What Happens If They Put In The Wrong Stuff

[Sunbeam2]

I have a 97 GC limited 4 x 4

What happens if they put regular rear end fossil oil 85-90 wt in the rear end instead of that synthetic 75-140 oil??
what are the symptoms????
How can I tell what is in there?

[Bob D.]

Won't hurt anything.
Most differentials call for 90 weight conventional oil, synthetic 75-140 is mainly for severe duty.

[Sunbeam2]

Just had the bearings in the rear axle's replaced and a week or so after the job was done a whining noise started back there and it is getting louder all the time. I took it back to the shop and they said the ring gear and pinion were making the noise and going bad.
I was wondering if it was supposed to have heavy thick oil and if they put in a thinner oil would that cause the gears to make that noise?

[msdz]

Sometimes when a person works on the rear bearings or any part of the differential the shims that MAY be holding the ring gear into the pinion gear can get shifted or the shims that MAY be there could also just get worn and need replacing.
Very seldom have I seen them get worn but have seen them fall out when the axles are pulled both at the same time and the mechanic forget to replace them. When they are not placed back in the ring gear will have some slop and can make noise.

This is a possibilty and does not mean that it is definitely the problem. The ring and pinion could also just be worn.