piratemike

I am planning on rebuilding the brake calipers on my '81 and I have a question about one of the steps mentioned in the manual. The manual says:" On 1978 and later models, before installing the pistons into the caliper apply a bead of (RTV) to the boot gooves in the piston( the groove closest to the concave end of the piston). The groove must be clean and dry for the sealant to adhere properly.Do not let the seal lip extend over the step in the edge of the groove". I am not exactly sure what they are saying here. Do you allow the RTV to cure before reassembly? What exactly are they trying to accomplish with this step?If any of you have rebuilt these before, any advise would be greatly appreciated.

Thanks,

Mike

Rowdy Rat

The RTV is intended to be used on the dust seal (the outer seal) to prevent water and other debris from entering and corroding the bore. There was a Technical Service Bulletin issued in 1978 that described the procedure and while your manual states "1978 and later," it's not a bad idea for 1965-77 calipers either.

I've posted the TSB here... Sorry for the "wide screen" look; all my attempts to edit this into a forum friendly format failed.



Regards,


[Modified by Rowdy Rat, 1:36 PM 11/22/2001]

MIKER

Hi Mike!
Here is a cut-n-paste taken from the The Big Block from Hell, Part 12. Most of everything you’d ever want to know about 65-’82 Brake Service
http://www.idavette.net/hib/BBfHInet12.htm
IF you liked that article, Here is a link to part TWO. The rest of everything you’d ever want to know about 65-’82 Brake Service http://www.idavette.net/hib/BBfHInet13.htm
I found those articles at www.corvettefaq.com
I recently made a post to discuss “Basic brake performance upgrades. (Medium to Low Dollar)” http://forums.corvetteforum.com/zerothread?id=185480

Rust and other Nasty Stuff
With ’65-’82 disc brakes, a durability issue many of us understand is corrosion. Defined as, "Gradual destruction of a metal or alloy due to chemical processes such as oxidation or the action of a chemical agent.", corrosion is caused by either: 1) contaminants in the cast iron, 2) water in the brake fluid or 3) water or other reactive material between the dust boot and the primary seal. The first results from poor metallurgy. The second results from brake fluid’s affinity for water. The third comes from poor sealing.
The corrosion causes pits in the cast iron. Once the pits grow deep enough…and it doesn’t take much, perhaps a few thousandths of an inch…the primary seal cannot conform to the caliper bore, then air gets in and brake fluid seeps out.
Another weakness is the secondary, "dust boot" which is only marginally effective. Abrasive material can work around the inner edge of the boot and lodge in the space between the caliper bore wall, the brake piston and both seals. As the brake pad wears, the piston slowly moves outward. The primary seal moves along the caliper bore trapping brake dust, or whatever, under the seal. Over time, this can abrade the seal enough that it begins to leak.
If the car sees use where salt is used to melt road ice, salt finds its way around the secondary seal. The caliper bore beyond the primary seal corrodes in short time due to the reactiveness of the salt. As the brake pads wear and the seals move out, they encounter the salt-induced pits and begin to leak.
It took 14 years, but Chevrolet indirectly admitted the secondary seal problem. Starting in 1979, they recommend adding beads of RTV silicone sealer in the secondary seal groove on each brake piston and, after the piston assembly has been installed, over the gap between the dust boot’s outer ring and the caliper half.

Hib Halverson

The RTV is to 1) seal the dust boot to the piston and 2) seal the small gap between the metal edges of the dust boot and the piston bore in the caliper. GM found (probably through input from enthusiasts and the aftermarket service business) that the gap was one of the many paths for moisture to enter the system.

I like the RTV sealer made by Valco Cincinnati Consumer Products but any reputable brand of RTV will work. Simply dab a little on your finger and work it into the dust boot groove in the outer end of each brake piston. Once you install the pistons and dust boots, dab more RTV on your finger qand smear it over the gap surrounding each dust boot. I usually go over it a second time with my finger to drive the RTV down inside the gap. If you're using an application device, such as Valco's "Tube-Grip" you can lay a very thin bead of RTV over the gap then go back over it, using your finger to pust the RTV into the gap.

BTW, I see some posting to this thread have referenced the Big-Block from Hell articles on brakes that are archived at http://www.idavette.net. I hate to rain on your parade but, Vette Magazine has killed the BBfH. :sad: Read the details at http://forums.corvetteforum.com/zerothread?id=187794


[Modified by Hib Halverson, 1:01 PM 11/22/2001]