brake problem: similar symptoms to reaction disk missing

[ta240]

what would cause similar symptoms in the brakes to a reaction disk missing?

I just replaced the booster and master cylinder and bled the brakes but the pedal travels almost freely most of the way down and then as soon as it hits some (3/4 way down) it goes from next to no braking to full braking with a rear wheel locked up in almost no travel.

I pulled the master cylinder and popped the clip out of the front of the booster and the reaction disk was where it was supposed to be. It wasn't glued onto the shaft but it was at the end of it.

Where should I look first?

Thanks,

Trevor

http://240z.me

[zKars]

Just in case there is confusion, the reaction disk is a little round chuck of black rubber. Sure you're seeing what you think you're seeing? Take it out and confirm, and then glue it to the end of the steel disk on the end of the rod from the master. Your decription is pretty classic "no reaction disk" so I'm asking silly questions to be sure before you look else where...

[ta240]

It's always good to confirm before heading off in other directions.

It was a little rubber disk and on the new booster it was somewhat stuck on the end of the steel disk (at the end of the output shaft) with grease. I cleaned it off and glued it in place.

After my test drive I was sure they had sent me a booster with a loose or missing reaction disk but it was there.

The only thing I can think to do is rebleed the brakes but I'd think if it was air in there the braking would be soft at the end too. I pumped a lot of fluid through the brakes and have the speedbleeders on all of them and still had the fluid hose go up and then back down into the recovery bag and didn't see any more bubbles.

Edited January 30, 2012 by ta240

[Diseazd]

http://www.autoshop101.com/forms/brake05.pdf

Try this site........It should help make sure you're set up correctly. Then go to bleeding. Guy

[black gold man]

If you haven't serviced the rear brakes and the rear wheels are locking up.

Lock up is a sign of bad rear cylinder it dose not have to leak to be bad.

They corrode inside and stick. If you don't have rear brakes adjusted right

you will have pedal travel. Service rear brakes adjust by hand until tire

spins one half rotation by hand. The auto adjust just don't work most the time.

spray ends of e brake cables and exercise them.

Edited January 30, 2012 by black gold man

[Zedyone_kenobi]

Just out of curiosity, did you ensure the distance between the push rod that goes into the master cylinder and the master cylinder piston is correct?

Part number 2 below:

If the pedal is crazy easy to push then you may be pushing air until the pushrod hits the master cylinder piston...

[ta240]

great description on the booster operation.

I'll check the rear wheel cylinders, I replaced the shoes back when I bought the car, about 30,000 miles ago and the cylinders looked pretty recent. And I adjusted the brakes last year but it can't hurt to inspect and check the adjustment.

Hopefully I'll get the brakes back to where they aren't an on/off only setup again.

[kjohnson2444]

Just a thought... did you bleed the master cylinder? Use the small bleeders on the master and bleed it right back into the MC until there are no bubbles. No amount of slave cylinder bleeding will get bubbles out of the master (that I know of).

[ta240]

I just finished working on it. And did bleed the master cylinder just in case. And it hit me. Could I be confusing good braking for bad?

The reason I was working on the brakes at all is for the longest time I've had a problem where the first press on the pedal after driving for awhile didn't feel the same as the next ones would. The second press had more 'feel' to it, resistance started higher and it had more resistance. It would brake like that again for awhile and then after longer time without braking would feel odd the first time again. I always thought there was some air in the system I just couldn't get out. But in looking at things I saw the master cylinder was leaking a bit at the back and found a good deal on a new one and reman booster so I figured it was time.

Anyways, it hit me tonight that all the pedal feel now is more like the first press was before all the replacements. Only even more pronounced. So what I'm thinking is with the old booster the first press on the brakes was the good one, with good vacuum in the booster and as soon as I moved the shaft on it it would bleed off pressure and not work as well, but since I got more feedback from the pedal it felt better to me with it less boosted, especially since 90% of the time it felt that way.

After bleeding things out and adjusting the rear brakes I found I could brake somewhat smoothly with it tonight and am wondering if I just have to relearn to drive the same car but with better boosted brakes.