Ralls

iTrader: (32)

My drive line consists of:
-4l60E
-3200 stall
-MWC 9in with tunnel mounted adjustable torque arm
-strange aluminum center section with tru-trac and 3.00 gears
-non-adjustable lower control arms
-adjustable panhard bar
-sfc's
-pst chromoly driveshaft
-all polyurethane bushings besides the rod ends on the torque arm
-stock ride height

I have this horrible clunking noise that I cannot figure out. It happens when it shifts into overdrive (torque converter locked) at 45mph and fades away above 65mph. You have to be cruising with little to no throttle like when you coast down a hill. No other issues at WOT or slow speeds. It's coming from the rear and you can feel it banging inconsistently through the shifter and generally the whole car. It sounds a lot like a backing firing noise like when you touch the throttle at a high rpm when cruising. But I doubt its actual engine backfire because you can feel it and my wideband doesn't go crazy. I usually drop it into 3rd gear to get it to stop.

I picture in my head the driveshaft u-joints are binding as if the angle is too much. I changed my pinion angle to -1 today and it seems like it's not banging as aggressively and goes away at like 60mph. I'm skeptical whether I'm setting the pinion angle correct because I'm still very confused on how to measure it no matter how many explanations I read. I do know the rear of the driveshaft is pointing down and the front of the pinion points down. Also just looking at the u-joint angle, they look almost straight. I'm using a mechanical angle finder with 360* face and the needle points up. The u-joints don't look chewed up and nothing is hitting against the body. If you guys have any ideas let me know.

Bob@BruteSpeed

iTrader: (16)

What does your rpm drop down to when you shift into overdrive at 45 mph with your 3.00 gears? I'm wondering if you're not just lugging the engine. Bob

garygnu

where the torque arm mounts to the cross member mite have a little play.make sure that bolt is really tight.

Ralls

iTrader: (32)

I actually thought the same thing, but kinda doubt it. It goes to about 1,500rpm when shifting to overdrive. I've thought about raising the shift tables so overdrive kicks in at like 55mph. I had 2.73 gears stock and it never did this. Plus my car is stoked to a 383 so I sure hope its not lugging. I did a lot of mods at once such as new engine and trans but the only suspension I added is the MWC rear end w/ torque arm and driveshaft.

I don't get any loose feeling when accelerating from a stop or shifting to reverse. It feels like the whole drivetrain has slack in it and it's just slapping back and forth while I'm cruising with little load.. and the only reason I feel it in overdrive is since the converter is locked.

Steve Gunn

Things that caused this on my car was the spherical rod end on the torque arm, which I can't fix and a loose lower rear shock bolt. It sounded like it was coming from under the console. Jack the car with the suspension loaded (rear end) and rock the wheels hard by hand forward and reverse in nuetral while under it. That's how I found it.