Howdy, I know brakes are a really popular topic here in the C3 world, but I searched and couldn't find what I'm looking for. I have a 78 vette that was all original brakes. One of my calipers was leaking so I decided to replace them all. Along the way, I realized a new M/C would probably be a good idea as well, since I'm switching to silicone fluid. My question is...I took off my old MC and compared it to my new one. Where the MC connects to the booster, there is a rubber-ring on my old one where there is no rubber ring on my new one. Is this rubber ring some sort of gasket? Do new MC's not come with these? I got my MC from Corvette Central. Also, when I mount the new one, should I use some sealer between the MC and booster or just bolt it up...thanks and I appreciate any help you can give me. I'm also a bit confused on bench bleeding the MC, what do I need to buy to do it...thanks!!!!

 

1. Not sure what rubber ring you are talking about.
2. No sealer needed between the booster and the M/C - just bolt on. fluid does not move through there.
3. To bench bleed, you clamp the new m/c in a vice, and fill the chambers 1/2 way or so. You are going to pump the m/c (with a blunt screwdriver, simulating the rod that pushes -on it when you push on the brakes. Of course as you push, fluid (and all the air hopefully) willl come out through where the brake lines attach so you will need to make a couple of hoses that will screw in and bend back into the fluid resevoirs, effectively putting the fluid and air bubbles back into the fluid. After a few minutes of pumping, you should have nice clear fluid with no air bubbles. You them will mount the m/c, leaving the hoses in place and then remove them to hook up the lines to the m/c.

You can make a couple of hoses for brake bleeding. Take your m/c to an auto parts store and buy a couple of short brake lines that will screww into the fittings - one may even do the trickj if you can find one with the correct size fitting on each end. (they sell generic ones that you can bend yourself- they should be $3-4.) Cut the lines about an inch from the fitting and attach an appropriate size clear rubber hose (also avaliable at the auto parts store) that you will bend into the m/c. I clamp the flexible hoses loosely to the little wall that divides the front and back chambers with an office type aligator clip that keep them in the fluid but doesn't clamp them shut.
4. Changing to silicone is complicated as the DOT 3 and DOT 5 can't be mixed and you will have to get all the old stuff out. You may want to stay with DOT 3.

 

FORGOT THE MOST IMPORTANT PART!!!
Brake fluid eats paint (and other things) DO NOT get it on the car. If you get a drop on the car, wash it off immediately!!!

 

Thanks a ton for the replies. I'm guessing that rubber ring isn't important since to fluid goes between and I can just bolt it up. It's a black rubber ring that's attached to the old MC around the fitting where the pump from the booster goes in.

Thanks for the bench bleeding advice too, looks like I'm gonna have to make another trip to the auto parts store, I swear it seems like I make at least 3 trips there everyday I'm working on the car. Hopefullly once these brakes are done i'll be all good to driver her.

 

My new MC didn't have the rubber ring either. I just transferred it from the old to the new. I don't see what it does. Why the choice for silicone fluid? It make not take on water, but it is slightly compressable I guess.

 

I have been told that some stores sell bleeder tubes for the m/c but I haven't found them. Do a thorough job bleeding the m/c or you will nver get the brakes bled. Good luck

 

I'm not too crazy about silicone fluid (DOT5). It is not hygroscopic, which means it does not absorb water. Might sound like a good thing, but what happens is that moisure stays as droplets in the lines and calipers. These droplots then form localized rust. DOT5 also tends to produce a spongy pedal as it is more compressible then DOT3 or DOT4.