C3-Front Rotors/Hubs

[Chris1977]

I was wondering if anyone can provide their opinions for me on this subject. I own a 77 that is in very original, "unmolested" condition. The car has 32k original miles however it sat for the last 10 without any of the brake parts being activated or driven with. The parking brake hardware was deteriorated and leaking rear calipers really killed the rotors in the back. I replaced those with NOS GM rotors.The front calipers need to be rehoned and rebuilt but did not leak so its reasonably clean up front. Is hope for the front rotors? Just how much surface rust can a rotor tolerate before it is deemed lost? My rotors have a lot of surface rust but considering the low mileage of the car and the fact that the car was never driven hard I think that I might be able to get the rotors resurfaced.

Is resurfacing possible on a rotor that has had a lot of surface rust on its face? i can run my fingers over the rotor an it is not deeply pitted but is very rusty. Is resurfacing even necceary once I rebuild the caliper and install new pads? I was optimistic that I could rebuild the caliper, brush away as much surface rust as possible and drive the car without resurfacing or replacing the rotor.

I am trying to keep the car original and replacing the rotors with even new GM parts would eat at me on top of being costly.

Thanks in advance for everyone's opinion.

Chris

[Dick W.]

Re: C3-Front Rotors/Hubs

First, lotsa luck rebuilding the calipers if they are not stainless steel sleeved. At best it is a stop gap measure before replacing the calipers with ones that have been stainless steel sleeved.

Before I had the rotors turned I would try using 3-M's discs that are designed to take the glaze off rotors. I am away from the shop right now or I would give you the part #. I feel sure that these would clean the surface of the rotors up.

Good luck

[Eugene B.]

Re: C3-Front Rotors/Hubs

Chris,
I think that the 3M rotor resurfacing kit that Dick told you about will solve the rotor problem.

Regarding the calipers, if they must be rebuilt and you want to keep your originals, I can recommend Lone Star Caliper. I had them sleeve, rebuild and return the originals for my '65. Procedure is costly, but it my be worth it to you.

Good luck,
Gene

[Michael W.]

It's too late now

but if the only problem you had with your rear rotors was surface rust/fluid contamination, there was no real reason to replace them.

Since you have installed new ones, make sure you measure them for surface runout before you put the car back on the road. The service limit is .008", but you should aim for .003" or less.

[Tom R.]

Re: C3-Front Rotors/Hubs

Chris:

You've got a safety issue here...the car has got to stop and you must depend on it to do so if you intend to drive it. While the rotors sound salvageable and others have suggested some methods to check it out...the calipers may be too far gone to salvage and you would be better off financially doing the route of core exchange for rebuilt stainless steel sleeves with O ring style pistons. I've been through this a couple of times with my 35k mile 78 as others have been with their classics. Do a search of the archives if you really wish to know what you're getting into before proceeding. Anyway...that's my opinion.

[Chris1977]

Re: C3-Front Rotors/Hubs

Tom,

What is the deal with the stock calipers? Everyone tells me about these calipers having issues but no one has really given me an good explanation as to why. If you have the time, I would love to hear what the "real deal" is. I bought a rebuild kit from mid america. I got halfway through the rear calipers before I got fed up and bought Delco Morraine rebuilds with the same casting number from Advanced Auto Parts. I was suprised that they had a set of these around because all the other places had some kind of casting information that was definitely not GM.

Are you saying that the rebuilt unit I bought from Advanced Auto Parts can also be a problem? Will this rebuilding kit(new seals,pistons, and springs) be a waste of time?

Thanks for all the help and the input. I found a place right down the road and resurface them if they even need it. All this for 38 bucks:). I can send the cheap repo rotors back to mid america for more worthwhile causes(maybe rebuilt front calipers?)

I look forward to your response.

[Dick W.]

Re: C3-Front Rotors/Hubs

More than likely the calipers from Advance were sleeved with steel, which in the long term will corrode and pit like the originals. I have seen the chain auto parts sell steel sleeved calipers for as much or more than you can buy quality stainless steel sleeved units.

Your original calipers are probably pitted from moisture. Rebuilding them is just a temporary measure. Go ahead and purchase SS sleeved calipers. Granted in the future they will also leak, but you will have something that you can install a kit in.

[chris1977]

Re: C3-Front Rotors/Hubs

Hi Dick,

I am going to look into it. One of the brake shops I spoke with yesterday suggested running a silicone based fluid instead of the original stuff. He said that the silicone will do a much better job of "coating" the system and slowing down the corrosion of the system. It sounds like it would work but what is your opinion of that.

Thanks,

Chris

[Mark Milner]

Re: C3-Front Rotors/Hubs

When you remove the original rotors and replace with others, you have to check the runout of the rotor. The spec like Mike said is .008 and you should try for .003 inch. If not, you have to shim under each stud hole to realign the rotor to get this.

Rust on rotors is common, but in most cases, they will clean up without problems. If rusty, you will coat the existing brake pads and they will not be effective as rust acts like a lubricant. You can put in old pads, drive “carefully” for a few miles and the rotors will be pretty much cleaned up. The other option is using the 3M kit or spinning the rotors while holding 100-200 grit sand paper on a block next to them.

Calipers leak because the moisture in the fluid sits and rusts small holes in the bores. As they deepen, they allow air and fluid to get past the seals. The stainless steel sleeves will not rust and pit, although the rubber seals can still go bad. The other problem is that the aluminum pistons will corrode under the seals, so that you lose the sealing there. That can sometimes be fixed one time by cleaning the seal grooves in the pistons. Otherwise, it is new pistons.

Sitting is the death of Corvette brakes.

Driving keeps them going. I try to drive at least once a week.

Silicone fluid tends to become filled with tiny air bubbles that do not move out easily. As such, they can be a problem in mountain driving where the air expands and you suddenly have no brakes, in racing where the heat expands the fluid (air) back in the MC, and then cools to contract away from the pistons and have no brakes, and usually have a characteristic spongy feel to the pedal. Many use it, and it works satisfactorily for most. You have to be careful filling so no air is created (bubbles).

However, normal fluid works fine if the car is driven and you do not leave it in there for 20 years.

[Mark Milner]

Expanding on Runout

The reason for having small runout is that excessive runout pumps the pistons in and out of the caliper. This pumps air into the system and gives you spongy or no brakes.