I drained my 95's rear end recently. There was a a fair amount of gray muck, about a teaspoon amount or little more, with some silver in the housing. No pieces just the powder size. While the car was up I noticed, by rotating one wheel that the other turned in the opposite direction, just like an open carrier. This told me that the limited slip auburn cone was out - or so I thought. I had another 95 on stands right next to it and when rotating one wheel the other turned with it in lock step.

I refilled the axle but didn't bother with the LS additive. I bought a barely used "factory" locker to repair the car sometime in the future.

The car is not a daily driver so when I took the car out and laid a patch just to verify that the cone was out I was surprised to see that there were two perfectly matched 6 foot patches. I tried it again a few weeks later, same result.

Is my diff actually good and the lack of the additive making the cone grip for a while or do I not understand how a limited slip differential is supposed to work? Like I said, I had another 95 with the auburn cone right next to it. One car's wheels rotated opposite while the other car's wheels were sync'd. Both diffs were auburn cones with the 4 visible yellow springs. Can someone shed some light on what I have going here?

Thanks

 

Try flooring it when you turn right and see if you just leave 1 tire mark. Thats how mine started going out, then eventually I would just leave 1 tire mark going straight when it got real bad.

 

I tried this and sure enough, one tire mark. However, I'm confused because it was the outside (driver side) tire that left the mark. This is not what I expected because I thought that when there is no limited slip in operation the right rear (passenger side) is the traction wheel. I then jumped on it in a straight line. The car left a hundred feet of black mark until it went into 2nd gear where it left another 50 feet of rubber; all from the driver side tire. Once again, I would have thought the tire marks should be from the passenger side if there is only one wheel grabbing.

I have another question regarding the limited slip additive. What exactly is the function of it, how does the differential work without it and what are the consquences of not using it.

Thanks.

 

You are correct that the passenger side tire is usually the one that spins. The driveshaft torques the rearend housing so that the right rear lifts and the left rear plants. That usually makes the right rear spin with a failing posi or an open diff, but I am used to cars from the 60s and 70s (no panhard bars).
The way most positractions work is they connect the side gears to the differential. There are various ways of achieving this:
Eaton uses clutch packs between the side gears and the differential and springs to preload the clutches.
An Auburn cone-type works basically on the same principle, but the end of the side gear is cone shaped instead of flat, and there are no clutch packs.
Then you also have lockers (Detroit Locker) and gear-type (Torsen) limited slips, but I am less familiar with those.

The consequence of not using some type of limited slip? The wheel with no grip is the one that gets power. I think I once read in Hot Rod, "the best way to get 200HP out of a 400HP car is to use an open differential." That about sums it up.

One more thing: limited slip additives are friction modifiers. That means they decrease friction (and therefore chattering), but you want friction with clutch or cone type limited slips. That's probably why your Auburn performed a little better without the limited slip additive.

 

if you run that diff without the limited slip additive, you will be putting a new ring and pinion in in a short time. the clutches wont usually have a friction material on them, but they still need the additive to keep them working properly. some posi's are really picky. The one in my 94 Z is aftermarket and it often does one wheelie peelies on any kind of uneven surface or often when turning corners. however, it will still do the posi thing around turns if you get on it hard enough, as well as in straight lines. some rears are just picky. not all rear ends will have both tires turning in the same direction when the rear is off the ground. the stock Z71's of the 5.7 litre generation often had a limited slip that turned in opposite directions on a lift. I'm not sure what determines this, but it's nothing to worry about as long as you can powerbrake it.

 

I've driven a little over a hundred miles since cleaning and refilling the rear end (without the additive). The gears at that time looked perfect but the gray muck in there gave me some concern so I bought a slightly used factory locker to replace at a later date. I'll open it up and refill with the additive this time. I hate to waste a gasket and $20 worth of lube but I sure don't want to toast the gears. Other than a clunk when going into reverse, the rear end is still very quiet.

Thanks

 

Okay thanks. I'll put the additive back in and treat the diff as if it is still good. If it turns out that only the passenger side puts down rubber afterwards, I'll just make plans to replace the differential.

 

Okay reading this makes me think is my rear end going out? When I do make a turn and get on the gas my passenger tire leaves a patch but my driver side. Also I used to be able to leave nice set of patch marks in a straight line , now not even a chicken scratch . What should I look for or replace. thanks guys

 

That doesn't sound like a rearend problem to me; is it possible that your trans is slipping?

 

Trans got rebuilt only a year ago, I hope its not slippin.

 

you can test your luck in a posi without an additive, but it'll be in the crapper within the next 500 miles.

 

I've scanned the net regarding the friction modifiers for rear differentials and here's my take on it.

All things being equal, friction modifiers are there to reduce or eliminate the chatter associated with slipping clutch surfaces in a limited slip differential while one axle rotates at a different speed than its counterpart. I know that is common knowledge to everyone here except I'm new to muscle cars and limited slip differentiation is a first for me since obtaining my Z28s.

Anyway, after reading for an hour or so and trying to decipher the facts from opinions I've found the following credible information:

Full synthetic gear lube reduces chatter simply by it's superior lubricating properties to the extent that some supposedly official factory advice is to not use the modifier. Other "official" recommedation is to use it anyway. At least one tech recommends using 16 oz. rather than 8 oz. So you can see the diversity in opinions. I can only go by how reasonable the writer seems and how believable s/he is when telling us this bit of information has come from an authority.

As a LSD accumulates wear, the need for additive decreases because the clutch pack loses its potency and therefore needs less help slipping (from the modifier) to keep from jumping or chattering when differentiating axle speeds.

Too much modifier lubricity can affect the LSD to the point that the clutch pack or cone will slip when it is supposed to grip. In which case the differential will then operate much the same as an open case.

An autoparts attendant tells me his 70 chevelle's inside tire chirps around corners even with the additive. Assuming he doesn't have a spool and after reading through several documents, I'm thinking he has a very effective (new) LSD that is a candidate for more and/or better friction modification.

Since my car is putting down rubber on the driver side, I'm concluding that my auburn cone with 100k on the clock is still working quite well although not to the extent that I can detect chirping or chatter in slow turns sans the modifier. By adding some friction modifier, I am hoping to balance the LSD grip and thereby reasonably equalize the traction. The amount of modifier I need to use at this point is still a bit of a question mark.

The amount of gray material initially found in the case is a concern but I simply don't know how much of it should be expected with that amount of miles. I'm still hoping someone here can tell me.

I am about to drain and refill the case again after only 150 miles or so. I will inspect the parts and conditions to the best of my ability and refill it with a synthetic blend and add some additive and hopefully come back with something helpful to report.

Like I said, I have a fresh factory locker and a pile of shims waiting in the event I need to do a rebuild. If I don't damage gears and trash out the axles or housing I'll be none the worse off. I will then have to ask if the FM is necessary with a locker that has no clutches or cone....

Regards

 

First off... limited slip additive only reduces chatter & in no way makes it grab better. Not using it will not break your rear end.

You should use additive in ALL GM limited slips (GM locker style included). The only exception would be a Detroit locker used in the Big HD trucks.

If you have a factory style locker, it has to be out of an S-10 or small van.... Ones from a full size truck will not fit & they were never installed in cars. They do have clutches behind 1 spider gear as well. They are known as a Gov-loc. These rears act like an open differential until 1 wheel spins to a certain percentage faster than the opposing wheel. Then it kicks in & attempts to lock the axles together. On dry pavement this usually results in breakage when used in a performance application. Don't waste your time with this type of rear.... it is the worst thing GM has ever used & I'm not sure why they still use them. I've replaced so many of these that if I ever buy a vehicle with one, I will immediately change it. I cannot stress enough how weak these things are. Sell it & do not waste your time.

 

This is what I gathered. However, I'm sure a chattering condition is ultimately detrimental but when I read that my gears would be destroyed in short order and that 500 miles without the additive would destroy the rear end, a went up.

I may have been hoodwinked but if I was, he did the best job of doing it I have encountered. I want to post a picture of this 2-series factory locker that came from a 2000 Z28 or at least that is what it was sold as. Here's the ebaymotors description:

This is a gear locking carrier,factory unit,from a 2000 camaro z28. It only has 6,000 miles.It also comes with a factory 2.73 ring and pinnion,bearings and shims.Will fit 93 and up camaro.Will also work with other ratio ring and pinions.It would be a great upgrade for a a clutch stlye unit,93-98.

I'm going to try and link the picture for you to examine:



If you don't see the image please click: http://tinypic.com/hv9oy1.jpg

Several emails with the seller convinced me he was knowledgeable. The differential (and gears which I won't use) arrived exactly as described. They are in visually perfect condition even if they aren't the right parts.

Thanks very much for your advice and comments....

Regards

 

Wow, I see a lot of mis-information in this thread IMO.
{1} I didn't see where you said what ratio your present gears are?
That Zexel carrier in the picture will work fine in you 95. I installed one exactly like it {except 3 series} in my 96 with Strange 3.73 gears 30k miles ago and it's working fine. If your going to run a 3 series ratio on your 2 series carrier, {3.23, 3.73. 4.10 ect.} you'll need to buy that ratio gears designed to fit a 2 series carrier available from most gear retailers, or use a spacer designed to mount them although I discourage using this as it is a weaker arrangement. The 7.625 10 bolt is already weak enough.
Don't be alarmed if you install the Zexel and ,when jacked up, one wheel spins one way and the other the opposite way just like an open diff. The Zexel works on a torque principal that requires both wheels to have a minimum amount of traction in order to enable locking. If you get one tire in a mudhole your going to be stuck.
---------
Not using limited slip additive will not hurt the ring and pinion nor bearings or bushings. The additive is used to prevent clutch chatter while turning. Also it has been known to eliminate a condition with the Zexel units refered to as 'rusty screw', which I have not seen with mine. I run Redline synthetic with no additive.
You are correct about synthetics having superior lubricating properties. I ran synthetic in my last f-body with factory Auburn diff with no additive and no chatter. That carrier went 150k miles before I sold it with no problem. But I have seen chatter with synthetics, so that's depending on the particular unit. Personally, I don't use additive unless I get chatter. And I don't recommend running a differential with chatter, use the additive if needed.
I believe the friction modifier reduces the ability for the clutches / cones to hold. When the cluthes slip in a turn on hard ground, it is a small amount of speed difference between the clutch and plate surfaces. When the clutches slip in a burnout because one wheel has better traction than the other, the greater difference of speed between the surfaces creates a tremendous amount of friction heat therefore burning/ glazing the clutch material - very bad. The chance of that happening is reduced without the additive.

The gray sediment in the bottom of your housing is common although a teaspoon is excessive on a regularly serviced unit, or a teaspoon is acceptable if the rearend fluid has not been changed regularly and the cover has never been off.
Unless your running a lot of power with DR's or slicks, the Zexel unit should work well for you. I was very precise with pinion depth, clearances ect. when installing my Zexel/Strange set-up and it has worked well for me for 30k miles, including several launches on my 315/35 BFG drag radials.
Have fun! .