Brake pedal occasionally sticking and needs to be pulled back up with my foot

[Kaeru]

Hi everyone, 

 

I restored my 510 about a year ago and everything is wonderful, except the brake pedal will occasionally get stuck down and I need to pull it up with my foot to get the brakes to release. When I restored the car, everything got replaced, including the master cylinder, wheel cylinders, brake lines, etc. The front brakes are early Porsche 911 calipers (Design Products kit) and rears are drums with 240z aluminum drums. 

 

It gets stuck about once or twice on any particular outing. I've gotten pretty quick at pulling it back up with my foot, but it's definitely concerning since it has happened on spirited canyon drives with other cars following closely. I assume the rears are sticking based on how the car slows down when the pedal is stuck, but I haven't actually been able to get it to stick while in the garage where I can get it up in the air. 

 

I've confirmed that the spring on the brake pedal is in place, everything is tight, and that the brake pedal isn't binding. I've confirmed that the brake shoes are orientated correctly, and that all the clips and springs are in place. I confirmed that the brake shoes move freely, nothing is binding and the backing plate is lubed in all the correct spots, etc etc etc. 

 

Unless anyone has any new things to check, I'm thinking I'm just going to start replacing hydraulics (brake master and then the wheel cylinders) and hope for the best. 

 

I'd greatly appreciate any advice, thanks very much!

Robert

[datzenmike]

You have about 2mm or 1/16" of brake pedal play??? just push on it with your thumb, it should move that much before there is firm resistance. A small amount of 'wiggle'.

 

Only way to really trouble shoot this, is to do while the pedal is stuck. That seems unlikely. Sounds like the master.

[Kaeru]

Thanks for the quick reply! Yep, there's 1/16" of play in the pedal. 

 

Looks like I'm going to start my hydraulics replacement process with the master. Thanks for confirming! 

[datzenmike]

I should imagine the piston inside is jamming in the bore. Replacement parts are not the quality they used to be.

[banzai510(hainz)]

If there is a spring on the brake pedal isnt that the same as putting your foot under and lifting it? So its stuck enought to not even spring tension to pull it back?

[Kaeru]

2 hours ago, banzai510(hainz) said:

If there is a spring on the brake pedal isnt that the same as putting your foot under and lifting it? So its stuck enought to not even spring tension to pull it back?

That's correct. The spring will retract the pedal 99.99% of the time. On the .01% where it gets stuck down, I need to lift it with my foot. It doesn't take a tremendous amount of force to lift the pedal, but apparently more than the spring can accommodate. As @datzenmike suggested, I'm guessing the piston gets cocked in the bore occasionally. I've ordered a new master, and I'll get it installed in a couple weeks and report back. 

 

Thanks again for all the help!

Robert

[Stoffregen Motorsports]

If you have to pull the pedal up, it's obviously in the pedal or master. Pretty common for a master to be sticky, but how about the pedal? Does the pedal move freely?

 

[Kaeru]

1 minute ago, Stoffregen Motorsports said:

If you have to pull the pedal up, it's obviously in the pedal or master. Pretty common for a master to be sticky, but how about the pedal? Does the pedal move freely?

 

Great question - with the clevis disconnected, the pedal moves freely - no binding, etc. I hadn't experienced this before, so I wasn't aware it was common. If that's the case, then I'm even more confident that replacing the master *should* fix it. 

 

Thanks again!

Robert

[banzai510(hainz)]

Most aftermarket Masters one has to cut them  shorter,Cause the threaded rod hit the back of the pedal if too long which can preload the master as it mounts to firewall as it pushes the master rod in when clevis is hooked up, Must be adjusted

Edited April 16 by banzai510(hainz)

[Kaeru]

3 minutes ago, banzai510(hainz) said:

Most aftermarket Masters one has to cut them  shorter,Cause the threaded rod hit the back of the pedal if too long which can preload the master as it mounts to firewall as it pushes the master rod in when clevis is hooked up, Must be adjusted

Thanks for that! I'm moderately confident the threads aren't fouling on the pedal, but I'll confirm when I pull everything apart. 

[Stoffregen Motorsports]

Out of curiosity, which master are you using? Does it have any casting marks? Like Nabco or Tokico?

[Kaeru]

39 minutes ago, Stoffregen Motorsports said:

Out of curiosity, which master are you using? Does it have any casting marks? Like Nabco or Tokico?

I just took a quick look and didn't see any markings. I purchased it a couple years ago, but I forget from where. I believe it's just one of the modern cheap generic ones. I plan to tear it down after I remove it - just out of curiosity. I'll give it a closer look then and see if I has any markings. I'll also let the group know if I can see any clear reason why it's sticking. For anyone's sense of morbid curiosity! 😀

 

Thanks again for all the help!

Robert

[banzai510(hainz)]

Its rare to even find a Tokico or Nabco Master anymore.Maybe in Austraila.

 

[Stoffregen Motorsports]

If you can find an original master, I'd rebuild that one, for sake of originality. I mean, you do have some pretty cool parts on that car. Why settle for a Chinese master?

[banzai510(hainz)]

just be careful if one takes the rod out off the master.

Frank and his sons SSS sedan they swapped the rod out and one day driving the clip that held the rod inside broke off or fell off cause it wasnt done right . Well going to stop light the rod delinked itself to the back inside the master and well the SSS grilee hodd ect all got smashed!!!!!!!!!! made in Japan of not make sure tHIS DONT HAPPEN

[Stoffregen Motorsports]

And not all pushrods are interchangeable with all masters. Some are too thick at the ball end and will make the brakes pack up because the piston never releases all the way.

[Kaeru]

Good point on the original master. I think I have a Nabco one in my pile of old stuff. I may (very carefully, diligently, and safely) rebuild one and then swap it in once I've confirmed the Chinese one solves the original issue. 

 

Thanks again for all the help!

Robert

[Stoffregen Motorsports]

Rebuilding a master cylinder is pretty straightforward. As long as the bore is smooth and clean, assembly is a snap.

 

If you can't find rebuild parts for the original master, you might be able to use parts out of the replacement master. Or you could source them from one of the rebuilders. Apple Hydraulics and White Post Restorations, both in the New England area. If the OG master is not in great shape, they can sleeve it and rebuild it for you.

 

 

[Kaeru]

I haven't had a chance to dig for the Nabco master, but the new Chinese master arrived yesterday.

 

Quick question on the pushrood. What I had done on the old master was install the 510 pushrod under the snap ring so it was held captive to the master. However, it just occurred to me that the 7/8 master would have been mated to a brake booster, so the pushrod wouldn't have been captive. What is the "correct" way to do it? Should I remove the snap ring and install the pushrod under it, or fabricate a new non-captive pushrod? 

 

I found a couple discussions, but I'm not sure the results were conclusive... 

 

 

 

Thanks again for all the help on this!

Robert 

[Stoffregen Motorsports]

The pushrod needs to be captive, or it will fall out. Just make sure that however you install the pushrod, there is freeplay between it and the piston. If there is not freeplay, you can adjust it by changing the thickness of the washer that holds it. Some washers had a bulge in them for this purpose.

[Kaeru]

2 hours ago, Stoffregen Motorsports said:

The pushrod needs to be captive, or it will fall out. Just make sure that however you install the pushrod, there is freeplay between it and the piston. If there is not freeplay, you can adjust it by changing the thickness of the washer that holds it. Some washers had a bulge in them for this purpose.

Thanks very much! I’m out n about today, but I have the conical  washer, so I should be able to get it installed this evening. Thanks again!

[Kaeru]

I just returned from the post-replacement test drive. Aside from the fact that the pedal is a bit soft, everything went great. I'll bleed the system again, and then it's just a matter of waiting to ensure the new master solved the pedal sticking issue.

 

Thanks again for all the help!

Robert