Hi Everyone. I have an 84 Trans Am 5 Speed--all stock with 188K miles. I noticed a humming noise in the car at about 65-70 MPH. My mechanic said the differential is making some noise & probably needs a rebuild at some point but I can still drive it for now.. He is saying it could be bearings or could be gears too. Just wondering if you all could give me an idea on how much a rebuild would cost given both scenarios. Thanks, Bobby

 

Probably not gears.

There's nothing special about "WS6" back then. Nobody even paid any attention to that RPO before they came out with the 98-up ones that had the GINORMOUS STICKERZZZZ!!!! Then all of a sudden it became the hottest buzzword evah, that people JUST HAD TO mention every chance they get; kinda like the truck people are about Z71. In 84, all it was AFAIK, was stiffer springs, stiffer shocks, and polyurethane sway bar end links. Might have included bigger sway bars than other cars that year, but even so, they are MUCH smaller than the ones later cars came with. All of which (except the bars) are completely wore out by now.

Your rear is a 7.5" 10-bolt, same as any other 84 Camaro or Firebird. 26-spline axles. Probably 3.23 gears. Probably not posi. Probably drum brakes. Probably nothing unusual or special in any way.

Most likely, the humming is either a U-joint, or the pinion bearings have lost their preload. Try replacing the U-joints first.

If the pinion bearings have lost their preload, it's because they're worn out. Replacing them requires pretty much a complete "rebuild". No idea how much that would cost, beyond just, too much. I would recommend STRONGLY against spending ANY money on THAT PARTICULAR rear, in any case. There are better options than that.

Let us know what happens after you change out the U-joints and we can go from there.

 

Thanks so much SofaKingdom. Really appreciate the advice. I am not sure if it a posi but it def has rear disc brakes. I wanted to try to keep the car as original as possible & dont want to break the bank on too many more repairs on the car at this time. My mechanic is great and has a ton of experience working on these cars.., just looking for a 2nd opinion on the rear end and a ball park on what it should cost.

 

The problem with "original as possible" in some cases is, you end up spending several times as much to achieve that as you would accomplishing the same functional result some other way; and, in the intervening years since your antique was built, MANY things have appeared that are FAR BETTER, and that practically bolt right up. This just happens to be one of those cases. "Original" is NOT the optimum solution if your rear end is farkled, not either functional, nor economical.

In the case of these cars, the early 7.5" rear was a weak, failure-prone POS. It has been improved upon in many ways repeatedly since then. Many of the parts that may be required to keep it "original", such as 26-spline axles, are VERY hard to get, because nobody wants them; nobody in his right mind spends money to put that stuff back into their car. Same for the disc brakes it came with; they're the old 82-88 cast-iron Saginaw ones, well and widely known to be troublesome, inferior, and outdated. The 89-up ones are FAR better. The posi that came in it, if it was posi, is an Auburn POS, almost certainly worn to the point of no longer having any detectable posi action. It's not rebuildable, so the only recourse, if you have one of those, is to replace it. But, since its splines have to match the axles', you then have to find a 26-spline carrier, and nobody makes those anymore either. No matter what, you end up needing to change both the axles and carrier together. It's almost certain that one or both of your axles are bad; they ARE the inner race for the rear wheel bearings, and when the bearings go bad, the axle gets destroyed along with the bearing. And when those go bad, they make noise too; it's entirely possible that that's what your actual problem is. Although those usually make more of a roaring kind of noise, and at all speeds, not just highway speeds.

All in all, the usual best course of action these days, is to replace it with a 98-02 Camaro/Firebird one. It bolts right up. The only difference is, it's a bit over an inch and a half longer on each side, which makes the wheels stick out and look ridiculous, if you use the original ones; BUT, wheels for 4th gen F-bodies, or 84-up Vette, bolt right up.

Anyway, the place to start is, replace the U-joints, and see where that takes you. They're not too $$$, and even if they're not "The Problem", 188k mile ones are CERTAINLY used up, if they're still the originals. Might not hurt to change the rear end fluid as well, and inspect what comes out carefully; probably never has been changed at all, and if there's problems in the rear, the fluid will show it.

 

That is great advice. Makes total sense. Thank you. Will let you know how it goes. Thanks Bobby

 

Good advice from sofakingdom. Last year I rebuilt a disc rear from a 91 car. Bearings, seals and carrier install kit will cost you around $100-$150. I also bought a zexel torsen posi unit to install. That cost me $130. Another $150 for new rotors, pads, brake lines (rubber and steel) and caliper rebuild kits. I reused my gears. So to rebuild a rear end completely from caliper to caliper will run you around $400 without a new carrier. You can get a complete 4th gen rear for around $300 from a salvage yard. I wanted to keep the 3rd gen rear that's why I spent the money to rebuild it. And you need to know what you are doing when rebuilding to set everything up correctly.

 

Thanks Fullmonte77. Really appreciate your input. I am really not looking to do the work myself--I would totally mess it up. I haven't worked on cars in over 30 years. If the wheels are going to stick out on a 4th gen rear then I would rather not go that route. Don't really feel like replacing the wheels etc. I am going to pick up the car from my mechanic tomorrow and see what they say. They are telling me I can still drive the car "for now" but not sure for how long until I run into real problems. I brought it in last week to have the tilt wheel tightened up and on the way over there when I got it up to about 70MPH I heard some noise but it was not shaking--thought it might have been coming from the front end but mechanic says rear noise. At slower speeds it rides like a dream.