brakes

[corky]

I am currently working on the brakes on my 74 and have two questions. First, while taking off the rotors, One of them in the rear dosen't have any rivets. I think there called rivets, I'm not sure. Anyway that one came off easily, but the one with the rivets will not come off easily, any suggestions? I am soaking it with penetrating oil hoping to losen it. The front rotors have rivets and emergency brake drums also, are they universal, front to rear? Secondly, what type of pad should I use, semi-metalic or non-metalic. Any preferences? Thanks for the info, corky

[Joe L.]

Re: brakes

Corky----

One of your rear rotors does not have rivets(yes, that's what they're called) because someone has previously worked on the brakes and drilled them out. I DO NOT RECOMMEND that rotors be seperated from the spindles unless absolutely necessary. This should occour only if you have to replace the rotors or spindles. If you have to do this, it can create many more problems due to the fact that it is difficult to reasemble and maintain a MAXIMUM total indicated runout on the rotor of .005". This is a long and involved subject that I can't get into here.

Penetrating oil is not an effective means of removing rivets, which is what you need to do if it is necessary to seperate the rotors from the spindles. You will need to drill out the rivets. This is quite a task. You need to center punch the rivets dead center, drill a small pilot hole, and drill gradually larger holes until you're just shy of 3/8". Then the rivet heads should seperate, although you may need a chisel as a final persuader. Then you can remove the rotor. Subsequently, you'll need to drive the remaining rivet ends out of the spindle or, at least, grind them COMPLETELY flush with the spindle flange. You do not need to replace the rivets; the wheel lug nuts will act to secure the assembly. Also, it is impractical or impossible to field-replace the rivets.

I ABSOLUTELY DO NOT RECOMMEND that you seperate the front hubs from the rotors. If the rotor needs to be turned, have it turned as an assembly with the hub attached. If the rotor needs to be replaced, I recommend replacing with complete rotor/hub assemblies. These are still available from GM/Delco. They're very expensive, but this is the way to go. GM part number for 65-68 is 3998278. 69-82 is GM# 3991024. If you can't afford this route, you'll need to drill out the front rivets as previously described, remove the unservicable rotor, and replace it. However, before installing on the car I recommend securing the rotor to the hub with lug nuts(torqued to 75 ft/lbs)and having them trued on a disc brake lathe as an assembly.

[Joe L.]

Re: brakes

Corky----

Sorry, I forgot to answer the second part to your question. The brake rotors are not the same front and rear. The castings are the same, which is why the fronts appear to have "emergency brake drums", However, the front and rear rotors are machined slightly differently. Some aftermarket rotors may be "universally" machined; I'd steer clear of those.

As far as brake pads go, I recommend an organic pad as was originally used on Corvettes. In my opinion, this pad has the best OVERALL characteristics, considering braking efficiency, long life, low rotor wear, and relative "squeel-free" operation. In fact, the best pad ever made for a Corvette is the OEM GM/Delco pad. Due to asbestos regulations it was discontinued several years ago. But not before I stocked-up with a twice-over lifetime supply for my car.

[Chester]

Re: BRAKES JOE!!

Joe, Are you saying that you/we don't have to replace the rivots?? I'm not questioning your knowledge/wisdom, but am in relief to hear this. I rebuilt a spare set of trailing arms with no rotor/drums attached and ached at what to do next, just slap the new rotor on and the lug nuts will hold it to the spindle. Correct!!??!! WHEW WE!! You could pound the rivots in--never mind--then you/ I for that matter could/would damage the spindle--- never could figure out why this set had no rotors on them. Had my vettes for 2 years and was puzzeled everytime I looked at them.

BIG THANKS JOE!!!!!

[Joe L.]

Re: BRAKES JOE!!

Chester----

There is no major functional purpose to installing the rivets. The lug nuts will retain the assembly. This is exactly what GM specifies in the 68 service manual for your car. There are only two reasons that I can think of to reinstall the rivets. The first is to insure the maintainence of the EXACT relationship of the spindle to the rotor. This and assembly convenience are the primary reasons that GM rivetted them in the first place. However, once the rotor has been seperated from the spindle, this EXACT relationship is forever lost so the rivets become essentially moot. The second reason to rivet them is for "originality" purposes. However, with the wheels installed on the car it is impossible to discern if the rivets are present or not.

The rivets CANNOT be installed with the rotor and spindle mounted on the car inasmuch as there is absolutely no way to set the rivet("mushroom" the rear of the rivet). They can only be set with the rotor and spindle OFF the car. Even then, it is a very difficult operation. Ever try to set a 3/8" STEEL rivet? GM did all 5 simultaneously with special tooling and a VERY HIGH PRESSURE PRESS. You won't find that capability outside of a MAJOR fectory environment. In service, the rivets can only be set individually using heat and machine shop type presses or a hammer. In my opinion, setting the rivets individually and with heat risks damage and/or distortion of the rotor and spindle.

Problems with the rear spindle/rotor assembly is one of the "Achille's Heels" of 65-82 Corvettes. It is CRITICALLY important that the spindle/rotor assembly result in a total indicated runout(TIR) on the rotor NOT TO EXCEED .005" and preferably, .002" MAX. That is VERY, VERY difficult to achieve. That's why I recommend that, whenever possible, THE ROTOR AND SPINDLES NOT BE SEPERATED. For the fronts it is equally important, but unlike the rears, for the front you can purchase the hub/rotor as an assembly. Very expensive, to be sure, but it is the way to go.

I learned how to properly correct rear rotor TIR problems and achieve/maintain .002" MAX TIR. But, it was a LONG AND EXPENSIVE EDUCATION PROCESS. It's far too lengthy an explanation for me to go into here.