Scary differential noise...

[MAP]

Greetings folks,

After the car is driven for about ten miles, and thereafter whenever I take slow, tight turns, the rear makes a very distressing clunking/groaning noise. The clunks can be literally felt as well as heard in the cabin.

The problem has been getting steadily worse over the past year, and that, despite regular fluid/posi-additive changes.

What's wrong here?

Today we suspended the car on a lift. With the trans in park, and with a person grabbing each rear wheel, we weren't strong enough to be able to rotate one wheel with respect to the other.

Is this to be expected? Is the (stock, original) posi-unit on the fritz? And if so, what's the likely cause/remedy?

Any advice or ideas would be very much appreciated!

Best regards,
MAP

 

[VIN7]

It's a pretty common clunking noise. Time to drain and refill the differential gear oil, make sure to add GM positraction fluid supplement. I think it is in a 4 oz. bottle. I had to use two bottles to completely eliminate the groan.

Pretty sure you can't rotate the wheels when the trans is in park, try neutral.

Mike

 

[GNVAIR]

Mine made the same noise when going around tight turns after the gear oil was changed in the rear. Adding a bottle of the GM Friction Modifier did wonders. Make sure you stick with non-synthetic oil in the rear. I have seen a lot of failures lately that occured to cars AFTER sythetic was added.

 

[MAP]

Thanks vin7!

You're right: the trans. was in neutral, not park during the test. Is adding two bottles the "standard" cure for this noise? If so, why didn't GM spec it that way? Just curious. The base oil was a standard 80/90-weight hypoid gear oil, btw, if that has any bearing on the matter.

Best,
MAP

 

[MAP]

Thanks GNVAIR, VIN7,

It seems so far that there's agreement that a friction reducer/modifier (do you know the GM p/n on that, btw, GNVAIR?) is the way to go.

But then my question is:

How do I know that my problem is solely of this nature, and not indicative of something more serious? How does one seriously inspect/troubleshoot the differential to ensure that the mechanicals are working to spec, but hopefully short of pulling the whole rear apart and measuring everything as if, say, for a full-blown ring/pinion swap? Or are there no shortcuts?

Or am I approaching this the wrong way?

Maybe I should just add the addiitonal friction modifier and note any change in condition. If the change is for the worse - obviously it's time to troubleshoot/R&R as necessary.

But - if the problem gets better or disappears altogether - can I then be sure that I've done something good? That is, how can I know whether I've treated the symptom or the root problem? Both?

Thanks so much!

Best,
MAP

 

[d0n_3d]

uhhhhhhh i just recently changed my gear lube to mobil 1 synthetic gear lube...

are you telling me that i am soon to have rear end failures???

 

[y-hate]

i had the same problem with my 87, when i take a right turn the rear end would make loud noises and it would jerk a little, so i had GEARS-R-US to rebuild my rearend. they found a lot of metal parts in my rearend cover, so i had Eaton posi put in.....my stock posi was shot also bearings and even my gears had damage.......check for wear when replacing your fluids..just a thought......

 

[salvageV6]

My car did the same thing when NEW, it turned out to be the posi clutches grabbing with the stock Goodyear tires around tight corners.

I'd try another set of tires such as snows or street tires, really.

Mine was higher pitched sound and kinda tink, tink, tink sounding around the slow tight turns such as parking lots.

Very embarassing and I had the car looked at under warranty and the dealer of course couldn't find anything. That was when they almost burned my car to the ground.

Anyway a very happy day when I switched to Dunlop D40M2 tires and the noises went away.

 

[MAP]

Greetings all,

As I understand it so far:

1.) The noise can be normal for some GN rears even with the recommended quantity/kind of posi additive. The solution for these is to add a second bottle.

2.) The noise can be eliminated by changing tires. This isn't clear to me - unless we're purposely reducing traction at the tires so they "slip" before the posi unit does? This seems far-fetched - I must be missing something here.

3.) The noise can be caused by real physical damage to the rear. This is evidenced by the external noise and metal debris inside the casing when the cover is pulled.

So far, then, I'm inclined to add the second bottle of posi additive and watch what happens - if the problem persists, then open the cover and do a careful visual inspection of the innards (there's not likely to be a problem here - I have the fluid changed every year, along with a visual inspection made of the innards. Everything has always checked-out fine, and the last fluid change was only a month ago.)

How does this sound? Could any other scenarios explain the noise I'm hearing?

Thanks again,
MAP

 

[salvageV6]

Humor me.

What tires you got on the back?

I swear it was the tires....damm Goodyears...

 

[MAP]

Hi SalvageV6,

They're Firestone 255-45 ZR-17, SZ50's.

Thanks,
MAP

 

[terryk]

I would assume that if one bottle of additive cures the shutter, then two bottles are not needed? I had a pretty bad shutter and with one bottle, it's as smooth as silk.

 

[MAP]

Greetings folks,

Here's today's update:

A little fluid was drained from the rear. Then a second bottle of positraction friction modifier was added, and finally re-topped off.

The results: no discernable change in status. The rear still makes a pronounced growling/clunking sound with tight turns and at low speed, with the drivetrain warmed-up. In addition, the clunking causes the entire car to twitch as it turns - almost as if the rear had a locker.

According to what I wrote before, it's now time to open the rear and do some careful damage control!

Any opinions on what I'm likely to find, and what's likely to be the best fix?

Thanks again,
MAP

 

[salvageV6]

Can you try a set of 215/65/15 tires or 235/60/15 first?

 

[MAP]

Greetings sv-6,

Thanks but no - the rear must work with these tires, or it doesn't work at all. But no matter - the rear will be opened tomorrow. If there's hard-parts damage, then the matter will be set aright at the source.

Only if no trace of damage is found, will I continue to try to explore other aveneus, but even then - there's no way I'm going back to skinnier tires. I want more, not less, traction.

But thanks for the suggestion.

Best,
MAP

 

[Buick From Hell]

Well, the BFH rearend has clunked since the day I bought it. Only mine does it in a STRAIGHT LINE! (figure that one out!) But it only does it at walking speed or less. You can see the wheel visibly jerk when it does it, too. Additive helps for awhile.

 

[y-hate]

When mine was making noise i think it was my wheel bearings e-mail Gears-r-us and tell them your problem, thats what i did

 

[MAP]

Greetings,

Since the noise/vibration occurs only during turns, then I'm presuming that the posi unit is bad, and that damage is most likely confined to this one component. There are no other signs of problems with the rear.

Is this logic correct, or can there be other related problems? As I wrote late yesterday, adding the second bottle of posi additive to the rear didn't alter any symptoms.

Thank you.

Best,
MAP

 

[MAP]

Hi Folks,

Mystery solved. The rear was opened and inspected; the posi's trashed. Thankfully, there was no visually-detectable damage to the rest of the innards, and no debris at the case bottom: just metal slivers inside the posi unit.

A new Eaton posi unit from Gears-R-Us is already on its way.

Thanks to everyone for your inputs!

Best,
MAP