Akshay

How long do rear differentials last in normal driving situations?

Akshay
1989 2.8 5-spd

MDv6man

Usually as long as the car does....

TomP

When I swapped a 3.73/posi/disc trans am axle in, and put my original '86 axle in the backyard, the differential was still working after 200,000 miles.

The posi in the t/a axle was an Eaton gov-lock locker, known for dying. (Auburn couldn't supply GM with posi's that year, so GM went with Eaton.) A governor mounts between the spider gears, and spins "apart" to engage the gears so both wheels turn. Problem- the governor didn't engage the gears perfectly. The spider gears chip. When I fixed my rear discs with the recall kit, I forgot about readjusting the emergency brake. I drove for a month or two with the brakes dragging, which confused the hell out of the Gov-lock, and it died it's normal death (extreme popping during turns) that all the other GovLocks have.

Cone-type Posi units are susceptible to burning out, in a very easy way. They sense slippage between the left and right tire (cones=friction), and apply power to either both tires, or one tire (for turns). Say you get a flat tire... no problem, you put on your tiny little emergency spare, and keep driving. Guess what? You're burning up the posi- as you're driving around, it "thinks" the little spare is spinning (it's smaller so it spins faster), and you drive around on the original sized tire. End result; a dead posi. The solution? Simple, but more work. If you get a flat on the rear axle, you need to put your mini-spare on the FRONT, and put your normal-sized front tire on the REAR.

Problem is when guys like me have larger rear tires (P275/60r15) than their front tires (P225/60r15). Even if I did put the temp spare on the front, and a front tire on the rear, it'll still be mismatched tire sizes. That's another reason why I think I'm going to lose the large rear tires this year. I could go "crazy", and put both front tires on the rear (if I get a flat), but no way that P275/60 would fit on the front. So I plan to buy tires that are a little larger than the front- not too much larger- and then I'll be okay. For the past year I've been carrying fix-a-flat in my car... I'm not really a fan of it, but if I had to use it, I would've.

Are you thinking of buying a junkyard axle?

Akshay

Are you thinking of buying a junkyard axle? [/B][/QUOTE]

No, I bought the car thinking it only had 85,000 miles on it.

But I found large amounts of metal shaving when I opened up the Diff. courier.

So, I guess the car has over 185,000 miles on it.
Otherwise the car sounds and drives awesome.


Akshay

TomP

Good call on taking the cover off! How do the ring and pinion gears look? Think it's just metal from the center, and not the gears?

pontiacguy1

As long as there has not been severe abuse, drag racing with slicks, extreme HP, heavy towing, etc... and the differential has clean oil at all times, I have never seen one wear out, at least not an open differential, ring gear or pinion gear. The posi units are a completely different story. The only rears that I have ever seen damaged were either highly abused, or allowed to run out of or low of oil.

I do know that some of the big rig manufacturers will guarantee the rears in their new trucks for unlimited mileage if you will let them fill it with 100% synthetic lube before you take delivery of it. My guess is that the oil in the rear of your car has not ever been changed, and it may have allowed some damage to occur. It could just have 85K miles on it, and have a bad seal that leaked some. Just my thoughts.

Akshay

I had someone check it and it turns out that the diff. is going bad. Ring and pinion is so-so. If I don't change it, sooner or later it'll lock-up on me while I'm driving.

I have two options:

1. Either get a used rear-end for $250 from recycle yard.

2. Or, buy a limited slip diff. and gears.

I'm leaning more towards the 2nd option with same 3.42 gear ration.

Why did the thirdgen Camaro only come with a 5-digit speedo instead of 6 and no glove box???

Akshay

pontiacguy1

If you are having to pay $250 for a non disc brake rear end at the junkyard, you are getting ripped off! Around here (Tennessee) the open differential rears out of those cars are usually about $60 to $80, and the positive traction ones are only about $120 or so. Both of those are for drum brake rear ends. A disc brake posi rear is usually about $350 or maybe more, since they are much more rare and much more desirable.

My suggestion would be to find a posi, Disc brake rear end and change the master cylinder and proportioning valve, and have yourself a 4 wheel disc brake car. That would solve your problem of the rear end, and would give you an improvement in another area. While you have the rear out, change all the bushings to polyurethane, too. I would say that getting a used rear out of the junkyard would definitely be the cheapest way to go.

The earlier cars have only a 5 digit odometer, like almost all cars at the time had. Mine is a 1992, and it has the 6 digit odometer in it. There is no glove box because behind the dash there is where most of the heater and air conditioning stuff is, as well as the computer. They didn't have room to put one there.

Hope you get your car fixed soon.

TomP

I bought my 3.73/posi/disc axle for $150, then spent an additional $600 restoring it and rebuilding the brakes so they worked like new. So a new gearset and posi might be your best option!!