Hi all,

I tried the search feature, but it didn't seem to work ("0 items found" regrdless of what the search terms were). I am planning on replacing my master cylinder on my 86' tonight (rear seal is leaking). I have the new master cylinder (Corvette Central supplied) and I have the following questions:

1)When I remove the brake lines (I bought line wrenches) will the fluid in the resevoir drain out the holes?

2)Should I bleed the driver front caliper to empty the resevoir before I start?

3)I have not been able to find a master cylinder bleed kit (I called Auto Zone, Advance, and Pep Boys), does anyone know where I can go to get one? If I can't find one, can I simply hold a tray under the master cylinder and bleed it that way?

4)Any tips/experience regarding this would be appreciated!

Thanks!

P.S. - I have other cars, so if something dosen't feel right then I'm not driving it anywhere until it's fixed.

 

my$.02 worth. no need to drain fluid. put the master in a vice and fill resivoir, use a screwdriver or drift ( preferred ), and manually push piston to force fluid out. have something to catch it or you'll have a mess.
loosen the master cyl from the booster and disconnect lines. very little will seep out, but place a rag under the master to catch. finish removing master and install new one and bleed the system. you will be able to see the color change when the new fluid goes through the caliper. start at rr, then lr, rf and lf last.
anyone else have a procedure ?
LOL

 

Thanks for the tips!

I don't have a vice installed yet. The guy at the auto parts store said I could bolt the master cylinder to the booster, but leave the lines disconnected, and bleed it that way since I don't have a vice yet. Any reason not to do this?

Thanks!

 

that'll work. if you can get some vacuum hose adapters to screw into the master, then run the hose into a can or some container. this will prevent fluid from being sprayed all over the place. otherwise, have some one with a towel or big rad to hold around the ports while the fluid come out.

 

You need to have a way to bleed the MC so that air does not get sucked back into the MC when the piston is retracted. In other words, just squirting out Brake fluid and releasing the piston to retract will not work. This may be messy and wasteful of brake fluid, but if you dont have a MC bleeder kit, simply submerge the lower part of the MC into a bucket of brake fluid while you push in and release the piston. All you need to do is to have both brake line holes covered by fluid while you accomplish the bleeding. Do it until you dont see bubbles coming out. Wipe off the MC and install and bleed the Calipers in the order of the farthest away from the MC first.

 

as far as system bleeding, if you have some time, just gravity bleed it...its a little slower, but it almost 100% guarantees no air in the system. put hoses on all the bleeder screws and lead them into catch containers. crack open all the bleeders at the same time and just keep an eye on the MC resevoirs. once clean fluid comes out of all the hoses and there is no more air, you are done. tighten all the bleeder screws. just make sure that the fluid level is NEVER lower than 1/4, or you might pull in air and have to start all over again. NASCAR does their brakes this way.

 

All good info here.

When I did mine, I couldn't get the lines loose - it opened up the ends of my line wrench (whataver brand NAPA sells)... If you're having problems, before you strip it all to hell, get a huge pair of channel locks, and just grip down on it and torque them off. (pipe wrenches, vice grips, etc - they'll just **** it up, so don't try it)

Also you want to hold the master cyl itself with a pair of vice grips or something while cracking the lines loose, to take the strain off the plastic booster (crackity crack!) that GM decided to use for "weight savings" (euphomised cost compromise)...

If your new one came with reservoirs, you're golden. if not, you'll have to fight the new ones on. Use brake fluid to lube up the bushings...

As for "bench bleeding" you want to do it so that %90 of all the air is gone, otherwise once the lines are on, it'll take for ever to bleed all the air out. Bolt it on, tape a baggy underneath the 2 holes, put straws in them, fill the res up with fluid, and start pumping. Don't let the fluid drop and let it suck in air, because that negates what you're doing. Once you pumped enough fluid through, bolt the lines back in.

If you have a mityvac, then the next part is super easy. Just go to each caliper and suck until no air comes out and the pedal has a good feel. If you don't (i recommend picking one up, its like 25 bucks and works for a lot of stuff) then just do as every one says and crack every bleeder bold open and let it drain on it's own. Make sure your car is fairly level (front is same height as rear, etc. Don't do this on a huge hill or anything)

If you have any other questions you can e-mail me and I'll be happy to wrtie you a whole essay on this.

Oh, use good brake fluid, and buy the "big bottle" cause you'll need it. You want to bleed a lot of fluid through. Old fluid is dirty and saturated with water (it's hydrophillic, absorbs it like no other and loses it's high-boiling point properties) so take the opportunity to get it all out

PS Your MC is new right? These are aluminum units, and the bore wears out. Remanufactured means new seals - so you'll be putting a new on in very very soon if you get a rebuilt.

 

All you need to bleed the mastercylinder, is a pair of 12" hoses with a plastic tip at one end that will fit into the hole where the brake line came off the cylinder, fill the master,and push the piston with a screw driver or center punch, several times, slowly in and out, have the hoses discharge into the master, do this several times til you see no air bubbles coming out of the hoses.
this will be enough for the master, mount it on the car, and then bleed the wheels normally, til you are sure there is no air in the lines.
PS those little rubber hoses normally come with the master cylinder when you buy one otherwise you can make them out of 1/8 plastic hose
and some adapter for the master.
good luck it's not hard

 

Thanks for all the advice guys!

I think I have it done.

The master cylinder came from Corvette Central. It looked just like the old one and had the resovoir already attached. The brake lines came out of the old master cylinder without a fuss, in fact the nuts holding the master cylinder to the booster were far more tedius than the brake lines were. I bleed the master cylinder on the car. I bought a "universal" bleed kit from Pep Boys. It was all they had in stock. basically 2 small cones that you shove into the holes and put tubes on the back ends of to run back to the resovoir. After that I then attached the lines and bleed the calipers. I took it for a short and careful test drive (slowly incresing speed between brake tests) and everything seems cool. I will check for leaking fluid tomorrow morning and drive carefully for a while until I have full confidence in my work.

Thanks for all your help!