Help! Differential Noise

[krscholz]

My 75 has a chattering feeling and sound from the differential when I make a left or right turn from a dead stop. The chattering goes away once the car is on its way down the road. The Vette is an off the shelf L48 with nothing performance special about it. Can you help me please.
Ken

 

[krscholz]

I did change the differential fluid and replaced it with a synthetic product. The chattering problem existed before and after the lube change. In researching this problem in our forum it was recommended that I use the following:

BG LSII
Limited Slip Axle Additive ConcentrateBG LSII is designed to prevent chatter in plate and clutch type limited slip differentials. BG LSII may be used with any GL-5 gear lubricant in limited slip applications. It is also excellent for eliminating chatter in full-time four wheel drive transfer cases. The ingredients in BG LSII smooth and quiet operation of gears in the differential and fortify the additives in the gear lubricant.Part No. 328
6 oz. (177 mL) tube

Have any of you had luck with this product? Should I go to a GM dealer and get the correct lube as well?

 

[Jimdvette]

I've always used the GM rear end oil 2 bottles and 1 GM posi additive . I think they are still available from Chevy . After adding it drive in a figure 8 a few times and see if the chatter stops. If not you may need posi clutches . You do have positraction?

 

[krscholz]

Help! Differential Noise. Thanks for the advice everyone. I went to my Chevrolet dealer this morning bought some lube and additive just as the above forum recommended. I left to go to NAPA to get a pump to remove the old lube. I just happened to run into the representative from BG while at the store and asked where I could get BG's LSII additive as the product is not sold in retail stores. I decided to keep my old lube since I installed it two weeks ago and just simply added the additive from BG. Did my figure eights at a Wal-Mart parking lot and now everything works great. Oh, by the way the additive was $13.00 and I returned $73.00 worth of lube and additive back to the dealer, nice deal wouldn’t you say?

On a personal note; I am very thankful for our forum as it gets a little lonely out there when you have a 33 year or car when you need advice.

 

[krscholz]

GREAT STUFF!!!!

 

[kvetty]

How do you check the diiferential lube? I took the car to Jiffy Lube, they got it on the rack, took a look then said they couldn't check it.

 

[petes74ttop]

Go to another Jiffy Lube!

Hi and welcome to the forum, to check the gear oil just remove the plug on the side of the differential, it should be full to the bottom of the hole with the car on level ground. PG.

 

[Hib Halverson]

Ok. Now, here's the real story on limited slip chatter.

Virtually all "additives" which seek to eliminate squeal or chatter are "friction modifiers." They mitigate the chatter or noise by degrading limited slip action--exactly what you don't want to do for best performance. In all cases when you use an additive, you do that. If you're putting the additive in a high-mileage or broken limited slip, you're just making a problem (lack of proper limited slip action) worse.

The key is to 1) start with an axle with a limited slip in good condition then 2) add only enough additive such that any chatter or squeal either goes away or, better yet, is reduced to a very subdued squeal.

Chances are a 77 with a chattering diff, if it's never had it's rear axle overhauled or the lube was not changed regularly (ie: ever 3 yrs or 36,000 miles), has a heavily worn or damaged limited slip unit. If that's the case, using an additive, be it one of BG's "overhaul in a bottle" products or other additive, all you've achieved is band-aiding the problem.

What you really need to do is get the diff apart and repair/replace the limited slip diff as necessary.

 

[GTR1999]

To add to Hib comments, the 65-79 eaton posi units are a 4 spring,2 plate loaded setup. The first design clutches are solid steels which were changed to slotted or my term of endearment "snowflakes". These was done to help with the chattering problem but only weakened the units to the point abusive driving styles associated with corvettes broke them.
I have stopped using the spring in these rebuilds and have not had any chattering or broken clutches. They perform better and last longer, the key is the proper setup of the posi. Stock posi will vary from one to another on how they were setup. Once the springs are added they try to be equalizer for spider backlash and result many times in hammering/chattering being too tight.


Take a look for yourself
http://www.digitalcorvettes.com/forums/showthread.php?t=77257

The only oil I use is Lucas 85-140 gear oil and GM additive. I use 1 bottle of additive in this setup.

 

[Hib Halverson]

Keep in mind that friction modifiers can be termpermental. Typically, mixing the GM additive, which is a petroleum-based product, with a synthetic gear lubricant is not a wise idea.

The lubricant I use is Red Line Heavy Shockproof Gear Lubricant. It has a small proportion of synthetic friction modifier blended in. If more is needed, the best stuff to use is Red Line synthetic F.M. which is blended to be compatible with a synthetic lubricant base.

 

[GTR1999]

I agree, I never use synthetic oil in the diff. If you can't find the Lucas 85-140 then 90 wt will work as well.

 

[Hib Halverson]

I think my earlier statement was misunderstood. I said it's not a good idea to mix a synthetic friction modifier with a petro based oil. I did not say that synthetic lubricants should not be used in a rear axle.

In fact, synthetic gear lubricants are a better choice and in fact, GM is now factory-filling a 50/50 blended synthetic in the diffs of C6es and a full synthetic in the rear axles of some trucks.

Red Line Heavy Shockproof is a gel-based synthetic lubricant suitable for clutch type, cone-type and "Torsen" limited slips as well as locking diffs. It's gel-based technology allows it to flow like a 75W90 but have the film thickness of a 75W250.

I've been using Heavy Shockproof for more than a decade in all my Corvettes, my Camaro, my Chevelle and my Blazer. I change it about every 3 years. In some cases I add Red Line's friction modifier in others I do not. It depends of the existence of any limited slip noise and how loud the noise is.

 

[Bolisk]

In all cases, how many quarts of gear oil do I need for a 1970 diff?

 

[JohnZ]

In all cases, how many quarts of gear oil do I need for a 1970 diff?

3-3/4 pints.