Brake pedal sticking

[grease]

I installed C5 brakes on my 69 Camaro using used corvette calipers, Kore3 brackets and hoses, new pads and discs, a wilwood master cylinder with proportioning valve, and a tuff stuff dual 9” booster. I replaced all the brake lines with new. I cut the booster mounting brackets and welded them to angle them down from the factory angle. I had a lot of problems getting the system free of air. Had to replace a master cylinder (it had a scoured piston and cylinder). Not sure if it came that way or if it occurred while I was trying to bleed the system. I replaced the master and still had issues. I figured out that the proportioning valve had some boogered flares, so I rep flared the lines and replaced the proportioning valve. I bench bled the master again, installed the new proportioning valve, and pressure bled the system. I had good pedal, not great, but ok. I started the car to see how it felt with vacuum. I pressed the pedal and it went down easy (maybe a little too far). And the pedal sticks. I have to pull it up with my foot. I drove it around the block to see what would happen, it stopped well, but the pedal stuck. I would press it and could remove my foot and the car would nearly come to a stop (it almost felt like the pedal was pulling itself down). I could pull it up with my foot and keep moving. Is this caused by a bad booster? I’m pulling my hair out. Not sure what to do.

[TheBandit]

I had a behavior like this on my Nova when I first installed a similar setup. I used the Tuff Stuff Dual 9" booster and a GM S10 master. The brakes were initially very touchy and almost felt like they stuck down whenever I pushed the pedal; the booster was sort of pulling the pedal out from under my foot. I found there was an issue with the rubber bellows getting caught up in the firewall hole, which was causing the firewall to keep pressure on the booster input allowing it to apply the brakes. I found a really nice engineered part from DSE to eliminate the bellows and prevent any sort of obstruction. That completely resolved the issue.

I noticed a few times while driving that the brakes felt just a tad slow to release. One thing I decided to recheck was the clearance with the firewall hole and the brake booster bellows/boot. As it turns out the boot was catching on the firewall hole. Sometimes I found it on one side of the hole or the other after a drive, so it was definitely getting hung up.



I decided to stop rolling the dice and take my booster out to resolve the issue. Thankfully with all the brake line service loops I put in, the brake lines were flexible enough to move the master forward and get the booster out without opening up the lines. No need to rebleed the brakes!





While I was in there, I decided to get the proper tool for checking master/booster pushrod clearance. A long while back when I put this master and booster together for the first time, I noticed through the compensating port that the piston was moving as I tightened the master to the booster. To identify how much interference there was, I added shims between the the master and booster until I no longer observed movement when tightening them together. Then I took the shim thickness and ground off approximately that thickness from the pushrod. It was a considerable amount of interference - I want to say around .100in - and I wanted to make sure I had at least 0.020in clearance, so I had to take quite a bit off the pushrod. I was really curious to see if I'd taken off too little or too much. So I got the tool on Amazon (search "Power Brake Booster Pin Adjustment Tool").





Using feeler gauges I found I have about 0.040in clearance, which should be good. I've read anywhere from 0.20min to around 1/16th (0.063in) is ideal.

Next, I had to decide how to fix the clearance issue with the firewall hole. Doing a little research, I found Detroid Speed Engineering sells a booster/master combination that uses a custom boot and seal plate. I called them up and asked if I could buy just the boot and seal plate, since I already have their booster brackets. They sent me part numbers 99050028 and 99050030. Perfect! This boot just takes up the space between the booster and firewall while providing a watertight seal at both ends. It allows the booster pushrod to move freely inside.



Here is the "old" bellows that protruded through the firewall and moved with the pushrod



Here is the "new" DSE seal and seal plate that allow the pushrod to move freely inside.



When bolted up to the firewall, everything is watertight.



I took the car out last night and hallelujah, this resolved my braking woes! The pedal releases immediately now and no longer feels touchy/sensitive on initial application. I suspect the bellows interference must have been putting a strange input force on the booster, causing weird stuff to happen. Now it acts like it should and I can modulate the brakes properly

[grease]

Awesome! That might be my issue. The bellows was a little tight when I installed it, but seemed to function fine until I started the engine. Pedal would depress and return like you would expect when the engine is off, but sticks or actually pulls the pedal down from your foot when the engine is on. I’ll check the DSE site for the part or add clearance around the bellows. Thank you for the help!

[TheBandit]

I don't think they list it as a separate part on their site. I called and asked about it and they were kind enough to sell it to me separately from their master/booster/bracket combo