Diff whine: Gears or bearings to blame?

-
Kern Dog

Kern Dog

Build your car to handle.
FABO Gold Member
Joined
May 23, 2010
Messages
9,808
Reaction score
28,226
Location
Granite Bay CA
I have a 3.91 diff with a clutch type SG in it. It is quiet as can be until about 50 mph. It sounds louder at light throttle but is still there at cruise or WOT. I can be cruising along at 65 and lift off of the gas and it goes away, ease back in it and the noise comes back.
The diff was rebuilt and is as tight as new. The bearings were original as was the ring and pinion. Years ago when I put this 3rd member in it was silent. I had a 4.10 3rd member in before that had the exact same thing happen. I use high quality 85w90 oil with the LSD additive.
Any ideas? Thanks, Greg
 
My money would be on axle bearing ..I could feel the back
of my backing plate and one side was hotter then the other side.
 
memike said:
My money would be on axle bearing ..I could feel the back
of my backing plate and one side was hotter then the other side.
Click to expand...


Interesting. I had to replace my "green" type bearings awhile back. The RR axle seal was replaced and is leaking again. I like the idea of feeling it for a temperature difference. thanks!
 
Pinion gear depth is incorrect. Roger wilco over and out.
 
............If they are factory gears they will always whine as the backlash was horribly loose and when set up to spec u changed their wear pattern.........kim.....
 
RustyRatRod said:
Pinion gear depth is incorrect. Roger wilco over and out.
Click to expand...


X2.

Only way to know for sure though is to take the pumpkin out and use marking compound to check the pattern on the gear teeth.

Steeper gears do whine some though, some more than others. That's just the nature of how those types of gears are cut. Try driving around with a 4.30:1 axle ratio.
 
memike said:
I could feel the back of my backing plate and one side was hotter then the other side.
Click to expand...

Brakes make heat, and one side doing a bit more than the other will be the reason for that, not the bearing

Frankenduster said:
Interesting. I had to replace my "green" type bearings awhile back. The RR axle seal was replaced and is leaking again. I like the idea of feeling it for a temperature difference. thanks!
Click to expand...

That feeling isn't going to tell you anything about the bearing

teringer said:
bad pinion bearing ,all pitted up. my guess..
Click to expand...

if that was the case it would do it both ways.


Set up is wrong

.
 
Yes brakes make heat, on my 66 /6 7 1/4 the heat was well over 100 degree's under there Supershafts, if my brake shoes was dragging so much to make heat on the housing I would have known it as I coast down hill, I drove it about 10 mile and came to a stop and stepped out of the car (not engaging my rear brakes) and the housing was hot just by touch right behind the backing plate.. Rear drums don't drag.. Or they should not be, if they was the hub would steam when hitting a water puddle . Just saying.
 
Axle bearings will make noise all the time, the fact that it makes noise under power tells me its in the center section.
 
I have a couple of other 3.91 3rd members and a ring and pinion I could have swapped in.
 
You must log in or register to reply here.
-

Back
Top