carrier bearing preload

rogue68 · Feb 15, 2003

I am replacing all the internals in a 12-bolt posi. Its a total rebuild. Going well but my instructions on carrier bearing preload are not very helpful.

The old carrier had a total of 242/1000" shim on each side (242 on the left, 242 on the right). It was really tight to get the carrier out. In fact, I needed a crowbar.

I just checked with the new carrier and I can slide in about 234/1000" on each side. But to get it to 242/1000", whoa, it is super super tight. Its gonna take a hammer to get 242/1000" on each side.

Maybe the old shims were good, maybe they weren't. What is the correct way to know?

Do I...

1. Measure with a feeler guage then add a set amount of additional spacers? If so, what is the value I should use?

2. Maybe I should use an inch-pound wrench and check the total resistance of pinion+carrier? If so, what is the best way to do this?

3. Maybe I should just use what it had?

4. Other approaches?

Thanks

Vintage 68 · Feb 15, 2003

There is no simple answer to your question -
Are you replacing the carrier and the gear set? if so you can probably not use your original spacers.
If you are using the original carrier they will at least give you a starting point for set-up - maybe. If they are as tight as you say, I would install the left (ring gear) side and use a large screw driver or pry bar to set the carrier over to the left side and tighten the caps - now check the backlash and see if it is close to spec.s - if so, you will have a starting point for shimming the right - if not you will need to adjust left side to get in the ballpark for backlash and then remeasure the right side and purchase shims to make up the distance - then add @.007 ~.008" 'preload' to the right shim pack and you're done.

"other approches" - yeah, a good rear-end shop.

[This message has been edited by Vintage 68 (edited 02-15-2003).]

davidpozzi · Feb 15, 2003

The ring and pinion usually come with instructions. Do you have those?
The GM factory manual shows how to do it in detail.
I'd say you probably need a shim kit and some GM "service" spacers. they are rings around .150" thick or so, they take up most of the space so you need less shims.

Shim till you are at zero preload, set backlash with the thin side shims by swapping left and right, then add same amount of side shims on each side to get preload in pinion inch pounds to spec while keeping the backlash correct.
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 02-15-2003).]

Vintage 68 · Feb 15, 2003

- and check gear contact pattern with marker dye to be sure you are in the right area before and after adding preload.

PDQUICK · Feb 15, 2003

Your question scares me a little! It makes nme sure you have never set up a rear end before.

Did you set the pinion gear depth when you installed it?

I'm all for doing it yourself, but a rear gear needs to be set up precisely, requires a few special tools, and is definitely one of those areas where a little "touchy-feely" experience goes a long way. If you want to avoid ruining a few hundred bucks worth of rear end parts, now might be a good time to yell uncle.

oger · Feb 15, 2003

You need to measure the total width of the old carrier plus shims and adjust the shims for the new one to come up with the same total number. It can be real tough if you don't have the correct tools.

big gear head · Feb 16, 2003

There are very, very few cases where you can use the original shims again. Even if you are just changing bearings and leaving everything else alone, sometims the original shims won't work. You NEED a good selection of shims to properly set the backlash and bearing preload. The Super Shim set is the easiest and most convient set of shims that I have found. You need to get the shims tight enough that you don't dammage them when you tap them in, but not loose enough that you can pull the differential out by hand. It is something that you kind of get a feel for after a few hundred rear end jobs. How far have you gone into this rear end?

------------------
'69 RS/SS396 pro street
427/4spd/9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead

rogue68 · Feb 16, 2003

Thanks for the answers. Yes, I am replacing everything.

The backlash checks out and I do have a full set of shims. So, I should be able to add the same amount of shims to both sides to set the preload, while at the same time keeping the backlash constant.

The ring gear instructions just say, "the carrier should not fall out of the housing, but should have to be tapped in during final installation". Helpful but not specific enough for me. But, I guess that is what you are telling me, big gear head - there is no spec? Get it tight but not too tight, and rely on your experience?

davidpozzi, it sounds like you are saying I should use the inch-pound method. I have an old Car Craft that gives a total bearing preload of 25-27 inch-pounds. So, once the pinion bearing preload is set I can just add shims to the carrier until I get the correct total? Maybe that is what I will do.

Thanks for the answers. Any additional thoughts on this are more than welcome.

[This message has been edited by rogue68 (edited 02-15-2003).]

big gear head · Feb 16, 2003

I don't like the inch pound method because it changes with the gear ratio. A 4.10 gear will turn easier than a 2.73 because of the torque multiplication.

------------------
'69 RS/SS396 pro street
427/4spd/9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead

rogue68 · Feb 16, 2003

Hmmm... interesting. Thanks. I have a lot of good information on rebuilding these rearends, except the carrier preload information seems incomplete. Perhaps its because of what you imply - it is a step that needs some experience. Unfortunately for me.

Everett#2390 · Feb 17, 2003

rogue,

davidpozzi has given the correct route.
In one Chevy manual I read back when I was learning, and still am, the instruction to set carrier bearing preload is .010." This is after removing the "looseness" (side-to-side motion) in the carrier.

I intrepeted this meant placing the dial indicator axially, in parallel with, the axle and measure the side-to-side movement of the carrier in the housing. Shim accordingly to remove the "slack." Then, with the presently installed amount of shims, set the backlash by swapping shims from one side to the other.

After setting backlash, then add .005 to each side to set preload of the carrier bearings.

It took me an afternoon to set, but, it was worth the effort. I later took the car to the track for trial runs and I was alittle slower. I measured the cover for temp and it was hot. One of the other mechanics there at the track suggested I remove some preload. He suggested I did the job correctly, but, made it alittle too tight.

So, I removed .002, tried again next week, it worked great. Cooler cover, and my et was back.

As suggested earlier, make sure your pinion depth is correct first and foremost. Then set pinion preload, then do the carrier stuff. Listen to big gear head, touchy-feely is a learned experience.

Vintage 68 · Feb 17, 2003

Everett:

Been learnin 'bout these Chevy's for 30+ years now - so I'm right there with you.
GM always recommended the preload spacer be added to the right (or non-ring) gear side as far back as I can remember, maybe they have changed something and I missed it. Adding the preload to the right side limits the changes to the backlash you worked so hard to achieve.
As a general rule the factory recommended preload for differentials under 9" was .007 ~ .008 and .008 ~ 0.10 for diff's over 9" that use spacers (light trucks). You're having to remove .002 (x2) from your unit put you back in the factory preload area and would have resulted in the better results you reported.

Hope Rogue continues to work on his set-up and everyone can talk him down until it's right - this ain't rocket science, but it's just as heart breaking sometimes.

Everett#2390 · Feb 18, 2003

Vintage, Thanks for the lesson, I'll keep it in mind next time.

It was a '68-'72 Nova Manual from Helm. Could have been a misprint on the .010", also I may not have read further into the paragraph(s) about the side of installation.

Thanks again!! You explanation does make sense. I hope rogue keeps trying........

carrier bearing preload

rogue68

Vintage 68

davidpozzi

Vintage 68

PDQUICK

oger

big gear head

rogue68

big gear head

rogue68

Everett#2390

Vintage 68

Everett#2390

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