Groaning New Summit LS Differential and Ring & Pinion

[Safarimeister]

I have a brand new Summit Limited Slip rear differential along with a new 3.73 ring and pinion. The rear end groans, growls, low binding sounds when turning. Typically louder if you turn more than 30 degrees. We used Valvoline limited-slip premix initially. I have since learned these premixes may not always get it right. I also contacted Summit to find out who makes this rear end, i.e. Yukon, but have yet to get an answer.

To remedy this, I removed some of the lube and added a 7 oz tube of TransX friction modifier, then topped off with more Dino 80-90 weight. I didn't realize how thin the TransX fluid was and may have spilled out an ounce or so before filling.

Once filled, I went to a parking lot and did figure 8's for about 10-15 minutes. Things seemed better as I did these, but then once I stopped groaning has pretty much reverted back to where it was. I have now driven it around 25 miles the TransX with little to no improvement.

I should ad, the noise from the rear-end "seems" normal. It does have a slight whine when coasting, but I have read these units are loud because of the cavity under the van, not to mention I now have it lifted.

Could this be: i) a defective LS unit, ii) a ring and pinion improperly shimmed... or iii) a combination of both?

I have around 180 miles on the rear-end.

[markmitch]

GM says never add posi additive to there axles but since you said its from summit I would suggest you give them a call.

[chevymaher]

Vans are loud anyway. The rear end they use is loud. They get louder breaking in then get quieter. 10 thousand miles it should be settling down. If it is a slight whine as your say. It is fine it will always make some noise.

The binding cornering. It is called chatter on a clutch type posi. Once the modifiers work in real good and it developes its wear pattern in the clutches and plates That also should settle down.

Mark you beat me to the post. GM has a posi additive. They burn up the clutches if you don't use one. I just talked to the tech guys at eaton on the chevelle's posi. He said use the ford stuff it is the best. I got 2 bottles I can get a picture if ya need it.

[Safarimeister]

I have asked Summit what to use..., but so far, they have been little help.

I am assuming it is a Yukon. Maybe I should drain it and then add the Yukon product?

[dcsleeper]

We need to identify the type first.

Is it a spring loaded side clutch disk type often referred to as an Auburn? Ford LS are this kind.
requires LS additive
This kind doesn't actually chatter, but more of a 'grumble', around turns.
Other then the true locker that lock and unlock through a turn, these are the only diff that make 'noise' in a turn.

or is it a Gov lock from GM?
no additive needed or wanted
Clunks when it locks

or is it a Truetrac type with helical gears
no additive needed or wanted
no sound

If there is no noise going straight it is likely NOT the pinion depth or side offset.

Perhaps you can post a link to the diff on Summit's site?

[Mmusicman]

If there is no noise going straight it is likely NOT the pinion depth or side offset.

^^ THIS. You need to separate and identify the sounds!

If it makes noise going straight (or coasting straight).. then it has NOTHING to do with the posi whatsoever, and EVERYTHING to do with pinion/ring gear setup (tolerances). Open rear-ends are subject to the SAME issue (again nothing to do with posi). Whining or gear noise is usually this. Improper setup can cause this. Some vehicles mildly do this naturally.. often times more noticeable when empty. The noise (if moderate) is typically not damaging.. just more of a nuisance. But it can be corrected with proper pinion/gear setup, unless the gear is already worn.

A continual growl (that changes with speed) can be a pinion bearing (nothing to do with posi).

Limited slip posi units that utilize clutch packs need additives.
They typically clunk, grumble, chatter, or bind in turns without it.

Then, as mentioned, there are mechanical posi units of various forms... which do not need additives since they don't have clutches. One more popular example is the factory G80 which has a locking mechanism which is physically engaged when one wheel spins. There are many other helical gear types, as well as those with pressure plates, again that do not utilize clutches. Additives will do nothing in these applications.

You need to know what you have, and what your noises mean.

[MechBob]

Yes,as DC has said.Don't know where Mark got his info,but the GM limited slip additive is still the best seller out there,and put many thousands of bottles in,at dealerships.However,as said,the "gov-lock" or G80,you should use no friction modifiers at all,they can actually lead to early wear out/problems.Also,where you live,I would recommend 75-80 gear oil.Do not be afraid of using the GM additive in synthetic gear oils,and,do not be afraid of putting 2 bottles in,instead of 1.

[Safarimeister]

Thanks for all the feedback.

So I drove it on the highway today for 2 ten-mile trips going highway speeds. This was the first time I drove over 40mph since I added the TransX modifier. I don't believe I am hearing any issues in the rear while driving, it's just louder than I am used to given I have no seats and it's an open box right now. I haven't driven it in awhile and am not used to driving it or how much louder it is generally speaking. It has been parked in my garage down in Scottsdale.

By the time I got home, the chatter/groaining seemed to settle down, but that was after everything had warmed up and been running for awhile. Once everything cools down overnight, I will be able to tell if the modifier is actually working when I run it tomorrow.

Here is the unit I had installed, looks like a Yukon?
https://www.summitracing.com/parts/sum- ... /year/2003

Vehicle is in Arizona.

[AstroWill]

Thanks for linking to the unit you purchased, makes it a lot easier. Clutch-type limited slip, YES, you will need the friction modifier, they also recommend that you do not use synthetic gear lube but Non-Synthetic GL-5. Here is the additive that they recommend: https://amzn.to/3hlTwcf

[MechBob]

So,as you have not replied reliably,is your "new"limited slip a aftermarket clutch limited slip.a thorsen,or that type, or a GM type,g80 slip/locker, or a "lunchbox locker"? Information is the key.

[AstroWill]

So,as you have not replied reliably,is your "new"limited slip a aftermarket clutch limited slip.a thorsen,or that type, or a GM type,g80 slip/locker, or a "lunchbox locker"? Information is the key.

He posted the link to the item, 2nd post above yours.

[MechBob]

Hey,Astrowill, I posted before the OP did,about my question/response.not my problem your site is so decrepit, that it comes out a bit later.Grow up.

[chevymaher]

All that matters is it is a clutch type and does use friction modifier.

[Mmusicman]

This was the first time I drove over 40mph since I added the TransX modifier. I don't believe I am hearing any issues in the rear while driving, it's just louder than I am used to given I have no seats and it's an open box right now.

You still haven't said whether you hear noise turning or going straight.
Then you go into a discussion about driving on the highway empty at over 40 and your not sure.

By the time I got home, the chatter/groaining seemed to settle down

Again, was this while turning, or going down the highway?
Your link shows clutch type limited slip.. which requires additives.

[Safarimeister]

... The rear end groans, growls, low binding sounds when turning. Typically louder if you turn more than 30 degrees...

Groans while turning.

[Safarimeister]

Finally got back to AZ this week to further address this issue.

After much reading, there was consensus that Ford's "smelly" limited slip additive in the 4 oz. bottle is the best. All others are questionable.

So after an unsuccessful effort adding TransX friction modifier with no improvement, I pumped out around half the gear lube and added the Ford product then topped off with gear lube.

Within 10 minutes and a few figure 8s voila! The groaning was all gone.

[markmitch]

My information was for the g-80 in our vans and not for other GM products-sorry if I posted it incorrectly -I mean we are talking about an Astro or Safari.

[AstroWill]

So after an unsuccessful effort adding TransX friction modifier with no improvement, I pumped out around half the gear lube and added the Ford product then topped off with gear lube.

Within 10 minutes and a few figure 8s voila! The groaning was all gone.

Fan-freaking-tastic! Thanks for letting us know.