Mystery of the re-occuring soft brake pedal

[wlivesey]

OK so I thought bleeding the brakes would be easy. During the fall it seemed the brake pedal would get soft and I had to pump up the pedal. No big deal. Now, since it was winter I had time to inspect the brakes and replace what looked suspicious. Sounds easy right! Never, with this car! I will spare rhe details but I went from rear wheel cylinder kits ($) to new rear wheel cylinders ($$$), rear axle seals, one brake line since the connection was completely mangled after I ended up going to vice grips.
Now after multiple bleeds (3 or 4), I still have a pedal that needs to be pumped up. By the way, every time I have re-bled the lines I get most of the air bubbles from the 2 rear wheels. The clutch cylinder has produced a fair amount of air also.
The new rear cylinders are dry. I don't see any dampness at the front calipers. All the line connections look dry - old but dry. I even pulled off the brake and clutch dust covers at the pedals; they look dry from that side.
I also bled the clutch cylinder. The one place I found dampness was along the brake line that goes from the front to the back of the car. Of course, there is a lot of oily crud under the car anyway. I didn't think a brake line would likely spring a leak along a straight portion of the line. What have I missed?? Any advise would be appreciated. I like working on this car but this is getting ridiculous. It's time to move on to some other problem.
Thanks,
Bill L
BT7
Cumberland RI

 

[Gary Lloyd]

Believe me!! I know how frustrating it can be!! First of, are you using the right brake fluid?? Secondly I never noticed anything about the master!! Have you checked it out?? I do not own a Healey, but I would guess it would be similar to a 'B. If the Master is shot, it can suck air, thus your problem!! GOOD LUCK!! As far as you clutch, let it be for now, deal with one at a time!

 

[Guest]

If it is anything like a B, you need to check the rubber hoses, they rot from the inside and can look good from the outside. LBCs are also notoriously hard to bleed and you might want to get a bleeding tool like a mityvac
to help you out. I wore my daughter out just bleeding a clutch slave cylinder

 

[Blonde Healey Girl]

You may want to think about replacing the three brake flex lines.They can cause strange behavior. One on each front caliper and one over the rear axel. They are tough to inspect because they can look fine and dry on the outside, but collapse or swell on the inside. I just rebuilt the brake system on my BT7 and tried to scrimp by using the old hoses. (they all looked good)However, the rear hose was completely collapsed/clogged.

 

[vette]

Hi Bill, It has been said that LBC are notoriously hard to bleed. That is the case with some of them. Although I never found it hard to bleed my MGs brakes, My healey was deffinately a different story. Ist off the clutch is separate from the brakes even if it looks like it has acommon resorvoir. The two resorvoirs are separated inside the common can. So pump up your brake pedal and then hold heavy pressure on it for about 2 to 3 full minutes. If you have no pedal fading you do not have a leak.
Now most of the time on a Healey the air is trapped inside the Master Cylinder or at the output line of the Master Cylinder because that is the highest point. These master cylinders have such a small capacity that they don't move much volume in a single stroke of the pedal. Hence you can acually bleed a system and not move out the air bubble trapped in the master or at the top of the pipe coming out of the master cyl. Believe it or not but the best way to bleed these things is by the two person pump the pedal method. But be meticulous and careful. Close off the bleeder valve at the end of ever down stroke. Don't let the partner move that brake pedal upwards at all with a bleeder open. If you were changing just one caliper or rear wheel cylinder the bleeding would not be that hard because you would not have been exchanging the fluid that is in the master cylinder and upper brake line. But if you are doing a complete system rebuild or have inadvertantly allowed most of the hydralic fluid to escape or get air then it is very difficult to get the air out of the master and upper pipe. Keep at it and be meticulous and it will come. Two last points, some big healeys will never get a full hard pedal but it should never take more than about one short stab to get the full pedal while driving. Also I have used most American DOT 3, 4, or 5 grade brake fluids in many British cars including Healeys for 20 years and never had any problems with brands.
Good luck,
Dave

 

[CDK]

Bill,a couple of other items to check, Adjust brake pads snug to help bleed and check pedal.Try gravity bleeding. To check for leaks push pedal down hard and hang out door and look under car for leaks or any funny sounds. Repete well pumping brake pedal. Straight sections leak as good as any where else check at hold down straps it rusts out there alot.I have experienced weepers also. If the pumping or gravity method still doesnt work try putting a small amount of psi to the fluid tank with one bledder open at a time.Another way is to pull vacume at the bleeder and pull fluid thru.I read a artical recently that suggested starting the bleed at the closest wheel as this would push the air out quicker rather then pushing thru the whole system and giving more places to get traped. If the master is air bound sometimes you need to bench bleed it first.And if after all this you still have a soft pedal swap out the master. Good luck

 

[John Turney]

I found that using the MityVac, if you don't seal the bleed screw threads, you get a lot of air, but not much bleeding. I had to pressurize the master cylinder or use the 2-person method.

Also, make sure the rear drums are adjusted properly.

The comments on hoses looking ok, but having a lot of expansion also hold. I've replaced mine with teflon-lined stainless steel braided hoses(warning: not original) to make sure they don't expand.

John, BN4

 

[wlivesey]

Hey thanks for all the advise! With this new encouragement and a few days away from the garage, I'm ready to give it another shot. Even my wife is ready for another round of bleeding. What a woman!
Just as a response to some of your comments:
I am using Prestone Dot 4, 5 fluid.
I replaced the rear flex hose early on before the bleeding. As suggested I will replace the front hoses if I continue to have problems.
I will adjust the shoes.
The Master cylinder was replaced about 1 year ago.
Sounds like I may still have air high up, around the Master cylinder. I am going to concentrate in this area.

Thanks again, I hope I get this done soon, I need to be able to say I got something done this Winter!

Bill L
BT7

 

[TypeRboy]

Welcome to the dark side! I would still suspect the Mcyl even if it was new.. Was it brand new or rebuilt? Sometimes the life expectancy of a rebuilt cyl is pretty short.

You know you can bleed the Mcyl in the car then attach the brake line(s) and have someone push the pedal down and hold it while you tighten the lines. Most times this allows you to change the cyl without any further bleeding on a system that has no other air in it..

Best of luck..

 

[jha2297255]

eezi bleed is the way to go, but when your wife gets tired of pumping there is a little known solution.

Get a large brick/cement block and put it on the brake pedal. Put plastic wrap under the MC cap so no air gets sucked in, open the farthest away, usually rear bleeder screw and let it go for 24 hours, repeat as needed. gravity works, but slowly. eezi bleed is good if you are in a hurry. -Josh

 

[vette]

Bill, here are a couple of other points that might add some comfort margin in your efforts. (we all have advice right, I like to call them points). I had changed out brakes and bled systems many times and as i have reported here on this site, one day I decided to have all my hydralic components refurbished for long term 'gaurantee' of 'no troubles'. HA HA. Anyway I did all my components ecept my two master cyls. Everything was fine for that summer. During the next winter I decided to rebuild the carbs and while I was at it i would do the master cylinders. Sending them out for reburbing. that started it. The clutch bled up well. Abeit I had to fab a braket to hold the piston still while I bled the slave dangling from the underside of the vehicle, BUT THE BRAKES were now a different story, it took me most of the summer to get my brakes back. Even though all the components were refurbished from the same company and I still have great confidence in that company the brake master just would not bleed. I pump bled, pressure bled, and reverse pressure bled. I bled it on the bench, I bled it in the car, I could not get more than 1/2 pedal. I finally bought another master from another company and in 20 minutes i had the whole system bled with the two person pump the pedal method. NOW, FILL THE MASTER ON THE BENCH IF IT IS OUT, THEN ALSO AFTER YOU GET ALL THE LINES CONNECTED AND THE RESOIVOUR FILLED, PUMP UP THE PEDAL HOLD GENTAL PRESSURE ON THE PEDAL THEN SLOWLY CRACK OPEN THE OUTPUT LINE ON THE TOP OF THE MASTER CYLINDER. jUST CRACK THE THREADS LOOSE AND YOU WILL SEE SMALL TINY BUBBLES PERCULATING UP AROUND THE THREADS. CLOSE THE THREADED FITTINGS AND YOUR MASTER WILL BE BLED. this can be none with the carbs in place. put copious rags under the master cylinders during this process, clean up from under the car through the hand whole in the body structure.
I,ll shut up now I'm sure I have rattled on enought about this. Good Luck,
Dave.