In a follow-up to our 1000km round trip back in march I neglected to mention a bit of a 'rumble' coming from the rear differential.
Friends and fellow travelers were of course full of advice and of the opinion I was imagining it, what with all the noise of the truck anyway.
I decided to drain the rear diff - just to check - and sure enough....metal 'bits'
At this point I have removed the diff and for your viewing pleasure I have attached a photo of the pinion drive.
Looks like a rat has been gnawing on it. Old Rusty is off the road at the moment...
Cheers.
Last edited by ChrisG on Sat Oct 17, 2015 1:15 pm, edited 1 time in total.
WOW........look at the contact patch on that ring gear.........the pinion was literally running on the ring gear teeth edges. Talk about point contact loading..........the pinion gear didn't have a chance. What's the background on this diff.........was it set up wrong recently or is it an older unit?
I noticed in the ORD the pinion shims weren't offered in a kit, just individually. How was the person rebuilding a diff supposed to know ahead of time what shims to order from supply? Or did units just keep lots of all size shims on-hand?
This is exactly what the blown heard that I have look like. Nearly identical contact patches. I'll get photos next time I am around them..... If I remember!
Somewhat on topic... What does the funny, tapered "differential screw" do? It looks almost like a drain plug but has a stop nut so it can be screwed in and locked at a certain depth.
Isaac
Fairbanks, AK
Civilian WM300 on DC3 tires
'52 M37 on 11x16 Michelin
'52 M37 on Apple R-1 tractor tires Photo Gallery
Isaac,
"What does the funny, tapered "differential screw" do?"
I believe what you're talking about is the screw that controls a "slider" that bears on the back surface of the ring gear under heavy loading. Under light load there's clearance.
Good question Bob,
At the moment I am in the middle of moving and unable to find all the receipts for work the previous owner had done on Old Rusty.
Previous owner MAY have had the diff 'rebuilt', however when my mechanic took a look his immediate thoughts were that it had been set up wrongly. Amazing wear eh?
I've done a few 000's kms in the truck since purchasing it a few years ago, not a great deal in the grand scheme of things...will be interesting to find the paperwork and have a look to see if it was 'done'.
Anyway it'll get sorted, somehow. I envy you lot living in the US, lots of parts 'lying' around. Literally a handful of M37's in Australia, makes getting parts more of an exercise in overseas importation.
Chris, i bet the gears you need will fit in a flat rate box and ship for about $30....i have 2 diffs that are out and look to be in good shape, but would require picking them up from storage, and dis-assembly. i saw one guy on here was selling an entire axle assembly for $150
Isaac
Fairbanks, AK
Civilian WM300 on DC3 tires
'52 M37 on 11x16 Michelin
'52 M37 on Apple R-1 tractor tires Photo Gallery
The problem Chris has is the pinion gear is made of hardened steel, which makes it very tough, but brittle. If even the smallest piece of that steel gets into a bearing........it's toast. And the bearings used in these diffs are getting ridiculously expensive (over $500). You can still find the diff kits (spider gears, blocks, etc) for under $100, but installing used gears in a different carrier is also a bit of a crapshoot. A complete used diff (hog's head) can be found here in the US for fairly cheap, but shipping it to Oz won't be cheap. This website did seem interesting and might be worth looking into;
Hello,
Firstly thanks for your offer MM but I had actually gone an ordered a set of new 4.88 ring and pinion gears from the US a while ago. Plus a repair kit, shims, and all new bearings.........
Hence the overseas importation reference.
Now this is going to sound odd but if someone can answer I'd be most grateful.
At this stage I have dropped the rear diff and given it to someone to repair with the new parts.
Now while I am waiting for it to be done (no idea of how long it'll take him) it is possible to stick the front diff into the rear so I can get some use out of the truck? Or am I simply playing with danger moving differentials around?
I understand I could run on front wheel drive but have heard the truck may "jump around" a bit?!
I'd be most interested in some informed information on either swapping 'em over or running on front wheel drive if anyone has it.
i'm not an expert on it, but i can't see any reason not to stick the front diff in the rear axle to drive it around. as far as i know there isn't anything clearance-wise or tolerance wise you need to be careful of, the whole unit should just bolt in and go. are you changing the truck to 2wd? i'm assuming so, unless you ordered two sets of gears and plan to rebuild the front diff as well. If you plan to run with two different gear ratios you might consider removing the front driveline or installing free-wheel hubs, or you are just begging to break something when someone accidentally puts it in 4wd on any kind of hard surface. looking for the "two pennies" smiley but i don't see it anywhere...
Isaac
Fairbanks, AK
Civilian WM300 on DC3 tires
'52 M37 on 11x16 Michelin
'52 M37 on Apple R-1 tractor tires Photo Gallery
Hi Isaac,
Yep, till I change the second diff over I was just going to remove drive shaft and go free wheeling ... can you imagine the outcome if someone did slip it into 4WD with two different ratios!!!
I'll miss the 4WD for a while but money and time make it a "one diff at a time" job for me.
My thinking is , stick the front into the rear, then when the new diff is repaired take it out, put the new one into the rear in and simply leave the old front diff stored till I get the second ring and pinion.... then do it and stick it back in the front - phew!
Sounds crazy but I would really like to use the truck while I'm waiting on the repairs.....
The front and rear Diff's. are the same and interchange.
I would cover the rear housing and drive on the front if needed, because I would not be down long.
Though I assume you plan to pull the front then leave the axles out cover the housing and put it all
Back together and drive on the rear?
Lot of unnecessary work but doable.
TGP
Absolutely no doubt, it was set up seriously WRONG. Anyone that would set one up that far out of Sync doesn't even need to walk around the truck, much less attempt any repair. You keep mentioning shims in a rebuild kit, there never was such a kit. The only such item used on the pinion shaft is the bearing preload spacers. There is a possibility of 8 different thicknesses. The real deal is this; difference between spacer thickness goes .002" between shims. Example, there is a .185; the next thicker is .187. If you need a .186, you have to install the .185 + a .001 that you must acquire from another source or custom cut to get the correct bearing preload setting. Another issue that isn't covered in the military manual is achieving the correct pinion depth. Military parts do not cover any adjustments for that. New 4.89 gears have the correct pinion depth setting embossed on the pinion. One in a million chance you will ever achieve a correct depth setting unless again you custom cut or acquire needed shims to go under the pinion bearing cup or the bearing cone, depending on which way the adjustment needs to go to come out right. Then there is the definite need for a pinion depth gauge to measure it correctly. You need not even think about an optimum tooth contact pattern until the pinion is installed and set up correctly. Special tooling is also required to install the spider / side gear, shaft, and thrust washer kit. The carrier housing needs to be checked very closely in all areas as it too wears. Installing the new interior kit components may not get it to where it needs to be because of interior housing wear. By all means you need to question your installer about all this; very few, even seasoned mechanics have proper tooling or know how to work on these units. Many will say oh sure, only to get a big surprise when they get into it. Some of the worst ones I've seen were those that were worked on by others before coming to us. Ask plenty of questions. Good luck with it.
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but money and time make it a "one diff at a time" job for me.