Tapping noise in 2004R and 200C

[pshimek]

I have a 2004R and a 200c transmissions that are both doing the same thing. They have a tapping noise that is constant in the 2004R and intermittent in the 200c (tends to become more pronounced when hot on the 200c. When cold, rarely any tapping). The noise almost sounds like a valve lifter.

I am an amature rebuilder. I have rebuilt 5 or 6 THM350's, 3 THM400's, 1 THM3L80 and the above 2004R which I rebuilt about 8 years ago. All rebuilds were stock rebuilds with good results except the 2004R. The 2004R rebuild was initiated due to the tapping noise, which seemed to be coming from the pump/torque converter area; same area on the 200C. When the 2004R was rebuilt, I put in a master kit, and a rebuilt pump (7 vane, original). After a short while the tapping came back, intermittently, and not as pronounced as it had sounded originally. I did notice that if the fluid level was a little low, the tapping would be louder.(Had a pan leak for a little while.) The tapping also changes a little when going thru the gears, (foot on brake, engine at idle). The transmission vintages are 2004R - 84, 200C - 80.

As far as operation, the 2004R,besides the tapping, works fine. The 200C has 100K on it, and there is some slow engaging intermittently when cold, but otherwise works ok. The 200C started the tapping one day out of the blue, sitting in traffic 95 degrees outside, but had no noticible effect on operation.

Before the 2004R overhaul, I researched to try to find out what was causing the tapping and what to do to cure it, and found nothing.

The only thing I had found broken in the original 2004R rebuild was the pump rotor to vane steel rings, which led to the pump replacement, and with the transmission having 115K, a rebuild. The transmission now has about 75K on the rebuild. Never had this problem with gear pumps. With both of these transmissions having vane pumps, and from the same family, I am suspecting something in the pump, a pressure regulator or something like that.

Going thru the existing posts, there are a lot of intelligent people out there, so I'm hoping someone might be able so shed some light on this problem.
I have 2 similar transmissions doing the same thing, I am guessing there have been more out there with the same problem.

Please help

 

[steve hughes]

This might be a long shot but have you checked end play on the crankshaft? It may not be a trans problem.

 

[pshimek]

I did look at the car with the 200C in it and there was very little end play (did not measure) but did not look out of the ordinary. The tapping, when listened to with a hose to the ear is definitly coming from the front of the transmission and not the engine block. I checked all around the rear of the engine and heard nothing.

 

[turbo nasty]

You check the flexplate?
They are notorious for cracking between the holes and it will tap/knock when cracked.

 

[pshimek]

The flex plate is a little out of true, but if you use a stethoscope or a piece of tubing to the ear, the sound is not at the engine or flexplate. It is loudest at the front of the transmission.

 

[pshimek]

Even though my stethoscope placed the sound at the front of the transmission, I disconnected the TC from the flex plate, and when rapped with the butt end of a screwdriver, rattled. Took off the plate, and I dont know how the plate didnt seperate from the crank.
Replaced, and no tapping.

Thanks !