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Old 05-16-2020, 06:05 PM
rohrt rohrt is offline
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Question Factory 8.5 pinion setup?

I'm taking baby steps on putting my 8.5 rear together. If I feel I'm getting to far out of my depth I will throw in the towel and take it somewhere to get finished. That said...

The factory 3:08 will be reused but with a Eaton carrier. I'm at the stage now where I would put the pinion back in. On the face of the pinion its stamped with "13:40 GM 24 1978 3984829" The factory shim is .040.

I know that aftermarket gears have a number etched on the pinion to set the depth. I assume GM did not write the depth on the pinion. I would guess they had certain shims for each gear type.

What do people normally do in this situation? Am I ok to just install the pinion the same way I took it out? I put in new Timken bearings/races. My past experience says they should be dead on.

If I had bought used factory gears how would I set the pinion in that situation, assuming no measurement was on the pinion?

One last question. For measuring the pinion drag what do you guys use? Beam style in/lb wrench?

Thanks

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Old 05-16-2020, 06:41 PM
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I can tell you what I did...being a non expert...

Roger where are you???

I put the factory pinion shim back in, same as original.

I used a beam type torque wrench for my pinion preload.

Make sure you are holding pressure on the ring gear when turning the pinion gear, to get your pattern.

The pinion bearings in my TA started crapping out way too early in their lifetime. I drove it as long as possible, until I couldn't keep oil in it...parked it for quite a while.

Rebuilt it in 2001, thought it might be a daily driver for a while, long story.
It's been doing great ever since, although not many miles...

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Old 05-16-2020, 07:47 PM
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You need a used pinion bearing you can use a flapper wheel on and make it slide on the pinion easy. This allows you to take it in and out and set the depth/ pattern. Hard to put into words, you might do well to watch some videos. You will need to address the crush seal situation. There are 3 options there. If you change the carrier, you will need to set the rear up properly. A lot can get wrecked trying to cut corners like assuming aftermarket carriers are 100 the same as originals

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Old 05-16-2020, 07:58 PM
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I also reused my gearset (3.42) on a new yukon diff. for the pinion shim i measured the heigth of the old pinion bering and compared it to the new pinion bearing, making sure they where both the excat same heigth. Then i hollowed out the inside diameter of the old pinion bearing so it can slip on and off the pinion. then i first started with the factory shim. and test fitted the diff with proper left and rigth shims including case preload, and torqed down the nearing caps to spec and painted the ring gear with test pattern marking compond. Then rinse and repeat the process til you have proper pinon depth, while beeing in spec on backlash, and have an acceptable wear pattern on the marking compond
Tip: to get a good transfer of the wear pattern between the ring and pion, insert an axle into the diff and put resistance on it to load the gearset.
And yes a beam style in-lb torque wrench is a must, it's cheaper than those dial ones and if you are not doing this on a regular basis it makes the most sense money wise.

This video made me attemped this myself, as it was very helpful in explaing the prosess in a easy to understand manner: https://www.youtube.com/watch?v=jh25DUyCWY8

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Last edited by djustice; 05-16-2020 at 08:01 PM. Reason: Adding video link
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Old 05-16-2020, 09:01 PM
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You seemed to have missed that the factory pinion has no depth engraved on it. I get the process of how to measure it.

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Old 05-16-2020, 10:02 PM
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I’ve always just started out with the shim that was under the pinion originally, or a shim pack that mic’s out the same. Usually a good starting point and sometimes dead on to what you’ll end up running.

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Old 05-17-2020, 12:26 AM
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Quote:
Originally Posted by rohrt View Post
You seemed to have missed that the factory pinion has no depth engraved on it. I get the process of how to measure it.
You will have to do it by pattern then, once you have it close ( original shim to start)

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Old 05-17-2020, 07:25 AM
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If you are putting the factory gear set back in the same housing use the original shim. If you didn't measure backlash you will need to re-establish what it had before you took it apart.

They make adjustable shim packs for that purpose or you can use thick shim packs as long as when finished you have the backlash where it needs to be and acceptable preload on the carrier bearings.

Decades ago things were easier with ring/pinion set-ups. 9 out of 10 times the original shim got you where it needed to be. These days it a complete crap-shoot so it's best to measure pinion depth and start there if it's etched on the bottom of the pinion.

No matter what the rules are when it comes to this topic you absolutely MUST establish a good pattern drive side BEFORE placing it in service. This can be a little more difficult with used gear sets and they are worn smooth and shiny/slippery finish on them. In any case spend the time to get it dead nuts on the money IF you want it nice and quiet in use and doesn't chew itself up.......Cliff

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Old 05-17-2020, 10:28 AM
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You said you're using the factory gear set you took out and you also mentioned you know how to measure for pinion depth.

I don't see any mention if you measured the pinion depth before you removed it.

That's what I always do if I plan to rebuild a rear and reuse the gear set. That way when the new bearings are installed I can make sure we are back where we started.

I'm guessing you don't have that measurement. Best bet is to do as described and start with the original shim, then assemble your carrier and check the pattern. Hopefully you checked the backlash before disassembly too so you can put that back where it was.

What I've found with used gears is that as everything wears in and they get happy, those measurements before disassembly is where they are going to be happy again. Trying to set things up on the snug side, or just going by a nice looking pattern, may work okay, but sometimes that's not close enough and they tend to make a little noise. Might be fine though.

At this point, I'd do as others suggest, go with the original shim, mock up the carrier, set backlash and check for a nice pattern, then roll with it.

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Old 05-17-2020, 03:08 PM
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Quote:
Originally Posted by Formulajones View Post
I don't see any mention if you measured the pinion depth before you removed it.

I did not.;(

As many times as I have seen it done, it was always with new gears.

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Old 05-17-2020, 07:32 PM
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Understandable.

In that case I'd do what others mentioned. Start with the original shim, mock up the carrier and backlash, and check the pattern. It'll probably be okay.

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Old 05-18-2020, 01:11 PM
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Change of subject slightly.

I'm questions if I should buy a new Pinion yoke or not. What yoke styles are available for the 8.5? I need an education on 3R vs 1330/11310? Was there ever a BOP 1330 U-joint for 8.5 rears?

  #13  
Old 05-18-2020, 01:59 PM
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Quote:
Originally Posted by rohrt View Post
Change of subject slightly.

I'm questions if I should buy a new Pinion yoke or not. What yoke styles are available for the 8.5? I need an education on 3R vs 1330/11310? Was there ever a BOP 1330 U-joint for 8.5 rears?
How much horsepower?

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Old 05-18-2020, 02:35 PM
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450 hp 500 torq.

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Old 05-18-2020, 04:21 PM
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If you plan to grow at all I would highly recommend a forged yoke with a 1350 U-joint, I used a Moser on my 8.5", and also get a new driveshaft made. I got a CM 3" shaft from Strange with 4340 yokes, work of art.

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Old 05-18-2020, 07:05 PM
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Quote:
Originally Posted by AG View Post
If you plan to grow at all I would highly recommend a forged yoke with a 1350 U-joint, I used a Moser on my 8.5", and also get a new driveshaft made. I got a CM 3" shaft from Strange with 4340 yokes, work of art.
X2 I did the upgrade also after I snapped a input yoke and cracked the case on the transmission and also messed up the diff yoke.

X2 on the Strange 3 inch..nice piece especially for the price..I also went with CM ends,input shaft ,diff yoke and their nice straps.

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Old 05-20-2020, 10:54 AM
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I'm sure I'm being picky for no good reason but I wanted to keep my U-Joints the same front to back. Either 1350 or 1330.

Since this rear was from a mid 70s Nova it would have 1310 pinion. I would rather have a 1330 pinion yoke like I have now for my 68 bird. I was have a difficult time finding one for an 8.5. I think I found a place that sells a 8.5 30 spline 1330 pinion yoke. I need to call them. I think most 8.5 had the 3R joints. I'm still in a learning curve on that one.
https://threepedals.com/products/cus...d-pinion-seal/

I have a few drive shafts around already that would be 1330, so I could save a little money having one them shortened verses starting from scratch on everything. I don't plan on going past the current power level. I don't run slicks and I run an automatic.

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Old 05-20-2020, 02:38 PM
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Most of the second gen F bodies use a 3R u joint almost as big as a 1350.

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Old 05-21-2020, 09:03 AM
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Quote:
Originally Posted by Skip Fix View Post
Most of the second gen F bodies use a 3R u joint almost as big as a 1350.
That is what I was finding too.

Series Width Cap
1310 3.219 1.062 All 4 caps
1330 3.622 1.062 All 4 caps
1350 3.622 1.188 All 4 caps
3RL 2.556 1.125

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Old 05-21-2020, 09:45 AM
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If you're changing from the 3R, you might as well go with a 1350. No grease fittings. 3 1/2 inch tube. The Strange forged pinion yoke is jewelry, shame its under the car where no one can see it.

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