I need some help on what looks to be turning into a summer project!

My rear had some coast noise, bearing noise and driveline vibration. It was getting louder, so I was planning on getting a replacement from the junk yard, but I figured I'd tear it down first to check it out. I've never worked on rear axles before, so I've been learning a lot.

(I have a 9-bolt Borg-Warner, Posi, 3.45 ratio, w/PBR Disc Brakes. Mileage = 172K.)

So, I tore down the rear up to the carrier and found I had a bad carrier bearing. Then I turned the drive shaft some more and realized I also had a bad pinion bearing. I examined the gears and they looked great (but what do I know). So.... I decided to rebuild.

I ordered a full rear install kit w/new bearings etc... I also got new wheel bearings and seals. Last week I had all the bearings pressed on.

This weekend I reassembled - with all the old spacers set the pinion preload (with old crush collar) set to about 18 (just for a test) and did a gear test. Here is what I found....

Backlash: .010 - .014

Gear Mesh (Heel-to-toe): I did it multiple times. With a light load it was on the toe side. With heavier loads it spread to 85% of the face width. Then I did another one that was centered on the heel side. Sort of makes you feel like your going batty! So, I got patterns on the toe side, on the heel side, and some spread (but mostly centered) across the full face.

Gear Mesh (Root-to-Crown): Centered but on the high side. The top edge never goes over the crown but comes within 1mm on the toe end. Except for that, I'd say the depth was OK.

Current/Original Spacers:
Carrier Shims: Drivers 0.192", Pass 0.200"
Pinion Shim: 0.020"

Factory/Other Specs:
Service Man Backlash: .004-.007 (new gears?)
Other spec from this board: .006-.010 (from Drain89's great post)


I mainly focused on the drive side and ignored the coast side (big mistake I realize now.) The Precision Gear install kit instructions I got didn't show the coast side patterns. (Everything is apart again now).

There seem to be two camps of thought on setting up used gears. One is to leave everything as is and the other says re-adjust to factory setting - possibly a little looser.

So my questions are:

- Should I reshim the carrier and if so, what backlash should I shoot for? From my understanding measuring 10-14 thousands I should use the low number as my base value right??? That would mean I'm "in spec"??? If I swapped left and right shims, my estimate is that I'd be in the .004-.008 range, I'd be nervous that is overly tight with my old gears though.

- If I decrease my backlash will that increase my pinion depth as a side effect? (I could use a little more depth.)

- How much load should I put on my gears when testing?
I seem to be able to affect the pattern a lot. The last test I had a friend hold the passenger tire while I turned the drive shaft hard with a ratchet.

- I split one of my factory carrier shims. Where can I find some replacements? The install kit did not come with enough shims to even fill one side.

I took some pictures and will try to post my gear patterns. They look better in picture than they do in real life.

Thanks for your assistance and comments!!

 

Set your pinion preload correctly at 12 to 15 inlbs and then set your backlash at the recomended .006 to .010. After this is done check where the pinion wear pattern is and adjust it to be in the middle of the tooth profile (root to crown) on both coasting and power. You want the heal to toe in the middle but you may not be able to get it in the middle of the tooth profile and there is nothing you can do about it. It my be the way the case is machined.

Just to let you know when I installed my 3.91 gears I had to set the pinnion shim at .093 and the drivers carrier shim at .181 and passanger side at .200.

 

you can change back lash by moving the carreir shims around. you don't need to change the thickness of the shims, just the location from side to side. you don't need to change anything on the pinion if the depth is correct.

 

JA_Formula_89:- Which company did you get the install kit from? Do you have the part number? Web-link or anything? Many thanks!

 

Ede:

Are you saying I should swap my left (single .192") shim with my right (single .200) shim?

I considered that, but by my estimates that would reduce my backlash by about .006". That would bring me down from [.010" - .014"] to [.004" - .008"]. It seems awfully tight to me. What do you think?

With my old gears (172K) what backlash should I shoot for just the standard .006-.010? Also, should I use my low number or my high number for doing the setting?

One of my shims also split... It could be usable, but it would not be optimal.

Dr G:

I got the kit from Reider Racing. My axle used the GM7A series kit.

www.reiderracing.com


Carrier Shims:

I just spoke to a tech at Reider Racing, he said they don't sell an individual carrier shim kit (just the install kits) and that for my axle, I'm supposed to get my shims surface ground and then add shims from the kit to make up any difference I need. I've never heard of that one before. I guess it sounds possible though.

I also checked the GM dealer today, they don't offer any carrier shims for my axle - at least that's what they told me.

- joe

 

yes that's what i mean. the way it works is you can't change the total shim thickness but you can change the arrangement to move the carrier right or left as you need. i'd shoot for .008 as for a range i'd go for .006 to .010.

 

Ede,

Thanks for your input.

Yes, I understand... Total (both sides) shim thickness will not change.

So, I should shoot for .006 - .010. I thought I read somewhere that for used gears the backlash should be higher - I'm not sure if that was correct or not though - but I'll take your advice and not add slop for being used. (Same as Bjankuski has suggested.)

I'm at .010 - .014, so I'll need to reduce backlash by .004.

I'm guessing means I want to shift the carrier by about .005 - .006 to the right. (Using the 70% rule.)

Split Spacer?:
What do you think about reusing a spacer that has a split in it? I was thinking if I put the split down in the groove and use the cap to lock it in - that it might be ok. I hate to do it, but if its going to be too much of a pain to replace, I might consider it.

Backlash affecting Pinion Depth?:
Will decreasing the backlash affect the marked pinion depth at all? I don't really know, but it seems to me that by moving the ring gear towards the pinion that the depth would increase slightly as a side effect. Is this true or am I way off?

 

OK, here are the pictures I took of my gear mesh last weekend. (This was with backlash still at .010 - .014)

Its hard to see, but the gear pattern is less than 1mm from the crown edge on the toe end. (Marked with red lines.)

Note how my center toe-to-heal shifted for each test although I changed nothing - except loading. (Green X's)

What do you guys think......

- Is my pinion depth ok?
- Will tightening up the backlash be enough for me?

 

what the contact pattern looks like is the last thing i worry about. if i set pinion depth and back lash it has to be pretty good. however i know you had to guess at pinion depth. i'd get the back lash down to .008.

 

Are you suppose to reuse the crush collar? I thought that was the first thing to trash.... Seriously. I am going to be posting real soon myself, as I am still debating which rear to build up..... 9 bolt or 10 bolt. later, shawn

 

don't reuse the crush sleeve, the solid spacer is reusable

 

Ede:
I didn't guess on the pinion depth. Its still all my original gears and spacers just new bearings. When I said "Used Rear", I meant all original just used with new bearings! Does this change the advice on changing the backlash????

Irocnroll89: (I like that username!)
If you get your install kit from Reider Racing, get a couple extra crush collars, just in case. At least that's what I did. It was like an extra $5 for them.

Technically (according to the service manual) you can reuse your crush collar as long as you don't over crush it. They list the procedure for replacing the pinion seal without changing it. In other places they say ALWAYS use a new crush collar. I think the best advice is to use a new one.

I ordered new shims from RATECH Mfg. Supposedly, their kit contains 0.590" worth of shims. This should be more than enough for me to make modifications on my carrier.

 

OK, last weekend I put everything back together. I think I might have a problem.

I set backlash at .0085. When tightening the pinion, it was incredibly hard to crush the spacer. I went from no preload to possibly too much preload. After turning on it and banging it a little to make sure the bearings were set I measured the preload again. It may be too tight, I'm not sure.

I finally measured preload at 23 in/lbs. After the carrier was installed, I had 37 in/lbs.

I was shooting for 15+ in/lbs, but I didn't want to do it again and in the service manual they list 12-25 in/lbs as their setting.

So, I put everything together, put in fluid, then I started it up. I ran it on the jackstands without the brakes/rotors.

At about 30-40MPH I start getting this loud whining and it gets louder with speed. I'm pretty sure its the bearings. It doesn't sound scratchy but its a piercing sort of noise and scares me to the point where I didn't want to drive it. My neighbor who helped me out said that he thought it was normal and that I should drive it.

Are my bearings too tight? Is this normal? Please provide some input! I've never done one before, so I can't say.

 

shouldn't make noise. your preload sounds ok, 25 in/lbs on the pinion, without the carrier installed. .008 back lash is good. contact pattern look ok? only thing i can think of is pinion depth.

 

The thing that bugs me is this sound sounds just like the whirring sound I heard - with the axles and carrier completely removed and running at similar speeds on jackstands. In that case, it made sense, since I had worn/pitted races on the pinion bearings.

My coast side contact pattern looked very good. That leads me to believe the pinion depth is ok.

I have still not driven it.

Is it possible that running the car at 45-60MPH on jackstands w/o a load would just be noisy like this? My old pinion made this noise, but I never heard it make noise on the highway.

Also, I am under the impression that gear noise would be most apparent under accelleration or deceleration conditions? I'm just coasting w/o a load on stands.

I hope I don't have to tear it apart AGAIN! :-(

 

Well, I put it together as is with the whine and it appears to be OK.

I tried a neighbors truck up on stands at speed and it also had a slight whine - though not as bad.

I'm thinking that the bearings need to work themselves in a bit.

When I test drove my car:
- I had no more float/coast noise
- The bearing scrape sound was gone
- The backlash was noticeably tighter
- No gear noise or whining while driving

I think it seems OK!

On to the next problem!!!