Differential Backlash Spec

[booze_rooster]

Hey guys, I'm in the process of doing a frame-off restoration of my father's 1952 M37 that's sat in his garage for 25 years untouched.

Tearing into the axles right now. Got the shafts pulled and my buddy and I wrestled the rear diff out of the housing. Felt around in the residual oil and found the remains of tiny roller bearing chunks. Ran the gears around by hand and inspected for damage. Miraculously there are no shattered teeth. Checked the inner pinion bearing and all rollers are accounted for. Pulling the carrier next once I get my dial indicator and holding fixture from work to record initial pattern and BL.

Just by hand I'm feeling excessive BL. I'd guess in the neighborhood of .020". Done plenty of Toyota 3rds and I'm rebuilding an insanely stupid D30 tapered rear for a 67 Jeepster at work right now. No stranger to rear ends.

Does anyone on here have a backlash Spec? My -10 manual omits this info and Google isn't turning anything up.

 

[Buck69]

It is not recommended to change the BL on a set of gears that are (warn in) matched. I would set it back to what you find before disassembly and confirm your pattern hasn't changed. If you haven't touched the pinion depth, that pattern should return to where it is now with BL.

 

[booze_rooster]

It is not recommended to change the BL on a set of gears that are (warn in) matched. I would set it back to what you find before disassembly and confirm your pattern hasn't changed. If you haven't touched the pinion depth, that pattern should return to where it is now with BL.

I'm not planning to change the BL spec on worn in gears. I want to know if this slop is the correct setting or if I'm going differential hunting. If it is somehow an acceptable backlash setting I can proceed with CSI: Third Member and figure out where the roller carnage came from

 

[booze_rooster]

https://jeepwillysworld.com/wp-content/uploads/2015/10/TM9-8031-2_power_train.pdf

On Page 496

Ring to pinion backlash setting range 0.005"-0.010"

Found it. Just updating to help anyone else searching in future.

 

[G744]

Does it have the original engine or a repower?

Reason being I put a Detroit 3-53 in one and logged almost 250K on it, but it cost me 13 sets of ring/pinion gears. Ate them to razor blades.

Lesson learned, they don't like higher torque & HP at faster road speeds.

All that was before synthetic gear oil was widely available, it might've made a difference there.

Anyways, enjoy restoring the best engineered real Power Wagon even built.

 

[booze_rooster]

Original 230. Been sitting 25 years. Ran like a top when my dad bought it. I was in kindergarten. I remember an awesome summer riding around in it. Basically it was my first experience with a beater truck with a stick shift. I was devastated when the brakes failed, the wiring started arcing out and my dad barely got us home in it, then parked it in the garage saying "we'll get to it soon". 25 years later and I have it stripped down practically to nuts and bolts. The engine has zero compression. Rings must be stuck pretty good. I can turn the fan with the side of a finger and roll the engine over. Working on springs and axles now. Frame is already sandblasted, acid etched and painted. Got it bagged up in plastic leaning against the wall while I demolish the axles and springs for rebuild.

I'll have my dial indicator with me from work tomorrow to get a reading and see how screwed I am.

 

[John Mc]

Original 230. Been sitting 25 years. Ran like a top when my dad bought it. I was in kindergarten. I remember an awesome summer riding around in it. Basically it was my first experience with a beater truck with a stick shift. I was devastated when the brakes failed, the wiring started arcing out and my dad barely got us home in it, then parked it in the garage saying "we'll get to it soon". 25 years later and I have it stripped down practically to nuts and bolts. The engine has zero compression. Rings must be stuck pretty good. I can turn the fan with the side of a finger and roll the engine over. Working on springs and axles now. Frame is already sandblasted, acid etched and painted. Got it bagged up in plastic leaning against the wall while I demolish the axles and springs for rebuild.

I'll have my dial indicator with me from work tomorrow to get a reading and see how screwed I am.

If you are not gong to rebuild the engine yourself, Ken Holmes is one of the best rebuilders for these 230 engines. He is just down the road from you in Worcester, MA. I can dig up contactinfo, if you are interested.

 

[booze_rooster]

I'll be doing the work myself. Five days a week I'm a restoration mechanic at a company that exclusively does old vehicles for guys with more money than brains. I'm tired of building millionaires beach toys. This M37 is my pet project to keep me sane

 

[John Mc]

I'll be doing the work myself. Five days a week I'm a restoration mechanic at a company that exclusively does old vehicles for guys with more money than brains. I'm tired of building millionaires beach toys. This M37 is my pet project to keep me sane

Have fun!
Wish I had your skils.

 

[87cr250r]

That backlash spec is for new gears. If you're looking to qualify your old set you need to look for the "service limit" which will be closer to that 0.020".

 

[booze_rooster]

That backlash spec is for new gears. If you're looking to qualify your old set you need to look for the "service limit" which will be closer to that 0.020".

I'll check page 497 then- that's an excellent point I almost overlooked that detail.

 

[booze_rooster]

Spec'd out at .035" BL

Page 490 of the same TM:

"341. General The repair and rebuild standards included herein give the minimum, maximum, and key clearances of new or rebuilt parts. They also give wear limits which indicate that point to which a part or parts may be worn before replacement, in order to receive maximum service with minimum replacement. Normally, all parts which have not been worn beyond the dimensions shown in the "Wear limits" column or damaged from corrosion will be approved for service. An asterisk (*) in the "Wear limits" column indicates that the part or parts should be replaced when worn beyond the limits given in the "Sizes and fits of new parts" column. All dimensions are in inches unless otherwise specified."

The BL range given for new parts is 0.05"-0.010". Wear limits are denoted as "*" so if one were to guess at the military's thinking now, if the gears are at depot level and exceed the maximum range for a new set (and 0.010" is pretty darn sloppy) you opt for a new set. Makes sense. I could see worn gears NOT exceeding 0.015" getting run in a slow and steady farm truck application and holding up.

So...who in in the Northeast US has a diff for sale?

 

[Valley Rock]

OP, you posted that the bl was .020 now it's .035, am I understanding this correctly ?

.020 on this diff wouldn't make me bat an eye, I would not bother to get out my dial indicator for that, I can feel it with my hand and know it's fine for tough old gears that use thick oil and superior metal that no longer exists .

.010 sloppy ?
Don't think so, I wouldn't set this up tighter than .010 when new .

You said you found QUOTE "the remains of tiny roller bearing chunks" UNQUOTE (in the bottom of the diff housing I presume) in your initial post, I've yet to hear anymore about that or what they are/were exactly or where they came from .

My money says if ring and pinion look good you could replace broken and defective bearings/parts, put it back together with same shims as stock and it will outlive both of us .

 

[MarkM]

With old gears just from past experience my go to would be .12. If you have too much BL the gears will get noisy. I would get some Prussian blue to check the contact path. It's all a best guess when dealing with worn parts. Just my .02 cents.

Mark

 

[booze_rooster]

I stated that the backlash FELT like 0.020 by just holding the pinion flange and rocking the ring gear. I didn't have my dial indicator with me until last night when it averaged 0.035.

I have no prior experience with these differentials, so I'm not as familiar with what they prefer. I'm used to setting up new gears for rock crawling and dialing in the BL on the tighter side of the spec'd range, even if it means tearing it back down a million times to get it just right.

I haven't had the time to remove the carrier assembly yet and investigate further. Work has that on hold until the weekend. I have not been able to ascertain where the debris originated. The bearing chunks appear to be much smaller in diameter than the visible pinion bearing rollers (all accounted for) and are much darker in color. Everything rotates smoothly though so I'm wondering if it's carnage that was simply never removed during a previous repair. The carrier case has many longitudinal score marks across it indicating past damage, but the gear teeth look immaculate.

I haven't had a chance to clean the diff out either and remove the oil residue to apply the vastly superior yellow gear marking compound and obtain a pattern. I'll report back when I do.