Clanking/Scraping noises from Rear

[Masonite]

Hey all,

I hope everyone's enjoying their summer so far, despite the crazy weather and tornadoes and such . I've got a problem with my TA, and I'm hoping I could get some advice and opinions on what's going on.

First, the story:
I was turning into a mall parking lot from the highway, braking, when I started hearing a metallic scrape/clunk noise coming from what sounded like the rear of the car. I don't remember what gear I was in or if the clutch was engaged at that moment. It went away for a minute or so. As I made my way around the parking lot; stopping, turning, moving, etc., it seemed like the noise came back (more so the "clunk" noise) every time I engaged the clutch, but would ALSO do it while the clutch was disengaged and I was turning sharply.

The specs:
1985 Pontiac Firebird Trans Am, 305 HO V8, 5-speed manual, Performance suspension-equipped, 9-bolt Borg Warner 3.70 posi rear, all stock except for a cat-back. ~64,000 original miles.

My father and I have been working on it, with various theories of what it could be. The rear end looks great, brakes are on solid with pads wearing evenly, the U-joint and drive shaft all look very well in-tact. We'll be replacing the brake pads while they're off anyway, cleaning the rotors, etc. After that, the only thing we can think of is that it might be the tail end in the transmission (I have heard whirring sounds in 3rd gear, and the syncro's in 2nd gear seem to be going), or the clutch plates in the differential, since we can't take it completely off.

Any advice is greatly appreciated! Thanks!

Right brake 1
Right brake 2
Left brake 1
Left brake 2
Left bushings 1
Differential 1
Differential 2
Differential 3
Differential 4
Differential 5
Differential 6
Differential 7
Differential 8
Differential 9
U-joint 1
U-joint 2
Driveshaft 1
Driveshaft 2
Driveshaft 3
Driveshaft 4
Driveshaft 5

Going to post a video of the noise when I can.

[Blacdout96]

Check the Pan Hard Bar bolts to see if they are loose, also look at the torque arm mount on the trans, make sure thats not slapping round up there. LCA's take a look at them too. Sway bar links? check em out Clunking usually would refer to suspension more then trans unless the trans mount was bad. the scrapping would be more contributed to it. I had a clunking noise on my car, couldnt figure it out, especially when I turned, found out my PHB bolt was loose, allowing it to wear the bushing it was in, and letting it slap around.

EDIT: replace those sway bar links, they've seen better days, not the problem, just saying lol.

[Masonite]

Thanks, Blacdout96. The torque arm mount looked pretty solid, but I'll climb back under there to check it out. Question--what are the "LCA's" you're talking about? I'm not familiar with that acronym.

Thanks again!


edit: Nevermind--google is my friend Lower Control Arms.

[Masonite]

We found that the rear has a little play in it... not much; between a 1/16" and 1/8" play, sounds like the gears slapping together when you go back and forth. Is this normal? Video link:

TA Rear play

[Masonite]

Anybody have any ideas on if that play in the differential ^^ is normal? I've got another video of the noise happening while under torque. This time, it's getting worse, and I don't need to be turning for the noise to happen. It's a bit hard to tell in the video, but the clunking seems to be coming from the transmission, while the clicking is coming from the differential. You can feel the clunking in the shifter, as well as if you put your hand on the transmission housing... is it possible that both my transmission AND my differential need work?

I also want to note that a few days before this problem, I noticed that whenever I turned sharply from a stop, not giving it any more gas than normally, the tires would chirp.

141MB Video, High Resolution

[Jensend]

The problem could be the emergency brake shoe assembly loosening up. It can get jarred out of place when you hit a bump and rubs on the wall of the drum inside the disc. Simple to check and easy to correct. Took me forever to find the problem when I had it. Worth checking.

[Masonite]

Originally Posted by Jensend

The problem could be the emergency brake shoe assembly loosening up. It can get jarred out of place when you hit a bump and rubs on the wall of the drum inside the disc. Simple to check and easy to correct. Took me forever to find the problem when I had it. Worth checking.

Thanks for the reply and advice, Jensend. I actually took the entire rear brakes off the car (bought new calipers, shoes, the works--ready for replacement), and if you check out the larger of the two posted videos, the tapping noise is still there after the removal. Any other ideas?

I gave my car to my uncle, who owns a transmission shop. My fear is that it's a problem with both the transmission and the rear differential, but before I get the final diagnosis from him, I want to have an idea as to what kind of parts I might have to have rebuilt or replaced.

[Tru2Chevy]

Originally Posted by Jensend

The problem could be the emergency brake shoe assembly loosening up. It can get jarred out of place when you hit a bump and rubs on the wall of the drum inside the disc. Simple to check and easy to correct. Took me forever to find the problem when I had it. Worth checking.

While an e-brake problem was possible, he's got a 3rd gen. No drum inside the disc setup there.

- Justin