So once I got all the electrical connections to the transmission and the selector in Park instead of 1st It fired up. The engine sounded great for a few seconds than a bad scratching / knocking sound started. I crawled under and pulled the tranny coolant tube off of the flywheel and it again sounded good. Listening to the engine with the stethoscope it sounded good and clean so now I am confident that the noise was coming from the transmission.

The transmission was definitely leaking fluid in a couple of places, one pan bolt is missing, and there is a dent in the pan from where the torsion / sway bar hit it. (bolt rusted / sheared off the driver side of the bar connector.)

Should I just put another one in or should I pull it apart and find out why the noise? It was shifting fine as far as I understand but since it wasn't tagged I never got past 2nd gear. How complicated a transmission is this to rebuild? I'm a mechanical engineer and have done a lot of parts swapping and a few head gasket jobs but never been inside a transmission. I'm guessing I would need at least one bearing that is NOT included in the rebuild kits. There is a transmission on craigslist for $250 but it is 3 hours each way. Nothing on car-part.com that costs less than an arm and a leg.

OR, I could just sell parts off it. The 3.slo with 138k on it might bring most of what I paid for the entire truck.

 

In hopes of finding a cracked flex plate I took it out of the vehicle and looked it over today. It looks fine so no luck having an easy fix. I'm contemplating 1) rebuild, a first for me, 2) buy another tranny, 3) get a cheap truck with a blown motor and part it out... keeping the tranny for this one.

 

Let me share a good and bullet proof way of finding a rod knock.

First a knock is a bit lower in tone and slower than valve noise.

Typically a rod if caught early only makes a knock at a specific point. Not necessarly load but RPM vs load.

What to do.

Rev the engine up, drop the throttle and as the engine RPM falls, open the throttle back up slowly trying to "meet" the falling engine RPM. For about 2 seconds the rods/pistons are in a neutral load (not being pushed and not being pulled) and at that specific time the rod will knock like crazy if there is play.

Once a bearing spins, it will typically knock all the time and has a very short life as the spun bearing blocks the oil supply for that specific rod.

Hope this helps someone in the future

 

BTW, does the noise change during a power brake? Change with the trans in Neutral or a specific gear?

Have you considered the torque converter is the failure and the trans is fine?

 

I didn't drive it enough to do a power brake as it was exhibiting this behavior when I bought it and thought it might be a bearing so I just went up and down the block.

It made the noise in park as soon as it was started I know that. Is it possible for a shop to check the torque converter?

Thanks for any tips.

 

Diagnosing a torque converter that hasnt fully failed isnt easy. A chatter is easy to figure out, delayed stall etc. A drivetrain noise tends to follow the driveline making it difficult to pin point.

There is no real way to determine a torque converter noise, especially after being removed. As far as my experience is, there is not bench test for a torque converter.

Buying a new one to see if it works is a crap shoot that cost a good bit of $$.