M916a1

[GFD200]

Just picked up a 1992 M916A1 today from our forestry yard. It's only got 25k on it and runs like a top.

i know due to the gearing, the top speed is around 60-62mph. Has anyone ever looked at swapping gears to achieve more speed? We'd really like to get 70-72 out of it, if possible.

I know going to a set of super single 14.00 x 20's and gain a little bit.

 

[wreckerman893]

I drove them in the Army and the main reason for the low gearing is to pull heavy loads on bad terrain. I suppose you could put civy rears under it but you would have to figure out how to regear the front end. One option would be to see if you could find a vehicle in a scrap yard that had the gearing you need. Think power company trucks that have driven front axles.

 

[quickfarms]

The front axle and transfer case are made by Oshkosh.

Most of the power company and civilian trucks use either Fabco or Mormon Herrington front axles.

The easiest and probably cheapest solution would be to swap the Allison 4 speed HT740 for a 6 speed Allison

 

[GFD200]

We've also thought about putting some 14.00x20 super single, 5-ton combat rims/rubber on it.

Thoughts?

 

[GFD200]

Would finding an HD4560p Allison from a 915 work? We have that tranny in our 915A4 tanker and it works excellent.

 

[Artisan]

Thread getting a little stale?


Click HERE for some interesting online calculators to see what happens when you change tire sizes.


Click HERE to get a tire size converter that works for these big boys. I get 42" from a 315/80R22.5


So the way I see it, the stock 42" tire comes off and you put on a 49" 14:00R20.
If you were going 60MPH w/ the stock tires you will now be going 70 w/ the 49's.
THAT is something to write home about.

With the taller tires the gear ratio changes from 4.44 to 5.18.

So conversely does that means that if you put 5.18 gears in a stock tire'd truck w/ 42" tall tires
you will now go 70 at the same RPM? (Yes you will need to change gears in ALL AXLES I thunk)
I think a taller tire would be sweet, remember, we have 400HP here.

 

[GFD200]

Thread getting a little stale?


Click HERE for some interesting online calculators to see what happens when you change tire sizes.


Click HERE to get a tire size converter that works for these big boys. I get 42" from a 315/80R22.5


So the way I see it, the stock 42" tire comes off and you put on a 49" 14:00R20.
If you were going 60MPH w/ the stock tires you will now be going 70 w/ the 49's.
THAT is something to write home about.

With the taller tires the gear ratio changes from 4.44 to 5.18.

So conversely does that means that if you put 5.18 gears in a stock tire'd truck w/ 42" tall tires
you will now go 70 at the same RPM? (Yes you will need to change gears in ALL AXLES I thunk)
I think a taller tire would be sweet, remember, we have 400HP here.

For what we are using it for, I really think the 1400/20's would be better anyway. My only fear is blowing or flattening one in a fire and being out of the fight where with the duals you can keep going.

 

[Artisan]

That is why God gave us spares...but certainly a pro for the duals vs singles conversation.

 

[zebedee]

.... BUT - does the extra height of the tires add to the problem of mating an off road tractor (6x6 with four way fifth wheel) to a civi trailer?
If that is what you are hauling.

I guess it only matters if you are pulling a high top box van (or you can't find blocks of wood to put under the landing gear!!) but then again - are you changing the mil' fifth wheel to a 2" one or upping the civi kingpin to 3 1/2"....

 

[jw4x4]

These trucks are not intended or designed to run the speeds you desire. 70+ mph is beyond the speed ratings for 14.00 and taller tires. One must choose between high speed and off road capability. The two simply don't go hand in hand. Please place safety above all else.