'67 brake problem

[William F.]

My pedal was going all the way to floor with "brake " light on dash going on. Master cylinder was full.Mechanic bled brakes, said had air and fluid was dirty but saw no leaks. I THINK? this temorarily made pedal firm or at least firmer but problem has returned. A knowledgeable friend says if bleeding temporarily cured problem, must be a small leak on one of the calipers instead of bypassing master cylinder. How can I tell for sure which is problem? Best way to detect a subtle leaking caliper?
Thanks in advance,
Bill Ford

[Joe L.]

Re: '67 brake problem

My pedal was going all the way to floor with "brake " light on dash going on. Master cylinder was full.Mechanic bled brakes, said had air and fluid was dirty but saw no leaks. I THINK? this temorarily made pedal firm or at least firmer but problem has returned. A knowledgeable friend says if bleeding temporarily cured problem, must be a small leak on one of the calipers instead of bypassing master cylinder. How can I tell for sure which is problem? Best way to detect a subtle leaking caliper?
Thanks in advance,
Bill Ford

Bill------


A caliper leak will not cause a soft or "to the floor" pedal unless the fluid in the system is seriously depleted. You'd know that instantly because there would be no fluid in the master cylinder when you checked it. Otherwise, a leak at a caliper or calipers will cause problems to be sure, but it won't cause the pedal to go to the floor while there's still fluid in the system.

For the condition you describe to occur, there MUST BE air entrapped somewhere in the system. If you have excessive runout on any of your disc brake rotors, that will cause the well-known "air pumping" phenomenon that will cause air to enter the system. This will occur under just the circumstances you describe. The first thing I would do is to check the rotors for excessive total indicated runout.

[John H.]

Re: '67 brake problem

Bill -

How long (time and miles) after the brakes were bled did the problem recur? If you don't see signs of brake fluid on any of the calipers, you probably don't have a leak issue. It takes a LOT of air in the system to let the pedal go to the floor; that's usually a sign that the master cylinder piston seals are gone.

[Donald O.]

Re: '67 brake problem

How old is your MC? It might be time for a rebuild, and hopefully you won't need it sleeved. After its rebuilt, flush out your entire bake system with fresh. If you are going to sick with DOT3, do this once a year.
I have a Motive pressure bleeder to do it and it takes more time to jack the car up and remove the wheels/tires than it does to do the bleeding.

[Nicholas K.]

Re: '67 brake problem

Don't know if this will help but I had the same problem recently. I noted air was being pulled into the braking system at the caliper seals when I used a vacuum brake bleeding kit. There was no loss of fluid. I don't recall when I rebuilt the calipers last, probably 15 years ago. I replaced the master cylinder with no success. I wound up replacing all the wheel calipers and the problem was fixed.

[Paul J.]

Re: '67 brake problem

Most of the time when the pedal goes to the floor, it's the master cylinder (as John said). When the master cylinder inner seals fail they will not hold pressure and fluid slips past them. Sitting still, pump the pedal up and then hold pressure on it. If the seals are bad you can feel the pressure bleed away and the pedal will go toward floor with no additional pressure on the pedal.

Rebuild kits are cheap and you can do it yourself.

Paul

[Gerard F.]

Re: '67 brake problem

Bill,

Had the same problem through the 80's and 90's with my 67 with it's original brake calipers. I would have to pump up the brakes everytime I used the car. Changed the M/C and bleed the brakes a number of times.

The problem would return.

About 10 years ago, I went to new calipers and a M/C in a kit.

No problems since. Still have my originals in a box in the garage.

[Joe L.]

Re: '67 brake problem

Most of the time when the pedal goes to the floor, it's the master cylinder (as John said). When the master cylinder inner seals fail they will not hold pressure and fluid slips past them. Sitting still, pump the pedal up and then hold pressure on it. If the seals are bad you can feel the pressure bleed away and the pedal will go toward floor with no additional pressure on the pedal.

Rebuild kits are cheap and you can do it yourself.

Paul

Paul-------


Yes, but if the master cylinder seals are bad I don't see how he'd be able to get a pedal firm enough to drive for awhile before the problem returned.

[Joe L.]

Re: '67 brake problem

Bill,

Had the same problem through the 80's and 90's with my 67 with it's original brake calipers. I would have to pump up the brakes everytime I used the car. Changed the M/C and bleed the brakes a number of times.

The problem would return.

About 10 years ago, I went to new calipers and a M/C in a kit.

No problems since. Still have my originals in a box in the garage.

Jerry------


Were the calipers that you replaced and now have in the garage ever stainless steel sleeved? Were the calipers you got in the kit stainless steel sleeved rebuilt calipers or were they actually brand new calipers?

[Paul J.]

Re: '67 brake problem

Paul-------


Yes, but if the master cylinder seals are bad I don't see how he'd be able to get a pedal firm enough to drive for awhile before the problem returned.

Joe,

He's faster than the leak. The bad seals are not that bad. By using the pedal quick and hard, and not maintaining pressure for any length of time the seals will hold long enough to function. I've done this many times. That's why I suggested holding firm pressure for a period of time. We should have asked him if the pedal went to the floor quickly or slowly. That would determine the extent of the seal failure. As you pointed out, this is not simply a leak in a caliper. If the pedal goes to the floor this is a problem with the master cylinder.

However, after rereading his original post, I'll bet that this is only part of the problem. He possibly also has a small leak which is probably letting air in and no fluid out.

Paul

[Gerard F.]

Re: '67 brake problem

Jerry------


Were the calipers that you replaced and now have in the garage ever stainless steel sleeved? Were the calipers you got in the kit stainless steel sleeved rebuilt calipers or were they actually brand new calipers?

Joe---

Greetings.

The calipers I took off about 10 years ago, were original to the car and never stainless steel sleeved. What a PITA getting them off with frozen caliper bolts on jacks in my garage. Finally resorted to a propane torch to heat them up, cool them and heat them up again, still had to use a breaker bar.

The new ones I put on were stainless steel sleeved rebuilt ones of similar but slightly later vintage then my 67. I remember we checked the numbers.

Rather than turn in my originals for a core charge which was slightly more than the shipping charge, I opted to keep my originals. Maybe someday they will be back on the car and stainless steel sleeved.

Getting any lobsters lately

[Joe L.]

Re: '67 brake problem

Joe---

Getting any lobsters lately

Jerry------


About a month ago Lucky Stores had cooked Maine lobsters on sale for $9.99 a pound. I bought a bunch of them and feasted. In fact, they have them on sale again now and thanks for reminding me. I need to get over and get some more.

My real "hunger" right now, though, is for New England steamer clams. Next week I'm going to order a bushel of them from my favorite fish market in Massachusetts and have them shipped out here overnight. It'll be expensive but it will be worth it. Absolutely. Positively.

[William F.]

Re: '67 brake problem

People atCorvette SS Brakes said I am probably sucking air into system due to reverse ocillation, probably due to too much lateral runout in one or more rotors. Said to test by pinching off rubber part of each brake hose,starting with any one;if pedal still soft, leave it pinched off; go to next, till you find one where pedal stays firm with line pinched off and that will be the one that's a problem. Do you agree? Then if lateral runout is problem, what's easiest way to correct-try indexing the rotor one stud at a time till runout is accectable?Shims?If indexing doesn't work, can rotors be turned on car if rotors are thick enough?What about just replacing rotor?
Thanks,
Bill

[Joe L.]

Re: '67 brake problem

People atCorvette SS Brakes said I am probably sucking air into system due to reverse ocillation, probably due to too much lateral runout in one or more rotors. Said to test by pinching off rubber part of each brake hose,starting with any one;if pedal still soft, leave it pinched off; go to next, till you find one where pedal stays firm with line pinched off and that will be the one that's a problem. Do you agree? Then if lateral runout is problem, what's easiest way to correct-try indexing the rotor one stud at a time till runout is accectable?Shims?If indexing doesn't work, can rotors be turned on car if rotors are thick enough?What about just replacing rotor?
Thanks,
Bill

Bill------


The situation that they've described is just what I postulated in my first response here. I've never used the procedure they've described to identify the caliper with an air pumping problem (and, thus, likely the rotor that's out of spec TIR-wise). However, it sounds interesting and I think it might work.

I think it might be easier just to check the runout on the calipers as I first mentioned. It might even be that there's a problem in more than one. All you need to do this is a dial indicator and a dial indicator stand. You can purchase these very economically from Harbor Freight and they'll be plenty good enough to do the job.

To correct the problem, re-indexing the rotor to the hub (front) or spindle (rear) might be enough IF the runout is not too bad. Usually, replacing the rotors will not do it because the problem is usually in the hub or rotor.

Have any of the rotors or the rear spindles ever been replaced on this car? One major "clue" is if the rivets retaining the rotor to the hub or spindle have been removed. This is easy to check for with the wheels off. If they are still all riveted together, then I really doubt that rotor runout is going to be a problem and you'll probably have to look elsewhere for the root of your problem..

[William F.]

Re: '67 brake problem

Previous owner replaced both front rotors since he scored originals with improper placement of brake pads. Rear spindles only, not the rear rotors were redone by "place in FL"-name?, apparently separately from rear rotors.How do you set up a dial indicator to be square with rotor so it will give accurate reading of runout? Any and all other suggestions also appreciated regarding SIMPLEST way to correct problem. Do calipers with O ring seals prevent this air sucking even if rotors/hubs are slightly out of specs?
Thanks