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Brake issues.

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K

Kensai

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Over the last few weeks my brakes have started to lose pressure when I have to apply steady pressure over a prolonged period of time. This happens mostly when I'm sitting at a light and am on an incline, so I have to keep the brakes on over a long period of time. After a few seconds (maybe 10 or so max after I'm stopped and applying continuous pressure) of applying pressure, the brakes start to lose pressure, and I have to pump them to regain pressure. When I'm braking when coming upon a light, or any other time, the pressure is fine. I'm guessing I need a master cylinder rebuild?

The car is a '69 B, factory brakes.
 
Yup. You can try putting a kit in it if the guts of yours are not all scored up. Or just bite the bullet and buy a new one.
A rebuild kit is around 13bucks or a complete new unit is 120. I try a kit first. You don't have much to lose.
 
Gday Kensai, I would suggest you look over your brake system , it my be a wheel cylinder or ? causing your problem. It would p.i.t.a.to do up a master that did not need it. jmho Bob
 
If you can pump up the pressure, you don't have a caliper,wheel cylinder or brake line leaking. (or else it couldn't possible pump up hard) Make sense?? :thumbsup:
 
After taking the master cylinder apart it became quite clear what the problem was. The rubber seal closest to the firewall had a hole worn in the edge that was about the thickness of a dime.

After bleeding the brakes for about an hour I've managed to get some resistance when pumping the pedal, but they will not pump up to have any pressure. I figured my bleeding technique is lacking, and checked the Bentley manual for the official method. Upon doing so I read the following:

Attach the bleeder tube to the bleeder screw of
the near side rear brake and immerse the open end of the tube in a
small quantity of brake fluid contained in a clean glass jar. Slacken
the bleed screw and depress the brake pedal slowly through its whole
stroke and allow it to return without assistance. Repeat this pumping
action with a slight pause before each depression of the pedal. When
fluid entering the jar is completely free of air bubbles hold the
pedal tightly against floorboard and tighten the bleeder screw.

Is the bleeder tube a special tool, or just a rubber tube that fits over the end of the bleeder screw? I've never used this method before.
 
Just a tube, available at the hardware in a clear plastic stuff. Get some of several of the smaller sizes to have available. each size aslo fits into the next size so you can go from one to another easly.
 
Thanks! I already have a clear medical grade tube that I keep in my toolbox for other various uses that may arise. I'll have to give this method a shot tomorrow.
 
You gotta love that convoluted method of bleeding brakes from the haynes manuals.

Get yourself a hot woman to pump the brakes and top off the reservoir. ALWAYS start at the farthest wheel cylinder or caliper. She pumps 7 or 8 times and HOLDS pedal to the floor. You crack the right rear bleeder screw just enough to let air and fluid escape. Try to be quick and have it closed before she bottoms out. Repeat! It might take 4 or 5 attempts untill you get a steady stream of just fluid. Then move to the rear left, then front right and last front left. Working your way to the closest caliper or wheel cylinder to the brake master cylinder. You don't need a glass jar, plastic hose or beer bong to bleed brakes. Just patience. Hot chick optional, ugly grease buddy will work too.

When I bleed the rear calipers on my jag, My wife plays the part of opening the bleeder screw. My hands are too big to fit up into the rear suspension. However you do it, don't let the brake pedal come back up until that bleeder screw is closed. Pumping is done with the screw closed and only open the screws with pedal pressure applied.

You can always buy one of these nightmares, mityvac I had one. It worked ok I guess, I garaged sale mine. Brake fluid washes off the driveway with a hose and you wouldn't dare recycle it back into your brake system anyhow!
 
Eezi-Bleed works much better than a vacuum IMO.

Jag rears? Ya don't access 'em from inside the back "seat" thru th' access "ports"? That's always been my solution.

...but then my elbows and wrists are conditioned to work on Lotus cars, too. Jag access seems cavernous by comparison. :shocked:
 
I've gotten the brakes back up to normal, but now I have to get the clutch bled. After about 10 minutes of getting a sputtering stream of fluid from the bleeder, I noticed that the connection between the hard line and the master banjo connection was letting in air. Upon inspection the fitting on the line is fouled and the line needs to be replaced. Now to wait until the new line gets here...
 
Mity vac's are great tools for other things than just bleeding systems. You are fortunate that you don't own a 123/124 series Benz. The vacuum door locks almost necessitate a mityvac(or some such) to trace down a leak.

vacuum diaphragms, vacuum source. I find the mity vac an invaluable tool. Plus it is a great tool for bleeding clutches. As I reverse bleed them. Solo, use the outlet port on the mityvac, hook to the slave cylinder, fill the reservoir of the mityvac with fluid, with a dry master cylinder, pump the fluid through the system into the master. clean, efficient, effective..
 
I've used Mity Vacs for years, very handy tool. Originally bought it to do diagnostic work when EGR valves first appeared.

Colin
 
Got the clutch back up this evening, but now, the brakes don't work.>_<

They have some pressure but are not firm, and do not pump up to regular firmness. They do pump up a little, but then slowly go to the floor when pressure is applied. Is this due to air in the lines? Or something else? (there are no leaks at the wheel cylinders, or anywhere else I can find)
 
If there are no leaks from the system and pedal still falls, quickly or slowly, with any pressure, the thing is by-passing internally. If you put a kit in it the parts are bad or you didn't do it right. If you used a new assembly it is bad and needs to be exchanged.

When putting either a new or rebuild cylinder into service always take it easy on the pumping. To over do it early on is to invite scuffing of the rubbers and early failure.

"Pumping" should be done gently and without haste. Rapid pumping aerates the fluid and you will never get all of the air out until you let everything sit over night and start again.

Never stroke the pedal all the way to the floor. To do so invites damage to the cylinder innards.

Bleeding is done of course starting with the right rear, left rear, right front and finally the left front.

Also, full stroking may cause the system splitting shuttle valve to be forced off center. If that happens the electrical trip must be removed to allow the shuttle to be moved back to center.

IMHO use LMA for normal road use and leave the silicon synthetic stuff to the racers.

Jack
 
That sounds like an internal leak in the Master Cylinder. Happened to me. The only cure is a correct rebuild of the master cylinder or replacement with a known good one.

Colin
 
I finally got a chance to look at the BC with Bclif last week. Turned out I had all three of the cups backwards because i thought they pushed this way > when they push like this <. Dumb mistake but an easy fix and I'll never make the same mistake again.
 
The great thing about this forum is that you can learn from other people's mistakes too. Wish it had been around for the last 25 years.
Bruce
 
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