Tsi_Xtreme

I think my master cylinder is faulty. I went to bleed my brakes today and the rears bleed just fine. When i went to do the front nothing came out. I removed the front line from the master and pumped and nothing came out the side. Is the master done? If so its a good thing I changed these brakes and rotors before race season. I thought it took longer to stop than normal but i thought it was just because one of my rear brakes was past the pad and down to the metal. Nope I think it was that I only had my passager rear brake stopping me. :o

trochoid

iTrader: (6)

There are 2 seperate outlet ports for the front brakes. One goes to the proportioning valve, then on to the right front caliper, the other goes directly to the left front brake. Check the left one. If it works, the problem may lie in the pp valve.

Tsi_Xtreme

i pulled the front line straight from the master cylinder nothing came out when i pumped it. so i don't think its the proportioning valve.

g prime

I had something like that happen to someone I know, did brakes, all bled except right front, turned out to be the master cylinder

woodonastick

iTrader: (1)

is it possible that the master cylinder inner seals are gone? maybe its not holding the pressure in the cups. just a thought cuz im having the some problem with my car except the rears wont bleed.

Kentetsu

If the seals were shot on the piston, it seems that at least something would still come out when the pedal was pressed and the line removed from the MC...

I think it might be more likely that there is some sort of blockage in the port. Maybe if you blow back through the port you can dislodge whatever is there. If the front left brake still works, then that would support this theory because bad seals on the MC piston would affect both sides the same. Right?

woodonastick

iTrader: (1)

^i think your right about the blockage part. blowing air will probably help it, but wat if it gets stuck again? the master has 2 sets of pistons that push the fluid. i think the primary moves the fluid into the rear and secondary piston moves fluid to the front calipers? if the seals in 1 chamber will fail, the other will still work. i think its a safety thing where its better with some brakes than none. correct me if im wrong please.

Kentetsu

I'm pretty sure that we only have one piston.

There are some MCs that have a setup of one piston sitting inside another, larger, piston. The large piston picks up all of the slack in the system, then the little piston extends out from the center of it to do the actual braking. The theory is that the smaller piston will exert more force on the brakes with less effort.

But I'm no MC expert either, so somebody please make sure we haven't wandered off the road and into the ditch with this discussion...

woodonastick

iTrader: (1)

i just looked up the 85 manual online.

trochoid

iTrader: (6)

Looking at the provided exploded diagram, the left front caliper has it's own seperate piston and seal set. The right front and rear brake outlet both go to the pp valve, then split off with 1 line going to the right front, the other going to the rear. If you disconnect the left front brake line, you should still see some fluid, even if the seals are going bad and leaking. The check valve is there to hold some residual pressure on the calipers for quicker brake pedal response. If there is no flow at all from that port, the check valve may be stuck.

If the rear brakes are working correctly, the right front should be too, unless the ppv is bad. Rarely happens.

Tsi_Xtreme

On the SE MC, there are two ports from it. A front and rear. The Rear (towards the front of the MC) is clearly marked with a R and the front (towards the rear of the MC) is clearly marked with a F on the MC. Those lines then run to the P.V. which is also clearly marked with a F and R. So what I'm gathering from whats stamped on the MC is that the F line isn't working and isn't flowing through to the P.V. I got a brand new one from Autozone for 62 with a new reservoir so I'm going to pop it on this afternoon and see whats up. I'm now just wondering if I should try to bench bleed it or just pop it on there and go forth.

j9fd3s

iTrader: (3)

bench bleeding makes bleeding the rest of the setup much easier and faster. in fact, if you bench bleed it right you dont always have to do the wheels

woodonastick

iTrader: (1)

so how is that new master cylinder working out? i bought one yesterday and turns out it was leaking too...brand new...and leaking..........the cylinder was fine but the bushings that hold the reservoir were leaking.

Tsi_Xtreme

So far its ok. It was the master cylinder. I bench bleed it and put it on and everything bleed correctly. I was going to take a joyride to see if everything was ok but my battery was dead where I left the door open the other day and the dome light drained the battery.