V8yunkie

My opinion:

If the leak is not too bad (i.e. you will have to add up gear oil every 2 months) I would not care too much about it. I have hardly ever seen an old Vette with a perfectly clean diff. The crud just gathers down there over the years - that might lead one to think there is a serious leak. But all it is is the total of a couple of years.

On my old diff there was some crud, too. But fluid loss was hardly recognizable (as checking through the side plug confirmed). Now I have installed (also an 25 year old, never rebuilt unit) a 3,55 from a friend - he was so nice as to clean and paint it. And wouldn't you know, after three months there is hardly a drop of oil anywhere - after another 2 years, I will probably see the first drops.

So if there is no other problem with the unit, I would just clean it. Or even have it rebuilt (bearings, clutch-plates) without new yokes and cleaned.
However, if you have it rebuild, do yourself a favor and ask for the Big-Block-yokes, because they are much better to work on as they come with caps and boldt to hold the half-shafts (rather then these stupid strap-bolts with nuts - they take ours to install).

Regards, Thomas

Tron79

Yeah, I'd have to agree with you. My only concern is that the end of the little u-strap bolts (holding the inner u-joint to the half-shaft) is just nicking a small piece of metal protruding from the side of the differential. So, I pull up to, or away from, a STOP sign and give everyone a good "cluncking" sound. It's fairly embarassing, but it can wait till winter.

tictocdok

Hey Tron,
I had a similar problem... I tightened the little Ubolts lopsided and one end of the bolt would hit the tit on the differential, after a few turns the yoke popped out, looks like the inner C clip popped off from the wedge-force of the ubolt whacking the bulge on the differential.
might be an idea to get under there and center the ubolt before it causes bigger problems.

VolVette

I visited the GM dealership and picked up some Positraction Additive. I talked to a mechanic there about the problem and he didn't think that the differential was the problem because he said that I would hear it all the time, and not just when I'm accelerating, if it was the differential.

What do the more experienced think of this?

Corellian Corvette

Again, I have to disagree. My chatter only happened at low speed in both cars, and in the case of the 99, only at low speed when I turned right.

Again, some good dinosaur gear oil and posi additive would be a real easy place to start :)

Sorry to hammer the same point -- it's just that I spend a year with this problem on my 99, and the gear oil changed fixed the problem.

Ron 75 L48

Stephen, I had the same problem that you are talking about. Mine started having the exact same symptons that you described when I was on the skyline drive last year. It turned out to be the differential fluid. I went to the dealer and bought the fluid and additive and changed it myself and it cured the problem. I was really worried that it was the differential itself so I did a post on here and the good people came through. The fluid change is definately the cheap route to go. Hope this helps.

Tron79

Well, I bought the additive from the dealer yesterday and put it in today. After about 100 miles, I don't seem to hear much difference. Do you think it's imperative to drain all of the old fluid and additive, then refill to potentially fix the grinding problem? I didn't drain the old fluid prior to adding the additive. I did, however, check the fluid level before adding the additive and it was fine. Does it maybe take a while before the new juice corrects the problem??

:confused:

StingRayPonyGirl

I'm curious about that myself. I replaced the gear oil and additive tonight and so far no difference, but I only test drove it about five miles. My noise happens after things warm up and upon slowing down to stop. Then it's an intermittent clunkclunkclunk....almost like a "dead spot" on something. I can't see anything rubbing, but tomorrow I'll check out some of the things mentioned here.

Ron 75 L48

I would drain the old fluid completely and start fresh. Mine was doing the same as yours where the grinding noise wouldn't start until everything was warm and I had driven it for awhile. After I changed the differential fluid and put in the additive I didn't have anymore problems.

Tron79

Hmmm... Thanks Ron. I guess I'll give draining it a shot. How did you manage to get all of the old fluid out? I barely had enough space to squeeze the contents of the little additive bottle into the filler hole. Did you use some kind of specialized siphon or evacuating tube?

Ron 75 L48

Marc, what I used was a suction tool that looks like a caulking gun with a long tube attached to it. I jacked one side of the rear end up used the suction tool then I jacked up the other side and did the same thing. I used the same tool (after I cleaned it up real good) to put the new fluid in. Hope this helps.

Ron

norvalwilhelm

As I was reading this post I was also thinking of the tunnel like JeffReed. Mine would grind on the passengers side of the tunnel just behind the slip yoke in the transmission. I solved it by carefully grinding the fiberglass in this area giving a little extra clearance that it was trying to do itself. I also noticed it was alot worse when i had a passenger.

Tron79

Thanks for the tip. I can probably put something together like what you've described. I just didn't want to build something if there was a tool already made to do it. I'll give it a try.

Jman

Yep. I'm having the same problem, and it's ONLY from a dead stop or a very slow roll then it goes away. I'm suspecting the rear end needs lube.