TH350 Question

[68Camaro]

I know the 200R4 is the main transmission discussed here, but I was hoping someone could help me with a TH350 issue. Recently purchased a 67 chevelle convertable with a non original 400 small block and a TH350, best I can tell the powertrain came from a 75 full size car.

The transmission makes a sound similar to a large treaded tire on a truck going down the street. I actually thought it was the tires until I ran the car on some jack stands and the noise was coming from the trans. (denfinately not the rear end)

Increases with speed and not effected by on or off throttle. The transmission performs well, relatively crisp shifts, no slipping and the fluid has good color and does not smell burnt. I have put about 1000 miles on the car with no problems, but the noise has me concerned.

Any ideas?

Thanks,
Greg

 

[blackplague]

Will the noise

change with a gear change, for example 1-2 ,2-3 , or does the noise change with engine rpm?

 

[68Camaro]

The noise is not effected by the gear selected. Actually with the car on jack stands, and brought up to 60 mph and then put in neutral, the noise is present until the driveline slows to about 10 or 15mph.

I intially thought it was tires, then rear end gears or a bearing because of the type of noise and that it didn't matter which gear the transmission was in. But having the car up on the stands and running, the noise is definately in the transmission.

Thanks,
Greg

 

[blackplague]

it might just be

That the output shaft bearing is bad making the noise. In 3rd gear {60 mph}the only two bearings in the trans that should be moving would be the output shaft bearing and the pump bearing {if it has one, earlier models had a thrust washer instead of a bearing}.

One other thought is that the low roller inner race may be pitting or have chatter marks. Because, at 10-15 mph the noise goes away on the stands. The low roller clutch is locked up in first gear which should be right around the 10-15 mph range. The low roller overruns in 2nd and 3rd gears.