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Brakes Locking Up

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H

healeygal

Jedi Warrior
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Now that my engine is running fine, my brakes are giving me a problem. During a ride, the brake pedal is acting like a one-way valve, getting less and less travel, until brakes lock up. Bleeding relieves the pressure.

Did a search of the archives and changed all three brake hoses as recommended in past threads, but still have the same problem. /ubbthreads/images/graemlins/confused.gif

Master cylinder? wheel cylinders?

Sharon
BN1
 
Hi Sharon,
Sounds to me like the MC needs a rebuild, mostly a guess, but the next thing I would look at.
 
Hi Sharon,
The BN1 & BN2 master cylinders have a couple of related problems that can cause lockup as you describe.

When the brake pedal is released, & the master cylinder piston fully retracts, a bleed port in the master cylinder is uncovered to allow fluid from the brakes to flow back into the fluid reservoir. If it doesn't, the brakes will not release.

A common problem is that the adjustment of the MC push rod is too long to allow the piston to fully retract & uncover the bleed port. The linkage is adjustable. Make sure that there is some free play, about 1/8", in the pushrod before it contacts the MC piston.

Failure of the pedal to fully return will cause the same problem. Make sure that the pedal is fully returning. A weak or missing spring can cause this problem. As can anything that prevents complete pedal return.

Less common but it still happens, the piston seal swells enough to keep the bleed port covered even though the piston is fully retracted. Replacing the inner seals will usually cure the problem. Some folks modify the master cylinder piston so that the bleed port is uncovered sooner in the pistons rearward travel.

This is just a design flaw in the BN1, BN2 master cylinders. The bleed port is located just a little too close to the end of the piston's travel.
D
 
Hi Greg and Dave,
Wow, you guys stay up later than I do! Thanks for the quick replies.

Just ordered the rebuild kit from Moss - their phone order desk was open and the kit should be here Tuesday! Can't wait to get the car in good order for this year's driving season.

Thanks again! /ubbthreads/images/graemlins/driving.gif

Sharon
 
Sharon, So. Cal has a driving SEASON? We are in the midst of a "winter" snow storm. Sixteen inches by tomorrow morning. Sometimes I miss the San Rernando Valley.
 
Hi Tahoe,

This year we're actually having a "rainy season" that started late and seems to have ended yesterday, just in time to wash out San Diego Rolling British Car Day! Only a few cars - mostly MG, Lotus, new Minis (and me in my Chevelle /ubbthreads/images/graemlins/blush.gif) showed up, then reluctantly departed when the other 200 cars they were expecting didn't make it.

Sharon

PS I wouldn't spend too much time missing the SFV!
 
Hello Sharon,
We had 80+ cars, and not much rain after the drive started.
Cooler weather helped us all run better ~60 degrees.

Lou
 
Hi Lou,

Glad to hear the event took place. I guess we came across those who stayed behind and didn't want to chance the rain (or showed up a bit late, like we did). The rain was pretty heavy in some areas and totally clear in others on the way down to San Diego.

Sounds like the San Diego group has been going on some pretty nice rides lately. We don't have so many great back roads up this way, and for the ones we do, it takes going thru the LA freeway system to get to them. /ubbthreads/images/graemlins/frown.gif I'll have to get up early (or just stay up a few hours longer) and head down there for one of them some time.

Sharon
 
[ QUOTE ]
Can't wait to get the car in good order for this year's driving season.
Sharon

[/ QUOTE ]

Are you Southies going to Nelson this year?
 
[ QUOTE ]
Are you Southies going to Nelson this year?

[/ QUOTE ]

Hi Tracy,
Hoping to do so. Of course, it all depends on getting everything on this car working correctly all at the same time for a few brief weeks this coming summer. It's been a long time since that's happened! George Keens and his red Hundred won't be going - neither of his sons can take the time off.


Sharon
 
Get a new master cylinder and bleed the system. It should fix you up. I bet Udo and the "Southies" would help you get it all sorted out in exchange for beer and pizza.
 
Hi Sharon,
These master cylinders are very expensive. Rebuild kits are relatively cheap & will do the job.

The particular problem of the brake pressure not relieving can be cured by a minor modification to the plunger pusher. I have a very comprehensive write up by Roger M. That details the whole problem & fix. I can send a copy of it to you if you wish. Just say the word. Is your email still at cs.com?
D
 
Hi Dave,
Just looked up the price of the master cylinder - ouch! Would appreciate that write up - the email's the same!

Sharon
 
Please send a copy of the M/C modification instructions here, too.
See you all at Calif Healey Week next month in Big Bear?
 
[ QUOTE ]
Please send a copy of the M/C modification instructions here, too.
See you all at Calif Healey Week next month in Big Bear?

[/ QUOTE ]

Hi Lou,

Copy has been sent. Will be at Big Bear, brakes willing...

Sharon
 
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