1973 Chattering in rear end

[Ted K.]

1973, 454, automatic has been sitting around for several years. When I am driving relatively slow and turning there is a chattering coming from the rear of the car. I am assuming it is the positrack clutches. I have tried driving in a very tight circle about 10 turns one direction and then 10 turns in the other direction to loosen them up. When I am doing the tight circle there is just a little chatter but with normal driving and taking a easy corner it is a hard chatter. No improvement with the circles.
I recall a GM additive that one could add to the gear oil for the clutches. I don't know if that additive is still available, or is there an additive that can be bought at the local parts store?

[Gary R.]

Re: 1973 Chattering in rear end

Ted
Sounds like you have a handle on it and you did the correct thing except for adding the additive first.

There is no drain plug on the diff, I tap one when I rebuild them which make a oil change about 10 minutes. You will have to get a suction gun or tool to remove as much of the gear oil as possible. I suggest you replace the oil vs just adding the additive- unless it is relatively new. I use Lucas 85-140 non synthetic gear oil and 2 bottles of the current GM additive, then do the figure 8's. You can use 90 wt if you like but Eaton has always stated to use non synthetic oil. The posi additive in my opinion changed a few years ago. I have no proof other then building a lot of diff's and using the GM additive over the years. I used to use just one bottle with a stock or tuned posi and never had a chatter issue but when the part number changed and I used it in my 72 I heard the chatter. I added a 2nd bottle and solved the problem. You can get it from any dealer or places like Summit, about $14 for a 4 oz bottle. That should take care of it for you. Good luck and be prepared for a nasty smelling oil when you remove the old stuff. If you have any questions let me know.

[Bob H.]

Re: 1973 Chattering in rear end

Hi Ted. Follow Gary's great advice and replace that gear oil. a suction pump can be bought for under $10 at auto parts or harbor freight. Good luck with the car

[Joe L.]

Re: 1973 Chattering in rear end

1973, 454, automatic has been sitting around for several years. When I am driving relatively slow and turning there is a chattering coming from the rear of the car. I am assuming it is the positrack clutches. I have tried driving in a very tight circle about 10 turns one direction and then 10 turns in the other direction to loosen them up. When I am doing the tight circle there is just a little chatter but with normal driving and taking a easy corner it is a hard chatter. No improvement with the circles.
I recall a GM additive that one could add to the gear oil for the clutches. I don't know if that additive is still available, or is there an additive that can be bought at the local parts store?

Ted------


The posi additive is currently GM #88900330. You could get it at most GM dealers as well as many ACDelco dealers. The AC Delco part number is 10-4003.

[Duke W.]

Re: 1973 Chattering in rear end

...no need to pay inflated dealer prices or mail order shipping charges. You can buy the additive (4 oz. bottle) at NAPA for less than ten bucks, NCB 4285V, and any other parts chain can probably cross reference the NAPA or GM/Delco numbers.

All OEMs that offer clutch type limited slip differentials use the same anti-chatter additive.

Fresh SAE 80W-90 GL-5 gear oil and a bottle of additive should solve the problem, but don't quite fill it up. It might need a couple of more ounces. Start with one bottle and test. If okay fill the axle to the bottom of the fill port (hot) or add another couple of ounces of additive.

Axle capacity if approximately 3.7 pints.

Duke

[John S.]

[Ted K.]

Re: 1973 Chattering in rear end

Thanks, good info. Will do ASAP>