10 bolt 8.5 ring gear pattern question - Chevy Nova Forum
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Old 31st-July-2019, 11:01 PM   #1
Truck21
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10 bolt 8.5 ring gear pattern question

I do not post much but I am a regular reader. I am grateful for all of the information on the site.

I have a 8.5 10 bolt that I put a 30 spline truck truetrac and 12 bolt moser axles. I changed the gears from stock to 4.10 and installed all the above with a great wear pattern. I reused the shim under the large pinion bearing. I never ran the gears because I and am now building an 80mm billet turbo lq4 4l80e combo.

I changed the gears to a more turbo friendly 3.42, and now the wear pattern looks off. It looks to my novice eye that the pinion is too high and needs a bigger shim. In all my lurking here and elsewhere the norm is the stock shim is reused and is usually fine. Can you please look at the pattern and tell me if I should add a shim? If so, how much would be a good guess?
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Last edited by Truck21; 1st-August-2019 at 07:20 PM.
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Old 1st-August-2019, 12:21 AM   #2
J Mark
 
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That is actually pretty good for the "coast" wear pattern. How does the "drive" pattern look, the other side of the tooth. I'm as novice as you can get as I just did one a couple of month's ago for the first time. Actually the same build with 3.73's. I used a pinon depth gauge to get the pinion set and I could not use the stock shim. I have a few pics of my setup on my build link but I think you are pretty close.
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Old 1st-August-2019, 07:55 AM   #3
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Agreed, both sides need to be good. Here is an awesome video, this may or may not already be known by you. Its to the point and no steps missed.

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Old 1st-August-2019, 10:34 AM   #4
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I agree with the OP that the gear contact pattern on both the DRIVE side and the COAST side looks a little high on the teeth of the ring gear.
I would increase the pinion shim thickness about .003-.004. If the contact pattern still looks a little high, then increase the pinion shim thickness an additional .003.

Below are some contact pattern images of when I rebuilt my 12 bolt a couple years ago. You can see how the gear pattern changed as different pinion shims were used. I started with a .031 pinion shim... increased to a .034 pinion shim... and then final set-up was a .037 pinion shim (with .009 -.010 backlash). As you can see in the photos, there was not that much change in the contact pattern between the .031 and the .034 pinion shim.
DRIVE SIDE


COAST SIDE


How are you turning the ring gear to get your contact pattern?... turning the pinion?
You will get the best (most defined) appearing contact pattern by inserting an axle into the differential and then turn the axle to move the ring gear. I used a piece of 1x2 inserted between a couple of the wheel lugs to turn the axle.

NOTE: You also do not need to put contact pattern compound on each tooth of the ring gear. I only coated about 3 teeth (both sides) in 4 different places on the ring gear.
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Old 1st-August-2019, 02:33 PM   #5
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I would add .002-.003" under the pinion assuming your backlash is good now.

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Old 1st-August-2019, 06:52 PM   #6
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Thank you all for responding!

MY backlash was at .009. I just tried to close it up a bit and only could get it to .005. Here is the pattern from that.

I think I will drop the pinion .003 and get the backlash between .006 and .009.

Thanks again for all the help!
Bill
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Old 13th-August-2019, 03:34 PM   #7
Truck21
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OK so I added a shim and here is what I got.
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Last edited by Truck21; 13th-August-2019 at 03:40 PM.
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Old 13th-August-2019, 04:56 PM   #8
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The above it with .007 backlash and I went from .020 to .030 shim. I know it is a lot but I found the original shim and it was .030.

Thank you for all the help!
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Old 13th-August-2019, 08:23 PM   #9
Truck21
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Ok, so I am waiting on the marking compound. I tried Prussian blue and Desitin with coloring. I don't like the way it looks. The marking compound should be here tomorrow. I'll post an update then.

Thank you,
Bill
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Last edited by Truck21; 14th-August-2019 at 11:24 AM.
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Old 15th-August-2019, 05:53 PM   #10
Truck21
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Update

Here is the new pattern with lightly coated teeth.
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Old 15th-August-2019, 06:26 PM   #11
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If backlash is where it needs to be...I’d run it. Pattern looks fine.
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Old 15th-August-2019, 06:48 PM   #12
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I agree that the pattern on both the drive and the coast sides of the ring gear look pretty good.
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