66 Differential - continued

[Gary Schisler]

Referencing my post below about my differential problem - Have any of you had experience with the aftermarket positraction additive versus the GM brand? As an attempt to see if my differential problem might be positraction related, I will change the diff. lube this afternoon. I plan on using the Mobil 1 synthetic diff. lube plus 2 bottles of additive. Any comments here?

BTW, thanks to all of you who have responded. Gary, #21316, 66 L-79 convertible

[Wayne M.]

Re: 66 Diff.Problem (maybe NOT)

Gary, as this rear side-shimmy problem was not there before, I'd re-check the items that you recently modified before considering tearing into the pumpkin. Did the trailing arm work involve new spindle bearings ? Sounds like they (or one side) might have zero or little clearance, and the wear-in heat generation is enough to cause what feels like something tugging on your rear bumper. What speed were you doing when these symptoms occured ? Was it on a straight or sharply curved road ? If it's new bearings, check heat rise at the spindle by removing rear hubcaps (this doesn't work with knock-offs) driving at (say) 50mph, then pulling over as soon as you sense the problem. Check for a temp difference left/right by pressing the back of your index and middle finger against the exposed spindle at the centre of the wheel. If one is almost too hot to touch, it's over-tight, and it will surely seize. Let it cool down and crawl home.

Were your parking brake shoes replaced, and were they adjusted ? It could be a shoe intermittently hanging up (again this will show up with one side hotter than the other). Good Luck

[Wayne M.]

Re: 66 Diff.Problem (maybe NOT)

Gary, as this rear side-shimmy problem was not there before, I'd re-check the items that you recently modified before considering tearing into the pumpkin. Did the trailing arm work involve new spindle bearings ? Sounds like they (or one side) might have zero or little clearance, and the wear-in heat generation is enough to cause what feels like something tugging on your rear bumper. What speed were you doing when these symptoms occured ? Was it on a straight or sharply curved road ? If it's new bearings, check heat rise at the spindle by removing rear hubcaps (this doesn't work with knock-offs) driving at (say) 50mph, then pulling over as soon as you sense the problem. Check for a temp difference left/right by pressing the back of your index and middle finger against the exposed spindle at the centre of the wheel. If one is almost too hot to touch, it's over-tight, and it will surely seize. Let it cool down and crawl home.

Were your parking brake shoes replaced, and were they adjusted ? It could be a shoe intermittently hanging up (again this will show up with one side hotter than the other). Good Luck

[Gary Schisler]

Good Suggestions!

Great suggestions! I did a complete swap out on the trailing arms - supposedly with all new bearings, the whole nine yards. I will check with the company to insure that all the work was done and what there standards are for play.

As a follow-up, this was on a straigt road and I was ususally going anywhere from 55-65 mph. It ususally happened after a lane change, but not always. It would go for perhaps 200 yards and then I would get this "lateral shimmy". I paid for new SS parking brakes set up, to include shoes. I can adjust those myself, but they sure don't feel like they are dragging. But then again, this parking brake set up is not the best and the engine could easily be overpowering the PB shoes. I'll break out my service manual and do a PB adjustment ASAP. As soon as it stops raining, I should be able to take this car out and road test it. I will pull the hubcaps and give your ideas a truu

Thanks for the input. I really don't want to pay for a differential rebuild so I will try these things first.

[Gary Schisler]

Good Suggestions!

Great suggestions! I did a complete swap out on the trailing arms - supposedly with all new bearings, the whole nine yards. I will check with the company to insure that all the work was done and what there standards are for play.

As a follow-up, this was on a straigt road and I was ususally going anywhere from 55-65 mph. It ususally happened after a lane change, but not always. It would go for perhaps 200 yards and then I would get this "lateral shimmy". I paid for new SS parking brakes set up, to include shoes. I can adjust those myself, but they sure don't feel like they are dragging. But then again, this parking brake set up is not the best and the engine could easily be overpowering the PB shoes. I'll break out my service manual and do a PB adjustment ASAP. As soon as it stops raining, I should be able to take this car out and road test it. I will pull the hubcaps and give your ideas a truu

Thanks for the input. I really don't want to pay for a differential rebuild so I will try these things first.