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M920 Differential Gears

NDT

Well-known member
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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

Member
479
12
18
Location
Polk County, Florida
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

Member
892
25
18
Location
chama/nm
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
 

jamboly

Active member
Steel Soldiers Supporter
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Location
Brenham, TX
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.
 

R Racing

Active member
2,767
16
38
Location
St. Leonard, MD
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 ?
 

Bighurt

New member
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Location
Minot, ND
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.
 

Bighurt

New member
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Location
Minot, ND
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

Feo, Fuerte y Formal
Supporting Vendor
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113
Location
Mason, TN
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)/


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.
 
Last edited:

155mm

Chief and Indian
Steel Soldiers Supporter
1,176
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Location
Guymon, OK
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

Feo, Fuerte y Formal
Supporting Vendor
12,122
9,367
113
Location
Mason, TN
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
 
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