Discussion Forum - Northstar Chevelle Club

ghaasl · Active Member

Batting around ideas….

Derek69SS · Founding Member

10-bolt will likely hold up just fine for what you're planning to do with the car, but I have to admit there's something kind of disappointing about seeing one behind a big block... it's always "just a 10-bolt"

Extra $2k is a lot to spend for what is essentially a talking point, but you'll never regret it down the road, and you'll never have any doubts about it if you decide to have some fun.

It's easy to justify when it's someone else's checkbook.

Bobs_Place · Vice President

Are you sure the vibration is coming from the rear end? Your comment, "The rear in the Chevelle is starting to vibrate." says that something is changing, that could be a loose yoke nut or pinion bearings failing, but also could be u joint failing or worn rear suspension bushings, also motor/trans mounts, tires and more.

Any changes on the rear suspension/motor or trans mounts?

What speed does the vibration happen and is it sensitive to throttle setting or when coasting?

Check for oil leaking at the front of the diff, push up on the D/L by the diff, should be no play in the pinion or U joint, the wheels must be up or trans in neutral, if all is good I would not blame the diff, Check u joint at front of D/L, look for places where balance weights may have come off. I have also heard of a failing alternator bearing causing a vibration!

Good luck with it, let us know what you find.

Larry Lucast · Active Member

Yeah. What Bob said. I would first check u-joints.

ghaasl · Active Member

So, here’s what I have so far: I changed the pinion seal in March. I made darn sure I set the yoke nut exactly where it was when I removed it. No leaks. I may have underfilled the rear by a slight amount, as I have long fingers. But, driving down to SMN in St. Paul and back to Otsego did not vibrate. It happens only between 55 and 60 mph, about 2900 rpm. When I changed the pinion seal, there were some shiny flecks in the old diff fluid that drained out. Mind you, this rear has been in the car since 1968, and to my knowledge, has the original gear set. I looked when I had it open to change fluid not long after I bought it. It may also be the u-joints. I may just be looking to justify the addition of a limited slip. I haven’t had it out in a couple of weeks due to a work trip. I might just take a spin and try to replicate said vibration.

-- Edited by ghaasl on Sunday 15th of August 2021 07:08:17 PM

-- Edited by ghaasl on Sunday 15th of August 2021 07:08:46 PM

Bobs_Place · Vice President

Have you checked for play (up and down movement) at the pinion, with a new seal you could have a small amount of play without any leakage at the seal? If there is play, the pinion nut has not loosened and metal in the oil there may be a bearing failing and then possible D/L vibration. Another symptom would be howling or a wining noise from the gears.

If there is no play in the pinion, and with the metal in the oil, you still could have the start of a bearing failure, however it is very possible that there is some worn wheel diff thrust washers. If the thrust washers are the cause of the metal in the oil, with fresh lub the diff will still run a long time.

ghaasl · Active Member

I'll check for play this evening when I get home from work. Play in the u-joints, play in the pinion, etc. I'm hoping it won't keep me sidelined. There's still a good 2-2.5 months of decent driving weather left and I haven't had it out very much this year. Thanks for the advice!

Lost in the 60s · President

If you decide to go to a 12 bolt, you can buy an original and rebuild it for HALF what the aftermarket units cost and you don't need all that extra strength built into the cost of the A/M units.

GM went to an 8.5 10 bolt in the early 70's on some models and they are nearly as strong as a twelve. They are still around to be had and we do have a member who rebuilds rear axles. He may know of an 8.5 and could build it out of the vehicle and then you could "just" swap. Still a much lower cost than aftermarket.

ghaasl · Active Member

So, I performed the checks needed and everything checked out okay. I took it out for a drive last night and the vibration had subsided a bit. I think it was maybe the condition of the road as the previous cruise was on an unknown route. Also, being that I hadn't driven it in a while, I was used to the ride of our daily drivers. Even the pickup rides quite smoothly. Probably in my head that it was time for something to be upgraded. I do need to recheck the carburetor, I'm getting raw fuel smell again. Likely just a loose bolt or screw somewhere as I rebuilt it in the spring. Thank you for the advice, everyone. If/When something in the rear does let go, I'll make my decision at that time.