serious discussion of 5-ton speed increase via gearing (transmission, differential)

Reference:http://www.steelsoldiers.com/5-ton-up/38278-m39-series-5-ton-transmision-swaps-axle-info.html

Seriously, I'd like to do entertain the possibility of trans. swaps or gear upgrades to increase the M818's top speed.

Not wanting to hijack another thread, as many seem to involve engine swaps or other mods, other vehicles. I also don't really want to talk about huge tires.

Since I've got the M818 now, what options might there be to help get up to speed? I did not like the way the 53" tires made the truck handle on the highway in traffic. I put 11.00x20's on it, much better.

A friend suggested a "compound transmission", but I am not sure what that is, and have not seen anything else in one piece with a significantly better OD than the stock 6453.
There is no problem at all with power on this truck because I don't have a trailer behind it and don't plan to get one. It would be really groovy to be able to do 60 or 65 MPH without redlining. With the 53's, I ran 60 from Illinois to Texas and there was no problem at all with power. Redline was 63. Therefore I see no issue (yet) with accomplishing the same result through gearing.

redlines -OD ratio -top speed -transmission - speed @ 1800r -- speed@ 1900r
2100RPM - 1.00 OD - 41.0MPH - Spicer 6453 - in 4th gear (stock)
2100RPM - 0.78 OD - 52.5MPH - Spicer 6453 - OD 1800RPM=45MPH (stock)
2100RPM - 0.71 OD - 57.7MPH - transmission? - 1800RPM=49.5MPH, 1900RPM=52.2
2100RPM - 0.69 OD - 59.4MPH - transmission? - 1800RPM=50.9MPH, 1900RPM=53.8
2100RPM - 0.59 OD - 69.5MPH - transmission? - 1800RPM=59.6MPH, 1900RPM=62.9
2100RPM - 0.55 OD - 74.5MPH - transmission? - 1800RPM=63.8MPH, 1900RPM=67.4

So, what's really out there? In the M818, the driveline between the transfer and the rears is rather short, so the only real options are to use a different transmission and move the transfer back a little, or remove the transfer and install an aux. trans, which is less desirable.

M-35Tom did a nice gear set for the Deuce 3053A. Nothing like that exists for the M818 and maybe that's not the right answer for the M818. There is an answer somewhere, though. I realize this kind of thing costs money, so be it. The larger challenge is finding the right components to make it work without it being a Rube Goldberg or Southern Engineered project.

There is absolutely no intention of driving over 60MPH.

Really a taller OD all you will do is twist off the input shaft of the trans. Axle gearing is the best way to go. A 10 speed or whatever trans with different axles would be the cats rear.
Adding a brownie box will get you a little more speed but again the drive shafts will be spinning over 3K RPM along with the gears in the axles. There going to starve or airrate the oil at the speeds and poof.. there gone. Like what has been stated many times... The trucks are what they are. I you want more speed its time to get a different truck or do some heavy mods.

I would like to add..... I seen this on ebay. I am sure you could hack that in to the stock 5 ton frame. Semi's have some high gears.. 3.73 ish. I talked to a friend who works at nordgear and he said for a price they could cut a new gear set of the 5 ton to any ratio you wanted. That might be the way to go is to fine a rear set off a semi and have a gear cut for the front.

I remember another member posting that the M939 series t-case is not a 1:1 ratio in high range, it is (and I'm going off of a bad memory here) somewhere around .8 to .9 to 1. That would help you get a good ways towards where you want to be, and still keep the drivelines at very similar lengths.

As another bonus you would get rid of the sprag also, but the downside is the risk of damange when in reverse / low range.

A few of the Guntruckers have modded the 5tons and achieved some good speed. I've seen the actual trucks, seen pics of the added parts and heard the theology of how it works....BUT....

I ain't gonna drive no 23K pound(GT) over 55.
I think the steering, suspension, brakes etc are built for that speed...so that's what I'll stay with.

So maybe a compromise. Some 46 inch 395-80R20's and a newer tranny out of a semi truck like a 10 speed with an overdrive ratio like you want.

The primary goals which both ought be met are:
to run 60MPH
to not redline it.

53 (M818 redline) is getting dangerously slow on a stretch of 2 lane highway where the limit is 70. Because I live in Dallas and have to drive 40-80 miles to "fun places", I got to use those highways and they are full of yuppies and 18 wheelers. The issue is that I will cause a backup of miles, and trap the poor truck drivers and motor homes and business trailers, etc, behind me. The yuppies I don't care about, except that they will act stupid, cut off other trucks, and probably cause accidents.

1800 RPM is a good spot for that engine to run all day, but the 2100 redline (53MPH) is probably not, unless I am missing something. I don't like to redline engines and I don't drive my pickup truck 100MPH, even though it will do it all day long. 60 seems reasonable from a safety standpoint on-highway, and not redlining it seems good too.

It might be worth it, because I am keeping the truck, to see about getting gears cut for the axles. The truck is in real nice shape, very little rust, CARC as well, and I'd rather not hack up the suspension to change axles. I have not done anything to the truck that can not be undone should someone in the future hate what I have done and want to put a 5th wheel back on it. I am not going to waste money and overpay on this project but I don't expect this project to be completed in a short time or on the cheap. It definitely is not a cheap project. It took 4 years work on the M35 I had before it was to my satisfaction, and even then it still needed a couple things. That communications truck was a work of art and a great learning experience. I want to apply everything I learned from that one to this M818.

I am glad some good points have already been brought up.
Westech,
I would be interested in knowing more about the friend at Nordgear and what they could do. I thought about the transmission and what it can take. That is why I mentioned the possibility of a different transmission, but upon considering that everything would be spinning faster, diff gears might make more sense.

To go from 2100RPM@53MPH to 1800@60MPH is a 32% increase in (driveshaft) speed, so that is significant and from a friction drag standpoint alone, it is a waste of energy unless there are no other decent options.
I am guessing that twisting input shafts happens more frequently because people are getting impatient, not using 1st gear, or trying to hot rod the vehicles but I could be wrong. The intended use in my case is fairly easy-going, no 'wheeling. The engine is stock, won't be getting turned up. And I won't mind if it slows down on hills, let it slow down. I'm used to that anyway from the M35 with half the power.

To go from 2100RPM@53MPH to 1800@60MPH if my math is correct is like going from 6.44 to 4.88 gears in the axle. Not sure if that much change is feasable by changing only one pair of the gears in the Rockwell. I need to go back to the TM and understand.

for fun, 5th gear - @1800RPM : 2100RPM
6.44=45MPH : 53MPH
5.12=56MPH : 65MPH
4.88=59MPH : 69MPH
4.72=61MPH : 71MPH
4.11=70MPH : 81MPH

Sure these figures are imprecise because I am not going to any decimal places, but it is unimportant right now becaue any proposed ratio depends on what -can- be made. A couple of them are attractive for a 60MPH cruising speed.

I don't know the torque curve of the NHC250 either, anyone got it? Limits permitting, the best place for the cruising RPM ought to be determined by that.

98hd,
On the 939 T-case, that is interesting and would be somewhat inexpensive option, if it would really do the job. It would need to have at the very least a ratio of at least 1:1.25 to do the job (65MPH redline).

Papabear,
I am glad you brought up the gun trucks. I would like to know more about how the gun trucks were modified so I could judge for myself. It looks very interesting. I hope they drive them safely.

As with the M35, it is very likely I'll end up with semi tractor steer tires on the front like I put on the M35, in the end probably go to tubeless budd rims and regular 18 wheeler tires all round, but that is down the road. Except for a proposal to increase driving speed from 53 to 60, I am doing nothing that I know of that will impact safety.

As with the M35, I generally pay professional diesel truck mechanics to do any of what I consider safety related and heavy maintenance based on what I find when I inspect. If I don't feel up to inspecting something, I pay them to do it. (I got to find another shop though after the last job got out of hand; the work and parts quality was excellent but there were huge cost overruns on parts and labor I was not advised of, and it was very embarrassing and stressful to have to go argue this)

Is 60 safe? I think so having driven the 20K# (as configured) M35 with its much smaller brakes and suspension about 16K miles at 55-57, and anyone is welcome to disagree and suggest things, because safety is an important concern of mine.

I have no objection to 55 at all and will probably be happy to run 55. That was where I cruised the M35 with its 11.00x20's. I object only to redlining the M818 to get to 53 and driving that speed in these crazy highways. I'd welcome a discussion the differences in the weight, suspension and brakes, etc. on the trucks, although my only qualifying experience is with the deuce, having only driven the 1K miles or so in the M818 taking it home doing 55-60 on the 53" tires, said tires which I did not like. I think they are too wide, have non-stiff sidewalls, and the M818 as configured is too light for them. (others seem to like them, go figure)

I was trolling pirate4x4 and found this info on the 5T rockwell. Any info from there is in "quotes and white" and the thread itself is by spidr, King of Booty Fab:
http://www.pirate4x4.com/forum/showthread.php?t=784718

"The upper reduction in the diff is 2.45:1, has 11t pinion and a 27t ring gear.
Ring gear is 9".
Since these are 6.44:1 diffs, the lower reduction on the bullgear would be 2.63:1"

discussing available ratios:
"6.44, 8.88, and 10.26 .... i've heard of a couple of other ratios that came in civilian trucks, but that could just be a rumor"

BTW please don't take my long-winded post above as the norm, I just wanted to be clear on my goals. It does not -have- to be axle gears, that is just what I'm thinking of at the moment.

The small picture is from the post in question. I don't make a habit of using other's pics, but this one shows what is being discussed and how it's arranged so dummies like me can understand this differential's gears a little better. The large pic. I took at Memphis Eq. co. and anyone is welcome to use it.

There is a bunch more info in that thread. have to go back to it later.

The TMs did not say how many teeth the differential has. spidr gave the number is the quote there.

So, 2.45:1 top -> 2.63:1 bottom = 6.4435:1
& 11:21 teeth on top, -> ? on bottom

The bottom tooth ratio could be any of these with come close to 2.63:1
11:29 - possibly
14:37 - possibly
19:50 - possibly

Does anyone know the tooth counts on the bottom section of the axle?

im curious by what you ment by how the larger tires handeled. ive never heard anything bad about them since there what im getting i would like to hear your input

The 819 is a #36000 truck, on the stock 1200s, it will do 65 at tack, on flat ground, that being said, I try to keep it at 60 just to be a bit safer, the REAL problem is the F#$%%NG TRANS, the HOLE between 3rd and 4th sucks, it is a terrible road unit, a older style 8 or ten speed would be the FIX

ouverson engineering has a 4.90 gear set for the 2.5 ton axles, they might be able to make one for the 5 ton.

Custom gears are going to run you a *lot* unfortunately

I would say that a transmission with more speeds would be the answer, however. Regearing the axles, or replacing the tires, is going to increase the top speed sure, but it will also lug the engine more in the lower gears, all it does is shift the bias more towards high speeds.

What transmissions bolt up to the 465? I'm an idiot when it comes to nearly any motor except the AMC I4 and I6.

The real best answer of course would be to go with the shallowest axle gearing possible and make up for it with the transmission to keep driveshaft RPMs down. But that's gonna cost a bundle.

It just amazes me how everybody wants to go FAST in a 30 to 40 year truck that was designed for mainly off road with 25% on road use, these trucks are SAFE for the intended use and intended speed , the truck design is basically a late 40s/early50s to start with, most have a single wet brake system, thay were designed for the road speeds at that time, who would have thought a #80000 semi could go down the road doing 90 all day. This is why we have the 900 series (don't know if the deuce A3 has air brakes), because of the change in usage and hence speed (25% off road,75% on)
As I said before, to make you 5Ts a better driving truck, something HAS to be done about the crap off road trans.

Remember the saying SPEED KILLS especially in a 30 to 40 year truck.

Well thats my RANT for to day

kastein said:

Custom gears are going to run you a *lot* unfortunately

I would say that a transmission with more speeds would be the answer, however. Regearing the axles, or replacing the tires, is going to increase the top speed sure, but it will also lug the engine more in the lower gears, all it does is shift the bias more towards high speeds.

What transmissions bolt up to the 465? I'm an idiot when it comes to nearly any motor except the AMC I4 and I6.

The real best answer of course would be to go with the shallowest axle gearing possible and make up for it with the transmission to keep driveshaft RPMs down. But that's gonna cost a bundle.

Click to expand...

I am considering all the options. A transmission upgrade is not out of the question, provided the OD ratio is enough.

The truck has the Cummins 250, with a 2100RPM redline. If it had a multifuel with a redline at 2600, there would be no issues. Changing the engine to gain RPM is not a good option because the present engine is like new with 8000 miles on it and it runs like new.

It is also possible to consider entire axle swaps for the rears and re-gearing just the front, but that is not my first choice. I'd like to find out more about gears.

The reason I did not like the 16.00x20's was as stated above, such large tires amplify every little imperfection in the behavior of the truck. The 818 truck is light, only 23000 lbs or so, and each of those tires is rated 17,000 for a total capacity of 102,000. In my opinion there was not enough truck for the big balloonish tires, and it bounced all over the place. Lowering the pressure would have helped, but then it would not have been possible to use the truck at highways speeds of 55MPH. The speed vs air pressure tables are very clear in the datasheet for the tires. Others may have different experiences, but that was my exprience and opinion.

Since tires were brought up, I found this thread about tire sizes.
http://www.steelsoldiers.com/deuce/3788-m35-top-speed-increase.html
12.5x20 - 40.7"
9.00x20 - 40.9"
14.5x20 - 43.4"
11.00x20 - 43.5" - 136.659" circumference
12.00x20 - 44.5" - 139.800" circumference
395/85R20 - 46.7"

For even tire sizes (11.00, 14.00, 16.00) a quick rule of thumb is to double the number and then add 20" for the rim size. Using this theory:

11.00x20 = 42"
12.00x20 = 44"
14.00x20 = 48"
16.00x20 = 52"

The truck has 11.00x20's in it and redlines at 53MPH.
12.00x20's are 1.0234 larger in circumference/faster than 11.00x20's.
53MPH * 1.0234 is 54.24 MPH on 12.00x20's

I am curious about the M819 being run at 60 with a 65 redline. If it has a cummins, then the tires would have to be 23% larger than 11.00x20's, or 54", to go from 53 to 65. My tach shows 2100RPM at 53MPH with 11.00x20's. What is the difference in the M819 running gear vs the M818?

Are the tire sizes above valid?
Is the math correct?

Larger tires will eliminate duals. I wish to retain duals. I do not wish to use spacers, and thwe 14.00's would not in my opinion get the speed vs RPM where it needs to be.

I am pleased that people are ranting about others wanting to make their trucks go faster, and using emphasis and the like. It is sure to keep the discussion lively.

I don't understand though, how driving at 60 is so much different than 55 or 53. There is a difference in stopping distance, but 60/53 is only a 12% increase in actual speed.

Maybe the objection is against the -capacity- to redline at 65 or 70. I myself object to redlining the engine just to run the target speed of 60. I am pleased to concede the transmission sucks for road use, but I am willing to live with it, as Texas is reasonably flat and once up to speed, that's where she'll stay for 40-80 miles. The 818 is light with no tralier, there wss no problem at all doing 60 with the 52" tires and staying in 5th uphill, except that 60 was redline.

So, anyway, sure I would like to explore gears, and transmissions whether a swap of the main or an added box (with the understanding that the target cruising speed and therefore drveshaft revolutions, is 12% higher, regardless of a capacity to do more). The machine is seldom going offroad except at the ATV park where it will be my overnight fort, and if necessary, the fronts can even be disconnected, but for obvious reasons I would rather not. That is the last thing I want to do.

This is a Diesel Fitter project. Phase I is complete and the vehicle is here in Dallas. The 53" tires did not work out, necessitating this exploration of the drivetrain.

The goals are clear but there are still many ways to reach them. The timeline is open for now and it will take a few years to finish. Other things that need done are refurb of the 109 body, completing the diesel generator enclosure and plumbing, A/C the cab, A/C the body, install the radar and the communications electronics, finish the body with a fold down bunk and some other amenities, adapt the lift gate for loading ATVs, remote the lift gate, etc. a bunch of little stuff. No fuzzy dice or chrome.

73M819. I am not bashing you so please don't take what I am going to post as such. I agree that safety is of upmost importance.

I am from Colorado but have driven the roads outside of Dallas TX that he is describing. They are two lane blacktop farm to market roads. They are good roads right up to where the traffic is running 65 to 70 MPH in a long conga line. Normally I would say just pull over every once in a while and let the line go by. But it's not just that easy. The shoulders don't always allow for pull out of traffic. There are no accel/decel lanes. And the typical borrow pit just outside the blacktop with the occasional farm driveway. Not much room to pull out unless you come to a full stop. Which does the same thing to the line of traffic.

Then we can use the just let them pass argument. Problem with that is that the LEO's write tickets for obstruction of traffic to the person holding up the show. And with the commercial trucks the conga line gets accentuated, people get impatient and try and desperately pass creating unsafe conditions. The LEO's just want the line moving safely. And rightfully so.

So this is a case where faster is actually safer. It has nothing to do with stopping distance or capability to stop. In this case operation of the vehicle within 5 MPH of the flow of traffic is what is the safest thing to do. 60 MPH creates a scenario where the traffic is not held up too bad but still has the opportunity to pass.

In my opinion the easiest way to achieve the goal is to change the tranny to something that has a higher OD ratio. They should be commercially available and ALMOST a bolt in type of scenario. I have seen other posts on here that deal with the commercial tranny swaps. Just search for that with the search feature.

that's the problem 65-70, whats the speed limit, bet its not 65-70, if your doing the speed limit, your NOT going to get a ticket, now if your doing 35 in a 60 zone , yes you will if your holding up traffic if there is no where to pass.
Anybody that's wants to do 65-70 in these truck needs to have to really RETHINK, they were NOT designed for that use or speed, nor safe for that speed (if someone thinks it is, there kidding them self). these 1600s look good, but at 65-70,or for that matter any speed, besides the weight of the truck, there is a massive increase in rolling innursia (the 1600s act as a flywheel) for the brakes to overcome. remember speed kills, just hope no one here is the cause
this is one of my pet peves, IM DONE

as far as the 819 doing 60 and 65 redlined, I got that from my wife who was following me in her car, my speedo was saying the same thing, though I didnt beleive it till she told me her readings

We have this discussion in aviation circles all the time. I am guilty of it just as often as the next guy. We have a guy with a 140 Hp piper who wants to add a custom exhaust, wheel fairings, and all kinds of other speed mods. He will spend thousands to go 5 knots faster. Not worth it is my book. The best thing to do is to buy a plane designed to do what you are asking it to do. Some planes haul big loads and some go fast. Some do both and the price will prove it. I enjoy the process of thinking outside the box, but I would just like to echo the other guys in saying that the truck better stop as well as it goes.... upgrade the brakes first. Lets see a thread about air brake conversions along side the new top speed mods. Good luck in your quest! I've enjoyed reading so far.

I guess I'll throw my 2 cents in bc I have the experience in this area.

my 818 has 1600's and I love the way it drives. the stock 1100's were overloaded with the additions I made to the truck(winch and gun ring) blew 2 new front tires on the highway. they overheated at proper pressures.

I wanted more speed and a safer tire. 1600s gave me that.

power with them was just fine without hauling a load so when I need to move some weight I added the turbo. now I have power and speed even with the huge hole between 3rd and 4th.
could it be better sure it could. a better 10spd trans would be great but then it wouldn't seem right to me.

My 818b tips the scales empty at 24,000lbs. yesterday I moved 2 deuces on my 40' flatbed and GVW was about 70,000.

it seems to me that if you start to try and turn the driveline faster then lots of problems could arise and with big tires you simply don't do that. The whole driveline stays the same and you still get the speed that I wanted.

Keep in mind I keep my truck in tip top condition with all new brakes, hose's, and it stops on a dime, I can and have locked up those 1600's before.

Could I overheat the brakes if I wanted,, sure but then again with a little skill and common sense, it's kept in check. My 40' trailer has proper air brakes and it makes a huge difference.

I just put some 53"s on my 813, haven't got it on the frw yet. but the other day some jackwade cut me off at about 40 and I know my breaks will LOCK up all six tires now. Theres something about the sound that bigaxx tires make when they skid that make everyone around you back off, I should get out on the highway this weekend, I'll let you know how it does.

On the NDT 11.00's on both my 5 tons I can lock them up empty at speed no problem. I know these trucks are old but I have not had a problem stopping them. Do I leave a ton of room to stop anyway? Absolutely. I don't depend on the fact that I can lock up the brakes just to tailgate people. That lock up constitutes a panic stop type situation. Not how the truck should be driven.

On 11.00's I can only get 56 MPH out of both my 5 tons. The Cummin's 250's I have are governed at 2200 RPM.

IMO the 900 series 5 tons with the full airbrake have too much brake. How is that possible? What would make me say that? It is the fact that they have been installing anti-lock brakes in the trucks because they have had too many accidents because the brakes lock up and spin the truck out of control.

Last time I was on those farm to market roads the speed limit was 65.

And I beg to differ about the obstuction of traffic ticket being issued only if you are far too slow. My Dad was issued an obstucting traffic ticket and he was going THE speed limit exactly. He had his 25 foot boat on behind the pickup and there was a line of cars that could not pass as they were not able to get around the truck and boat. I was following in my crew cab with my 23 foot boat on. I was leaving enough room for people to be able to leap frog me and then pass him. But to the trooper that was not good enough. The Trooper pulled out from 10 cars back and pulled us both over. Dad got the ticket because he was in the lead. I got a warning.