65 Brake Seize - Caliper?

[Earle Downes]

I hadn't driven my 65 in months while doing other restoration. When I finally got it back on the road, my right rear brake seizes after traveling a mile or two, and I mean seizes! I can't overcome it in either 1st or reverse gear.
Finally had to get under it and release pressure through the bleeder screw to get it to turn loose. This has happened twice in succession. I obviously suspect corroded caliper pistons/bores, but haven't gone into them yet. Are there any opinions out there, based on my description?

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,I had the same problem with with the left rear caliper on my 1972 several years ago. The brake caliper will not release unless the fluid pressure is relieved,as by opening the bleeder screw. Mine was so bad that it placed deep grooves in the brake rotor; I assume that in an extreme situation,the bearings could also be affected due to heat being generated. These were freshly resleeved calipers with
new brake pads;the pads were down to the rivits after a fourty five minute drive.The problem: the rubber flex hoses that interface the steel lines deteriorate from the inside out and can act as a one way valve allowing brake fluid to pressurize the caliper but not allow for pressure release,thereby cause the brakes to"lockup" the affected wheel. Hose replacement is needed,but a good system flush is also indicated,possibly to the point where the caliper halves will need to be seperated to remove any foreign materials and corrosion in the lines. Regards,Kieran #11373

[Earle Downes]

Re: 65 Brake Seize - Caliper?

Kieran,
The '65 has no rubber interface hoses in the rear. Mine has steel lines throughout, right up to the caliper.
Good response though, I even went out to look just to be sure.
Thanks, Earle

[Michael W.]

Re: 65 Brake Seize - Caliper?

Keiran is right about the hoses, very common problem. Look further up the trailing arm to where it meets the frame - that's were the rubber hose is.

[John Fowler]

Re: 65 Brake Seize - Caliper?

So what are you saying ... every time the rear wheel goes up or down your steel brake line bends ... somehow I doubt it.

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,Mike is correct; the rubber hose is more forward or towards the front of the car,near the hinge point of the rear trailing arm. It is the rubber section that allows for up and down travel of the rear trailng arm. On the rear portion of the brake line,this rubber hose goes into a steel line that goes into the caliper unlike the front brakes where the rubber section connects directly to the caliper.When you remove the rear rubber line,try blowing air into it;if I am correct,the air flow will be allowed in only one direction (like a one way valve is in the line). Regards, Kieran #11373

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,Just a thought...... The original lines were a black rubber like material with fittings on each end.I have seen aftermarket lines that are reinforced with a metal braid exterior,and could be causing this confusion about steel versus rubber lines. I also have seen these braided type of lines fail internally,causing the problem you describe.Regards,Kieran #11373

[Earle Downes]

Re: 65 Brake Seize - Caliper?

Kieran,
As you suggested, someone HAD replaced the rubber hoses with braided stainless. Most of the line was covered with a plastic-like material, which is what gave it the solid feel. Only the last 1/2 inch on each end was exposed braid. Soooo.... I changed both hoses for the standard rubber ones, with no success.
When I went for a test ride (with my handy 5/16 in my back pocket) the right rear (original problem child) locked up after 2-3 miles. I released the pressure in the right rear, only to find that the left rear was also locked up. Released the pressure in the left, drove 2 miles home, and pulled into the garage with both wheels smoking.
Before I changed the hoses, I disassembled the caliper halves and found nothing suspicious. All four pistons seemed to travel freely, although in their 'extended' position they were pretty wobbly (not completely in their bores I surmise). When I pushed them fully into the bore they seemed to 'seat' within the bore nicely. I drained all of the fluid from the M/C connection out, blew it out with 130 pounds of pressure, gravity fed a cup of denatured alchohol through the lines, blew that out with 130 pounds of pressure and waited and hour before refilling the system with new DOT4, cleaning out the crud in the M/C and refilling, and bleeding twice around. I've got great pedal (apparently too much).
Any other ideas on the seizing problem?
Thanks, Earle

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,So the plot thickens! I am assuming that the replacment hoses were new,as these items can look great on the outside and be collapsed on the inside. Also make sure that the hoses were not twisted during installation. If "cracking" the bleeder screw releases lock-up,there is a line restriction preventing pressure relief.What was the condition of the fluid when the hoses were changed? I have seen a tremendous amount of debris flushed out of systems that were operating well! Unfortunatly,when a problem like this occurs,replacing the offending component results in the need to completely cleanse the entire system. You can also try gravity bleeding the lines to determine if a line has become plugged or collapsed.If the hoses check out OK,I would supect debris plugging the line in the rear brake system.Let me know,Kieran #11373

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,I went back and re-read your post to make sure I didn't miss anything. When you blew out the M/C,did you blow out and flush the entire rear line also? Either both rear hoses are bad or the cleaning procedure you followed moved the blockage to a point common to both rear calipers.The way you described the calipers sounds like all is OK in that department.Hope this helps,Kieran #11373

[Earle Downes]

Re: 65 Brake Seize - Caliper?

Kieran,
I bought the hoses brand new from a local Corvette sales/repair shop in Atlanta. I didn't flush the m/c itself, just from the (detached) m/c to line fitting. I cleaned the system with alchohol from the m/s line fitting to ALL calipers, including the front ones. Then I replaced the fluid with gravity feed until I got fluid drip from all four calipers.

When doing the final bleed, I got a lot of debris from the right rear caliper, but not the left. I bled until I had clear fluid from all calipers. Bleed sequence was right rear, left rear, right front, left front.

The new hoses might have a slight twist, but only enough to seat the six-point nut of the new hose into the mounting bracket where it attaches to the steel line running to the caliper.

I hear what you're saying about moving the point of blockage, but can't imagine why it would have moved 'upstream' from affecting only the right rear to affecting both right and left rear.

Your continued tolerance and assistance it greatly appreciated.

Earle

[Jim T.]

Re: 65 Brake Seize - Caliper?

If I understand all the posts you have cleaned and replaced everything except the internals of the master cylinder.
When you are driving and apply the brakes both rear calipers are affected with applied pressure.
Make a note of the fluid in the master cylinder and go drive the car. When the rear calipers will not release check the fluid in the master cylinder. If the fluid is lower for the rear brakes and you have full pedal this could mean that the master cylinder is not allowing the fluid to release from applied pressure and reenter the master cylinder.
I have had a smoking caliper on the front of my 68, it was in fact just a collapsed hose. At first I thought the car was on fire seeing all the smoke. Being 20 miles for home I just waited until the front wheel cooled off and the pressure released and then drove home using gearing for braking to get home.

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle,I agree with the point that Jim is making. Given your latest post it seems that you are thinking this through in an orderly fashion. I agree that the blockage would not tend to move closer to the master cylinder,given the flushing you described.Any chance that both wheels were binding all along and that cracking the bleeder at the affect wheel took the pressure off of both rear calipers or the possibiltiy that two seperate problems exist simultaeously? There are bleed passages in the M/C which must be open to allow the pressure in the lines escape once the brake pedal is released,as Jim mentioned. The most common cause of this is an incorrectly adjusted rod,but heavy debris in the M/C can also do the same.M/C rebuild kits are reasonable and the process is straight-forward as long as the bore is in good shape.That's where I would check next.Let me know how you make out and what you find.Regards,Kieran #11373

[Earle Downes]

Re: 65 Brake Seize - Caliper?

Kieran/Jim,
The 65 is a single cylinder M/C. Therefore, I presume that if it were a M/C relief problem, I should have the problem with both front and rear. When I came home from my last smokin' trip, I raised the front to ensure that both front wheels spun free, which they did.

Given all the input I've received from you guys, I'm suspecting debris in the system somewhere. The only indication I've got otherwise is a clear flow of fluid from all wheels when I bleed.

I'm ready and willing to go through any detailed, step by step diagnostic procedure that anybody can suggest.

Thanks for stickin' with me guys!

Stumped in Georgia,
Earle

[Kieran A.]

Re: 65 Brake Seize - Caliper?

Earle, Yup,the correct M/C for your year car should be of the single reservoir type and the test you did would eliminate that as the culprit.I still think there is a blockage in the rear section.Maybe some other members would give their input.Keep me posted,Kieran #11373