Rear Wheel Bearings

[Cream79L82]

Well it turns out I was wrong again with what I thought my problem was. As soon as I took the dust cap off of the bearing assembly and saw grease that was still blue I knew they were fine. The noise that I was hearing was from my brake pads rubbing on the rotor under no pressure. I replaced four seals and boots.
Of course, I still have a number of questions... is it necessary to bleed the whole brake system if just the fronts were opened? How freely should the wheel spin when jacked up under no pressure? Is it normal for the pads to engage the rotors when the brakes are not applied due to the piston spring pressing out or should the seals keep the pistons back and clear of the rotor when rolling down the road?? And finally, how much play should there be on the rear wheels with the rear end jacked up when you push in on the top/ pull the bottom, etc?? There is alot of noise when spinning the rear wheels in neutral, but I don't know enough to discern whether its drivetrain noise or farther out. There is a fair amount of play when pulling in and out on the tire, so I don't know whether to worry or not....

Thanks.

-Jon

 

[Stingray6974]

Jon,
If the master cylinder lost all the fluid in one or both chambers then you will need to bleed all 4. The brake pads will be in constant contact with the rotor at all times due to the springs behind the pistons. There will be some resistance turning the front rotors by hand.
Ideal end play in the rear yokes (in and out of the diff) is .005 to .010 . This is hard to achieve and requires a correct differential overhaul and proper shimming of the posi discs. "Acceptable" play is .050 to .080 . If you have more than this your yokes are worn out. Prefered spindle end play is .008 however I set up the bearings for 0.00 to 0.001 play. It is my understanding that the rockwell hardness of the inner yokes was lowered in 76 -77 resulting in faster wear of the yokes. JohnZ may need to correct me on this.

Mike

 

[Stingray6974]

differential

 

[Bullitt]

That differential looks familiar. I busted a few knuckles and bled a bit getting it out and back in. You do great work, Mike.

BTW, has anyone heard from Russ, lately? Did he really sell his Vette?

--Bullitt

 

[JohnZ]

And finally, how much play should there be on the rear wheels with the rear end jacked up when you push in on the top/ pull the bottom, etc?? There is alot of noise when spinning the rear wheels in neutral, but I don't know enough to discern whether its drivetrain noise or farther out. There is a fair amount of play when pulling in and out on the tire, so I don't know whether to worry or not....

Thanks.

-Jon

If you have the rear end jacked up and the wheels are hanging free while you spin the wheels, you're probably hearing U-joint interference noise; better to use two jacks, under the trailing arms, so the suspension is at normal ride height and the U-joints are at their normal running angle.

When checking for rear wheel bearing play, don't grasp the tire and rock it at 12 and 6; that way you're also feeling the compliance of the lower strut rod bushing play and the torsional (twist) compliance of the front trailing arm bushing, in addition to the bearings. Grasp the tire and rock it at 3 and 9 for a more accurate feel - you should hardly feel any play at all. The only truly accurate way to measure the end play in the bearing pack is to disconnect the outer half-shaft flange at the spindle (4 bolts), mount a dial indicator on the inner side of the trailing arm, and measure the in-out play at the end of the spindle. Spec is .001"-.008", but that's to allow for manufacturing tolerances; for long life, .001"-.002" is a much better target.

The problem with the yokes (as Mike's photo shows) is that the case-hardening on the inner end of the yoke (which is only about .010" deep) eventually is worn through, and then the wear accelerates in a hurry, and they can wear right past the groove for the clip (like the middle ones in the photo). There's no published spec for yoke end play, but when it gets to .060"-.080" it's time to change them before they start grinding away at the side of the case itself where the seal is.

 

[Cream79L82]

Thanks alot for the info and the pics/diagrams guys. I hadn't thought of the 3 and 9 method.... or even to jack up by the trailing arms. I really don't want those things seizing up on me though.... after Wayne Burnham shared his terrifying story of crossing four lanes of traffic without a left rear rotor/spindle etc etc. I've only been working on her last night and today, and I'm already mad I can't drive her. I might be out there a whole lot today... Thanks again.
-Jon

 

[Stingray6974]

Thanks Bullitt. I thought you might reconize that pic. I haven't heard from Russ in quite a while. I guess he sold it.

Thanks for replying John. I needed you to confirm my settings.

Mike