Whining rear end on deceleration?

[Tonefiend]

I have a 8-3/4 rear end that was recently installed, Supposedly it's a sure grip. along with a disc brake conversion.  I have a few hundred miles on the car now and it just started making a whine on deacceleration.  It dies it in gear or out of gear.  I only notice it when deaccelerating.  It seems to be getting worse.  Any ideas?

[Aussie Challenger]

  If it is a sure grip did you use the correct oil?
  Was this a new/rebuilt unit or second hand?
  Does it have excess back lash?

[tactransman]

That usually means a bad FRONT pinion bearing.

[Tonefiend]

I recently aquired the car so I am not too familiar with what was done.  The rear end came out of a 'cuda so it is second hand.    I found a bottle of posi rear end oil in the trunk so i assume the right stuff was used.  It worked fine for a few hundred miles. 
I'll check the backlash and look into the front pinion bearing.   How do I go about opening one of these things up?  I am used to Chevys with the plate in the back.

[Moparal]

you might want to see if the big nut behind the u joint is tight. It may have loosend up if he changed the yoke

[73Chally]

With the 8 3/4 you have to disconnect the drive shaft at the rear end, and the whole rear housing pulls out, gears and all.

[moparmaniac59]

Do you have the proper fluid level in the housing? If it's a 489 case the pinion depth is set with a crush sleeve. The 742 case uses shims to set the pinion depth. Tightening and loosening the pinion shaft nut won't effect pinion depth on a 742 case, but can effect the pinion depth if retightened too much and would put more 'crush' on the crush sleeve on a 489 case rear end.


                                                  Matt B.

[Tonefiend]

New developments. I drove the car over to my shop <wood not mechanic> about 5 miles.  The last leg it started to get really noisy.  Parked the car and fluid was draining out of the front seal.  Went back home on my motorcycle and noticed a few small drops on the driveway. 


I spoke with the prior owner, he and his friend got it out of a wrecking yard and rebuilt it.  New seals, same old gears, they looked brand new he told me. The rear end was dead quiet and performed flawlessly the first few hundred miles.  However these guys are no mechanics they installed a new gas tank and now the gas guage doesnt work and when they installed the axel they didn't have a locking pawl so the axel came out and chewed the crap out of the brakes, so one can only imagine the work was not done to spec. Also he does not know if it is a sure grip or not.


Any thoughts on this would be much appreciated! If I can sort it out myself I will.

[Bullitt-]

All of the disk brake conversions I've seen require changing to the Green Bearing which eliminates the adjuster & lock. 

[moparmaniac59]

If you put the car up on jack stands, turn one of the rear wheels and if the other wheel turns in the same direction.....then you have a sure grip (positive traction) rear end.



                                                Matt B.

[mikerallye]

The whine while decelerating means not enough  back lash. Chevy mechanics screw up 8 3/4's often this way. Sounds like something got tighter in there....

[moper]

Stop driving it immediately and remove the driveshaft. Look for the pinion nut to be loose. What is the castign number on the side of the center section end in? (last three digits)  These rears may need a very high torque value, and all should be checked by a rotating torque wrench during that torquing to ake sure they are done right. Sounds like these guys might have missed that part...

[Tonefiend]

Thanks for all the great advice, it's a 489 case.

[Tonefiend]

I am going to yank the pumpkin and take it in to a gear shop.

[Tonefiend]

Stop driving it immediately and remove the driveshaft. Look for the pinion nut to be loose. What is the castign number on the side of the center section end in? (last three digits)  These rears may need a very high torque value, and all should be checked by a rotating torque wrench during that torquing to ake sure they are done right. Sounds like these guys might have missed that part...

Today I jacked it up, put it on stands so I could get under it to pull the hogs head out.  Grabbing the driveshaft and jerking it around, the shaft is attached to the pinion and yoke solidly, but the pinion slops around in the casing.  The pinion shaft is loose and wobbly.  It looks like the pinion nut came loose which caused the whole thing to slop around which in turn took out the seal causing the fluid to dump out. I left the car as is for now. 

What would the extent of the damage be at this point? 

Is this an external fix, or do I need to pull the hogs head?

At this point I am going to leave it to a professional, I would just like to get some opinions on what needs to be done. 

Thanks in advance!!