I know this has been discussed before, I found several threads on it. But Im afraid I still dont understand, so maybe someone can shed a little more light on it.

I am redoing a good portion of my 78. It has been sitting outside for several years so the rotors are shot (deep pitting). In my search I found that they are riveted to the hub. I also see that there are some that say you cannot simply remove the two, bolt on a new rotor and go. Something about an air gap and bleeding the brakes frequently. This really just doesnt make any sense to me. So whats the real problem here. Why would I not want to just put a new rotor on go? Is it the same for the front and rear?

thanks gang

 

dont know what you have available, but a drill press would help....if not, a heavy duty drill with a drill bit larger than the head of the 5 rivets. What you want to do is cut the head of the rivets off and then drive the rivets out with a larger drift....Use a 'brass hammer and knock the 5 studs out and the hub and rotor can be separated...Clean the hub throughly and then drive the studs back in to hold the rotor together....not hard at all...you may need to have the rotors trued up with a brake lathe...another simple job....

 

Thanks for the reply. I think i have figured out how to get them apart (just havnt done it yet, yes it involves a drill a brass punch and a BFH). The rotors are completley shot. Need replaced. Its getting the new rotors and the old hubs back together that seems like some have had issues with. Im trying to figure out exactly what those issues are and why.

 

I was trying to think of how to reply to this before, but, I couldn't come up with a simple explanation. Then I found this posted by Wilcox on another thread:

Rotor "Runnout" is the wobble of the rotor measured from it's most inner point to its most outer point while turning on the spindle. If you have it bad enough it will suck air in to your system.

GM put the rotors on the spindle, then machined them to guarantee minimum runout. When you replace the rotor, you need to check the runout and put shims between the hub and rotor to get the runout to .003 or less. That will prevent air from being sucked into the caliper pistons and prevent the frequent bleeding problem.

 

thats the part I dont fully understand. To start with, how would this introduce air into the system? I dont get how that is possible. beyond that, I can see the wobble being a problem, so how do you measure for this to shim it correctly?

 

YOU DONT NEED SHIMS....you just clean the now bare hub and then re-hub the new rotor with the wheel studs by driving them back in...then chuck the hub in the brake lathe and resurface them if necessary...they should now be 'dead nuts true. And as for the rears they are as simple as a front wheel drive car with hubless rotors.

 

Vette-kid please don't listen to this.
If you turn the rotor to 0 runout on a machine and bolt it to the hub it will most likely have TOO much runout. Now the rotor is junk because it is now too thin to turn again. Just bolting up a rotor is a crap shoot ,odds are not in your favor.
Any body knows that you must check the the hub or spindle face for runout before bolting a perfect rotor to it , Ironcross didn't tell you that.
My 76 ray is right on !


Caliper sucking air : when the over .005 runout rotor spins between the 4 pistons it smacks the pistons and causes air to be sucked in past the factory style lip seals.

 

I knew this would happen...again. There seem to be two sides to this issue and strong believers in both. But at least we seem to be getting somewhere. So part of the issue is really the seals on the calipers? Is there an upgraded seal that fixes this issue? And howdo you measure for the wobble? Is this a task better left to a machine shop? Drive the studs back into the new rotor/hub assembly and have them spin and true them with shims (not by grinding the rotors down)?

 

The rotor hub assembly is turned after riveting. So theoretically there is no run out. If you put on a new rotor (I did this last spring) you need to minimize run out. This is easy to do get a dial on a magnetic stand and where needed compensate run out either with shims or with aluminum tape (like I did).

This is important! The lip seal on the caliper pistons work like a "pump" is there is a wobble. Air from the out side can enter if the piston is moved. It is also a good moment to switch to o-ring pistons, these tent to not have this pump effect.



.

 

You seem to have a good basic idea of what to do but this might help,
http://www.corvettemagazine.com/comp...-overhaul.html

As for the runout, here's how to check that
www.brakealign.com/

 

First thing. What have you done in the rear of your car ? If its all original ,take the trailing arms off and have them done.
This is not easy to do for a first timer. Do a search on rotor shimming,here is one where shimming was being discussed.
http://forums.corvetteforum.com/c3-t...ed-rotors.html

 

Confusion on this is common- usually because of misuse of terminology and assumptions being made that C2/C3 cars can be serviced like any modern car. They cannot.

On modern cars, rotors can be swapped indiscriminately with no worries about runout. They were designed from the ground up to be able to do that and the rotors are considered routine service items. The Corvette system is different. The rotors were NOT designed to be separated from their hubs in the field, and only replaceable in sets complete with hubs or spindles depending on front or rear.

The problem started years ago when suppliers started selling individual rotors with no hubs (just like any other car). Many owners started reporting loss of brake pedal or a frequent need to bleed air out of the system.

Cause?

The new rotor, although machined perfectly flat, was mated to an old hub that is not flat or 100% perpendicular to the axle. The effect is that the rotor surface now 'wobbles' by .008" or more. This knocks the caliper pistons back into their bores while driving and air makes it way around the seal as the internal spring tries to push the piston back into contact with the rotor.

Solution?

The real one is don't change rotors- they usually last the life of the car and beyond. In cases where there is no choice- like yours, then be prepared for some extra work.

The best method by far is to replicate the factory assembly method. Mate the rotor and hub, re-rivet them, and then have them machined as a set.

Second best method is to put shims in between the hub and rotor at the low spot to minimize or eliminate the runout as measured on the rotor face.

The bubba method is to do nothing about the runout and install o-ring pistons and hope for the best.

The message is that you MUST address the runout one way or another- this forum is full of stories about owners who did not, out of ignorance or misguidance and got to do the job all over again.

 

Do yourself a HUGE favor and have the trailing arms done , then you can use Autozone or Advanced calipers. I do my own but here is a poll on rear arms. I have good friends that have used Bairs for years and are very happy with their work.
http://forums.corvetteforum.com/c3-g...-or-vtech.html

 

to whom it may concern, any one turning a rotor before-hubing is a fool to even suggest that. You put them together and use the bearing races to center the hub as normal with any other car and true the rotor up {after} the rehubbing....run out should be zero by then...One of our businesses was auto parts and service, and brake jobs was a big part of it...so this shimming is just that..watch out for some of the know it all back alley mechanics that dont know the parts business.....there the ones that *** um up and then blame the supplier