what causes my rearend to whine mostly on decel at 40-45 mph i have a posi rearend. i bought the car and it had no oil in the diff i put some in and it didn't seem to help. do i need a new one or what can i do to fix this i have a 84 z28 L69 with 4 wheel disc brakes also can anyone tell me what ratio i have and type of rearend. ive been told a 7.5 with 3:73 but im not really sure. sorry for thr repetative questions im new to the site.

 

A whine that comes and goes is cause by two things. Either the gear set is junk, or the diff as not been set up right.

 

I agree. The gears are probably going bad. You can drive it like it is until it gets too bad to drive, or spend the money and get a new set of gears installed now. You might also check to see if the pinion nut has backed off a little. Hold on to the yoke on the rear end and see if it will move in and out or side to side. Any movement, other than rotation, means that the nut is loose or you have a bad pinion bearing.

 

Are you sure it whines on decel? Usually the ring and pinion whines at speed when accelerating. Have you put in any posi additive? You put SOME rear end fluid in? did you put in enough? What did you use? you either have the 3.73 or the 3.42. gears. The 3.42 was stock for the automatic but it could have been upgraded to 3.73 Do you know for sure it's a posi? Post your RPO codes.

 

it whines slightly at accel and i put 80-90 in it and i didnt put posi additive i didnt even know there was such a thing i thought all the gear oils came with the additives needed.how do you get the rpo's? and yes im 100% positive its posi all 4 wheel discs came with the lockers, and ive done some posi black marks from take off on dry pavement.

 

Yes, there is a posi additive you get. I think it comes in a 10oz squeeze bottle

 

The RPO codes are listed on the inside of your console glove box.

 

Does your pinion seal leak? Look underneath at where the driveshaft connects to the axle center housing - is it all wet?

 

Use GM additive 1052358. It is best to put the additive in to the first bottle of oil that you put in. It usually takes 2 quarts of oil to fill a rear end. I doubt that the oil aditive is causing your problem. It's most likely a bad set of gears, a bad bearing or a loose pinion nut.

 

I have seen bad gear sets, whine on accell, whine on decell, whine all the time, and whine at a certain speed.

 

it does leak and i checked the oil, and there was none so i put in 32oz and it filled the rearend i called the lady i bought it from and she said its been whinig for a long time and she never had it looked at. yea me.