Got an 85 Blazer with a 6.2 diesel and a T400 trans.Knocking from torque converter when warmed up. Why?

Question

I replaced the filter, powerflushed the trans, checked for debris. Nothing noticeable when I look at it. It sounds like a bad rod knock but its coming from the torque converter. There is also a bare metal stripe around the outside edge like something is rubbing it but the noise only appears when the engine is warm and strain is on the trans. I.E. when driving only. I checked the flexplate bolts and everything is torqued properly. No shimmy or shake or vibration, just that damn noise! If I drive it for more than 20 minutes with the knocking then the truck stalls out when I hit the brakes. Fuel pressure good, timing good, injector pump good too. It's an ex military CUCV M1009. No shop wants to look at it because its ex military and totally different from civilian but a trans is a trans. Motor is different but trans is not.

Answer 1

My wife brought this to my attention, I believe it is probably your rear main bearing, which is obviously just in front of your torque convert-in the motor. I suggest pulling the pan and checking it immediately,you may be able to effect repairs prior to losing the motor-replace the bearing. A micrometer and spec. manual will be needed.
It could also be a bad converter or loose bell housing bolts but I doubt it. Additionally a rod may very well exhibit these symptoms, yet the rear main is most likely the cause.
I am a competent mechanic who is VERY familiar with Chevy trucks, and have blown an '84 blazer with the 6.2, although it had a different trans.At any rate I drive /repair and rebuild my own Chevy trucks,and I do mean motors and transmissions,etc, as well as a large variety of other mechanical work professionally. Hope this helps.

Answer 2

you could have a broken flex plate, try removeing dust sheild, and unbolting torque converter. use a pry bar to push converter back and hold it there. then have someone start engine. if noise is gone you will know it is your converter, other wise your flex plate is broke or cracked.

Answer 3

the only thing different on your truck is the starting and charging system there 24v. as for the rest of the truck they are the same.Just a wild guess maybe a cracked flywheel.

Answer 4

just like you said, its turbo 400, just replace the damn torque converter, its not that expensive

Answer 5

It's the rear main bearing.
shop owner for many years.

Answer 6

another vote for a cracked flexplate.
they are notorious for that on these trucks.