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05-22-2023, 03:39 PM | #1 |
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12 bolt pinion shim
To all, anyone have a good guess at a pinion shim for an oem 3.31 gear in a 12 bolt? There’s nothing scribed on the head of the pinion or ring gear. I could be wrong, but I feel like there had to be a quick reference when gm was setting up hundreds of rear ends a year back in the day. Any help is much appreciated. (NOTE: I did find documentation that said 12 bolts got a .030 shim).
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05-22-2023, 04:27 PM | #2 | |
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Re: 12 bolt pinion shim
Quote:
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05-22-2023, 04:31 PM | #3 |
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Re: 12 bolt pinion shim
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05-24-2023, 09:53 AM | #4 |
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Re: 12 bolt pinion shim
Back in the 60.s I did lots of GM muscle cars with 12 bolts & typical shims from .028 to .032 ..start with the .28 & old trick to prevent bearing from getting wrecked on & off many times to change shim is to heat the bearing up to expand so it slips on & off off easy
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05-28-2023, 08:58 AM | #5 |
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Re: 12 bolt pinion shim
I use the reference when I'm having a problem setting up a ring and pinion or I do not have access to the original shim or the old gear was not set up correctly.
GM .035 FORD 8"-9" *020 FORD 8.8"-7.5" .030 ALL DANA'S .035 8 3/4 X 1 3/4 PIN .090 8 3/4 X 1 7/8 PIN .020 MOPAR 9 1/4 .020 |
05-28-2023, 09:43 PM | #6 |
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Re: 12 bolt pinion shim
12 bolts usually take the following, in my experience:
2, 3 ratios...mid to high .020's 4, 5, 6 ratios...low to mid .030's
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05-30-2023, 01:17 PM | #7 |
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Re: 12 bolt pinion shim
.026 to .028 will get you close. Remember when setting a used gear set that it is highly possible that you will not see a good pattern. you can get close adjust backlash a little on the loose side monitor noise on coast adjust if necessary.
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05-30-2023, 05:54 PM | #8 |
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Re: 12 bolt pinion shim
Doing a new set, .030-.032 is my default. On a used set, I'll hedge thinner by a couple thou. and pay more attention to the coast side. A bit of red Loctite on the pinion shaft where the front bearing registers and eliminate the crush sleeve.
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05-31-2023, 09:04 PM | #9 |
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Re: 12 bolt pinion shim
Thanks everyone. We’re on the right track for sure. I set it up with a .030 and based on the master housing depth of 4.670, it’s dead nuts on (pinion depth of 2.755 plus the thickness of the pinion head 1.915 equals 4.670).
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06-01-2023, 06:46 AM | #10 |
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Re: 12 bolt pinion shim
That's fine but pattern and backlash are what matter.
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