Brake booster question

[Weasel73240Z]

I'm having some trouble getting my brakes right. They're working, but not the way they should. At first, they stopped the car fine, the vacuum assist seemed to work fine, but the pedal went down to the floor when I came to a full stop. Now, I'm feeling like theres almost no vacuum assist about half of the time. Sometimes the assist seems to still be working.

I replaced the rear brake cylinders, rebuilt the MC, and bled everything (bench bled the MC). Parking brake is adjusted right. I did an "informal" vacuum test on the booster because I only have a MightyVac, and it seems to hold a vacuum fine, and it releases the vacuum when I step on the pedal. I checked the lines going to the manifold for cracks (none), the check valve works fine, and the line from the check valve to the booster for cracks (none). The lines both hold a vacuum with no loss. Still, somethings not quite right.

I think I may have displaced something in my booster during tear-down. When I took it apart, I think I may remember hearing something drop when I pulled out the pushrod (which I know now I probably shouldn't have done, but didn't at the time). I think I remember reading about this issue, but I couldn't find the thread again. Did I maybe cause some seal to fall out of place, and could that be my braking issue?

If I can just get these brakes right I'll be about done for now, very aggravating.:mad:

[xray]

Sounds like the reaction disk may have been displaced. BTDT...

See if this thread matches your symptoms...

http://classiczcars.com/forums/showthread.php?t=17072&highlight=reaction+disk

[Weasel73240Z]

I think that was the thread I read the first time. I'll check out the reaction disc when I get home. Thanks.

[kinfish]

You also must adjust the pushrod between booster and MC in the free state so that the piston in the master cylinder starts moving immediately after touching the brake pedal. Only a small gap is required to insure the brakes are not dragging. If you have a large gap you are consuming brake pedal travel but not moving the piston in the master cylinder. There are several pushrod configurations for the Z's and sometimes they get mixed up with refurbished boosters.

[Weasel73240Z]

I checked out the booster today. I think the reaction disc is missing. After I removed the pushrod, retainer and seal, I could see the end of the bright brass pushrod that connects to the brake pedal when I looked into the booster. It had a small black retainer of some kind that looks like its part of the booster body. No pics, wife had the camera. But based on the cross sections I've seen, the reaction disc is a pretty thick thing thats not a part of the booster.

My question is, can the reaction disc be bought separate from the whole rebuild kit? The rebuild kit at BD is $40 more than buying a re-manufactured one!?!?! If I can get the reaction disc alone, I'll put it in and see if that works.

But I think this will be my last shot myself. I've got a friend who owns a shop, with all the right equipment. I think brakes are too important to fool around with. Still not working the way I want them to, so I'm gonna bring in a pro. I guess brakes are the one thing I don't mind paying someone else to fix. :beard:

[Weasel73240Z]

Success!!!! It was the reaction disc. I have a new one on the way from one the the other guys on the site, but I couldn't wait any longer. So I decided to make one yesterday. I guess its the engineer in me. Anyway, if anyone ever needs to make one, I just used a flexible plastic body putty squeege. Its almost exactly 3/16" thick, and real easy to cut with a sharp utility knife. I cut it to the correct diameter, threw it in, adjusted the pushrod length, and the brakes work great.

I think the PO may have lost the reaction disc before I ever got the car. Somebody had definitely worked on the brakes, and the pushrod was extended all the way out, I think to make up for the missing disc. I never found an old one inside the booster. After I put in the "new" reaction disc, I had to adjust the pushrod in about 1/4" to get it to 4mm from the flange.

I also had some luck with exhaust vapors. I used the 1" wide x 1/2" thick adhesive weatherstripping that they sell at home depot. I adhered it to the hatch itself, basically doubled up the weatherstripping, and the fumes are almost totally gone.

[xray]

Nothing builds confidence like willing brakes! Glad it's fixed.

[74L28Z]

Sorry to dig up an old thread, but I had recently replaced my brake booster with a spare and had the same symptoms. Of course the reaction disk fell out on mine too, but I failed to check before installing it. I just wanted to contribute a photo of what the disk looks like and what a hell of a difference a tiny piece of rubber can make on your brake function. As mentioned elsewhere I also HIGHLY recommend checking your booster before installing it! Thanks guys, for your help and the search function.

Lee

[Reverend]

Hey i have that part on the left! That's one of "mysterious" parts that came with the car. What is the function of that and where it belongs? I have to know because i have problems with brakes, wich i'll explain in different thread.