the Snap-On ratchet test. On level ground, set hand brake and chock rear tires fore & aft. Jack up one front tire just enough to clear the ground. Be careful, the tire might spin if residual driveshaft torque is present .. Test is done with truck engine off and air at full pressure

Step 1, rotate tire forward with tranny in reverse , it should lock up but should also spin freely in opposite direction ..
Step 2, rotate tire backwards with tranny in neutral or a fwd gear, it should lock up but spin freely in opposite direction

If the tire locks for both tests, the sprag is working ..

Now Dump the air and repeat the 2 steps.. The tire should rotate freely in both directions.
If tire locks up in either direction with no air present, the sprag cylinder is sticking ..

Also keep in mind sometimes poppets get worn and air gets put to the sprag cylinder when it shouldn't be, but sprag & poppet issues are simple issues. It's just that they are a PITA if you are short of time to deal with it

9: the 673 mack's have their highest torque at 1400-1600rpm, they are proven exceptional luggers, they will pull down to that rpm and just sit there most of the time ..

the cummins 855's however, do not like to be lugged .. i've literally heard rod knock develop after certain drivers constantly lugged loads up hills at under 1700rpm .. Myself, i've always tried to not let any-sized 855 cummins lug below 1800.. A wise man somewhere once said something like this; "lugging a cummins hurts it far faster than over-speeding it"

i have never been a fan of multifuel 5-tons .. Many of us in heavy transport ran to the gassers or the macks or the (not in winter) cummins' instead.. As mentioned, my armor BN had A2's that got stuffed with macks and got the OD tranny. The multifuels are a great match for a deuce , but the LDS in 5-tons lack for OTR performance .. There's an old railroad formula, "HP is proportionate to speed" .. At the time, the multifuel 5-tons had their reason to exist and they did the job they were expected to do . They just couldn't be expected to pull heavy uphill without holding up the rest of the show

 

[firefinder]

db72,
Should I have a CDL? Maybe a longer answer than you want to hear! In general, I would answer YES, you do need a Commercial Driver's License to operate a Commercial Motor Vehicle. But, there are more questions and it's not just a simple answer! There are also several things to consider besides the obvious. To add to the complexity, the answers vary from state to state and may be subjective based on the agency / enforcement officer's determination. Personally, I contact the enforcement agency of the state I will be traveling through and ask their requirements. In Missouri, that would be the Missouri State Highway Patrol, Commercial Vehicle Enforcement. Here are some questions to ask yourself before contacting your enforcement agency:

REGULATORY - Federal, State or Local regulations enforced by fines, etc.
1) Are you operating for hire?

Are you being compensated in any way to convey, operate or work with this vehicle? Is someone paying you to drive the vehicle? Has anyone compensated you with fuel or other form of compensation to transport items for them? Do you receive compensation for work from this vehicle?​

2) Do you own the vehicle you are operating and the items being transported?

Are you operating your own vehicle? Are you consigned or transporting goods for someone else?​

3) Are you operating a Commercial Motor Vehicle?

Federal Definition: Any self-propelled or towed vehicle used on public highways in interstate commerce to transport passengers or property, if it: 1) has a gross vehicle weight rating or gross vehicle weight of 10,001 pounds or more, or 2) is designed to transport more than 15 passengers (including the driver), or 3) is used to transport hazardous materials requiring placards.​

4) There is a list of other subcategories of that may include or exclude you from exemptions.

Is the vehicle used only as a farm vehicle? Does the vehicle classify as a recreational vehicle? Does the vehicle have air brakes?​

​

OTHER CONSIDERATIONS
1) Insurance - will your insurance company insure you without a CDL to operate this vehicle?
2) Liability - if you should be involved in an accident, even if the accident is not your fault, does operating this vehicle without a CDL increase your liability?

Sorry, for the long answer and definitely not trying to curb your enthusiasm! I really enjoy my 5 ton FMTV, but I was asked a lot of questions along the way to getting it registered and insured. I think it is important to be able to articulate these items before you operate a vehicle that could potentially be considered a Commercial Motor Vehicle. In your location, Illinois's and Iowa's requirements are different than Missouri's. I sent you a PM and hope I can clarify any additional questions you have.

Stay safe and stay in touch,

firefinder

 

[G744]

As far as your license is concerned, a lot depends on your state.

In AZ, we have an exemption from commercial restrictions: A 25-year or older Historic Vehicle plate.

I carry a copy of the Arizona Revised Statute outlining type of licensing, and have had to have a cop read it, usually chagrined.

One has to have insurance of course, but no scales, DL checks, weight fees, log books, compliant lighting, eTc.

My M54A1 runs that type of plate, 5 years for $90. It carries the same exemptions in all 50 states by reciprocity agreement.

I'd inquire at your DMV office if such licensing is available, and if it has exemptions. Lots easier that asking a cop for "His Opinion".

G744

 

[db72]

Ummm...Most all the G744 drop-ins (the top loader Timkin/Rockwell units) have the same 6.44:1 ratio, as they're interchangeable between locations. Missile trucks used a gearset in the 10:1 range.

The Sprag unit runs free if everything is turning the SAME speed. They lock if the rears slip going forward in mud or some such traction-slipping event by 6% or more than the front. Vice-versa in reverse.

Sorry to rain on your parade about front gearing having different ratios.

G744

You're certainly not raining on my parade. It makes a lot more sense to me that all of the axles have the same ratio. At least the only times I've heard of having different axle ratios front to rear would be if you were running different sized tires front to rear like you might see on a front wheel assist tractor. What I understood from the '5 ton t-case confusion' post was that there was some overdrive built into the front output on the transfer case:

Ok...The M-39 series 5-ton trucks all have transfer cases with over-running clutches for the front axle engegement. (Commonly known as a sprag clutch but usually not, most usually they are roller clutches, but still an over-running clutch.) The clutch engages either in the forward drive or rear drive position by connecting to the poppet valve assembly on the low/reverse shifter rail of the transmission. This is where it gets different from the 2-1/2 case. The 5-ton front drive actually has 3 positions; forward, reverse and NETURAL. The 2-1/2 case with the "sprag" only has forward and reverse to my knowledge. HOWEVER, the only way to access netural is to bleed off all air pressuer on the control cylinder. (The manual indicates to open the air bleed to reverse tow the 5-ton.)

Now, the valve that has been ADDED to your dash. It is not an uncommon alteration to install a front drive engage/disengage valve from a 2-1/2 to allow the 5-ton transfer to be bled of air and operate in the netural position. (I have one and recommend it.)

Other than the above, size and rated torque are the only other differences. They still have a 6% overdrive on the front shaft, but problems with the over-run clutch locking-up like the plague of the M-35 front drive (pre-air shift) just does not occur. [ I assume that the fact that just the front axle on the 5-ton has over 75% of the total weight of a 2-1/2 on it combined with the specific caution of "DO NOT ALLOW TRUCK TO ROLL BACK" has a lot to do with the dependability of the front drive system.

Hope this helps.

I'm still learning about these trucks so I really don't know one way or another. I suspect the only way for me to really understand the t-case would be to take one apart. Either way, thank you for the clarification!


DougB

 

[db72]

2: that's one of the things the hand brake is handy for .

26001# and up is the magic number regardless whether a vehicle has air brakes or not . The M39-series and M809-series are considered hydraulic brakes

although federalization was supposed to make all the rules standard in all states , they are not .. Some states are written "registered GVW", others go by the tag GVW , and as you have found, exceptions vary by state . a state's definition/interpretation of "commercial" is key

3: it is an odd feeling, it has everything to do with change of momentum... for example, at road speeds the slipping truck will all of a sudden enter supersonic forward pull as the G-force sinks you into the back of the seat .. but BS aside, OTR you can feel (barely) an increase in momentum as long as the front wheels have a good bite

for lack of a mud puddle or steep bank or gravel pile to test the sprag and transfer case, the difficult option would be to pull the driveshaft behind the transfer case and see if truck moves fwd/back ..

there is a compromise though, i will call it the Snap-On ratchet test. On level ground, set hand brake and chock rear tires fore & aft. Jack up one front tire just enough to clear the ground. Be careful, the tire might spin if residual driveshaft torque is present .. Test is done with truck engine off and air at full pressure

Step 1, rotate tire forward with tranny in reverse , it should lock up but should also spin freely in opposite direction ..
Step 2, rotate tire backwards with tranny in neutral or a fwd gear, it should lock up but spin freely in opposite direction

If the tire locks for both tests, the sprag is working ..

Now Dump the air and repeat the 2 steps.. The tire should rotate freely in both directions.
If tire locks up in either direction with no air present, the sprag cylinder is sticking ..

Also keep in mind sometimes poppets get worn and air gets put to an inappropriate side of the sprag cylinder, but sprag & poppet issues are simple issues. It's just that they are a PITA if you are short of time to deal with it

9: the 673 mack's have their highest torque at 1400-1600rpm, they are proven exceptional luggers, they will pull down to that rpm and just sit there most of the time ..

the cummins 855's however, do not like to be lugged .. i've literally heard rod knock develop after certain drivers constantly lugged loads up hills at under 1700rpm .. Myself, i've always tried to not let any-sized 855 cummins lug below 1800.. A wise man somewhere once said something like this; "lugging a cummins hurts it far faster than over-speeding it"

i have never been a fan of multifuel 5-tons .. Many of us in heavy transport ran to the gassers or the macks or the (not in winter) cummins' instead.. As mentioned, my armor BN had A2's that got stuffed with macks and got the OD tranny. The multifuels are a great match for a deuce , but the LDS in 5-tons lack for OTR performance .. There's an old railroad formula, "HP is proportionate to speed" .. At the time, the multifuel 5-tons had their reason to exist and they did the job they were expected to do . They just couldn't be expected to pull heavy uphill without holding up the rest of the show

2. Ahhh, I thought using the hand brake was cheating ! In all seriousness though, I'd hope that after driving the truck for a while I wouldn't need to use the hand brake to keep from rolling back, but I'll keep that in mind as I learn.

3. Excellent info on checking t-case operation! I think I may just print that out to have on hand when inspecting a truck (ideally before I bought it but definitely before driving much).

9. Again, excellent information. As I'd expect to have the truck on the road more than off, it sounds like I would be wise to stay away from the multifuel 5-tons strictly from the power perspective. I could see how one would perform perfectly acceptable in other situations, though.

It sounds like the Mack would be nice to have considering the 5 speed doesn't give you that many different options for keeping the rpms up. I have also heard that the Cummins are hard to start in the winter and that the Macks were a little easier which is certainly another plus. I suppose most of these trucks don't have block heaters - do they? I have heard people having good luck with the kind that you stick on with a big magnet, at least on smaller equipment. I would like to be able to drive the truck on the occasion where we got a big snow or if I needed to move something when it was cold outside.

If I do end up with a Cummins, I'll take the advice to keep the rpms up above 17-1800 rpm, especially on long pulls. I've heard that same advice from people talking about "steering wheel holders" killing 400 Big Cams from lugging them. I'm guessing that means you end up downshifting until you find a gear where it will about sit on the governor if you are climbing a long hill?


Thanks,

DougB

 

[db72]

db72,
Should I have a CDL? Maybe a longer answer than you want to hear! In general, I would answer YES, you do need a Commercial Driver's License to operate a Commercial Motor Vehicle. But, there are more questions and it's not just a simple answer! There are also several things to consider besides the obvious. To add to the complexity, the answers vary from state to state and may be subjective based on the agency / enforcement officer's determination. Personally, I contact the enforcement agency of the state I will be traveling through and ask their requirements. In Missouri, that would be the Missouri State Highway Patrol, Commercial Vehicle Enforcement. Here are some questions to ask yourself before contacting your enforcement agency:

REGULATORY - Federal, State or Local regulations enforced by fines, etc.
1) Are you operating for hire?

Are you being compensated in any way to convey, operate or work with this vehicle? Is someone paying you to drive the vehicle? Has anyone compensated you with fuel or other form of compensation to transport items for them? Do you receive compensation for work from this vehicle?​

2) Do you own the vehicle you are operating and the items being transported?

Are you operating your own vehicle? Are you consigned or transporting goods for someone else?​

3) Are you operating a Commercial Motor Vehicle?

Federal Definition: Any self-propelled or towed vehicle used on public highways in interstate commerce to transport passengers or property, if it: 1) has a gross vehicle weight rating or gross vehicle weight of 10,001 pounds or more, or 2) is designed to transport more than 15 passengers (including the driver), or 3) is used to transport hazardous materials requiring placards.​

4) There is a list of other subcategories of that may include or exclude you from exemptions.

Is the vehicle used only as a farm vehicle? Does the vehicle classify as a recreational vehicle? Does the vehicle have air brakes?​

​

OTHER CONSIDERATIONS
1) Insurance - will your insurance company insure you without a CDL to operate this vehicle?
2) Liability - if you should be involved in an accident, even if the accident is not your fault, does operating this vehicle without a CDL increase your liability?

Sorry, for the long answer and definitely not trying to curb your enthusiasm! I really enjoy my 5 ton FMTV, but I was asked a lot of questions along the way to getting it registered and insured. I think it is important to be able to articulate these items before you operate a vehicle that could potentially be considered a Commercial Motor Vehicle. In your location, Illinois's and Iowa's requirements are different than Missouri's. I sent you a PM and hope I can clarify any additional questions you have.

Stay safe and stay in touch,

firefinder

Very good information, both in your post and over the phone here a few minutes ago. Thank you very much! It does sound like I would be better off with a CDL, which I expected, so I will continue looking into that.


Thanks,

DougB

 

[db72]

As far as your license is concerned, a lot depends on your state.

In AZ, we have an exemption from commercial restrictions: A 25-year or older Historic Vehicle plate.

I carry a copy of the Arizona Revised Statute outlining type of licensing, and have had to have a cop read it, usually chagrined.

One has to have insurance of course, but no scales, DL checks, weight fees, log books, compliant lighting, eTc.

My M54A1 runs that type of plate, 5 years for $90. It carries the same exemptions in all 50 states by reciprocity agreement.

I'd inquire at your DMV office if such licensing is available, and if it has exemptions. Lots easier that asking a cop for "His Opinion".

G744

Those are good notes. Talking to firefinder, I was pointed in the direction of the Supervisor for Commercial Vehicle Enforcement for my local Highway Patrol, which I would expect to be a good resource for knowing how enforcement will work in my area.

I have heard of some states having certain exemptions for historic or military vehicles, though I'm not aware of one for Missouri. I agree that it wouldn't hurt to contact my local DMV. If I could get that type of plate, that would be fantastic considering commercial vehicle licensing is not cheap.


Thank you,

DougB

 

[msgjd]

It sounds like the Mack would be nice to have considering the 5 speed doesn't give you that many different options for keeping the rpms up. I have also heard that the Cummins are hard to start in the winter and that the Macks were a little easier which is certainly another plus. I suppose most of these trucks don't have block heaters - do they?

If I do end up with a Cummins, I'll take the advice to keep the rpms up above 17-1800 rpm, especially on long pulls. I've heard that same advice from people talking about "steering wheel holders" killing 400 Big Cams from lugging them. I'm guessing that means you end up downshifting until you find a gear where it will about sit on the governor if you are climbing a long hill?

Thanks,
DougB

Oh there's more gears to choose from than we actually need.. Once a driver learns how to use the shift points (per the dash tag) and use both the high and low sides of the transfer case when pulling heavy loads, the dreaded "3rd-4th hole" of the overdrive spicers can be avoided, . Depends on the load and the grade .. There's 4 sequential "half-splits' available when split-shifting the transfer case and 4th/5th gear.. Most drivers don't know about this, or perhaps don't bother with, nor need to utilize. But it's a real handy gear ratio sequence in the hills , especially with loads

If you're not trying to make time there's no shame in staying on the high side and getting forced to drop into the 3rd hole .. It will just mean you got an easy shift that 90% of 5-ton drivers do. You will pull the hill maybe slow enough to count butterflies while maybe sitting on the governor.. If the grade is enough, you may even have to drop into 2nd and count blades of grass.. Don't be alarmed when i pass you, it might take a minute but i will get past you, LOL , i will be in 5th Low as you're bogging down in 3rd high .. If you're forced down to a crawl in 2nd high, i will be passing you in 4th low

There is a commercial block heater than inserts in to one of the threaded waterjacket ports on commercial 855's , it's on the right rearward side. I believe this plugged port is also on the military blocks, but i would have to look-see .. It would be almost behind the muffler on an M809-series

BTW , G744 is 200% correct about the front axle ratio .. i ignored a little voice yelling at me when i got lost in ,the moment, and have corrected my post.. i am part of the confusion related to the % of "overdrive" created for the sprag to act like an overrunning clutch , and just how the "6%" of slippage of the rears is actually sensed by the sprag if the front axle ratio is the same .. I was overthinking it.. It's just that the sprag works like magic when the system is working properly

If and when you install the underdash front axle cutout valve mod, you probably should only use it when you have a problem .. The sprag system needs exercise to stay limber .. I know this because my trucks sit too much nowadays and the sprag cylinders stick sometimes until they get enough "pshhht - thunk" to be happy again

 

[G744]

Another thing about the M39-series and M809-series trucks is the transfer is fully synchronized, and it can (with sufficient practice) be used to split a shift on a hill so as not to loose too much speed. I've seen another Mack engined rig with the hi-lo lever arranged akin to a 5&3 shift setup, to that end.

In my experience, on flat ground an 809 may outrun my M54A1 on a good day. According to my portable GPS, it will top out at just 0ver 59 MPH with 14.00-20 singles.

On an incline of any degree, It'll eat his lunch.

 

[db72]

Oh there's more gears to choose from than we actually need.. Once a driver learns how to use the shift points (per the dash tag) and use both the high and low sides of the transfer case when pulling heavy loads, the dreaded "3rd-4th hole" of the overdrive spicers can be avoided, . Depends on the load and the grade .. There's 4 sequential "half-splits' available when split-shifting the transfer case and 4th/5th gear.. Most drivers don't know about this, or perhaps don't bother with, nor need to utilize. But it's a real handy gear ratio sequence in the hills , especially with loads

If you're not trying to make time there's no shame in staying on the high side and getting forced to drop into the 3rd hole .. It will just mean you got an easy shift that 90% of 5-ton drivers do. You will pull the hill maybe slow enough to count butterflies while maybe sitting on the governor.. If the grade is enough, you may even have to drop into 2nd and count blades of grass.. Don't be alarmed when i pass you, it might take a minute but i will get past you, LOL , i will be in 5th Low as you're bogging down in 3rd high .. If you're forced down to a crawl in 2nd high, i will be passing you in 4th low

There is a commercial block heater than inserts in to one of the threaded waterjacket ports on commercial 855's , it's on the right rearward side. I believe this plugged port is also on the military blocks, but i would have to look-see .. It would be almost behind the muffler on an M809-series

BTW , G744 is 200% correct about the front axle ratio .. i ignored a little voice yelling at me when i got lost in ,the moment, and have corrected my post.. i am part of the confusion related to the % of "overdrive" created for the sprag to act like an overrunning clutch , and just how the "6%" of slippage of the rears is actually sensed by the sprag if the front axle ratio is the same .. I was overthinking it.. It's just that the sprag works like magic when the system is working properly

If and when you install the underdash front axle cutout valve mod, you probably should only use it when you have a problem .. The sprag system needs exercise to stay limber .. I know this because my trucks sit too much nowadays and the sprag cylinders stick sometimes until they get enough "pshhht - thunk" to be happy again

Ahh I had considered that you could use the transfer case to split gears but I wasn't sure if that would be hard on it - especially downshifting from the high side to low side. I suppose there are some tricks to be learned about how to keep the t-case and transmission happy and in sync when "2 stick shifting".

Since I'm an enginerd (Mechanical Engineer) and my idea of fun one day when I was ~13 was to create a "Gear Ratio Calculations" spreadsheet, I can pretty quickly plug some numbers in and see that the jump from 4 High to 5 Low would be more attractive than 4 High to 3 High. The percent step between 4 High and 3 High being ~79% while between 4 High and 5 Low is ~56%. That also means you downshift 4 High to 5 Low at ~1350 rpm rather than 4 High to 3 High at ~1150 rpm (I know the dash tag says 1100 rpm). I put a little table below with speeds calculated with 53" tires since that would be easier for me to understand anyway. The speeds are at 2100 engine rpm in that gear. I'm assuming someone else has gone through the same exercise here before, but I actually had already started updating my spreadsheet, so oh well. There's always a chance someone other than me will find it useful .

Gear	Speed (mph)	Downshift Rpm	Gear	Speed (mph)	Downshift Rpm
1 Low	4​
2 Low	8​	1176​
3 Low	14​	1106​	1 High	8​
4 Low	26​	1173​	2 High	15​	1176​
5 Low	33​	1638​	3 High	29​	1106​
4 High	51​	1346​	4 High	51​	1173​
5 High	66​	1638​	5 High	66​	1638​

If someone thinks I've made an error above, please let me know.



I'd say that adding a block heater like the commercial 855s had would be on my (long) list of things to do then as well. Definitely worth looking into anyway.

I'm glad that we have things cleared up on the overdrive for the front axle - rather the lack thereof. It makes the most sense to me that everything would be geared the same, but I am certainly not an expert on these trucks or even transfer cases in general.

In that case, I'll put the front axle cutout valve mod lower on my list. That totally makes sense that if moving parts like that don't get plenty of exercise, they will get sticky. I do think it could be a handy feature in certain situations, like if I was having issues with it.


Thanks again for all of the great notes!

DougB

 

[db72]

Another thing about the M39-series and M809-series trucks is the transfer is fully synchronized, and it can (with sufficient practice) be used to split a shift on a hill so as not to loose too much speed. I've seen another Mack engined rig with the hi-lo lever arranged akin to a 5&3 shift setup, to that end.

In my experience, on flat ground an 809 may outrun my M54A1 on a good day. According to my portable GPS, it will top out at just 0ver 59 MPH with 14.00-20 singles.

On an incline of any degree, It'll eat his lunch.

Ahhh for some reason I was under the impression that the t-case was not synchronized. Excellent!

You are making me like the sound of the Mack more and more. I think I have enough posts to send you a PM now.


Thanks,

DougB

 

[98G]

Ahhh for some reason I was under the impression that the t-case was not synchronized. Excellent!

You are making me like the sound of the Mack more and more. I think I have enough posts to send you a PM now.


Thanks,

DougB

The Macks are generally considered rare and exotic and are more highly prized than their multifuel counterparts.

If you and Dennis end up making a deal that involves driving it from AZ to MO, let me know....Maybe I could provide a ride there and a chase vehicle back.

 

[db72]

The Macks are generally considered rare and exotic and are more highly prized than their multifuel counterparts.

If you and Dennis end up making a deal that involves driving it from AZ to MO, let me know....Maybe I could provide a ride there and a chase vehicle back.

That would be great! I think I've got quite a few things to figure out between now and then, but if the time comes I will keep you in mind.


Thank you,

DougB

 

[US6x4]

I suppose there are some tricks to be learned about how to keep the t-case and transmission happy and in sync when "2 stick shifting".

Gear	Speed (mph)	Downshift Rpm	Gear	Speed (mph)	Downshift Rpm
1 Low	4​
2 Low	8​	1176​
3 Low	14​	1106​	1 High	8​
4 Low	26​	1173​	2 High	15​	1176​
5 Low	33​	1638​	3 High	29​	1106​
4 High	51​	1346​	4 High	51​	1173​
5 High	66​	1638​	5 High	66​	1638​

I've heard it said that when split shifting with these that you make the low to high shift first like if you're going from 5-low to 4-high, you would shift the transfer case first (low to high) and then shift the transmission (higher to lower). All in the same shifting maneuver but whichever gearbox needs to go higher gets shifted first.

 

[msgjd]

Ahh I had considered that you could use the transfer case to split gears but I wasn't sure if that would be hard on it - especially downshifting from the high side to low side. I suppose there are some tricks to be learned about how to keep the t-case and transmission happy and in sync when "2 stick shifting".

Since I'm an enginerd (Mechanical Engineer) and my idea of fun one day when I was ~13 was to create a "Gear Ratio Calculations" spreadsheet, I can pretty quickly plug some numbers in and see that the jump from 4 High to 5 Low would be more attractive than 4 High to 3 High. The percent step between 4 High and 3 High being ~79% while between 4 High and 5 Low is ~56%. That also means you downshift 4 High to 5 Low at ~1350 rpm rather than 4 High to 3 High at ~1150 rpm (I know the dash tag says 1100 rpm). I put a little table below with speeds calculated with 53" tires since that would be easier for me to understand anyway. The speeds are at 2100 engine rpm in that gear. I'm assuming someone else has gone through the same exercise here before, but I actually had already started updating my spreadsheet, so oh well. There's always a chance someone other than me will find it useful .

Gear	Speed (mph)	Downshift Rpm	Gear	Speed (mph)	Downshift Rpm
1 Low	4​
2 Low	8​	1176​
3 Low	14​	1106​	1 High	8​
4 Low	26​	1173​	2 High	15​	1176​
5 Low	33​	1638​	3 High	29​	1106​
4 High	51​	1346​	4 High	51​	1173​
5 High	66​	1638​	5 High	66​	1638​

If someone thinks I've made an error above, please let me know.

DougB

the downshift trick (same goes with multifuel deuces) is take 5H to 4H as normal but then you avoid the 4th/3rd hole by hitting 5H , drop the transfer into neutral, double-clutch the rpms up and slide transfer into low range cleanly. . Then you're in 5L which is faster than 3H.. You have avoided the dreaded hole and have a half-step into 4L if need be, which is faster than 2H .. Some drivers put tranny in neutral before moving transfer to low but some transfer cases will whine when that's done, and some don't mind it.. I prefer to double-clutch the transfer case shift to match the tranny output shaft ratio with the transfer case output shaft ratio

I can take most hills around here in 5L where others would be in 3H (going slower) up against the pump .. Many of us have experienced there's very little hope to overcome the big step up into 4H while on any hill, whereas if instead climbing same in 5L , if there's enough reduction in the grade i can make the close step between 5L and 4H while still on the hill and then i'm gone see ya. In transportation we used to practice that quite a bit with each other on truck lane hills, seeing who could get around the other

as i mentioned, the method is only practical when heavily loaded .. I've also done it empty on very steep hills but it takes practice and a knowledge of matching rpm's to the gear ratios.. I grew up with a couple 1950's trucks with no synchro's.. Some hills are so steep that one can actually be worse off if trying to do a split and miss it .. It's not something you're going to want to play around on a hill right out of the gate .. If you want to play on the level, learn how to split the upshift sequence first and get good at it.. I use it every time i have a load .. 2L thru 5L, split into 4H and then hit 5H .. 4 nice half-splits right there on top .. Yes the dreaded 3rd/4th hole exists regardless of the transfer case position but its effect is not as severe when in low range

 

[db72]

I've heard it said that when split shifting with these that you make the low to high shift first like if you're going from 5-low to 4-high, you would shift the transfer case first (low to high) and then shift the transmission (higher to lower). All in the same shifting maneuver but whichever gearbox needs to go higher gets shifted first.

Seems like it would be easier on stuff that way, and keep you out of a scenario where you could over rev the engine. Good video!


Thanks,

DougB

 

[db72]

the downshift trick (same goes with multifuel deuces) is take 5H to 4H as normal but then you avoid the 4th/3rd hole by hitting 5H , drop the transfer into neutral, double-clutch the rpms up and slide transfer into low range cleanly. . Then you're in 5L which is faster than 3H.. You have avoided the dreaded hole and have a half-step into 4L if need be, which is faster than 2H .. Some drivers put tranny in neutral before moving transfer to low but some transfer cases will whine when that's done, and some don't mind it.. I prefer to double-clutch the transfer case shift to match the tranny output shaft ratio with the transfer case output shaft ratio

I can take most hills around here in 5L where others would be in 3H (going slower) up against the pump .. Many of us have experienced there's very little hope to overcome the big step up into 4H while on any hill, whereas if instead climbing same in 5L , if there's enough reduction in the grade i can make the close step between 5L and 4H while still on the hill and then i'm gone see ya. In transportation we used to practice that quite a bit with each other on truck lane hills, seeing who could get around the other

as i mentioned, the method is only practical when heavily loaded .. I've also done it empty on very steep hills but it takes practice and a knowledge of matching rpm's to the gear ratios.. I grew up with a couple 1950's trucks with no synchro's.. Some hills are so steep that one can actually be worse off if trying to do a split and miss it .. It's not something you're going to want to play around on a hill right out of the gate .. If you want to play on the level, learn how to split the upshift sequence first and get good at it.. I use it every time i have a load .. 2L thru 5L, split into 4H and then hit 5H .. 4 nice half-splits right there on top .. Yes the dreaded 3rd/4th hole exists regardless of the transfer case position but its effect is not as severe when in low range

I believe I would probably try to double clutch the transfer case in that scenario too. I double clutch other synchronized transmissions when I'm doing something different (like dropping 5th to 2nd to pass) because it seems like it would be better on the synchros in the long run.

I plan to practice all kinds of shifting like that on the flat before I go out and try to do new stuff on the highway. I sure don't want to miss a shift and then end up in 2nd or worse. Fortunately, around here most of the hills aren't super long. There is one that's pretty notorious, but I'll make sure I'm confident shifting before trying anything there. Knowing how to split 5L to 4H and back would be good to know though as I do plan to put a load on the truck occasionally.

I'm sure it's one of those things that as time goes on, I'll get better at it, and learn what to do in different situations. I'm a firm believer in learn by doing, but the information you all are giving me here sure helps!


Thank you,

Douglas Bross