M915A1 gear change

[Westech]

How silly would it to be to change out the rear ends to 3.36?
I can find Eaton rear ends on Egay in the 300-500 range.
what model numbers would interchange with the RS 401 type rears in the M915?

I would like to be able to run in the mid 60's at 2100 RPM.
I plan on hauling a M871 trailer with a deuce on it and a small camper.

 

[Bighurt]

You modifying the M871? Cause a duece and anything would be a seriously tight fit. Not to mention tall, the deck height on a standard M871 is 55" which leaves you 107" of payload room.

Wish i had got one of the M872a2 last week that had ramps...

 

[wreckerman893]

We pulled two deuces on the M872 trailers when we went to NTC in CA.

We had to remove the tarps, bows and troop seats, exhaust stack and lower the windshield.

To pull one without lowering the silhouette you need a lowboy or stepdeck.

 

[Westech]

This is how we roll over here.... Now they started chaining down BEFORE they leave the yard. Yes you would think you would chain down before you even moved the truck... but there some real winners working here.

 

[markmontana]

"oh crap..."

Looks like there are chains.

 

[Ferroequinologist]

Not sure about the interchange of the rears- I too would like to know as I use mine all the time, about 2000 miles a month at least.

 

[Westech]

They were installed after the fact. The only thing keeping that truck on the trailer was one lug of the tires grabbing on to pocket. How it did not just roll off I do not fully understand.

 

[bearboley]

Engine RPM x 60 / (Axle Ratio x Tire Revolutions per Mile x Transmission Ratio) = Top Road Speed (MPH) 3.36 Gears would be way too high at 2100 rpm road speed would be 75mph. 4.11 gears would give you a road speed of 60mph at 2100rpm.

 

[swbradley1]

Do you just want to run the engine at a lower RPM or gain more speed? The speedo says 80 and guys are running them at 70. We only ran yours at 55 because of the stupid red idiot light that flashes when you go faster than 55MPH.

 

[swbradley1]

Wait a few minutes and I'll go out and see how fast I can get it up to and I'll check the RPMs.


Oh yeah.

 

[Westech]

that is what the truck has in it now... 411. i want to be able to do 70 ish so 340-360 is where i am looking

 

[wreckerman893]

The M915's with the CAT tranny would run 75 MPH at 2100 RPM......a little better if the fuel was turned up.

Unless they changed the rears when they installed the Allisons the transmission is what's holding the truck back.

I don't know how hard it would be to put in a ten-speed Road Ranger in a M915 but that might solve the problem.

 

[swbradley1]

Why do you want this thing to run faster at a lower RPM? We sent you pics of during the recovery and after didn't we?

 

[bearboley]

I run 4.33's in my everyday truck with a 400 Cummins and it tops out at 78, but I have 11r24.5 tires and a 13spd. I get 6mpg with this combo and it goes up mountains like it has a rocket on the back. I agree with wreckerman the trans is the limiter here. Bolt a set of 11r24.5's on it you will gain around 8mph on the top side. You won't be happy with 3.36's if you plan to haul a load with it . Back in the day 3.90's was a real good ratio for a freight hauler with a 400 that wanted to cover some ground.

 

[73m819]

The 915 I drove for Ziggy would do 65 easy, work to get to 70, that is till I sucked the tank dry and craped up the filters, then a job to get to 65, got dead on 6 mpg

 

[EMD567]

Ferro's 915 will do 60 all day with 40k behind it. Other than maybe going to 24's, I wouldn't change a thing.

 

[319]

This is how we roll over here.... Now they started chaining down BEFORE they leave the yard. Yes you would think you would chain down before you even moved the truck... but there some real winners working here.

CAREFUL WITH THAT LOADER THERE! YOU'RE GONNA SCRATCH THE PRETTY TAN PAINT!!!


Westy, what do you need to go so fast for? Young fella like you ought to just take it slow and easy.......kinda like Gimpy.