transmission swap

[green goat]

I won an M925a2 a few months back and like the truck but not too happy with the Allison, I miss shifting. I have been playing with the idea of swapping the trans. out with a five speed from an M54 that I parted out. I'm not sure if the manual from the multi-fuel will hold up to the Cummins or if I need to find another donor. Another option I had thought of was robbing the trans from an 800 series with a Cummins so that it would (or should) bolt up to my engine. I'm still learning my way around this truck and though it wouldn't be original anymore atleast it would be all military parts. Any thoughts, tips, or opinions that may help will be appreciated.

 

[Trango]

IMO, a 5 speed offers about half as many gears as you should have on a big diesel.

 

[LanceRobson]

Hmmm....I have an M813A1 with 11K miles on the transmission. What are you going to do with the Allison?

Lance

 

[green goat]

I'm sure I don't use the truck to it's full potential and may never but I would like to keep from adding alot more weight to it. I don't have alot of experience with different engine/ trans combo but I would be happy with it if it ran like my M52a2. It has the Mack with a 5spd. and scoots along pretty good. Does the 800 series with 14.00x20 tires accelerate and pull long hills anything like either of these trucks?

As far as the Allison it will be sold off when or after I am able to get another trans in and working.

 

[eldgenb]

IMO, a 5 speed offers about half as many gears as you should have on a big diesel.

I agree completely, get an eaton fuller 9 or 10 speed and enjoy, you will like it much better than the 5 speed.

 

[green goat]

I'm not familiar with an Eaton. Is that more of an over the road type trans or would it have that somewhat mechanical feel like the 5spd. when moving the stick?

 

[M813A1]

Get a Eaton Road Ranger RTO950LL or similar transmission it will have the low gear for hard pulling !! And that will work with your 400 Cummins in the M915,M916 and M920 . That trans will handle the power and torque and give you good highway speed !!

 

[eldgenb]

Get a Eaton Road Ranger RTO950LL or similar transmission it will have the low gear for hard pulling !! And that will work with your 400 Cummins in the M915,M916 and M920 . That trans will handle the power and torque and give you good highway speed !!

That truck does not have a 400 cummins it has the 250 cummins or the 8.3 cummins I don't remember and yes its an over the road transmission. There are a ton of models rto rtlo rtoo, the last two letters are more of the design, the O stands for overdrive, the L stands for low gearing which means the first few gears are built lower to get a load moving or in our case slow offroad use. With that truck any will work fine, I would stick to the 9 or 10 speed, any more gears and you will just end up skipping them all.

 

[13F10]

I won an M925a2 a few months back and like the truck but not too happy with the Allison, I miss shifting. I have been playing with the idea of swapping the trans. out with a five speed from an M54 that I parted out. I'm not sure if the manual from the multi-fuel will hold up to the Cummins or if I need to find another donor. Another option I had thought of was robbing the trans from an 800 series with a Cummins so that it would (or should) bolt up to my engine. I'm still learning my way around this truck and though it wouldn't be original anymore atleast it would be all military parts. Any thoughts, tips, or opinions that may help will be appreciated.

If your serious about the swap, give STEVENS TRANSPORT INC., in Dallas, Tx. a call, they CONSTANTLY rotate their inventory and sell parts from wrecked Kenworth T2000 trucks.
Almost everything they have is relatively recent inventory, and they let it go retard cheap!

I used to work for them back in 03-05.

Best transmission evar, Eaton-Fuller 10LLO! 10spd pnuematic spliter 5low 5 high, with 2 reduction lows.. Slow, and Low Crawl! LMAO

 

[Trango]

Do the math on what final gear ratio you want. There is surely an Eaton Fuller tranny that either exists, or can be built, to provide your desired ratios.

As an explanation, all 9/10 or 13/15 speed trannies work like this: there is a manually shifted, very tight ratio 5 speed gearbox in the front of the tranny, and then an pneumatically-shifted, 2, 3, or 4 speed "aux box" in the back of the tranny.

The front tranny doesn't have syncros, which is ok because the splits are literally that close together. This tranny will let you get up to about 20 or so MPH when the rear airshift box is in low. Top out the RPM's in 5th gear, and then you shift the airshift to the next highest ratio and shift to "1st" (or "2nd", read below) and then repeat the manual shift pattern. Having this aux box either doubles, triples, or quadruples the 5 gears available in the front, yielding boxes that are either 10, 15, or 20 gears.

Bear in mind that 9, 13, and other "counts" of effective gears often take into account that you often don't reuse "1st" in the front box, and just repeat the top four gears.


This is a very quick and dirty explanation. Bottom line is that it yields a very easy to drive/shift tight ratio box that, through multiplication in the airshift box, yields enough RPM to drive at both very low speeds or at a comfortable cruising RPM at highway pace.

Best,
Bob

 

[Floridianson]

[QUOTE Bottom line is that it yields a very easy to drive/shift tight ratio box
Bob[/QUOTE]

Not if you have never driven one. Practice Practice.
The only problem I see with changing out to a nonsyncro is you might be the only one that can drive it. The simpleisity of what is there is just about anyone can drive an MV.

 

[eldgenb]

[QUOTE Bottom line is that it yields a very easy to drive/shift tight ratio box
Bob

Not if you have never driven one. Practice Practice.
The only problem I see with changing out to a nonsyncro is you might be the only one that can drive it. The simpleisity of what is there is just about anyone can drive an MV.

I don't see that as much of a bad thing, I think it might keep inexperienced friends and sticky fingers out of my drivers seat.

 

[Trango]

True, you have to know how to speed shift it, and how to use either a clutch brake or a countershaft brake.

 

[green goat]

Thanks for all the response and explinations on how the Eaton works. I'm still wondering why the M52 will get up to speed so much faster, is it trans. or the mack engine? It just seems to keep the acceleration going right up to 50. Does the M813 with 14.00x20 tires move kinda sluggish like the M925a2?

 

[73m819]

Thanks for all the response and explinations on how the Eaton works. I'm still wondering why the M52 will get up to speed so much faster, is it trans. or the mack engine? It just seems to keep the acceleration going right up to 50. Does the M813 with 14.00x20 tires move kinda sluggish like the M925a2?

Is this JUST the m52, without a trailer, if so, the tractor is the LIGHTEST of all the 5Ts

 

[Floridianson]

Just a bump to get it out, a bump to get it in and never to the floor. Clutch break when truck is at stand still.
I don't think speed is the key feel and timming is how I drive.

 

[73m819]

Just a bump to get it out, a bump to get it in and never to the floor. Clutch break when truck is at stand still.
I don't think speed is the key feel and timming is how I drive.[/QUOT

Same here

 

[eldgenb]

Just a bump to get it out, a bump to get it in and never to the floor. Clutch break when truck is at stand still.
I don't think speed is the key feel and timming is how I drive.

Yep I agree, the mack engine will flat out run away from an NHC250 plus being a tractor it also has the weight advantage. You will be sorely disappointed if you put a 5 speed behind the cummins, you will not gain much if anything at all.

 

[green goat]

Of course it moves faster just the tractor but pulling the M750 or M969 (both empty) still moves as good or better than my 925a2.

 

[eldgenb]

Of course it moves faster just the tractor but pulling the M750 or M969 (both empty) still moves as good or better than my 925a2.

again that is because the mack engine is by far and away more powerful then the cummins. The auto transmission behind the mack would be an even better combo but you will not improve performance behind the cummins unless you can stay in the sweet spot all the time and that is what the more gears will allow you to do. The gear spacing in the 5 speed is too wide and the cummins is constantly having to rebuild momentum after every shift.