Help? Tranny / Diff Seal Grease? (Squeal)

[Stan]

I have an intermittent squeal coming from the center or rear of my RWD car. Wheel bearings and driveshaft are new. It's loud enough to hear from a block away when it starts. Before it starts you can sometimes hear a whirring or winding up sound and then the squeal but I am not sure about that it could be my stressed out imagination, lol.

The sound is road speed related, you can change gears at a given speed and the sound continues. If you apply or release throttle there is a slight change to the sound but the same basic nature. As you slow down, you can pick up a change as in squeeeeal…squeeal…squeal. At higher speeds that all blends together. Braking or e-braking has no effect.

The Diff seems tight, no pinion whine or clunks. Transmission and Diff fluid levels are good. CV joint half shafts seem unlikely as those don't squeal when they go bad they clunk and make low rumblings. Rear disc brakes are fine, and recent. Possible slight oil dampness near the diff input.

The squeal is present if you floor it hard after about 15 minutes of driving. it will continue indefinitely until you stop. If you stop the car and then proceed again it may or may not squeal. Going in reverse changes but tends not to stop the sound. Going around in tight circles either L or R does not change the sound compared to driving at the same speed straight ahead.

I'm wondering about the transmission output seal where the driveshaft yoke inserts into the rear of the transmission. As well as the input seal of the differential. I figure the differential outputs are fine as the sound is not altered by turning which would change the inner/outer wheel RPMs.

Any suggestions? I'm wondering if some grease and maybe a seal swap is in order. Thanks.

 

[Stan]

I think I'm going to try greasing those two oil seals…output from transmission and input to differential. It can't hurt I suppose.

 

[unDummy]

year, make, model.... always helps.

If there is a slip joint, repack it with a 3% or higher moly grease.

If there are u-joints, pump them with a grease gun.

 

[mechtech2]

Any chance it is brakes?

 

[Stan]

Originally Posted By: unDummy
year, make, model.... always helps.

If there is a slip joint, repack it with a 3% or higher moly grease.

If there are u-joints, pump them with a grease gun.



It's a Miata fwiw. I've greased the seals either end of the driveshaft and there has been no squeal for a few days. That's the frustrating thing about a noise like this one…it comes and goes and when you put the car up on a lift all seems to be fine. I'll redo the grease with some moly grease. And wait and see if things stay quiet.

 

[Stan]

Originally Posted By: mechtech2
Any chance it is brakes?


It does not seem to be…they are fresh on the car. No rubbing anywhere. Spash shield is not touching. Brake pad squealer strips are not present. Lubed sliders. Stops and e-brakes fine. With a partner walking by the car the sound seems to be along the front to rear centerline. Since it sounds the same from either side of the moving car. Generally when it does act up, it does not do so below about 5-10 mph. And it often fixes itself for awhile after a full stop so this makes diagnosis under the car trickier as it always seems to be ship-shape at those times. It's not speedometer cable related as unscrewing it from the transmission does not prevent the sound.

 

[Stan]

Found it…transmission output oil seal.