'67 Camaro front 4 piston calipers locking up... - Team Camaro Tech
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post #1 of 12 (permalink) Old May 21st, 17, 06:45 PM Thread Starter
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'67 Camaro front 4 piston calipers locking up...

The front calipers are locking up/sticking on my '67 to the point when the front of the car is jacked up, you can barely spin the wheels.

Some background:
I am finishing up a restoration on the car, so everything is new. My car is all stock, a '67 convertible, with Power front disc brakes, rear drums. A new master cylinder, proportioning valve, new stainless sleeved 4 piston front calipers, new repro 2 piece rotors and all new stainless brake lines.

When I took it for it's first test drive (about 10 miles), I came back and the front brakes were smoking. I thought maybe since all the parts are new, it might go away, but it hasn't. Yesterday I took it down the road, same thing, smelling brake pads, so I jack it up and I could barely spin the front wheels. I left it alone until this morning................
With the front of the car jacked up (car is cold, not driven since the day before), I pump the brake pedal, ...step out, and the front wheels barely spin. Note that this is BOTH sides. I had only removed the wheel from the driver side, however the symptoms are noticed on both wheels.

Here's what I've done so far:

* First check was the rod from the power booster. I do have the 4" rod, and the master that is recessed about 1 5/8". I went as far as unbolting the master from the booster, where the booster was simply being held up by the brake lines, ...no difference. (for the record, the clevis pin on my pedal is in the lower hole, and I have the brake light switch way back to eliminate that)
* I checked the booster itself, using a screwdriver to push the plunger in the back, and it moves freely, and seats back on the c-clip just fine.
* Since I have an extra set of calipers, (even though the issue is on both sides) I figured, might as well try. I swapped out the driver side caliper, ...no change.

I had the new caliper bolted up, the pads do 'float', but once I pump the brake pedal, go to check, ...the darn wheels barely spin. If I crack the lines open at the output of the junction block, I get a bit of fluid seapage, but if I then pull the pads out, they do loosen up. Put everything back together, pump the brakes, check (it's locked up again), ...then I crack the line at the (front) output of the master, it barely seaps, ...but again if I pry the pads away from the rotor, some fluid comes out, and they loosen up a bit. My current guess is the proportioning valve, but I'm really wondering.

Hopefully someone has experienced something similar, but moreso has some insight...

Thanks,

Kevin


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post #2 of 12 (permalink) Old May 21st, 17, 10:28 PM
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Re: '67 Camaro front 4 piston calipers locking up...

When you stated that you "unbolted the master from the booster, where the booster was simply being held up by the brake lines"... Did you mean to say where the "master" was simply being held up by the brake lines (since the booster is bolted to the firewall)?
Anyway, It looks like already checked to confirm the rod from your brake pedal... and from your booster to your master was not causing this issue.

I've only had experience with one side of a front brake caliper locking up. Turned out to be a clogged rubber brake line at the caliper.

A couple of other things to check.
After you pump the brakes, how are the rear wheels... do they turn freely if the rear is lifted and your trans is in neutral?
If so, you might be able to try this (but I am only guessing as I have not done this myself).
If I remember correctly, one brake line that's connected to the master goes to your front brakes, and the other line goes to your rear brakes (after first going thru proportion valve).
If possible, try switching the position of the brake lines that go into the master (move front line to the back port and back line to the front port). Bleed brakes.

Now pump the brake pedal again. Are the rear wheels locked up, or do they still turn freely. If they are locked up, my guess is you have a bad master cylinder.

If both front brake calipers are still locked up (and the rear wheels still turn freely), there is something that is blocking the release of break fluid pressure between your proportioning valve and master. It could be a bad or clogged proportioning valve (as you mentioned)... or there could be a kink/blockage somewhere in the brake line that runs from the master to the proportioning valve. Check the brake lines to confirm there are no sharp bends or crimps.

Hope this helps.
Mike
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post #3 of 12 (permalink) Old May 22nd, 17, 06:34 AM Thread Starter
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Re: '67 Camaro front 4 piston calipers locking up...

Mike,
Thanks for your reply. You're correct, I meant to say "...the master was held up by the brake lines" (not booster).


I haven't done anything with the rears yet.

As for kinks in the lines, ...none. The line from the master to the proportioning valve is only about 6" long anyway. For the record, I had also blown air through the lines before installing them.
Even though they are new, I may also pick up another set of flex lines. I doubt it is them (since it would mean both are bad), but I'm at that point I need to eliminate things.

What I plan on doing next is to build a 'jumper' brake line to bypass the proportioning valve.
If that doesn't change anything, then I will probably swap out the master cylinder.

Thanks,

Kevin


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post #4 of 12 (permalink) Old May 22nd, 17, 07:09 AM Thread Starter
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Re: '67 Camaro front 4 piston calipers locking up...

To add, I was thinking maybe the repro rotors where thicker than the originals. I measured the new and old. New=1.008", ...Old=1.007".

Also, the caliper pistons move freely, don't stick at all, but I do have a CALIPER question here..

I know the pistons on the 4-piston calipers have springs behind them, but when you push the pistons back in (to the caliper body), while brake lines are connected, do the pistons normally stay back? (My experience with typical calipers is that they do stay back.)
The reason I ask (and this may simply be a symptom of the problem I'm experiencing) is that unless I crack a brake line open I almost can not get them to stay back. Normally when you compress pistons into a caliper, it simply pushes the brake fluid back through the lines to the master. I suspect that if there is something preventing the fluid from getting back (ie. the issue I'm having) then the pistons will not stay back.


Thanks,

Kevin


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post #5 of 12 (permalink) Old May 22nd, 17, 07:55 AM
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Re: '67 Camaro front 4 piston calipers locking up...

I'm wondering if you have a problem with the metering valve or distribution block, or the master itself. If you crack the line where it connects at the master, do the brakes release? That would possibly isolate it to originating at the master cylinder. I would try that before I went to the trouble of replacing flex lines.

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post #6 of 12 (permalink) Old May 22nd, 17, 08:51 AM
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Re: '67 Camaro front 4 piston calipers locking up...

Are you sure it is a disc master cylinder? Don't some drum master cylinders have a residual pressure valve?
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post #7 of 12 (permalink) Old May 22nd, 17, 09:54 AM Thread Starter
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Re: '67 Camaro front 4 piston calipers locking up...

Quote:
Originally Posted by cam67 View Post
Are you sure it is a disc master cylinder? Don't some drum master cylinders have a residual pressure valve?
I purchased it as a disc master, and believe it is, but at this point I'm clueless...



A couple pics during restoration...




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post #8 of 12 (permalink) Old May 22nd, 17, 10:24 AM
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Re: '67 Camaro front 4 piston calipers locking up...

Definitely does not look to be a drum/drum master, so that should rule out the residual valve. I would systematically crack the lines starting at the master cylinder, too see if it relieves the pressure and releases the brakes. Somewhere along the line something is not allowing fluid to flow back to the MC, or the MC itself is defective, or maybe has some crud clogging an orifice inside of it.

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post #9 of 12 (permalink) Old May 23rd, 17, 12:21 AM
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Re: '67 Camaro front 4 piston calipers locking up...

press the brake pedal, release, then open the bleeder on the master cyl, see if that works as well as opening the bleeder on the caliper. I imagine it won't work as well and if so, it points towards the master cyl being faulty. The piston needs to travel rearward enough to uncover vent ports to the reservoir. With fluid out, you may be able to see the piston seal position but the hole is pretty small...

A proper disc master cyl from the factory had a stop bolt screwed into the bottom of the MC. It stopped the front piston assy from traveling too far rearward. I don't know if these reproduction MC's have those. I can't see one in your photos. If they don't use the stop bolt, then they are depending on the return springs inside the MC to push the pistons to the correct position. That may not work as well as a stop bolt version & prevent venting of front MC bore fluid on pedal release.

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post #10 of 12 (permalink) Old May 23rd, 17, 10:34 AM Thread Starter
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Re: '67 Camaro front 4 piston calipers locking up...

Thanks for the replies.
I won't be able to get back to work on the car until the weekend, but will post my findings. I have ordered a new MC and prop valve, which I'd have to guess it's one of those two. Based on your comments Dave (and your site Brakes is a huge help, Thank You) I am starting to wonder about the master.
One of the things I had done was crack the MC front bleeder when the (front) wheels would not spin, and I got little to no fluid coming out. I did get some when I cracked the line just below it, but it had (has) my thinking.

Anyway, I'll post over the weekend (hopefully that I got my brakes working )

Thanks,

Kevin


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post #11 of 12 (permalink) Old May 29th, 17, 09:11 AM Thread Starter
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Re: '67 Camaro front 4 piston calipers locking up...

Still having the issue of the front brakes not releasing...

I first swapped out the Master, ...then swapped out the Metering valve, little to no change from either. Front pads still not releasing after pumping brakes. I did bench bleed the MC, installed it and pumped brakes. With front of car jacked up, I checked and wheels barely spin. Note, I did not do a full bleed, but pumped brakes with line at distribution block cracked to push through some fluid.
Then tried the metering valve. I swapped in the new one (did similar bleed at junction block), pump brakes, ......wheels barely spin.
- I then cracked the line at the front of the junction block, get a good flow fluid, pressure does release some and wheels start to loosen up (still seem a bit tight though).
- Tighten lines, repump brakes, then loosen fitting at the front INPUT to the junction block, same result, good fluid flow (see pic below).
- Tighten lines, repump brakes, then loosen fitting at front OUTput of MC, fluid only drips (not nearly as freely as observed at Junction block)

What now?
- I am about to make a 'jumper' line to bypass the metering block and run line direct to junction block from MC.
- Is a 'full bleed' necessary? In the end of course, but I am assuming air in the system is not a contribuiting factor to non release of front brakes.

Even though I checked the Booster to Master rod length, etc. I am having a hard time not thinking (as I've read in a number of threads) that the MC piston isn't getting full return to uncover replenishment port, hence not venting built up pressure in the lines.
Previously, I unbolted the MC from the booster. I am assuming pressure in the lines would have released IF the rod length was the issue...?
Moreso, with the MC unbolted, am I correct to assume my issue is not the Booster to MC rod, nor anything to do with the pedal? (I just want to rule this area out, ... if I can).

Thanks,

Kevin
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post #12 of 12 (permalink) Old May 29th, 17, 01:28 PM
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Re: '67 Camaro front 4 piston calipers locking up...

I had the same problem with my install. I ended up removing the round metering valve and disassembled it. Everything looked fine. Reassembled and reinstalled. Bled the brakes the old fashioned two person method and the brakes have worked perfectly since. Don't know why, but I'm guessing something in that metering valve wasn't moving like it was supposed until I disassembled it.

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