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Discussion Starter #1
To any rear end rebuild experts out there my 8.8 pinon depth has got me scratching my head. I believe that I understand the concept of how to adjust pinon depth but my adding or subtracting of shim seems to have little or no effect on the gear pattern. To start off I used the shim that came off of my old pinon (.026). My marking came out with the drive side mark way at the heel and the coast side down at the tow. From everything I understand that needs I need to add shim to move the pinon deeper. I have tried this up to .050" and it seems to have no real effect on my pattern.
To take my measurements I'm using a bored out bearing(that came with the race I'm using), no crush sleeve, torqueing the nut down to about 16-24"/lb, ans shimming the differential to 8-12 backlash.
NO MATTER HOW MUCH SHIM I ADD OR REMOVE MY PATTERN STAYS ALMOST THE SAME! What am I missing?

I also bought a Ratech tool which told me to you about a .041" shim should work and measured my old pinon as about .01 thicker than my new one, so it stands to reason I should be using somewhere in the ballpark of .040".

Any ideas greatly appreciated
 

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Try spread spreading you’re dye thinner. When you spread then dye on thick, you will get this effect. When I say thin, spread it very thin, just enough to see it. Try it and change up your pinion depth and you will see what I’m talking about.
 

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I'm in the process of rebuilding an 8.8 for my Roadster, so I've been doing a lot of research on the subject. One of the things I found to watch for was to make sure your test bearing and race are the same brand (Koyo v. Timken). There is a difference between them and trying to set the pinion depth is near impossible if they aren't the same.
 

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I'm in the process of rebuilding an 8.8 for my Roadster, so I've been doing a lot of research on the subject. One of the things I found to watch for was to make sure your test bearing and race are the same brand (Koyo v. Timken). There is a difference between them and trying to set the pinion depth is near impossible if they aren't the same.
Not only that but be certain to check the angle of the bearing rollers and race. If your using the old bearing as your test bearing and you placed the new race in the housing, you probably have different angles between the two and the bearing will not sit fully inside the race. Best to buy two new bearings of the same brand and sacrifice one of the new bearings to use as your test bearing.
 

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Discussion Starter #5
Otee, I will definitely try spreading the marker thinner. hopefully, that will work. I'm using a new bearing and the race it came with, I had heard about that issue too and got around it.
Thanks for the help guys I'll let you know how it goes.
 

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Discussion Starter #6
Out of curiosity, what is the most amount of shim you've ever heard of someone needing on an 8.8? If I do need to keep adding shim I'm wondering when I can say for sure I've gone too far and it must be another issue.
 

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Out of curiosity, what is the most amount of shim you've ever heard of someone needing on an 8.8? If I do need to keep adding shim I'm wondering when I can say for sure I've gone too far and it must be another issue.
That’s a question I can’t answer. I’ve done a few Ford diffs over the last 25 years and I’ve only needed to vary slightly, if at all from what the original had. I’ve never actually built from a bare housing. A good friend of mine who is a Chevy guy has told me his experience with gm rear ends is similar.... rarely/never needs to change significantly. But neither of us are rear end experts (unless it’s a blond, then I am expert)
 

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Watch these videos (link). I rebuilt a 1995 with pre-1994 axles and it helped a LOT! Also rather than a crush washer( which caused so much frustration) I went the non crushable shims. There is also a simple pinion depth tool from summit that saved my sanity. (LINK) To use the pinion depth tool, take about a dozen readings with it and take the average for the amount of shims. I did this and it came out perfect.
 

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Discussion Starter #9
Tom,
I actually bought that tool. What's destroying my sanity is that even with the measurement that I get from the tool, which coincides with my ballpark guess, My marking aren't centered. I'm going to reattack today and try putting a very thin layer of marker on as suggested above.
 

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I know what you are going thru. I redid my 8.8 and got tired of putting it together and taking it apart, not an easy task, even when the car is up on the lift. I put mine all together filled it with lube took it for a ride and had a wine. Had to pull it out again and redid it. Second time was a charm and it's been fine now for thousands of miles. My advise is to get it close and button it up and take it for a ride. Good luck
 

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Hey man - you didn't say what gear set you are using. I would recommend sticking with Ford Performance if possible. They seem to have good reputation for consistency and being quiet. I just finished doing my second gear swap yesterday and just reused the original pinion shim and only had to fine tune the backlash to get a good pattern. One thing I have discovered is when looking at the pattern it is more important to have it centered between the root and the crown rather than the heel and toe. I also concentrate more on the drive side rather than coast as that is the side that will see the highest load. Also , in my experience, the pattern will never be perfect and look like all the pictures you see. Maybe you should post up some pics of what yours looks like.
 

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Discussion Starter #12
Thanks for all the help guys. I think I finally got it figured out. Using a much thinner layer of gear marker definitely helped. In the end something very close to my original shim did the trick. I do have Ford Performance gears and consulted with an expert at Summit where I bought them and he thought my marking on the drive side looked good with that, the coast side is just inexplicably way in toward the toe. I feel pretty confident about it now, of course I won't know until I build the car to go with it and get it out on the road!
 
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