Sullyvette

When I make a slow turn, I feel, don't hear, a slight klunking in the rear end. Is this normal? no grinding at all. This would be at 5-10 mph. Chuck

capevettes

Try changing the rear diff fluid. 80/90 weight gear oil and one 4 ounce bottle of GM posi lube. Sounds like the clutches sticking in the rear diff.

RoadKing96

Depending on when you last changed differential fluid, you might be able to get a way with just adding one 4 ounce bottle of GM posi lube.

I had very same issue. I took a bit of fluid out and added Posi Lube. Fixed her right up....Good Luck !!!

RK

MasterDave

I used two bottles of posi fluid and drove in opposing circles (figure 8's) for a bit. Worked great.....

Sullyvette

Thanks, is that something I can add myself? Can I do that crawling under the rear-end? Or, maybe slightly lifting the rear-end? There must be a thread for this right? Thx, Guys

Gary's '66

Same symptoms, same fix!

Yes, you will DEFINITELY need to either raise the rear end or, better yet, find someone who has lift as there's no drain plug (fluid has to be siphoned) and the access plug is a bit hard to, well access.....

Gary

63split63

Before you go to the trouble of removing fluid and adding posi lube take the car to a parking lot where you can run tight figure 8s in both directions . Do it 4 or five times in both directions . Bill

Sullyvette

1965 4spd. vert. OK, I had the rear end fluid changed by the dealer. $ 126. not too bad. Mechanic stated that the fluid was pretty dirty. Thought that would cure the rear end clunk. Nope! Did the suggested figure 8's in an empty lot.
At low speeds and turning, I hear and feel a clung from the rear when taking a slow turn. What's up with that? Any suggestions? Thx, as always. Chuck

erb64

Isn't there a bushing back there that can cause the noise. Big bugger about the size of a tennis ball. Differential bushing?

capevettes

Did the dealer put the 4 oz bottle of GM posi lube in? If so, you could try a 2nd bottle. If that doesn't do it you may need Gary Ramedei for a rear diff rebuild.

Sullyvette

Hi Capevettes, The dealer put in Part# 88862624 fluid, 2 units. No mention of GM Posi lube. This was done at a Chev. dealer.

DansYellow66

That still sounds like the problem. They should know better but they don't know much about these old cars. You still need to put in the posi additive - that's what makes the clutches in the posi work smoothly.

6T5RUSH

I'll 2nd, 3rd, 4th & 5th what all these guys are suggesting to do. It does sound like the dealer replaced the 80/90 gear lube and didn't add the posi additive.This is the GM posi additive you need to add: GM 88900330. Comes in 4 oz bottles. You can buy it here:




Jim
In God We Trust!

Sullyvette

Its going right back to the dealer to correct the Posi additive. Thanks for your experience guy's. I'll let you know what I don't feel. Chuck

Gary's '66

I'd have them to add TWO bottles of the "proper" 88900330 additive. If they say they DID use an additive, they most likely used 8886224 which, is wrong and, btw costs twice as much. I would insist they remove ALL the fluid, refill with 8 oz. (2 bottles) of Delco part # 88900330 and top off with 80/90. Then, IMMEDIATELY find an empty parking lot (possibly theirs) and do the figure 8's. Do them in "both" directions. Good luck!

Gary

Sullyvette

This is the fluid they used. Chev. says it contains the additive needed, it's already mixed in? Thoughts?

Sullyvette

This is what was added. Chev. dealer says the additive is now mixed in? Thoughts?

SWCDuke

It appears the GM product is okay and does contain the limited slip additive. I prefer using a generic API-certified SAE 80W-90 GL-5 gear oil, and you can buy the limited slip friction modifier additive at NAPA for about 8 bucks per 4-oz. bottle. This additive is a generic product that is used in all manufacturers' clutch-type limit slip differentials.

You may have other problems. As miles accumulate the Positraction clutches wear, which increases differential gear backlash. This can be determined externally by checking side yoke end play. With the car on a frame lift push the wheel in and out with someone placing a finger on the side yoke to estimate play. A new axle should have no more than about five thou end play.

As this backlash increases you typically hear occasional "clunks" from the axle, especially on tight turns. At some point the backlash grows to a point where the clunking becomes increasing noticeable and yoke end play increases. The increasing differential gear backlash combined with hard use increases internal shock loading and can eventually cause a differential side gear or pinion to fail.

At this point it sounds like the your axle doesn't have excessive internal clutch wear, but you should try to get a measure of axle yoke end play. Once it gets to .030" you should consider overhauling the axle including a new Eaton loaded Positraction case.

Later models in the C3 era can also suffer from axle yoke end wear due to inadequately hardened yokes, which increases diff. gear backlash, but this type of wear is much less common in the C2 era.

Duke

Sullyvette

I have noticed it occurs when making a right hand turn. I'll check the play measurement. Can this wait till fall? Or, is this something that should be attended to asap? Approx. cost of axel overhaul? Easton Posi case? Dealer or competent garage? Thank you. Chuck

66/427

On a similar note I put a fresh rebuild on a 69 mopar posi unit re-installed back in car, used royal purple 75-80 with the posi additive, so no additional additive needed.Well when I went to try it out a little noise was heard at first drove several miles returned home backed into the garage I thought the rear-end was going to brake there was so much loading on the clutches as i turned 90 degrees into the garage. I was PO. Next day as I took the car back out of the garage same thing the rear was going to brake. Drained off 8 oz of dope added Chrysler post additive topped of fluid went for a ride slowly leaving garage. When I returned home, backed into garage 90 degree turn not a peep quiet as a mouse. Contacted royal purple about this was told the additive was for new style clutching not stuff from the 60s ??? 3 years later still quiet.... I will never use a dope with additive already added. Ric