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MG MGB Technical - stuck brakes after bleeding

I just replaced my front calipers, pads, disks, and flex lines. got it all together and bleed the brakes with ezibleed. My first time doing any of the above mentioned jobs. I have a nice firm pedal but noticed that after pumping brakes a few times the calipers do not fully release the disks. If I really force it I can move the disks but they are essentially stuck. Did I screw somthing up? My car is an 80 B.

Also, how bad is Castrol LMA for tires, I got a fair amount on one of my rear tires when bleeding, cleaned as much off as I could. Will this ruin my tire?

Thanks,
Brian
Brian

Brian - Before panicing, try driving the car. There are no springs to withdraw the pads from the rotors on the front wheels, instead it is the small amount of runnout of the front rotors that push the pads away from the rotors, thus if the wheels are not turning, the pads will remain pressed against the rotors. The brake fluid should not harm the tires at all. Good luck - Dave
David DuBois

Brian,

The most common reason for brakes binding hard is no free play in the master cylinder pushrod. If there is no free play the system will hold pressure.This should be explained in your Workshop Manual.
Did you do anything to the master cylinder or pushrod?
After pressing the brake pedal with new pads you should be able to freely turn the rotors.
The runout of the rotors, when to specification, does not set the pad clearance.
For example in my mga twin cam Workshop Manual the pad clearance must be 0.008-0.010" and the maximum rotor runout is 0.006".
Clearly rotor runout does not set the clearance. Then what does?
It is a long story, I will email it to you and David.

Mick
M F Anderson

Brian,

A quick test. With the brakes binding, just open and close one bleeder, without pumping the pedal.
Do the brakes release?

Mick
M F Anderson

M F thanks for the article. I'll check the clearance in my workshop manual after work today. I did not intentionally do anything to my Master Cylinder or any other part of the braking system other than the flex hoses, calipers, pads, rotors all of which are new parts. Does the 1980 B have that adjustment (brake light switch ?) just behind the pedal like the 1977 B does? Or is there any adjustment for the caliper?

Thanks....so close to being back on the road.
Brian

I opened the bleeder and nothing came out so I guess that means there is no excess pressure assuming lines and calipers are all clear of any blockage. I think it's just a combination of new rotors and new pads just being a tiny bit too snug. The pads don't seize the rotor but just grip it slightly. With the wheel on I can spin it pretty freely. Just a note, the workshop manual does note that the fluid seal will deflect allowing the pressure piston to move back and thus providing the required clearance for the friction pads.
Brian

Brian,

When you bed your pads in the polished pad surface will have the right clearance, providing the new caliper seal has the correct deformation quality.
New pads have a rough surface and can give the impression of non specification clearance.
Do you have a scanner? That page on how the clearance sets itself is interesting. My MGA Twin Cam workshop manual has it all wrong.

Mick
M F Anderson

I do have a scanner, did you want the page from the workshop manual? I can try to get it to you. You can email me off board.
Brian

As I read thru this thread one thing was not mentioned,the caliper pistons. When replacing the front brake system you push back the piston to account for the new pads. If the pistons were exposed to the elements for a long period they rust. Pushing them back may cause them to stick inside the caliper thus freezing the system.
Kevin

Kevin..note that I installed brand new calipers (which included new pistons of course).
Brian

Brian,
Whoops, I must improve my reading and comprehension skills. Please disregard my .02 on your brake problem.
I am curious on this scanner thing that was talked about. What is it?
Kevin

Mick just wanted me to scan a page from my workshop manual so he could keep it for reference.
Brian

Hi,
I own a 1980 B and thats the nature of the beast take it from me if you can rotate the disk but still appears to be stiff thats normal or at least it is on my car. There are no springs to release the brakes but if you could drive the car and stop it with the parking brake without using the pedal then you would see that the disk are freer. Use the brakes again and it's the same again but in my opinion it's normal

Cec
Cec Fry

This exact thing happened to me a couple of years ago after renewing the seals on the calipers.

Although the brake pedal felt great - it nearly fried my disks and ruined a brand new set of V8 pads.

Working the caliper pistons in & out a few times did the trick for me. My guess is that it probably
help seat the seals properly against the piston outter surface.

1) Install an old set of pads. The more worn (and thinner) - the better.

2) Press on the brake pedal until it feels firm. This will extend the pistons out.

3) Remove the pads and press the pistons back fully into the caliper(s).

4) Repeat steps 1-3 several times.

5) Install new pads and press on the brake pedal until firm.

6) The pistons should retract slightly when you release the brake pedal. Try rotating
the brake disk by hand. It should feel relatively free of friction.

7) Road test.
Daniel Wong

This thread was discussed between 23/03/2003 and 27/03/2003

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