Gummie

I just swapped out a 700r4 for a new BW T-56 that should have gone to a 93 according to the part number. Everything that went into the swap is new. New Centerforce flywheel, new Spec Stage 3 clutch, new trans, new Spohn chrome moly crossmember & torque arm (the one that moves the torque arm mount to the crossmember and off the trans), and a poly trans mount. The car runs/drives beautifully but there’s a weird knocking sound that comes from under the car under certain conditions. The car is a more or less stock 88 GTA. No lowering other than the factory springs and sagging over the years.

I experience the knock when I’m taking tight low speed corners at full or close to full lock (usually when I’m pulling into a parking spot). It will knock in perfect rhythm like something’s hitting the tire during the duration of the turn. It’s not a loose rim – I left the tires on during the swap. I also hear it when I engage gears hard or get on the gas while costing in gear. So it knocks when I load the drivetrain. It only happens once. It will also knock some when I start going in first and I let the engine bog down while just getting off the clutch (like 600 rpm). If I keep the RPMs at/above 1,000 while getting into first it won’t knock unless I’m getting on it. It will knock like a mother when I start engaging reverse.

There’s also this weird squeaking sound that’s recently started occurring. It seems to happen when I shift the weight of the car forward/backward. It might be the poly mount on the torque arm. I don’t think it got greased and it will have to wait until Monday until I can get my hands on a grease gun.

I thought it might be the driveshaft bottoming out in the trans so I disconnected the rear yolk and pushed the driveshaft another inch into the transmission. I eliminated that as the problem but I might have discovered another source for the squeak. There’s a rubber thing that rubs against the driveshaft on the back of the trans. The rubber thing doesn’t rotate. It’s missing on the 700r4 and it’s clearly been in contact with the trans. The back of the trans is also a very little wet around this mystery black seal thing.

While I was under the car I gave everything a good shakedown and everything felt/looked extremely solid. The torque arm might just be barely rubbing against the underbody in the typical Spohn spot but there’s not a dent there, it’s just a scratch. Hardly enough to cause a loud knock.

Rotating the driveshaft at the rear tire allows me to hear the backlash in the rear end. Rotating the DS by the trans brings out a bit of play/sound also (might be the rear end carrying up the shaft and making it sound like it’s coming from the trans?) but again, hardly a loud knock.

I’m completely at a loss. The turning thing really baffles me. It almost has to be involving the torque arm because of this.

cheppibear

Would not hurt to check the front and rear universal joints in the driveshaft.

Some questions:

1. You took the driveshaft out to install the trans. How did the u-joints look?

2. Did you replace them when the shaft was out?

3. Where does the knocking sound like it is coming from? The front or rear of the car.

Gummie

1 - the u-joints looked fine but I didn't really inspect them during the swap. When I dropped the end of the shaft today I did play with the rear joint and it felt fine but I didn't take it through its full range of motion.

2 - Nope. They’re old but I don’t think they’re likely culprits. It’s something physically hitting something else.

3 - The knocking sounds like it's coming from the transmission area. If I didn't know the crossmember was tight I would swear it was knocking against the frame or the trans was loose (ie blow trans mount). The squeaking sound seems to be coming from the rear end area. Might be the torque arm hitting the body? Might even be the rear but I doubt it. Also, there's a rattle coming from the front of the car now about where the cat is. It's possible that it might be the exhaust (there's no hanger going to the transmission now) but I doubt it given that the exhaust didn't move much when we cut off the old hanger.

Edit: it's weird that it does the turning knock under low speed turns but it won't under higher speed turns. Then again, I might not be turning the wheel enough during a high speed turn to make whatever it is that's knocking knock.

irocman7

driveshaft loop? Mine was hitting on my driveshaft, there is adjustments in the tourque arm, to line it up.

ssean92

iTrader: (10)

mine has that knock also after my swap, but only during hard excelerations.

Ricktpi

Check to see if the torque arm hits the body, especially at the seat belt anchor brackets in the driveline tunnel. Also make sure that the slip yoke is not being pushed into the trans so far that it bottoms out. With the car raised up & the weight on all 4 wheels (suspension loaded) the drive shaft should clear the rear pinion yoke enough to removed. 3/8" to 3/4" clearance.

Gummie

I'm reasonably sure that the drive shaft isn't bottoming out. With the rear jacked up about a foot and the front tires on the ground I was able to shove the shaft about an inch into the trans - more than enough to get it out of the rear yoke.

I will check the other clearance spots later today. Curretly cold/raining in NJ so I'm going to hide inside for a little while.

Thanks for the ideas everyone and keep them coming

cheppibear

Gummie

Yeah, hear you on the Rain. Can't do to much. Anyway, change out the u-joints the next time you have the shaft out. Get some spicers.

Two annoying problems with more power in front of my 5 speed.

1. I replaced the trans mount with the poly one, then I used a huge hose clamp to hold the trans down to the crossmember. Not too tight, just snug enough to stop the trans from lifting under a hard load. This fix the trans mount problem and the trans tailshaft stopped banging against the floor. Have not replaced the mount in years, the key is the hose clamp.

2. My y pipe is custom bent - Two 2.5 inch pipes into a flowmaster Y collector, 3 inches out. Had to fab a bracket to keep that up and align with the original cat to trans bracket.

Also when you check your clearances under the car, remember that everything torques over to the driver's side when you mash the gas.