i had removed the front calipers when i rebuilt my front suspension this month. in the process i cracked the passengers side caliper, requiring me to replace the o-ring. i used a pipe wrench to compress the pistons on both sides.

last week a friend and i bleed the system (all four corners). now the front calipers are not releasing. There is plenty of pressure.

as an experiment, i pulled the pads on the drivers side caliper, and compressed the pistons again. then i reinstalled the pads, pressed the brake pedal, and they locked again.

is there an easy, fast fix to this?



Edited 1 time(s). Last edit at 05/12/2012 11:49AM by DiBiaso.

The question is whether the brakes are releasing all at oncce or over time.

If it is assembled correctly the calipers are just a cylinder full of fluid. press the pedal more fluid goes in release the pedal that extra fluid comes out.

If they do not release on their own and you can release them by using a clamp, lever or whatever then you have one of two problems, the caliper is not releasing and needs rebuilding, or the flex hose is acting as a one way valve and the fluid cannot go back out the hose.

Test:
Press the pedal hard so the brakes clamp down.
go to your caliper and release the bleeder screw.
If the caliper releases right away (squirt of fluid maybe?)
The caliper is OK and the problem is likely the flex hose.

If the caliper does not release the caliper is bad... Did you perhaps get the O ring off center and it is blocking the passage?

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Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.

with the brakes clamped down, i released the bleeder screw. the brakes staid clamped, and the only a drip or two of fluid came out of the screw.

would it be safe to assume the calipers need replacement now?

don't understand what i could have done to ruin them when i took them off. they were removed from the hubs gently, and support under the car on paint cans (no tension on the hoses).

beginning to feel like i am doing more damage to the car than good... kind of discouraged

back off the brake light switch....work now?

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“Better to remain silent and be thought a fool than to speak out and remove all doubt”.
- Abraham Lincoln

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."

how often have we read this symptom with the causation being bad hose?

very, very many times.

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1973 Roadster. A nice 50-footer!
SUs, Datsun 5-speed
MGB Tips and Tricks: www.mgrescue.com

If bad hose, when you open the bleeder the caliper releases.

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Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.

Ad'm, but the smile that will come when the problem is solved is worth all the doubt and anguish............male version of childbirth.

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Chris Howells

1968 MGB Purchased already dis-assembled which is why I'm often ignorant about what some parts are, and even more ignorant of where they go.

This came up on the Midget forum and it was the REAR flex hose of all things... I would never logic that but worth a try, eh?

My opinion
I had the same issue last year.

I had replaced a leaking master. Bleeding was easy. However, the caliper would not release, If I cracked a bleed screw they would release. Not retract.

In this case logic wise it is an issue that plagues both calipers. Thus you have to address issues where the hydraulic system is joined to one. I.E the valve/switch then the line to the master and the master. Your master has two circuits, front and back.

Item one. The brake light switch must not be restricting the pedal.

Item two. The spring must be on the pedal. Grab the pedal and see if it pulls up at all.

One and two ok then it is the switch or the master.

The rear brake has a set of springs that moves the pads away from the shoes. The front does not. Therefore the banging of the pads on the disc is what moves the pistons out. Thus the fronts will always be hotter than the rears. 30-40 degrees. They will not move out much on a stationary car.

It takes more fluid volume to move the front calipers than the drums. The rears start doing something first. If hydraulic fluid cannot get back to the master the brakes in front do not move.

I have not messed with the cars with the switch. As I recall the switch has to be moved out to bleed the front brakes. As I remember they can lock up in a position that causes this issue.

On our ford we fixed recently you had to alternate bleeding in a special way to reset the switch. Otherwise one circuit was a mess. Some kind of a safety issue. I use a power bleeder and for some reason it resets the switch. (on our ford and Chevrolet).

When you mess with an old car other stuff expires sometimes.

The tool to compress the pistons is a C clamp, not a pipe wrench. The piston is a delicate/machined item and a pipe wrench is a crude tool. A screwdriver is another not so good tool for this.

When changing pads I use two carpenter shims or a piece of hardwood to push the pistons out.

I am dyslexic and writing is a chore.

Call me for any questions. (937)885-3090 This is not hard. You got the hard part done already. I think it could be a bleeding issue. Look up the switch thing. Bleeding only take s few minutes. A dinner out will get my wife to help me bleed the car. She bought me a Motive power bleeder.

I cannot imagine two calipers failing in the same way at one time. Illogical. They do this but, not two at a time. You did not change brake fluids recently?

Last year I chased my tail for a week. I had a defective new master, Who would have thought it.

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L.W.(Larry)Baygents
63B
77 Spit

you write much better than most people who are not dyslexic.

After 62 years of practice I am getting better.

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L.W.(Larry)Baygents
63B
77 Spit

In the B the caliper pistons move on both sides of the caliper so it actually DOES squeeze the rotor. On most cars the disc brake caliper has a piston on one side and the caliper slides on a pin pressing tone pad against the rotor and a stationary outer pad.
For this reason a C-clamp is inadequate, compressing one piston only actuates the other rather than returning fluid to the reservoir.

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Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.

Interesting. I've been struggling with the same issue in my 77B. Just today replaced the LH caliper as I assumed that the piston must have been sticking causing this condition where the pads stay pressured to the rotors. The PO had replaced the RH caliper because the rh brake was locking up on the road upon start-up.

Now I have three new rubber hoses, 2 replaced (rebuilt from O'Reilly's) calipers and, oh yes, the PO also put in a rebuilt MC recently.

As apparantly is Adam, I am also stumped and trying to come up with the solution to this mystery. Again, brakes bled fine but when I apply foot pressure, the pads don't retract and the front wheels, expecially the left, won't turn, unless I pry the pads apart. And the brake switch is pulled back sufficiently. I think I sort of "hi-jacked" Adam's thread, so apologies up front!!

Best,

Dan

How are you progressing with this, Adam?

Dan

Just had the same problem ,cracked the brake lines back to the new master cylinder to see if they would release and they did. So I Removed the brake light switch and solved the problem.. Guess it was restricting the cylinder from retracting fully as Lloyd has suggested (thanks for the lead). I remember having trouble with the brake light operating properly back when I was putting the beast back together again. Now have to figure out whether to replace the switch or back it off a bit from the master cover and hopefully still works.