[esc-351m]

Help!

I bought a 1971 Mustang Mach 1 about 2 weeks ago, everything was great with the car.

Then, one day last week, on a trip to the gas station, the car started making a hellatious noise (related to wheel/drivetrain speed), and I pulled off the road right away. I got it back home, and tried to diagnose it.

First thing I thought was a U-Joint - replaced the rear one but it didn't help (and the old one didn't feel worn out). Next, I thought it might be the pinion bearings in the differential. So I pulled the pinion, replaced the bearings, still got the same noise.

Next, I pulled the axles to check the axle bearings, they feel fine. One thing I did notice when pulling the axles was that the brake adjuster on the left side was rubbing the brake drum. I fixed that, but still the problem (noise) persists.

What the noise is:
When accelerating or under power, it is only a slight whine. (Didn't do that before the problem occurred, but it isn't a terribly loud whine).
When letting off the gas slightly, the whine is much higher pitched and louder.
When decelerating (letting car coast while in Drive, or braking) loud growling/grinding noise that has a rapidly repeating pattern (it's not constant, more on the frequency of what an out-of-balance tire would do.)

Here's the work I've done so far:
Replaced:
Rear U Joint
Rear End Fluid
Front & Rear Pinion Bearings
1 brake spring

Checked, looks OK:
Axle bearings
Pinion Gear
Ring Gear (the part I could see)

Have any suggestions? Something that I could look at in it, or something I could doto fix it?

Thanks so much for your help - I really am stumped.

[merlynr]

Might be the rear bearing in the transmission if it is a manual

[esc-351m]

Thanks for the reply!!

Unfortunately, it does not have a manual transmission.

Tranny is C-6 Auto, and I did check the fluid level in park - it's good.
Just a side note - while I am 95% sure the noise is rear-end, it is so loud that I cannot 100% prove it isn't the tranny. Perhaps there is something in the tranny to check, also? (I've worked on manuals for years, but this is my first automatic.)

[Quick66]

sounds like you have lost your proper backlash.You may have faulty carrier bearings to blame, but regardless of the cause, it sounds to me like your gears are the culprit. If the noise lessens under acceleration than the load on the ring gear from the pinion is what is behind the variation . While decellarating the pinion gear is being turned by the ring gear on 1 side of the teeth. While under acceleration, the ring gear is being driven by the pinion on the other side of the teeth.Hence the difference in pitch and intensity of the whine. Hope this helps

[Jess]

Did you check the rear end fluid level. Also what type of rear end do you have, open, posi or locker. Each needs its own type of fluid. On a posi the clutches could be going away, locker not locking, open check the pinion angel off. Pinion angel could be off on all of these causing noise. Pinion bearing/race got off on me one time created all kinds of noise. Have the axles slipped out of position sideways or up or down. Did you loose a rubber leaf spring saddle/perch on one side.

Jess

[gjz30075]

Put the rear end up on jack stands and then put it in drive. Have someone in the driver's seat while you can get under the car to check closer. This is definitely a two man job to be safe.