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serious discussion of 5-ton speed increase via gearing (transmission, differential)
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The PIG Smith
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LOL...If I find TWO, complete, in running order, parked side by side xm757...I will buy them both and GIVE you the second one! HAHAHAHAHA
Are you holding your breath yet? <snicker>
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patrick, you may want to consider a special 6000 series spicer that most people do not know of. from about 1975 to 1985 some fire equipment had .66 od 5th. when i built my cat powered truck in 2002 they were still available as well as new trans parts. if you need i can look up the trans number, but you want to start with the trans from a 700 series ford i think. one that is new enough to have all the gears mounted on needle brngs. it will be a 6####CM as 1st and rev, while not syncro, are always in mesh. then you can just buy the new gears for 5th and have .66
if you want to know more call me.
tom
if you want to know more call me.
tom
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The time has come! Monday AM I take the beast over to Tidwell and we start the job of swapping the T-case!
Tom, I had looked at a 6000 spicer with the 0.66. This was also discussed with Mr. Tidwell over at Tidwell transmissions. (they do custom mods and such to 18-wheeler tractors so nothing like this is wierd to them - and they got all the big tools and fixtures)
.66 would make the 2100RPM redline at 62MPH instead of 52MPH. While it's not a bad idea, the T-case is already bought, and will make the redline 71MPH. To me, this gives me a lot of safety margin running 60MPH with the occasional sag to 50 and surge to 62, depending on hills, and the like.
Since there will be no towed or hauled load (M109 body), the maximum weight is a mere 23000. My goal is to stay off the stock redline and run 60-62MPH. If I hit a hill and need a lower gear, I can always go to 4th and just slow down, or even 3rd. I'm used to slowing down for hills, just turn on the flashers when I see the speed dropping to 45.
Stock 5-speed 2100RPM redline speeds for the M818:
7
12
23
40
52
- same redlines with that scary 939 transfer:
9.6
16.4
31
54
71
I think it will be OK. I won't be pulling stumps or pulling down houses, so a very low 1st is not that necessary.
There might be a combination of transmision and gears gears that could get closer to something like comfy 1900RPM@60 (instead of 1900@47MPH stock), but I have not found any, and Tidwell spent a lot of time with me going through transmission and gear manuals, they have been in the big truck transmission biz doing special mods and custom work for a few decades. So in addition to all the discussion here including your knowledge and others, my research, and going over the many choices based on gear sets and boxes in greays old transmission manuals, we have not seen anything that would place the 2100RPM redline at perhaps 65-66, the closest best choices seem to be 62 or 71. Since I really want to cruise at 60 and the goal is to stay off the redline for hours at a time, I thought the best choice was to go for the 71MPH redline and then turn the engine a little slower.
These are the speeds with the upcoming transfer case swap, notice my favorite highway speed range in yellow:
1478RPM=50MPH
1621RPM=55MPH
1768RPM=60MPH
1827RPM=62MPH
1916RPM=65MPH
2063RPM=70MPH
Anyway, wish me luck as the M8109 project takes one step further. I'll try to get pics as we go. I think it will take us about 30 hours total, so maybe a week to get it done. The biggest concern so far from their side is the air lines and servos, I'll have to help there as to where the lines went, will go, and what they do.
One thing I will need to get a holt of is an under-dash switch and valve for the front axle engagement, like in the M35. That was an automatic function in the M939.
The 818's t-case is sprag and requires air signals from the transmission, but the 939 is geared so that part of it seems simple.
For some reason, "Millenium 5-Ton" does not have the same ring to it as "Millenium Deuce".
Tom, I had looked at a 6000 spicer with the 0.66. This was also discussed with Mr. Tidwell over at Tidwell transmissions. (they do custom mods and such to 18-wheeler tractors so nothing like this is wierd to them - and they got all the big tools and fixtures)
.66 would make the 2100RPM redline at 62MPH instead of 52MPH. While it's not a bad idea, the T-case is already bought, and will make the redline 71MPH. To me, this gives me a lot of safety margin running 60MPH with the occasional sag to 50 and surge to 62, depending on hills, and the like.
Since there will be no towed or hauled load (M109 body), the maximum weight is a mere 23000. My goal is to stay off the stock redline and run 60-62MPH. If I hit a hill and need a lower gear, I can always go to 4th and just slow down, or even 3rd. I'm used to slowing down for hills, just turn on the flashers when I see the speed dropping to 45.
Stock 5-speed 2100RPM redline speeds for the M818:
7
12
23
40
52
- same redlines with that scary 939 transfer:
9.6
16.4
31
54
71
I think it will be OK. I won't be pulling stumps or pulling down houses, so a very low 1st is not that necessary.
There might be a combination of transmision and gears gears that could get closer to something like comfy 1900RPM@60 (instead of 1900@47MPH stock), but I have not found any, and Tidwell spent a lot of time with me going through transmission and gear manuals, they have been in the big truck transmission biz doing special mods and custom work for a few decades. So in addition to all the discussion here including your knowledge and others, my research, and going over the many choices based on gear sets and boxes in greays old transmission manuals, we have not seen anything that would place the 2100RPM redline at perhaps 65-66, the closest best choices seem to be 62 or 71. Since I really want to cruise at 60 and the goal is to stay off the redline for hours at a time, I thought the best choice was to go for the 71MPH redline and then turn the engine a little slower.
These are the speeds with the upcoming transfer case swap, notice my favorite highway speed range in yellow:
1478RPM=50MPH
1621RPM=55MPH
1768RPM=60MPH
1827RPM=62MPH
1916RPM=65MPH
2063RPM=70MPH
Anyway, wish me luck as the M8109 project takes one step further. I'll try to get pics as we go. I think it will take us about 30 hours total, so maybe a week to get it done. The biggest concern so far from their side is the air lines and servos, I'll have to help there as to where the lines went, will go, and what they do.
One thing I will need to get a holt of is an under-dash switch and valve for the front axle engagement, like in the M35. That was an automatic function in the M939.
The 818's t-case is sprag and requires air signals from the transmission, but the 939 is geared so that part of it seems simple.
For some reason, "Millenium 5-Ton" does not have the same ring to it as "Millenium Deuce".
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Last edited:
Hammer
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What I like about those gear ratios is that you can do 54 mph at redline in 4th gear. That should really help have decent speeds on the hills if need be.
Can't wait to see how this one turns out...
Can't wait to see how this one turns out...
kastein
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hmmmm... I like the way this is going.
How much did the new tranny run you? Might have already been posted, I seem to have forgotten.
I am still thinking about adding an auxiliary OD tranny in the rear driveshaft of mine and converting the T138 to air shift though. At the very least I'd like to airshift the T138, just can't find a manual that shows how it's assembled internally so I can get an idea of what will be necessary before opening it up.
How much did the new tranny run you? Might have already been posted, I seem to have forgotten.
I am still thinking about adding an auxiliary OD tranny in the rear driveshaft of mine and converting the T138 to air shift though. At the very least I'd like to airshift the T138, just can't find a manual that shows how it's assembled internally so I can get an idea of what will be necessary before opening it up.
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With 1621rpm for 55 to 1827rpm for 62 makes me wonder if this rpm is LOW for OPP. power for the 250,. with 1621, as soon as power is called for, a down shift is called for. 1800 is not much better. it just seems that the 250 runs best between 1900 and 2000
just my thoughts
"just can't find a manual that shows how it's assembled internally so I can get an idea of what will be necessary before opening it up"
The tm-260-34p, and the g-744 ord-9 has what your looking for
just my thoughts
"just can't find a manual that shows how it's assembled internally so I can get an idea of what will be necessary before opening it up"
The tm-260-34p, and the g-744 ord-9 has what your looking for
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gimpyrobb
dumpsterlandingfromorbit!
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T-case, not trans.
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I have thought about that. The engine I got seems to have pretty flat torque from 1500 up. I could be wrong, have not seen a torque curve on the NC250 engine.
I don't think 1500 could be considered 'lugging', and for sure there is that awful 3-4 hole to consider where the pickup will be about 1100. The hole does not look bad on the chart, but the chart axis is RPM, so I added another chart to the right showing torque numbers (not curves). I don't have a real curve for the 250. One would be helpful!
Is the chart clear? The board keeps sizing it down into unusefulness, refuzing the zipfile, and changing everything JPGs. annoyance! How an I supposed to communicate!
All are the same chart. Try the PDF.
The setup might not be good for everywhere, but in Texas the roads are mostly very flat and very long. Same can be said for some other lands as well.
The charts are wrong because we know the torque at 1500RPM is about 650 FT LBS
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kastein
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yep... I ninja edited it just after you quoted this apparently
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The case is in. It is narrower than the original, physically a bit smaller but that should not be an issue if it can push a 939 it can push an 818. Brackets had to be made to mount it up, and at this point the shift linkage has been done. The parking brake is being worked on now. It is on the other side from the original. The front driveshaft has to be lengthened a little. Pictures will come after the job is done.
spicergear
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I’m chocking this info away so maybe the 475hp ‘Silver 92’ Detroit and RTO 12513 OD I've been saving for a 5 ton may work in stock form without having to flop gears in the transmission for a taller overdrive making it and RTOO ßdouble overdrive tranny. With the M939 t-case in high/OD and my Road Range 13 speed in 8th overdrive (.87:1) the combination of those two .13 + the .268 t-case OD = .398:1 overall high gear, high range ratio. That’s a near 40% overdrive!
http://www.steelsoldiers.com/5-ton-up/51175-m939-speed-mystery-solved.html
6.44 R&P, 46” tire, 65mph, .60 OD = 1835rpm
6.44 R&P, 48” tire, 65mph, .60 OD = 1758rpm
6.44 R&P, 52” tire, 65mph, .60 OD = 1623rpm
Are we having fun yet?
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Today as a matter of fact...
4th seems like the old 5th.
60MPH was as expected 1800RPM.
City streets at 30-45 are pleasant in 4th.
5th is great on open road as we have in Texas.
There is slowing down to about 45 on inclines but I did not have to downshift.
I have no objection to doing so if the speed drops below 45 as would be the case no matter what.
Note the transfer case shift lever angular travel in the M818 is much less than in the 900 series and the 1138 case has a long throw on the shift rod. This means that the 900 case is quite a bit harder to shift using M35 mechanicals.
There is added to the dash an air switch for front axle engagement.
There is added to the dash an air switch to lock the case in HI or LO.
In the 900, the case is to be locked in when the truck is not in neutral. That may be due to the automatic transmission.
I'll post the drivetrain pr0n later.
I still cherish the memory of my dearly departed old cat of many years, Abby the siamese tabby, but the avatar has to change now. The bite marks will remain.
4th seems like the old 5th.
60MPH was as expected 1800RPM.
City streets at 30-45 are pleasant in 4th.
5th is great on open road as we have in Texas.
There is slowing down to about 45 on inclines but I did not have to downshift.
I have no objection to doing so if the speed drops below 45 as would be the case no matter what.
Note the transfer case shift lever angular travel in the M818 is much less than in the 900 series and the 1138 case has a long throw on the shift rod. This means that the 900 case is quite a bit harder to shift using M35 mechanicals.
There is added to the dash an air switch for front axle engagement.
There is added to the dash an air switch to lock the case in HI or LO.
In the 900, the case is to be locked in when the truck is not in neutral. That may be due to the automatic transmission.
I'll post the drivetrain pr0n later.
I still cherish the memory of my dearly departed old cat of many years, Abby the siamese tabby, but the avatar has to change now. The bite marks will remain.
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gimpyrobb
dumpsterlandingfromorbit!
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SWEET! Glad it worked out for you. How did you fix the driveshaft issue? I remember you sent an email looking for a 900 series shaft.
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The trans-transfer intershaft was redone with a special end worked out by a machinist. Pictures would be best. The yoke on the 900 transfer case T-1138 was much larger than the yoke on the original shaft. the 800 series with the T-138 case have smaller yokes there.
I would rather encourage this thread to continue with a serious discussion of 5-ton speed increase via gearingand post the pics of this completed work in another thread, linking to this one.
I do not believe that 5-ton pre-900 trucks should be driven especially fast nor appreciably laden when being driven much over 45-50. I do believe that getting a redlined 50 MPH truck safely up to 55-60MPH at 80-85% of redline is do-able and prudent as long as all of the running gear is well maintained importantly the brakes and tires. The military tires are only rated for 55, so any increase above that should be met with a change to OTR semi tractor tires. The goal of this entire post is to help find ways to stay off the Cummins 2100RPM redline yet move along at 55-60. The multifuels are not excluded, i just don't happen to have one; let them be talked about as well.I believe the goal of "5-ton speed increase via gearing" has been reasonably well accomplished, but only in one manner.
I hope others will work with the many other solutions available to help the 800 series do a little better. It can't hurt the fuel economy either.
Sadly, in some parts of the USA, it is crowded and small with few open roads and as few wide blue skies. In those places, maybe this topic means little. In Texas, it means everything. Especially to the mile of cars trapped behind you in the slow lane of I-80 halfway to Louisiana!
I talked to a mechanic on the phone at Cummins a few weeks ago and was told the torque curve is intended to be flat from as low as 1500 to 2100 depending on the pump, and that the engine operating range should good at 1500-2100. I still want to find documentation about the operating range.
Upsetting things have been said about "sucking down liners" at low RPMs and also it was said that the engine wants to be run at 1900-2000. Can the range be so narrow? (Nothing is said in the TM IIRC and that is a "dummies" book if there ever was one, explaining almost everything in great detail)
I am not going to dispute any diesel mechanics on these subjects but I do ask for any sort of documentation, individual's reports, mechanic's notes, anything, that will help to better quantify the service characteristics of the NHC250 engine. Those belong in this topic.
I would rather encourage this thread to continue with a serious discussion of 5-ton speed increase via gearingand post the pics of this completed work in another thread, linking to this one.
I do not believe that 5-ton pre-900 trucks should be driven especially fast nor appreciably laden when being driven much over 45-50. I do believe that getting a redlined 50 MPH truck safely up to 55-60MPH at 80-85% of redline is do-able and prudent as long as all of the running gear is well maintained importantly the brakes and tires. The military tires are only rated for 55, so any increase above that should be met with a change to OTR semi tractor tires. The goal of this entire post is to help find ways to stay off the Cummins 2100RPM redline yet move along at 55-60. The multifuels are not excluded, i just don't happen to have one; let them be talked about as well.I believe the goal of "5-ton speed increase via gearing" has been reasonably well accomplished, but only in one manner.
I hope others will work with the many other solutions available to help the 800 series do a little better. It can't hurt the fuel economy either.
Sadly, in some parts of the USA, it is crowded and small with few open roads and as few wide blue skies. In those places, maybe this topic means little. In Texas, it means everything. Especially to the mile of cars trapped behind you in the slow lane of I-80 halfway to Louisiana!
I talked to a mechanic on the phone at Cummins a few weeks ago and was told the torque curve is intended to be flat from as low as 1500 to 2100 depending on the pump, and that the engine operating range should good at 1500-2100. I still want to find documentation about the operating range.
Upsetting things have been said about "sucking down liners" at low RPMs and also it was said that the engine wants to be run at 1900-2000. Can the range be so narrow? (Nothing is said in the TM IIRC and that is a "dummies" book if there ever was one, explaining almost everything in great detail)
I am not going to dispute any diesel mechanics on these subjects but I do ask for any sort of documentation, individual's reports, mechanic's notes, anything, that will help to better quantify the service characteristics of the NHC250 engine. Those belong in this topic.
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gimpyrobb
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Stan
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Glad to hear it worked out.
jwaller
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very cool my friend. now I'm wanting to give it a try. wonder what this xcase and my 1600's would do? 80mph?