Sticky brake pedal

[Nate S]

A year ago I put Leeds disc brakes in my car. They work well, happy with the fit and performance. Booster and master are more chebby-ish but I’m not losing any sleep.

Odd problem though. Pedal is fine at first, then slowly stops coming back up so much. Eventually the brakes drag ever so slightly but enough to heat them up. Bitched to Leeds who gave me a new booster. Put that in and all seemed well but then the problem came back. Always can put my toes under the pedal and pull back up and it’s fine.

As time went on I realized it’s related to heat. It didn’t happen in the spring when it was cool. Doesn’t happen when I start the car, only once it’s good and warm. The other day it did this and I parked it. Left the pedal “down”. Popped off the booster vac valve to be sure the pedal didn’t pop back up (typical bad booster check). It stayed down. By the next morning it was back up.

My hypothesis is that the MC has an aluminum piston without enough clearance and it swells when hot increasing drag. There isn’t enough remaining spring force to push the booster back. If you pull the booster it’ll follow, but not enough on it’s own. Considering honing the MC for a little more clearance and maybe upping the spring size.

Any thoughts? Anyone else had something like this?

 

[khryslerkid]

My '62 uses a external spring to assist with piston return.

 

[R413]

Is there something that connects the master cylinder piston to your booster? Because pulling up on the Brake pedal will not pull back on the Master cylinder piston when you have a Brake booster between.

The booster pushrod can only push the master cylinder piston forward and the internal spring makes the master cylinder return.

I have a 1970 B body with all factory disc brakes that does the exact same thing as you describe. Sticks down only when it’s gets warm. Cold winter day it’s fine.

 

[Nate S]

My '62 uses a external spring to assist with piston return.
View attachment 994443

That’s on the list of possible fixes. If I can get the root cause I’d rather do that though.

 

[Nate S]

Is there something that connects the master cylinder piston to your booster? Because pulling up on the Brake pedal will not pull back on the Master cylinder piston when you have a Brake booster between.

The booster pushrod can only push the master cylinder piston forward and the internal spring makes the master cylinder return.

I have a 1970 B body with all factory disc brakes that does the exact same thing as you describe. Sticks down only when it’s gets warm. Cold winter day it’s fine.

There is nothing connecting the pushrod to the MC. I thought about that a bit and it's an open spot in my thoughts. Just the same, for the booster / pedal to return, the MC does need to push back to reset the servo valve. So for instance, I unbolted the MC and hit the pedal, it goes to the floor and stays there. If I then go under the hood and push on the pin that goes into the MC, it resets the servo and the pedal goes back up. My thoughts were more that the MC was pushing back less and not that it was physically stuck. I'm picturing o-rings getting softer with temp, clearances decreasing, it can still return on its own but doesn't have the excess force to push back the booster.

The other side of my thinking is that this is the second booster with an identical issue. What are the odds? Yeah, I know, they could be from the same lot etc. At least I'm not the only one who's seen this. Would love to resolve it though.

 

[Ron H]

Going on 2.5 years with my disk conversion ills. I've posted a few times already about this and all the different fixes that haven't struck the bullseye. I put on new MC couple weeks ago and new booster should be here shortly. The old MC seemed to have air that would not release or end after endless pumping on bench (bleed). That didn't solve the issue though of odd pedal sink. The system has been bled out half dozen times over the duration of fix efforts. In my case though this has never caused brake engagement! Yet the pedal could sink 2 inches or more? I'd have my car bud's come alongside me saying 'hey your brake lights have been on the past few miles'. I could slip into neutral and coast freely. The rod from boost to MC requires a gap tolerance and have checked that out with a gauge I bought. There could be a boost flaw, but now also onto a pressure loss possibility. I've futzed with the pedal throw several times while also wanting a pedal that it at the proper height. Might be that the booster rod travel isn't plunging into the MC far enough. The oddity includes a return spring in the booster and MC return that 'should' bring the pedal back. If I have the booster apart from the MC I have free pedal snap back all day. The SSBC disks are four piston so a lot has to go on the ensure ample pressure. Well - will see what happens with the new booster and adjustment...

 

[Nate S]

Going on 2.5 years with my disk conversion ills. I've posted a few times already about this and all the different fixes that haven't struck the bullseye. I put on new MC couple weeks ago and new booster should be here shortly. The old MC seemed to have air that would not release or end after endless pumping on bench (bleed). That didn't solve the issue though of odd pedal sink. The system has been bled out half dozen times over the duration of fix efforts. In my case though this has never caused brake engagement! Yet the pedal could sink 2 inches or more? I'd have my car bud's come alongside me saying 'hey your brake lights have been on the past few miles'. I could slip into neutral and coast freely. The rod from boost to MC requires a gap tolerance and have checked that out with a gauge I bought. There could be a boost flaw, but now also onto a pressure loss possibility. I've futzed with the pedal throw several times while also wanting a pedal that it at the proper height. Might be that the booster rod travel isn't plunging into the MC far enough. The oddity includes a return spring in the booster and MC return that 'should' bring the pedal back. If I have the booster apart from the MC I have free pedal snap back all day. The SSBC disks are four piston so a lot has to go on the ensure ample pressure. Well - will see what happens with the new booster and adjustment...

Wow, interesting to hear you've had related troubles. My next step is this evening, when I get home from work and the car is hot and the pedal is down, I'm going to pop off the MC and see if I can push the pedal back up with the MC drive pin. There IS an answer here and it's not just pluck -n- chuck. I too have had the brake light comments, arg! The brakes aren't engaging very much but enough so that if I leave it alone I'll start feeling a slight vibration from them dragging slightly and warming up. Pull the pedal back and it quiets right down. What does your booster / MC look like? Modern stuff? Who were the brakes from?

 

[Ron H]

Wow, interesting to hear you've had related troubles. My next step is this evening, when I get home from work and the car is hot and the pedal is down, I'm going to pop off the MC and see if I can push the pedal back up with the MC drive pin. There IS an answer here and it's not just pluck -n- chuck. I too have had the brake light comments, arg! The brakes aren't engaging very much but enough so that if I leave it alone I'll start feeling a slight vibration from them dragging slightly and warming up. Pull the pedal back and it quiets right down. What does your booster / MC look like? Modern stuff? Who were the brakes from?

SSBC kit - GM MC setup. Among the 'questions' is proper pedal ratio. My car was manual brakes so conversion to power. Mopar OEM setups had a bell crank pedal linkage; but the GM setup doesn't call for this. The pedal arm has two holes one for manual and lower one for power; mine is still in the top hole as it aligns well with the booster rod. Among the fix hunt was pondering on this though. If I angle the booster I could connect to the lower hole (with some other chit I'd have to do). GM setups if you recall the booster/mc was angled - a noticeable odd look on the older gm power brake systems. As I understand they did this for two reasons: accomplish power brake pedal ratio and 2nd clearance for BB motors. Manual calls for around a 6 to 1 ratio where power is more 4 to 1. I see kits having angled booster brackets to do this or you can buy them separately. Anyway - as mentioned I need to assure the booster rod travels far enough into the mc, and will take the added move to put in a new booster, one or the other 'should' be a fix. Ahh, no longer have supreme confidence after all this friggin time. If that don't do it will look into angling to mate with the lower pedal hole. If not I'll add a garage door return spring...lol

 

[Nate S]

SSBC kit - GM MC setup. Among the 'questions' is proper pedal ratio. My car was manual brakes so conversion to power. Mopar OEM setups had a bell crank pedal linkage; but the GM setup doesn't call for this. The pedal arm has two holes one for manual and lower one for power; mine is still in the top hole as it aligns well with the booster rod. Among the fix hunt was pondering on this though. If I angle the booster I could connect to the lower hole (with some other chit I'd have to do). GM setups if you recall the booster/mc was angled - a noticeable odd look on the older gm power brake systems. As I understand they did this for two reasons: accomplish power brake pedal ratio and 2nd clearance for BB motors. Manual calls for around a 6 to 1 ratio where power is more 4 to 1. I see kits having angled booster brackets to do this or you can buy them separately. Anyway - as mentioned I need to assure the booster rod travels far enough into the mc, and will take the added move to put in a new booster, one or the other 'should' be a fix. Ahh, no longer have supreme confidence after all this friggin time. If that don't do it will look into angling to mate with the lower pedal hole. If not I'll add a garage door return spring...lol

Sounds like a similar mount to mine. I have the 2:1 toggle on the booster mounting bracket so I hooked the linkage to the lower hole on the pedal arm. The feel is about right, still need to push the pedal relatively hard, pedal comes up to a good height (when cold). I'll report what I find tonight. Kinda thinking a heavier spring inside the MC, not that I really want to re-bleed etc. Yuck.

 

[Ron H]

Sounds like a similar mount to mine. I have the 2:1 toggle on the booster mounting bracket so I hooked the linkage to the lower hole on the pedal arm. The feel is about right, still need to push the pedal relatively hard, pedal comes up to a good height (when cold). I'll report what I find tonight. Kinda thinking a heavier spring inside the MC, not that I really want to re-bleed etc. Yuck.

Thanks - yeah lemme know and I'll do the same. Good luck!

 

[Nate S]

It’s all the booster. MC is fine. Booster is getting sticky when hot. Second shitty one from Leeds. I’ll keep you posted on what they choose to do with this.

 

[Ron H]

It’s all the booster. MC is fine. Booster is getting sticky when hot. Second shitty one from Leeds. I’ll keep you posted on what they choose to do with this.

Wow, not something I've come across; but others having similar hassles have said a new booster did the trick. I ahh...ordered a booster thru Summit...last April! Last week I asked them if the place making them has some demand (like the t-paper glut was) or just ain't making them? They don't know of course, but offered another more pricey one at a discount so ordered that which should arrive in next few days so I'm told..

 

[khryslerkid]

It’s all the booster. MC is fine. Booster is getting sticky when hot. Second shitty one from Leeds. I’ll keep you posted on what they choose to do with this.

Just curious, what kind of vacuum do you have?

 

[Nate S]

Just curious, what kind of vacuum do you have?

Not sure right off hand. Upper teens I’m pretty sure. Figure it’s a good running stock 426 with a roadrunner cam.

When I got home tonight it was good and sticky. Left the pedal in it’s stuck position and removed the MC. MC pushed off the booster as it reset to normal position. Pushrod was projecting from booster. Normally you could take a wood block and push it back in without too much effort. Wouldn’t budge. Sometimes boosters have a valving issue and will reset when you pull the check valve. I did that, pfssst, let the air in. Still wouldn’t budge. Went under the dash and really cranked the pedal up and down. It moved ok after a bit of a workout.

Seems pretty possible that there’s an oring in there with the wrong kind of grease or something.

 

[Ron H]

Just curious, what kind of vacuum do you have?

Your asking Nate S but thought I'd chime in...I get around 15-16" of vac. I installed a vacuum reserve tank that didn't make a diff. Figured, with the minuscule vac that might be needed (17-ish) did the install.

 

[khryslerkid]

Your asking Nate S but thought I'd chime in...I get around 15-16" of vac. I installed a vacuum reserve tank that didn't make a diff. Figured, with the minuscule vac that might be needed (17-ish) did the install.

He's stating it's close to stock so vacuum wouldn't be an issue. It's why I asked.

Seems pretty possible that there’s an oring in there with the wrong kind of grease or something.

Could very well be something out of tolerance.

 

[dadsbee]

My Bee.. I use to have to lift the pedal or my RR shoe would drag. I concluded it to two things... 50 year old return springs too weak to push the the wheel cylinder back and a booster that wasn't returning properly on it's own as it was full of crud.

 

[Nate S]

Gotta say Leed Brakes lived up to it. I contacted them about the sticky pedal and the analysis steps I had taken and they shipped me a new booster immediately.

 

[Ron H]

Gotta say Leed Brakes lived up to it. I contacted them about the sticky pedal and the analysis steps I had taken and they shipped me a new booster immediately.

I'm putting in the new booster I this week...finally. I've posted about the long list of things I had done to hunt down the pedal sink gremlin and shared this with the kit mfg, SSBC. Good luck and hope I'll have some of it too.

 

[RRChris]

I had the same problem with these after market generic boosters. The comments above are correct. It is the heat on the booster that causes the seal on the bakelite piston on the input rod to get tight. This is because they hang off brackets from the firewall and are more exposed to engine bay heat - in particular the back of them.
Changing the booster and master cylinder set-up back to factory solved my problem.
Why does that help? Because the booster is mounted directly to the firewall and the back of it is not exposed to heat from the engine bay. Therefore, the seal and bakelite piston at the back don't get hot and cause the sticking. Also, apparently these aftermarket generic boosters return springs are not as strong.
Since changing back to the booster mounted on the firewall I have had no more pedal return problems.
Also, check for what might contribute to engine bay heat. Retarded timing will give more heat in the engine bay. Extractors??