FMTV High Speed Gears

[Mike Wryley]

If you asking about the m1078 Meritor/Rockwell axles yes, I called Meritor and have the
pns for the 6.14 gear sets along with the distributors that handle them, can forward in the am when at the office,
list is between two and three grand per set,

 

[steve6x6x6]

I have been thinking about this myself, with the 5. something ratio of the MRAP axle,
a huge reduction in rpm if you are sticking to more of a road environment
what about replacing the entire axle ? if the punkins are in the right position, that might be easier,,,

The MRAP in tan color are 6.14 on the driver side and the LMTV in green are 7.80 on the is driver side.

 

[steve6x6x6]

If you asking about the m1078 Meritor/Rockwell axles yes, I called Meritor and have the
pns for the 6.14 gear sets along with the distributors that handle them, can forward in the am when at the office,
list is between two and three grand per set,

You can buy new complete fronts with 6.14 for $800.00 ea.

 

[blhar15]

You will get close to 70 MPH with the high speed gears, we have done several of them.

 

[Mike Wryley]

Steve,

So can you take a gear set (ring gear/pinion) from the front and install the in the second and third rear axles ?
may I call you ?

 

[Mike Wryley]

Bihar,
i would really like to change the guesting in my 1083 and maybe 1088, May I call you ?
i am in Council Bluffs
thanks
mike

 

[sstephens637]

Can the ring and pinion gears be taken from a 3.07 diff and swapped in the 3.90 diff? Or does the whole differential need to be swapped? Trying to save on some shipping if possible. It seems the recycler dismantles these axles anyways, so why not just get some sets of the gears, since thats really what we're after here. Dont want to ship the whole case if I dont have to. I know it would need to be respaced with shims, but is there anything different like shaft diameters or anything?
And if this is the case, does anyone know the specs on the 3.07 gears to source from a gear specialty shop if needed?

another note, the cost from recycler is the same whether you get the whole axle or just the diff, so why not just get the parts that might be needed. Shoes, hubs, planetary/reduction gears, ring / pinion gears...right? And save a ton on shipping?

 

[sstephens637]

Transmission swap

Does anyone know if the allison 3500 can replace the stock 3700? Wouldnt that mean a higher top speed as well? 6 gears instead of 7, but 3500 sixth is 0.65:1 vs seventh in the 3700 0.78:1 .
1st in the 3500 is 4.59:1 vs in the 3700 6.93:1, so low end would suffer.
Someone better at math than I can maybe determine final speed? Other than that they have nearly identical specs. 3500 actually has higher input torque rating.
several 3500's up for auction, so it may be a solution? Anyone care to input?
id assume the contoller programming wouldnt be to hard by a mechanic in the know.

edited: my calculation put speed at 67.5mph at 2500rpm vs 56.23mph, so 11mph gained, assuming transmission swap will fit.

throw in the diff change to 3.07 gears and top end is theoretically 85.7!!!

fwiw the second gear ratio on the 3700 is 4.18:1, so basically you are dropping first and getting a slightly lower 2nd in its place. (4.59:1) the truck starts in second most of the time anyways, correct?

 

[Oxyacetylene]

Does anyone know if the allison 3500 can replace the stock 3700? Wouldnt that mean a higher top speed as well? 6 gears instead of 7, but 3500 sixth is 0.65:1 vs seventh in the 3700 0.78:1 .
1st in the 3500 is 4.59:1 vs in the 3700 6.93:1, so low end would suffer.
Someone better at math than I can maybe determine final speed? Other than that they have nearly identical specs. 3500 actually has higher input torque rating.
several 3500's up for auction, so it may be a solution? Anyone care to input?
id assume the contoller programming wouldnt be to hard by a mechanic in the know.

edited: my calculation put speed at 67.5mph at 2500rpm vs 56.23mph, so 11mph gained, assuming transmission swap will fit.

throw in the diff change to 3.07 gears and top end is theoretically 85.7!!!

fwiw the second gear ratio on the 3700 is 4.18:1, so basically you are dropping first and getting a slightly lower 2nd in its place. (4.59:1) the truck starts in second most of the time anyways, correct?

The truck does start in second unless you put it into "MODE" which is not supposed to be used on hard surfaces like the road. Not sure about the higher ratio transmission, that would spin the driveshaft faster, and there is a thread here already about a study done on the FMTV driveshafts. Basically I don't know that I would want to spin the rear shaft any faster for any length of time. I would read that PDF for more detailed info.

 

[Shark Bait]

The truck does start in second unless you put it into "MODE" which is not supposed to be used on hard surfaces like the road. Not sure about the higher ratio transmission, that would spin the driveshaft faster, and there is a thread here already about a study done on the FMTV driveshafts. Basically I don't know that I would want to spin the rear shaft any faster for any length of time. I would read that PDF for more detailed info.

If I remember correctly, the all wheel drive is split 30/70 power front/rear. The "Mode" button will split it 50/50. 1st gear is only manually selected, as a "Low" range.

 

[sstephens637]

But does anyone know if the 3500 is the same case as the 3700? Looking at the spec sheet pdfs they look pretty much identical in the drawings. The 3700 has the transfer case (which looks like it will bolt right on) but other than that i see no physical external difference. Maybe the oil pan depth, but not sure. I dont have the dimensions on both, but have hope for this possibility. May even be cheaper parts wise than the diffs. Was quoted 16 hours labor if i have the local allison mechanic swap out , assuming they bolt up.
anyone know how easy it is to set up the program, or how long i can expect to pay the mechanic for that?
i can include screen shots of the pdf if anyone is interested.

could make for better mpgs i would think.

 

[sstephens637]

Anyone in okc area want to help me try it out? I dont have the equipment for it, but know my way around a wrench... Would be nice for everyone else to know what's possible on these LMTV's. Maybe someone that would like to start doing conversions on the side???
Also from what im told above, it appears 1st gear is in the transfer case, so the transmission would still have 7 gears, they would actually end up wider than the 3700SP. A plus is the 3500SP is rated for MORE torque, which to me just means tougher, cause its the same engine. Probably just because of the gearing, my best guess.
Someone please let me know if this is way off base.

 

[DSD277]

sstephens637
I haven't followed the FMTV section closely since my War Pig (the FDT) build a couple years back, but you do know that your LMTV has a Allison MD3070 trans? ( or least left the factory with one )

 

[sstephens637]

Looks same

Not sure. Im looking at a BAE spec sheet that says Allison 3700SP. It is for an A1 with the CAT C7...
oh what a tangled web...

found a spec sheet on the 3070PT, looks identical from my eye. Gearing is identical to the 3500SP, so @2500rpm, should be going 67.5 mph...@2200 59mph.

im thinking all of the 3000 series transmissions share a case?

 

[DSD277]

That was the latest , greatest. Your truck has a Cat 3116
In the '90s, the MD3060 series ( which the 3070 belongs) was the auto trans going into everything with 230HP+ RVs and medium duty trucks and FMTV.
My F700 was one of the last MD trucks built from Ford with a 230hp B5.9 and a Allison 654 in '94... 3 months later, only MD3050 ( 5 speed) were available in the Ford

 

[sstephens637]

Found another stewart and stevenson m-1078A1 spec sheet that says cat 3126, with a 3700SP
I'm no master mechanic but from my view all things are pointing to very similar specs on all of these. My biggest fear right now is that the electronics won't jive if i have a 3700 and want to swap.
interestingly the 3070 and the 3700 both list an "integrated transfer case" which just looks like it's bolted on the back where the drive line would normally attach (like on the 3500) both parts show a 20 bolt pattern (ish - i didnt count every bolt). Im going to go ahead and post the spec sheet diagrams so it makes more sense. If mine is already a 3070 then no swap would be needed. It already has the .65 7th gear. If thats the case however then mine should do better than 55 max, assuming 2500rpm governor.
once the diffs are swapped it should be mid 80's when wrapped out. Not that i plan to drive 80, but cruising along at 1800-2000rpms has got to be better on mileage! I hope.

any idea where the model number would be located on the case? Mine (truck) is taking forever to ship here. Was supposed to be picked up on the 21st, and last i heard they were "for sure" going to pick it up this morning.

That was the latest , greatest. Your truck has a Cat 3116
In the '90s, the MD3060 series ( which the 3070 belongs) was the auto trans going into everything with 230HP+ RVs and medium duty trucks and FMTV.
My F700 was one of the last MD trucks built from Ford with a 230hp B5.9 and a Allison 654 in '94... 3 months later, only MD3050 ( 5 speed) were available in the Ford

 

[sstephens637]

Specs sheets

Here are the specs on the parts mentioned.

 

[sstephens637]

M1078A1 spec sheets

In case anyont wants to read these...

 

[sstephens637]

They all show SAE No. 2 engine mounting...

 

[DSD277]

sstephens637
I don't know why you are posting all this info on a A1. The truck in your sig line and the one you posted pics of in another thread is a M1078 A0.
It has a Cat 3116, Allison 3070 and has a WTEC11 trans selector. They were upgraded a few years later to the WTEC111. BAE had an updated wire harness to convert the older shifter to the new one when they went bad.