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Figuring out correct size differential shims.
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duginabug
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PostPosted: Fri Feb 25, 2011 4:29 pm    Post subject: Figuring out correct size differential shims. Reply with quote

I had to replace the ring and pinion in my split case gearbox, so while I was in there I replaced all the bearings as well, including the differential bearings. Now I’m to the point of reassembling everything and need to figure out what size differential shims I need.

From what I understand, this takes a special tool, which I can get a hold of easy enough, and I found a source for shims. I’m just hoping for a basic step by step from somebody who’s done this before.

The gearbox is a split case, swing axle out of a 1960 bug.

Thanks
Doug
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Bruce
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PostPosted: Sat Feb 26, 2011 1:52 am    Post subject: Re: Figuring out correct size differential shims. Reply with quote

duginabug wrote:
.... I replaced all the bearings as well, including the differential bearings.

What was wrong with the original diff bearings?
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dugsgms
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PostPosted: Sat Feb 26, 2011 4:31 am    Post subject: Reply with quote

Im not gonna tell you that im a expert on VW transmissions but Ive done alot of ring and pinion set ups in straight axles so maybe I can help. Where do the shims go? under the pinion gear or on either side of the ring gear carrier?
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duginabug
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PostPosted: Sat Feb 26, 2011 12:04 pm    Post subject: Re: Figuring out correct size differential shims. Reply with quote

Bruce wrote:
duginabug wrote:
.... I replaced all the bearings as well, including the differential bearings.

What was wrong with the original diff bearings?


Lots of pitting in the bearing races. They were only like $42 each so I figured I might as well. I really don't want to have to pull the engine and gear box again.
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PostPosted: Sat Feb 26, 2011 12:11 pm    Post subject: Reply with quote

dugsgms wrote:
Im not gonna tell you that im a expert on VW transmissions but Ive done alot of ring and pinion set ups in straight axles so maybe I can help. Where do the shims go? under the pinion gear or on either side of the ring gear carrier?


On either side of the ring gear carrier between it and the differential bearings.
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PostPosted: Sat Feb 26, 2011 6:40 pm    Post subject: Reply with quote

So youve already set pinion depth(the shims on the pinion gear)?
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PostPosted: Sat Feb 26, 2011 7:27 pm    Post subject: Reply with quote

Cant do that without establishing ring gear carrier end play,then set pinion depth,then set contact pattern by adjusting depth or shifting ring gear shims from one side or another...
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dugsgms
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PostPosted: Sat Feb 26, 2011 8:07 pm    Post subject: Reply with quote

Exactly, but there might be a easier way to do it. Looking at the bentley, the gears are marked with +/- measurement on the pinion gear, not sure if thats the case w/ aftermarket gear sets. If you do have that measurement on both the old and new gear sets then you can set pinion depth pretty accurately w/o having to do a marking pattern. Then, since you didnt change the diff carrier and its the same case, the total amount of diff carrier shims should still work to set diff carrier preload in the case.. It will just be a matter of arranging those shims left to right properly to get the correct backlash. Measuring back lash is alot harder to do in a VW transaxle than it is in a straight axle though. It looks like VW wanted you to bolt a tool to the the carrier so that measurement could be taken out side of the transaxle. That tool would be the way to go although Id imagine you could make something that would work. You might have to remove the diff and side covers a few times trying to get it right but it look doable. Bentley wants about".008-".009 backlash.[/quote]

Last edited by dugsgms on Sat Feb 26, 2011 8:14 pm; edited 1 time in total
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Bruce
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PostPosted: Sat Feb 26, 2011 8:07 pm    Post subject: Reply with quote

Pinion depth will remain the same.

Measure the widths of both the inner and outer races of the old bearings, and the new ones with a micrometer. Likely they will be within a very small tolerance. If so, reuse the original shims. Verify the contact pattern with gear marking compound.
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PostPosted: Sat Feb 26, 2011 8:12 pm    Post subject: Reply with quote

Maybe VWs are different but usually if you change the ring and pinion you have to reset pinion depth. I do agree with reusing all the old shims for initial assembly though. Thats usually a good starting point.
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PostPosted: Sat Feb 26, 2011 9:14 pm    Post subject: Reply with quote

You're right. I missed the part where he's changing the R&P.
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PostPosted: Sat Feb 26, 2011 10:06 pm    Post subject: Reply with quote

Excellent information. Just what I was looking for.

Now...the R&P is a NOS matched set I found in the classifieds here and they do have several numbers scribed on them just like the old ones. I will get out my old man magnifying glass and write them down tomorrow or Monday.

I assembled the pinion exactly the same as the old one and left the differential shims where they were. When I bolted the case together I could not turn the main shaft at all. Very tight.

I opened the case and removed the diff shims, then reassembled it and I could easily turn the main shaft so it seems like that is where the binding is.

The NOS R&P is the same ratio 7:31 442 -- however, it is a different brand and there are some differences so I am basically starting from step one as far as setting up all the correct tolerances.

That being said, what is the correct order in the setting of...pretty much everything.

I do have manuals, but unfortunately I do not have a Bentley Embarassed

Thanks guys for the input.
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PostPosted: Sat Feb 26, 2011 10:45 pm    Post subject: Reply with quote

Any shortcuts can lead to premature failure of the bearings or gears ...an unpleasant situation give the amount of labor it takes to tear it back down.When setting tapered roller bearings that have end play,always set to the loose side of the measurement if you cant hit dead on,never to the tight side...
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PostPosted: Sun Feb 27, 2011 8:11 pm    Post subject: Reply with quote

If you cant determine the correct pinion shim by using the deviation numbers on the pinion gear then your best off using the old shim as a starting point. You said that when you assembled it before with the old diff shims it was hard to turn, you did have the gaskets on the side cover right? If you did then its likely insufficient backlash, add some more shims to the tooth side of the ring gear and take the same amount out of the bolt side to bring it away from the pinion. Once you get close on backlash(doesn't have to be perfect at this point, as long as it has some play it should be OK) run a pattern on the gears w/ some marking compound. After you have the pattern go on the internet to find some info on reading a pattern. After you understand what wrong with the pattern(if anything) you may have to remove or add shims from the pinion to get the pattern you want(sometimes you get lucky and the factory shim is the right one, or it might take a few attempts). Once you have a pattern you like you may have to move shims around on the diff carrier to get the proper backlash. Truthfully, I would highly recommend getting a Bentley. People even post them on file sharing websites from time to time. Good Luck, you're attempting a job that a lot of people on this form wouldn't attempt but really it isn't that hard.
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PostPosted: Mon Feb 28, 2011 1:24 am    Post subject: Reply with quote

dugsgms wrote:
you did have the gaskets on the side cover right?

He's building a split case gearbox, so no sidecovers.

You should be able to calculate the pinion shim from the difference in the markings on the pinions. If you can do this calc, I think it'll be close to 100% correct. Work the ring gear backlash until you get the best contact pattern. I bet the pinion depth will be dead on.
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PostPosted: Mon Feb 28, 2011 10:01 pm    Post subject: Reply with quote

Okay I have some pictures to help/confuse the situation.
I hope you guys can decipher all those numbers.
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New R&P set
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And this is why I changed them in the first place.
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PostPosted: Wed Mar 02, 2011 12:28 am    Post subject: Reply with quote

Ok, up to 65 the deviation number was scribed onto the pinion gear, 65 and later on the ring gear. Looks like the old one was either .05 or zero, cant make heads or tails of the new one. Theres going to be matching numbers on the ring and pinion for both sets, these are not the numbers you want, they're just there to show that they are indeed a matching set. You really need a Bentley.
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PostPosted: Mon Mar 07, 2011 1:10 pm    Post subject: Reply with quote

Okay, tell me what you guys think of this pattern.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


This is with everything in the case and the case halves bolted together. My side bearing preload is good and backlash is good as well. I'm thinking that pinion is slightly too deep and it needs to move forward some (away from ring gear). Problem is that it's as far forward as it will go so...damn.

I have a line on another NOS R&P that I may have to go to.
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PostPosted: Tue Mar 08, 2011 9:13 am    Post subject: Reply with quote

Here's another set of patterns I took yesterday. They seem a little better.
Any thoughts?
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PostPosted: Tue Mar 08, 2011 10:01 am    Post subject: Reply with quote

You are still miles off.
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