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MG MGA - air or self adjustment (brakes)?

Hi again,

I was 95% sure I would need new pistons for my calipers since the ones I had were rusted on the ends, but to my surprise I cleaned them off and installed them with new seals and they seem to be working now...

But here's the weird bit; when I step on the brakes once, the brakes engage but not all the way before the pedal hits the floor. If I step on them again right away, they engage much better and I only have to push the pedal 2/3 of the way for the brakes to engage all the way and they work great. Sometimes it does this the first time, but usually I have to hit the brakes twice really fast for them to work to their full potential.

I just put in new seals yesterday. Is this just the brakes adjusting themselves, or do I have air in the lines? My master cylinder is completely full, and I bleed the brakes for a long time with Eezibleed and found no air.

Any ideas?

Thanks,

Darian
Darian Henderson

Sounds almost as if the rear brakes are not adjuusted properly or else you still have air in the lines. Either one is enough reason to require more fluid than one stroke of the MC can deliver.
David "I vote for air" Lieb
David Lieb

I neglected to ask what kind of fluid you are using. Silicone is notorious for holding air bubbles in suspension and taking time to work them out.
David Lieb

Hi David,

I'm using DOT 4. Is it possible that I need to wait a few days and try to bleed them again? Like I said, I ran a lot of brake fluid through the brakes and didn't see any air.

Thanks,

Darian
Darian Henderson

Try pushing the fluid through harder. You may get more air out.

Steve "I vote for air also" Simmons
Steve Simmons

After a rebuild, it can be difficult to get the air out of the far side of the calipers.
David Lieb

Also try pulling on the parking brake and then check pedal pressure, If it better than before you will have to re=adjust the rear brake shoes.
Sandy
Sandy Sanders

A system that I use which often helps to locate a problem is as follows.
Get three clamps and clamp the three flexible brake hoses (2 front and 1 rear).
Press the brake pedal. Excessive pedal movement is a master cylinder problem, air in the fluid, or fluid cannot pass from the reservoir to the cylinder, or poor MC component assembly, or incorrect pushrod adjustment.
If there is only a little pedal movement remove one clamp at a time and test again.
If the problem is the front it is air in the fluid or the retractor pin is not operating correctly (I believe the only place for these pins is the trash can).
If the rear, it is air or badly adjusted drum brakes.

Silicone fluid can take days for the tiny air bubbles to amalgamate into larger bubbles to be removed. Don't just let the car stand, keep operating the brakes for several days.

Mick
Mick Anderson

I was having a similar problem when I rebuilt my drum brakes. I bleed and bleed and bleed, but could not get the brakes to firm up. Like you I could pump them up so I assumed that I had air in the lines.

This time it was the DCO (dumb current owner). I had failed to tighten the brake shoes up to the drums with the adjuster nut before bleeding the system.

Obvoulsy the situation is much different for your disc brakes. Pumping the brake pedal should set the pistons and brake pads in relation to the brake disc. But it would not hurt to go back over the rebuild process to be sure you didn't miss anything.

Check the adjusters on the rear drums. They may be so worn that they are not holding an adjustment. If the parking brake is not holding, the rear drums are likely out of adjustment. Make sure that the MC fluid level does not fall below half full during the bleeding process. As others have mentioned, adjust and bleed the back drums first.

John
jjb Backman

A quick check to see if it is rear brake adjustment Set the parking brake to "just before" engagement. This acts the same as the adjusters. If your problem goes away, then you know that you need to adjust the rear brakes. If not, then the problem is not there. Spend your time elswhere.

Chuck
C Schaefer

Darian, did this problem crop up after changing the seals, or have you had this problem for awhile? And having to pump the pedal twice, is this sitting in the garage, or has the car been driven for this to happen? If its in the garage then i go with the magority and think it might still be air, but if it is after a run in the car, check you disks for run out, you could be getting the pads kicked back in farther than they should be. First push on the pedal moves them out, second push and they do what they are supposed to do..............
Mitch Smith

Thanks everyone,

This problem came up after I replaced the seals. I've tried doing it with the emergency brake on and it does the same thing - two pumps to get them to work. I'm convinced that there is air in my calipers, but I've bled and bled and still can't get the air out.

On the other hand I've noticed that the pistons don't retract all the way back after I've pumped the brakes a few times, so I think I'm going to order new pistons to match my new seals. Next time should I add fluid to the calipers before I install them? Has anyone had better luck with a vacuum bleeder than a pressure bleeder? I've been using Eezibleed.
Darian Henderson

Darian,

What do you mean "the pistons don't retract all the way back"?
They should only come back a few thou, almost touching the rotors.
Also, any lack of retraction would make the pedal travel less.

Mick
Mick Anderson

Darian

The pistons in the callipers will only retract far enough to relieve pressure on the pads - that is normal. If the wheel turns then all is well.

Your symptoms are of air in the system. Did you notice that there are TWO bleed nipples each side on the front?

I have mailed you too, would like to borrow something!

Dominic
dominic clancy

Well, John, don't feel so bad. I am now a DCO as well. I had the calipers with the bleed nipples pointed down. Since air is lighter than brake fluid, the calipers weren't bleeding. Pretty obvious now, but hey, I think I know everything I need to now about the front brakes since I had to do it all the hard way.

It's always satisfying when you solve a problem, even if you feel a little silly afterwards...

Thanks everyone for your help.

Darian
Darian Henderson

Hey Darian,

Maybe we should start a new thread just for DCO's (just kidding). It is a great relief to have figured out the problem only to realize another awaits around the bend. I have little doubt that I will be in the DCO circle of winners more than once.

Now if we could just do something about getting past a pretty ugly winter here in the Puget Sound area....

John
jjb Backman

This thread was discussed between 04/02/2008 and 07/02/2008

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