Muncie M20 Noisy in 4th Gear
 

I have a 69 M20 from a GTO in my 65 GTO. At the end of last season the trans got really noisy in 4th gear which prompted a rebuild over winter.

I got the trans back in the car over the weekend and tested it with the car on jackstands. Unfortunately the noise is still there and maybe even worse.

I used an All State kit with new bearings, synchros, keys, springs, and cluster needles.

Laying under the car it would seem like the noise is coming from the front of the trans. Could it be the front bearing? Maybe I got a bad one...

I took the trans out, took it apart and can see no reason for the noise. Gear teeth are in good shape, assembly is correct per the Cangialosi Muncie rebuild guide.

Any help or suggestions you may have would be greatly appreciated.

After a little more investigation I discovered I have a badly worn pilot bushing. I went back to the car today and discovered the pilot bushing was out of the back of the crank. Took the clutch out, got the bushing out and found it to be very loose (worn) on the trans input. It also has some markings on it that indicate it may have been cocked and not seated properly in the crank. That along with the worn pilot bore was likely causing my 4th gear issue all along.

If your trans is only noisy in 4th gear I would very carefully inspect the 4th gear and the cluster gear. 4th is the one that is attatched to the input shaft so that would make sense why it sounds like it's from the front of the trans.

Your pilot bushing may be bad but its doubtful that's where your noise is from.

All my gears are in great shape. I believe the input pilot bearing/bushing plays a significant role in 4th since the input and main shafts are coupled (1:1) and there are no gear reaction/separating loads inside the trans. I'll report back after I get everything back together.

Badly worn pilot bearing/bushing can wreak havoc on front main bearing, front main to case fitment and main shaft to rear of pilot shaft.

And could have had gear whine (in 4th) from pilot to cluster alignment being off. No load, just noisy from not meshing good.

Fingers crossed everything survived
Clay

Input or main shaft bearing noise for sure. Cluster would make noise in every gear. IMO