Transmission noise

[Mustang_Charly]

I know it's difficult to troubleshoot noises long distance, but I would still appreciate some guidance. The car is a basically stock, (with the exception of an Edelbrock carb & manifold), 68 C-code coupe with the C4 automatic.

The engine runs very quietly, but there is a constant howling / whining noise coming from somewhere behind the engine. It is quite annoying and only becomes bearable at high speeds, probably because it reaches a frequency that I killed by listening to loud rock music in college many, many years ago.

The noise changes frequency with engine speed, and is present in neutral, reverse, and all forward gears. I have changed fluid (using Type F), put in a new filter, and checked fluid level (hot, idling in park).

I have removed the inspection plate, and looked (as best as possible) for signs of flex plate rubbing or any thing else unusual: Nothing obvious.

I am getting used to the idea of doing a trans overhaul (my first) over the winter, but would like some ideas of what might be making this noise, so that I don't miss it. Thanks in advance.

[fireme]

Sounds like a pump going bad. I would get the car up in the air and use a mechanic's stethoscope to check around the transmission, especially near the rear of the bellhousing. Also check the cooler lines as hydraulic noise will be transmitted by them as well.

Jay

[Mustang_Charly]

Thanks for the feedback, Jay.

Can a trans pump be rebuilt? or should I replace it?

[Candoo]

Might want to consider the differential as the noise source. Pinion bearings sure can whine.

[fireme]

The rear axle can definitely make those kinds of noises, but he said it happens in neutral, which I took as 'stopped,' and when revving the engine. Perhaps an assumption I shouldn't make.

David:

The C4 is a simple trans and is easily rebuilt. If you determine that it is the pump that is noisy, you might want to consider just rebuilding the whole thing. By the time you get the pump out, you are already half way to a rebuild anyway. And yes, rebuilt pumps are available.

Again, a stethoscope is inexpensive and a very valuable tool. Diagnose, don't just throw parts at it.

Jay

[duckmonkeyman]

+1 on the stethoscope. i had a noise which sounded like it was coming from the engine but ended up being a loose pulley on the alternator. The stethoscope narrowed it down. You probably already did this, but did you double check the fluid level after running through all gears and warmed up? Mine whined during break-in till the fluid circulated.