Need help understanding rear differential

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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ghiltgen
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Need help understanding rear differential

Post by ghiltgen » Tue Dec 12, 2017 8:58 pm

My general understanding of the rear diferential pinion:
1. The shims behind the race/ bearing cup of the deep pressed on bearing sets the pinion depth.
2.The shims behind the outer bearing sets the preload /"squeeze on the bearing"/rotational torque
What is the function of the pinion shaft spacer? Why did my pinion shim pack come with small shims that only seem to fit on the spline end of the shaft?
When I disassembled the differential, there were no shims behind the outer bearing cup, no small shims like what came in the replacement shim pack. Maybe that's why big chunks of metal pieces where found inside and defects in the ring gear and pinion?

Please educate me,

Greg
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Re: Need help understanding rear differential

Post by artificer » Tue Dec 12, 2017 10:15 pm

When assembling one must FIRST get the correct pinion depth:
1. This is achieved by either adding or subtracting shims from the inner bearing cup.
2. The spacer has shims added or subtracted to alter space between the bearing inner bearing cones thus altering preload [This is SECOND & these are the small shims you may have].
3. Tighten the flange to check this pre-load, then once right remove the flange, fit the seal then refit & torque the flange nut to about 120 ft.lb & split pin.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Need help understanding rear differential

Post by Wolfman » Wed Dec 13, 2017 7:19 am

:shock: Obviously, you have never done this. Set up a differential. There are entire manuals written on how to do this. You want to buy one as well as Tech. Manual with the specs.
Requires special tools like an inch pound and foot pound torque wrench. A pinion depth gauge and a dial indicator. And a good bearing puller and installing tool. Bearings will need to removed and shims adjusted. You need to be able to get the bearings off and back on without damaging them.
1. On disassembly, keep all the shim packs removed and note there location. This will give you a starting point for shim pack thickness on reassembly instead of guessing.
2. First, get the pinion depth set. This is the shims behind the inner pinion bearing race. This locates the pinion teeth in relation to the ring gear teeth. More shims at this location moves the pinion gear farther back. Less shims moves the pinion gear farther forward. This sets the pinion gear so the pinion gear is in correct position in relation to the ring gear teeth.
3. Set the pinion bearing preload. The small shims that go on pinion shaft between the spacer and front bearing cone. Less shims increases preload and more shims decreases preload on the bearings. The preload is checked by installing the pinion with bearings, races, shims, spacer and yoke, torgued to specs and then check the rolling torque on the pinion shaft with an inch pound torque wrench on the pinion shaft nut. Like John said. Don't install the pinion seal until this is set and on final assembly. Be careful tightening the pinion nut on first assembly. If you don't have enough shims and torque the pinion nut to specs, you could overload the bearings and damage them. Tighten the nut slowly to begin with and check to be sure the shaft is not getting too tight before proper torque is reached. Once you think you have the correct set up, rotate the pinion shaft several turns to set the rollers before making the last check. It will make a difference.
4. Once the pinion is set, move to the ring gear and carrier. Two things to set here. Carrier bearing pre load and ring gear backlash in relation to the pinion gear.
5. Start with carrier bearing preload. Shims are added or removed under the carrier bearing cones to move the bearings farther apart or closer together, on the carrier, to set the preload. To check this, you need to put the carrier with shims, races and bearings in place, into the differential housing. Again, be careful initially that the ring gear teeth are not jambed into the pinion gear teeth on first assembly, causing damage.
6. Once the carrier bearing preload is set, you are ready to set the ring gear backlash. Check the backlash of the ring gear teeth in relation to the pinion teeth. This is done with a dial indiacator on the outer diameter of the installed carrier assembly. With the dial indicator in place, gently rock the carrier back and forth without turning the pinion shaft. Check the free play. Too much backlash, the ring gear teeth are not deep enough into the pinion teeth. Shims need to be moved from under the bearing opposite the ring gear side of the carrier and put under the bearing on the ring gear side of the carrier. Not enough backlash, the opposite. Shims from the ring gear carrier side to the other side. This moves the carrier from side to side, changing the ring gear tooth depth in the pinion gear without changing the carrier bearing preload.
Once this is done. Pinion seal installed. All bolts torqued to specs. You are good to go.
Didn't mean to write a book but this was about as brief as I could go and still cover all the basics.
Mike Wolford
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Re: Need help understanding rear differential

Post by ghiltgen » Wed Dec 13, 2017 9:22 am

Very helpful. And yes this will be the first differential for me. I did get a good bearing puller for the carrier bearings, have an inch lb torque wrench with dial indicator, a dial measure to check end play, and have a set of set up bearings which I changed the ID or OD (in the case of the deep bearing cup) so I can disassemble easily to reshim as needed and not damage the shim packs. I even have a yoke withe splines machined out so I don't have to use the puller on the yoke if I need to do multiple shim attempts on the preload check. I am replacing the ring and pinion due to chips in the teeth so multiple shim attempts maybe needed. I kept and measured the old shim packs and will use those as a starting point.

Before both of your responses I thought the preload was set with shims between the recess for the front bearing cup and the cup itself (like the deep bearing). But your telling me that the front bearing cup gets seated into the case recess and the small shims placed in front of the pinion spacer sleeve ( WO A 799), adjust the preload by limiting how tightly the bearing seats in the front cup when the pinion yoke is at torque. (I see said the blind man as he picked his hammer and saw!)

On disassembly I thought it was a washer placed in front of the pinion spacer sleeve but it must be a shim pack frozen together or one large shim (seen in the picture)

One last question. I got a new old stock ring and pinion gear and new bolts for the ring gear which came together in a box. The box was old and had been open. All were in cosmolene. But he ring gear is stamped 1945 and the pinion has a 48 on is (not 1948, so I think it means 1948?). If it's important for the ring and pinion gear to be "matched" to each other from machining, I a little worried these may not be a matched set. Should I worry ?

Thanks again
Greg
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Re: Need help understanding rear differential

Post by artificer » Wed Dec 13, 2017 10:02 am

Don't go buying any TM's or books until you have checked out www.jeepdraw.com
Here is one that will help you on your endeavour.....there are 3 or 4 others for free as well:
http://jeepdraw.com/images/TM9-1803B.pdf
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Need help understanding rear differential

Post by ghiltgen » Wed Dec 13, 2017 12:05 pm

Wow I did find the numbers made with the electric pen after all the cosmolene was finally off! Very subtle! I'm not reusing any shims I meant I was measure the thickness of each shim that was originally used then adding them up to use the same thickness using new shims as a starting point. The set up bearings are timkin bearings with the same number so I'm hopeful it will get me close!
The "washer" that was in line with the spacer sleeve was a shim pack as you predicted. The OD was like all melted together but when you look at the ID you can clearly see the different shims!

Thanks as always for the advice and direction all!

Greg
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Re: Need help understanding rear differential

Post by artificer » Wed Dec 13, 2017 12:40 pm

Not sure why all this stuff about Greg's sensible idea of using setup bearings, that don't necessarily need to be the same brand.
This is what 'experienced tradesmen' in diff & transmission shops use all the time.
There are outfits such as East Coast Gear Supply who sell set up bearings specifically for that purpose & some diff shops have solid steel cutouts that fit in place of the bearings for setting up differentials.
ECGS wrote:These bearings are perfect for the master installer or the first timer. They are honed to slide on and off the bearing surface by hand allowing you to easily change the carrier shims to achieve that ideal backlash. Once you get your correct pattern and backlash press on your new bearings and you're done. If you do not have a clamshell style puller, these are essential to ensuring you don't damage your new bearings by pulling them on and off. Even if you do have a clamshell puller these eliminate the possibility of a costly accident.
Greg see PM sent earlier.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Need help understanding rear differential

Post by Wolfman » Thu Dec 14, 2017 6:23 am

The way it is done by the manufactures, Luc.
They don't have time to waste pulling and installing bearings. Time is money and production quotas need to be met, so they have set up blocks that take the place of bearings. Once the set up is done, then install the bearings.
When doing 10,000 differentials, it is the only way to go.
I don't do enough of any one type differential to buy set blocks for each different type.
I did not know Greg until now, but I am starting to get a good feeling about his ability.
He is going to be just fine.
Mike Wolford
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AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

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Re: Need help understanding rear differential

Post by W. Winget » Thu Dec 14, 2017 6:49 am

Sometimes this board scares me...
If I had read all this back when I changed my Ring and Pinon for my '82 F350 while laying on my back in the desert dirt at National Training Center in '93, I likely would not have driven the (many times, overburdened) truck back across the US, up and down the East Coast several times and so many trips since then without dripping sweat every time I rolled out the driveway.
All I had then was a long breaker bar to get the nut off, a torque wrench and some white spray paint for checking the tooth pattern. I do recall having to add pinon shims and one side set with only one re-disassembly that night to get the pattern right, but then I buttoned it up and drove on.

As they say, ignorance is bliss!
I do hope you take on the differential and not have to seek out a professional to help sort it out, it's not a super complex piece of machinery.
V/R W. Winget
Looking for 1918 Standard B 'Liberty' truck parts

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Re: Need help understanding rear differential

Post by Wolfman » Thu Dec 14, 2017 7:13 am

:D
The world is full of folks that do things your way, and they get along just fine.
My former father-in-law was a master mechanic at the local IH truck garage. Got me my first job there.
He didn't own a torque wrench.
I watched him overhaul engines. Rebuild transmissions and rear ends. All with a break over bar. Said he had done it so long he could feel when the torque was right.
Must have been so. I don't remember him ever having any failures when the job was done.
Everyone has their own way of doing things. As long as it works, must be OK. 8)
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

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Re: Need help understanding rear differential

Post by ghiltgen » Sun Dec 17, 2017 7:30 am

Thanks again to all. I post a follow up after I am done (prob 2 weeks). Just sandblasted axle case and I am waiting for the NOS pinion spacer sleeve to come in so I am cleaning the inside and then going to paint with primer before the rebuild.
ghiltgen
1943 MB SN 226406
Veteran Award, Motorpool Class 2021
GPW 127386
1948 CJ2A
MVPA member 36543


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