5abivt

When I brake hard the pedal holds firm. Even if I Brake hard and hold the pedal (even stopped) down it won't sink. If I brake and slightly let off the pedal and continue to push down it will sink further down if I do it 2-3 times it goes all the way to the floor.

I noticed in the summer the rubber boot under the master cap was grossly swollen. I replaced it with a new one but it happened again within 2 weeks. I tried bleeding all corners with a friend to get any air out and there aren't any leaks anywhere. Fluid isn't dropping.

Is it fluid contamination? My booster or master? Any thoughts are appreciated.

86PACER

Booster has no effect on pedal travel. When the booster goes bad the pedal will be stiff and hard to press.

You need a new master. You must bench bleed the new one out of the vehicle before installing it. You can't just take it out of the box and slap it on the car. If you do you'll have air trapped in the master that will not purge no matter how much you bleed the brakes.

Some masters come with bleeder kits and some don't. If yours does not you should get one.

What often happens is when people bleed their brakes they push the brake all the way to the floor during the procedure. On older cars this often damages the master cylinder piston seal. When you do this you are moving the master cylinder piston into a possibly contaminated portion of the bore that it normally does not reach during normal operation. This can result in damaging the piston seal. To prevent this you should place a block of wood under the brake pedal when bleeding to limit the pedal travel to within the normal operating range and avoid the chance of ruining a master.

5abivt

Thanks for that info. I believe that's a strong possibility that I ruined the master I had my brother push the pedal and I'm sure he two-footed the pumps. Ill get to ordering one.

If I may, the original problem with the brakes before the pedal would sink is I would brake moderately hard slowing off the freeway and after about 5-6 seconds of braking the pedal would get firm and it wasn't slowing down as much. I would really have to stand on it to stop. I'm familiar with brake fade and I'll admit I dont know what pads are on the car but I just can't think it was fade because of the firm pedal.

What do you think about the swelling of the rubber boot? I guess a full flush and new master is in order

oldalaskaman

bench bleed the master prior to installing, and a good fush is always best for these older cars.

RLDaily

Either air in the lines or internal leak in the master cylinder...No big deal.

Bleed from back to front and if it still happens either rebuild or replace the master. Rebuilding the master yourself will require honing and cleaning but good.

Sandpiper59

Likely internal leak, rubbers are probably old and stiff. If you hit the pedal hard, the rubbers will get forced out against the walls, but pushing gently and they will allow fluid to pass around them.

By the way, brake fade from heat will still be firm, can even force the pedal back at you a bit as the rotors expand. If you were getting fade that easy on a Vette then either pads were contaminated with oil (or even tire shine stuff) or your rotors had substantial rust rings at the edges giving far less clean steel to grab.

5abivt

Can contamination have that much of an effect on the pedal? The rubber boot swelling up makes me wonder if the previous owner put something other thank brake fluid in there. Even the brand new cap and boot after 2 weeks was so swollen It took 20 minutes of wrestling it to stay under the cap when putting it back on


Thanks for the input so far! Got the new fluid and am debating in doing a full flush first and if that doesn't help then do the master?

oldalaskaman

they will develop condensation over the years, and the water has an adverse effect. Actaully saw a guy that claimed to be a mechanic, put hydraulic fluid in one, swelled the rubbers up bigtime.

Sandpiper59

Agreed. wouldn't worry about the puffy cap liner, mine is no different, it certainly won't effect braking.

I'd expect the flushing the system will do little to nothing to cure your slow drop to the floor and to be hounest, I'd do it after the new master. The master is a big source of crud, black crap and the only location (baring any leaks) where moisture can get in. Flushing now will simply move that into the system.

TJM

Little or no doubt

TJM

5abivt

Ok thanks again guys. Ordered a new master and will do the fluid as well. Will let you guys know how it goes !

RLDaily

While you're at it take care of calipers too...minor cost to rebuild (make sure you clean 'em out good before you put new pistons and boots in)

jaa1992

Or get rebuilt ones from your favoite auto parts place.
The BEST thing I did for my brakes last year was to replace the booster, master and all 4 calipers. After that I had the best brake feel I've had since purchasing the car.