M920 Differential Gears

[NDT]

I found the pinion gear and ring gear. Alan, of Houston Drive Train 713-675-6375 was able to find two pinion and ring gear sets, of which I got one. Tell him you need 6.17:1 gears for a Rockwell/ SUHD rear end.

Good deal! Now comes the agony of pulling the pumpkin and replacing the ring and pinion. If it were me, I would bring it to them and let them install the parts as well. It is quite a complicated operation to set up a ring and pinion, especially if you have never done one.

 

[oldMan99]

I found the pinion gear and ring gear. Alan, of Houston Drive Train 713-675-6375 was able to find two pinion and ring gear sets, of which I got one. Tell him you need 6.17:1 gears for a Rockwell/ SUHD rear end.

Good deal, glad you find the stock parts you need.

I'm still looking for 4.88/4.89 gears. It seems they are completely unobtainable.

 

[M920]

He guys can you dumb down a little for me. You guys are way beyond me with trying to improve the mileage, speed etc. I am just trying to see what it would take (if parts are available), to fix my M920. The problem I have is that when I went to pick it up, the fluids had been drained in engine and transmission because of EPA concerns with leaks. We got a wrecker to roll it on the low boy trailer (brakes were already caged), back end first. As the rear wheels were going on to the trailer, we heard a loud pop. The pinion gear shaft broke just inside the seal of the differential. Aside from trying to understand why it broke, what are my odds of finding the parts to fix it? Who would I check with for parts availability and cost?

I have the original 6.17:1 ring and pinions that came out of my M920 available. PM me if you're interested in a set.
For the reason on why you broke the pinion....there is really only one possible reason: Since the tires can totally lock up and not brake the pinion, the angle on the drive shaft to pinion u-joint was most likely exceeded, when backing the truck up the ramps. You might make sure that the bolt-on axle travel stops are in place and not missing or bent.

Soni

 

[jaxsof]

just find yourself a fuller RTO or RTLO tranny with the taller OD and swap the whole tranny.

Elgen, I was also considdering an RTX, any issues with this tranny?

 

[eldgenb]

Elgen, I was also considdering an RTX, any issues with this tranny?

none that I am aware of. First gear is not as deep so you will not be able to creep around like we currently can as much. od is the same, standard 9 or 10 speed.

 

[jamboly]

Good deal! Now comes the agony of pulling the pumpkin and replacing the ring and pinion. If it were me, I would bring it to them and let them install the parts as well. It is quite a complicated operation to set up a ring and pinion, especially if you have never done one.

As far as me doing the work, you are right. I am going to have someone else do it. All it took was for me to see the shims in the parts diagram. Besides, I don't even have what it takes to pull the rear axle. I'll have to get someone else to do that to.

 

[Ferroequinologist]

I also would be very interested to find a set of 4.88 gears for a m915.

 

[quickfarms]

Very interesting

 

[eldgenb]

I also would be very interested to find a set of 4.88 gears for a m915.

Pretty sure the 915 already has 4.30's or 4.88's stock, its the final drive on the transmission that makes them slower.

 

[R Racing]

Your really close !! the M915 has 4:44 to 1 ratio. I wonder if they will fit in the pumpkins of the m920? I have heard the axles are smaller on the m915 than the m916 and up . but is the ring and pinion same size ?

 

[Ferroequinologist]

Dang, well, that shoots my idea out of the water! I wonder if some 3.90s would fit.

 

[Bighurt]

Your really close !! the M915 has 4:44 to 1 ratio. I wonder if they will fit in the pumpkins of the m920? I have heard the axles are smaller on the m915 than the m916 and up . but is the ring and pinion same size ?

I don' have the info in front of me but I seam to recall when researching this earlier that the M915 uses a different size gear than it's bigger brothers.

 

[R Racing]

I figured that may be the case . But would be nice to throw a set of 4:44 in a m920

 

[crestviewsport]

Did anyone ever identify where these pinions could be purchased from?

 

[Bighurt]

Did anyone ever identify where these pinions could be purchased from?

The National Stock Number's are;

3020-01-092-9230 Intermediate
http://www.dlis.dla.mil/webflis/pub/pub_search.aspx?niin=3020010929230&newpage=1
AM General Part #MA129-21092 $1312.15

​

2520-01-100-9991 Rear
http://www.dlis.dla.mil/webflis/pub/pub_search.aspx?niin=2520011009991&newpage=1
AM General Part #MA207-22734 $389.46

AM General
Switch Board - (574)237-6222
Parts - (574)258-6636
Mon- Fri Hours 7:30 a.m. - 4:30 p.m. Eastern Time

 

[simp5782]

Front axles can be replaced with an FDS-1808 and FDS-2100. They are found in front discharge mixers. Every axle tag i have is a FDS-180RSA11. 11 being the customer build but it isn't listed in the meritor manual for a build reference. The 1800s and 2100s have the same setup entirely. Some hubs use wide budd so don't go for those.

1808s are most common. https://lkqheavytruck.com/inventory/MERITOR/FDS-1808/Axle-Assembly,-Front-(Driving)/

FDS1808 Meritor Rockwell Used Rear Diff. Good Inspected Takeout, 4.63 Ratio | eBay

Differential Model. (Rear): FDS1808. GEAR SET P/N A35910-8 REPLACED BY A40172-5. Ratio: 4.63. Condition: Used.

www.ebay.com

Rear SSHD chunks will interchange. These are common in 4.56 ratios.

Or go to a 13spd RTOO14613 that has .83, .74, .62 OD to increase speed.

 

[155mm]

Is there a big enough difference in gear ratio between front and back to be concerned with loading up transfer. Front 4.63, rear4.56

 

[simp5782]

Is there a big enough difference in gear ratio between front and back to be concerned with loading up transfer. Front 4.63, rear4.56

The link to the front axles lists 4.56 and 4.63 front chunks. I just only found a 4.63 rear on ebay to show the chunk itself

I found all ratio types for the rear on the junk yard sites

You would be fine as long as you ran the front only when on slick or muddy terrain. I split mine so my front end lock is different from my the interaxle lock

If you have 1100r24s on the rear and a 445 65 22.5 on the front the 1in difference would help