Hot Rods Locking caliper mystery game

I'm having a problem with my '32 roadster. The drivers side front caliper gets hung up after 30 miles or so of driving around town. I thought it was just a bad caliper so I replaced it only to have it happen again yesterday. If I have the wife apply pressure to the brake pedal while I crack the bleeder it resets itself for another 30 miles or so (I don't know why I use miles as a reference, it's just a series of stop and goes). I'm starting to think it may be a bad front residual check valve but I'm not noticing it on the passengers side (but then again the drivers is the closer caliper to the valve and the mc). The master cylinder is mounted onto the frame so it has front and rear RCV's. Any thoughts??

 

It's the rubber hose to the caliper. It has a flap in it causing it to lock up the caliper. Replace the hose, cure the problem.

 

Deterioration (inside) the brake hose will cause it. Even though it looks good on the outside. Had it happen once.
Yep, what he said! ^^^^^^

 

Ya is sounds like a rubber hose problem. Replace all of them.

 

I thought about the hose (uses stainless braided lines like shown) and I did consider that, I guess that's where I start.
Thanks

 

If hoses are the same age replace both.

 

is there free play at the pedal? The master cylinder piston needs to return fully when you let off the pedal.

 

How's your Brake Pedal return spring?
The Wizzard

 

The stainless braided lines sold for brake usage that I’m familiar with have Teflon liners and not rubber. Top quality -3 (3/16”) brake hoses will be Teflon lined; compare the appearance of a typical rubber line to an AN brake line. The thinner wall thickness of the AN hose liners requires Teflon for the rigidity needed under pressure. They could be rubber but I’d be surprised.

 

Pedal feels good (returns fully, checked on that yesterday)

 

Strong, pops right back

 

I'm sure you have some air gap when the pedal is fully up between push rod and piston.
The Wizzard

 

The pedal returns fully...does it have a little play before it starts moving the piston, when you push the pedal?

 

I bought this car late last year. It was built by East Coast Rod Shop in 2015 and only had 900 miles on the car. Since it was barely driven I was thinking it was just a bad caliper so I changed that out first. Pretty basic brake set up, master cylinder (on the frame), a couple of RCV's (front and rear), couple splitter boxes, frame

I'll have to check later, thanks for the response.

 

2 things tell me to start at the hose, 1-it's only on one side not both. 2- you pop the bleeder and it's good for a few miles, so that tells me something is holding pressure in that caliper only, in 99.9% of those situations it's a hose.

Let us know what you find out.

 

I think Squirrel is on the right track here. If there is insufficient free play in the pedal, that will keep a very slight pressure in the line, that over time will cause heating of and expansion of the fluid, causing the brake to be applied. I've had it happen myself when I adjusted the free play too tight.

 

The most important thing about checking the pedal free play...it don't cost nuthin

 

...and it's a lot easier than anything else.

 

If it's possible, try swapping the front hoses from side to side and see if your problem moves with the hose.

 

^^^^^^^^^^^^^^^^This is your problem^^^^^^^^^^^^^^^^

 

Hose..if it was the return spring, both sides would be affected.

 

If it's been okay to date, and now it's starting to lock up, I would check for sticking caliper, but since you've done that, pretty sure it's the hose. Happened to me twice now-2 different vehicles.

 

Hose

Bones

 

Also check to make sure the hard lines or proportioning valve isn't too close to the exhaust. Had that happen on my '63 pickup; from cold the brakes worked fine but once the engine warmed up the front brakes would lock up. If I "bleed" a little brake fluid out the caliper would release, at least until the next time I pumped the brakes. Moving the proportioning valve solved the problem.

 

Master cylinders meant for drum brakes are supposed to hold some pressure in the brake line. Could be the wrong master cylinder or seals used in rebuilding it?

Sent from my SM-J320FN using Tapatalk

 

Another stab at the one sided problem could be the caliper mounting being not square to the rotor for some reason - bent, failed wheel bearing.

Is the caliper and rotor on the 'good' side cool when the 'bad' side is locking up and presumably hot (or at least hotter)? Infrared thermometer might help here, or a plant water spray. Just trying to eliminate whether the problem might be applicable to both sides but just registering on the bad side first. I wonder if the bleed release performed on the good side would free off the bad side?

Chris

 

You say there are RCV's on the front and back. I think you mean residual check valves. If this is the case there shouldn't be one on disc brakes. The function of a rcv is to keep pressure on the cup lips so they stay in contact with the wheel cylinder bore and prevent leaks. Disc brakes don't have cup seals and don't need rcv's.

 

Make sure you have checked that hard line as well as the hose for kinks. Maybe something got bent on a big bump.

 

Well it's been over a year with this locking caliper post and so far the following has performed. First thing, changed out both front calipers, both front hoses, and replaced front residual valve. I would drive the car and everything was rainbows and unicorns until the pressure would eventually build up again and I would have to pull over, have the ol' lady put pressure on the brake pedal and I'd crack the bleeder. Then it was okay for whatever time. I finally decided to dig into it and fix it once and for all. The MC/booster is on the frame under the car and when I pulled off my MC I noticed it was leaking a little into the power booster and the rear (drum) brakes reservoir was empty. Then I noticed that there was no space between the MC and the booster rod (in fact the rod was pushing the MC in approx .750") which would explain the calipers dragging and building pressure. I bench bled the MC and once it was in, I placed the new MC/booster in the car (I made sure there was 1/6" between them) I pumped the pedal and I immediately found the rear brake leak. Whoever made the rear line (that goes into a junction block) didn't flair the end of the fitting. I replaced the line and now I can't bleed the air out of the pedal. Filling the reservoir cap is a real challenge since there's no access from the top so I'm cutting a hole and making a cover in the floor. Then I'm going to power bleed the system and hope for the best. Everyone please pray, sacrifice a squirrel or squeeze a goats balls (whatever your belief system advises) because I might go off the deep end if this isn't fixed soon.

 

This question was #7. Thought you would have already have checked for it.