So I've had a vibration in the rear for a while, not bad and usually only feel it right around 50 MPH. Slower or faster speeds are pretty smooth. I'm also feeling a slight wobble at around that same speed. I checked the rear and everything looks pretty good with the exception of the driver's side yoke end play. I haven't measured how much, but I took a quick video of me just pushing up and down on the rotor (wheel was off). Is this what I'm feeling?


I would like to get through the summer if I could without having to drop the diff, probably no more than 1,000 miles. Is this bad enough that I should just bite the bullet and fix it now or can it wait?

 

oh yeah. thats way too much play

 

Looks like carrier shims and/or bearings need to be addressed.

 

It will need attention soon but you should get another 1000 miles out of it. I don't think its the cause of your vibration.

 

Thanks for the input everyone. Been chasing that vibration for a while. Over the past 3 years I've replaced all 4 wheels, new tires, Van Steel coil-overs in the front, Borgeson steering, and had a 4-wheel alignment done. The car drives great, just an annoying vibration around that 50mph speed. All that's left in the suspension are the trailing arms/rear wheel bearing assembly and the diff. My plan is to address both this winter. I'm concerned whether or not the differential will make it until then.

 

Check how much play you have. I was up to 0.120" and my car was still running fine. Some guys remove the retaining clips.

 

OK, my youngest son works at Advanced Drive Line.... all they do is rear ends & drive shafts. I showed him your post & video. He says your bearings are shot. Typically, vibrations at 50 MPH would be drive shaft related, but in your case, it is the rear. He says the more you drive it, the more damage it will do to the ring gear and carrier. He says it should be fixed immediately. But if you keep driving it, keep your Triple A card handy, and be prepared for a more expensive repair when you DO get to it.

 

Seen lots worse than that. The video doesn't show any bearing movement, just end play from the end of the yoke wearing.

 

You have worn axles most likely. You didn't mention what year it is but 73-79 original axles were junk, soft faced. You have to make sure the axle isn't grinding into the axle seal lip - it looks pretty close. If so stop driving and drop the diff when you can.

Axle endplay comes from
1- worn axle faces
2- posi set up
3- worn case cross shaft holes

 

It is a 69. Would disconnecting the half-shaft and measuring end-play with a dial indicator be enough to tell how much is left? Or are there too many other variables to account for like clutch and cross shaft wear?

 

69 axles were pretty good but can still wear. Did you check the casting date to see if it's the original 69?

The axle is supported in the housing by full compliment roller bearings, the spline end slides through the posi spider side gear and is held in place with a snap ring. They always ride against the cross shaft which is hardened. So if the axle face is worn down you get endplay, posi clutches don't wear down as much as people think but the setup with the springs is sloppy a lot of times and the spring tension weakens over time, the cross shaft hole wear is not as common but I have had some come in and one comes to mind that had good axles and .100 ,movement because the holes were worn open.

If you remove the 1/2 shaft you can certainly measure it but you probably can rig up a mag base and catch the edge of the axle and do the same thing. The lip I refer to is part of the housing and should be about an 1/8", you can pull the axle out as you did and shine a light to see if the lip is being ground down. If the lip is not being hit yet you should be able to drive the car a while but keep it in mind. If it is hitting you should fix it before it hits the seal and wrecks the housing.

 

Thanks for taking the time to respond Gary. Your advice is always appreciated. I ended up using feeler gauges to measure end play. I came up with .077 so definitely worn, but hopefully not critically worn yet. I didn't see any wear on the lip either. I'm going to try and wait until the winter when I'll have more time to do this right and address all of the other "while I'm at it" stuff that always comes up.

I took a quick ride and recorded the rear suspension. Nothing looked out of whack to my untrained eyes.

 

yeah 077" isn't good. The IRS looks like you went through it. I see a HD rear cover, did you replace it or someone else? Just curious if the axles were checked at that time? If you plan on breaking it down and need any advice contact me directly and I will coach you in what to look for and check. Were you still getting the vibration?

 

someone put a lot of time into that rear sujspension, kinda surprised they overlooked the yokes

 

That would be me. When I first bought the car 14-15 years ago the original leaf spring was sagging, the strut rods were badly bent (I assume for alignment purposes), and the original diff cover had one of the ears broken off. I pulled everthing off except the trailing arm assembly. I added the Vette Brake smart struts, a HD diff cover from Muskegon, and the TRW style fiberglass spring from Muskegon. I wish I had gone with Vette Brakes fiberglass spring instead since I have to use 10" bolts to get the Muskegon spring low enough, but I didn't know any better at the time. When I replaced the diff cover I did visually inspect the diff, but I don't recall how thorough I was and didn't realize I should have more closely checked the side yokes for wear.

I'm still very much a novice at this. But I enjoy working on it and learning as I go.

Gary, during the drive I took in the video, the vibration was actually pretty minimal. It was just a brief cruise with the wife through town and I hit the magic 50mph mark only a couple of times. I'll take some more videos soon and post if anything interesting shows up. I will definitely hit you up for some more guidance as I plan my tear down this winter.

 

Updating this thread:

I just pulled the diff and measured end-play using feeler gauges between the cross pin and axles. I got .045 on one side and .039 on the other so not as bad as I had thought. I took one of the axles out and measured from the tip to the groove where the snap ring goes and got .173". I saw on some older threads that on average new they are .18"?

So should I just stick the axle back in, seal it back up and run it? My front pinion is leaking pretty badly so I'm going to replace that seal for sure.

 

same answer as before:

Axle endplay comes from
1- worn axle faces
2- posi set up
3- worn case cross shaft holes

your axles have wear at 173" the axles that are called rebuilt are all over the place for dimensions, apparently no one who rebuilds them knows what the factory set them to? I do but I'll let it go.

I would get those axles on a hardness tester or use hardness files to see what the face hardness is. Buying rebuilt axles will give you a hardened face but more then likely won't help with the endplay. You will have to address the posi setup to do that- unless the less likely problem of opened up cross shaft holes is present. Interestingly the 79 diff I just built had a bad posi because the cross shaft holes were too far gone to even machine them for a 12 bolt cross shaft.

You have want appears to be a common diff, with the inherent issues associated with them. If you have the time and inclination I would go through the diff, replace the bearings, seals, if you want to strengthen it up some then polish and tune it. Not the wimpy window only polishing described by some here as polishing. Remove the sharp edges, seams, and smooth the surface and don't worry you won't remove enough material to make it weaker. Use ARP RG bolts and socket heads in the caps, check the caps for 001" rock, use solid steel clutches. If your budget allows step up to 10-17 spiders over the 18's in a 69.

Also that housing does not look like a 67-69, I suspect it might be a swap out diff, does the posi have a 1 sq window or larger tear drop window? the tear drop is the better case.

 

Thanks for your help on this, I really appreciate the advice. Looks like I have the square window. I'm pulling my trailing arms out at the same time since the bushings are shot so I have some decisions to make on how much I want to spend all at once since this is the perfect opportunity to redo wheel bearings, etc.

 

That is a better view of the housing and I can see the jogs in the vertical walls by the case bearings, where it is wider. That was used from 67-79, there will be a date code on the side of the RG as well.

 

Word of caution from somebody who been at least part way into this rabbit hole.

If you get "rebuilt" T/A's from a vendor, you'll more than likely get offshore axle stubs in them not the more closely machined splines of OEM parts. Offshore stubs will give you rotational slop (my issue) between the splines. It'll sound, look and feel like u-joint movement, but it won't be.

If you or somebody you trust can rebuild the bearing packs in the T/A's and reuse your OEM stubs you may be better off. OR a re-build service to re-do YOUR arms with YOUR stubs (as opposed to an exchange, which is what I did, when I didn't know any better).

You need to pull the arms to re-do the bushings, bite the bullet and redo the bearings while the arms are out.