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Master Cylinder problem?

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TexasSprite

TexasSprite

Jedi Hopeful
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Not having much luck in bleeding the brakes in my 59 BE, but I don't think it is air in the lines. The pedal is soft all the way to the floor unless you punp it rapidly. Then it will harden up for a moment. When the pedal is pumped, I can see fluid movement in the MC resivoir as if instead of being compressed, it is getting shunted to the resivoir. FYI this is a resleeved unit that was resized to 3/4" as to better fit the disk brake setup. Still have the original set up on the back brakes. The MC was rebuilt as part of the resleeve process, so I don't know for sure if it was reassembled correctly. .

This subject may have been beat to death, but I'd appreciate any comments on how you tell if the MC is working as opposed to just air in the lines.

I thought I would come in, cool off, and leave a SOS for the experts here. This is supposed to be fun after all!

Geez, I haven't even got to the clutch yet and that's supposed to be the hard part.

Mike
 
If it hardens for a moment, but then sinks to the floor it suggests a leak in the system or a leak by in the MC.

Do you see any leaks?
 
Rear right first, then left, then front left then right.
 
Trevor is right! You could also check MC pushrod lengths. If the cups are not at the correct position in the bore, fluid will cycle through the cylinder and back into the reservoir without exerting pressure in the lines.!
 
Yes, order matters with a single line system. Good point.
 
I hate to ask, but who did the resleeve to 3/4?
 
Think I would check the MC inards. Can do that without pulling it, just empty of fluid and the two front screws and the push rod. Out it comes.
 
Sierra Specialty did the work. They've got a good reputation, so it's probably something I am overlooking. They did alter one of the pushrods to fit the 3/4" sleeved brake bore. I don't think I got them in backwards, but I guess the only way is to pull the guts out and take a look at it. Compared to other cars I've worked on, it this MC didn't seem to generate much pressure at the bleed valve when the pedal was depressed. I'm used to seeing more of a rush of fluid when I crack the valve.

There is a 1/4" slop in the pushrod legnth (from end of pushrod to where it seats in the cup). I'll adjust that to see if it makes any difference.
 
The "slack" should only be about 1/32"!!! That could be the problem...1/4" is way too much, the cups in the bore are not in the right location with that much slack, you are just cycling fluid around in the resevoir and not creating pressure!! Another potential problem if the pushrod adjustment doesn't do it, is the valve (#7 in the diagram below), though I do think the pushrod adjustment is the problem!
 

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:iagree:
 
Over the many years of Spridget ownership, one of the most reccuring (and agravating!) systems to deal with for me has been the hydraulics! If it can happen, I've probably had to deal with it! It is a system that is great when it is working right, but can be so frustrating when it's not!! I'm no expert at dealing with it but I've had to overcome pretty much everything from no pressure at the pedal to brake lock-up!!!
 
Mike,

Thanks for the good advice. I'll give it a try tomorrow when it is a bit warmer her in Dallas. We actually had snow on the ground this morning!

Mike
 
Mike,
Your description that if you pump it rapidly you get hard pedal for a moment is telling. Does the pedal stay hard at that point, or does it go soft as you keep your foot on it? If it goes soft quickly, then the stuff below may not be pertinent.

If your rear brake shoes are not adjusted out properly, then you have to give several rapid pumps to keep the wheel cylinder pistons out, and catch them before they retract. The master can only move so much fluid, and not enough to give full travel on the cylinders. The front calipers don't retract, and so alleviate that potential problem. (unless your wheel bearings allow lots of disc runout... another topic) Many people overlook adjusting until they are done bleeding, when in fact you should do the opposite.

To test rear adjustment, the handbrake should have only 3 clicks up to lock the brakes.

Peter
 
Update on the MC problem:

Good news is that it is probably not the MC. I contacted Joe at Sierra Designs who suggested that a quick troubleshooting trick is to replace the brake line coming out of the back of the MC with a bleeder nut and see what happens. I got a rock hard pedal doing this, so it is obviously something downstream.

I'm ashamed to say that I did't think of such an elementary diagnostic trick, but now I know I don't have to pull the MC and send it back. Maybe I will get to finally go for a drive this weekend.

I'll re check the rear shoe and ebrake to see if that makes any difference.

There must be some big monster bubble hanging in the lines somewhere!

PS: I used the bleeder nut trick to isolate the rear brakes from the front. Problem appears to be with the rear brakes.
 
Narowing it down nicely, now isolate each side at the three way spliter by the differencal and you can tell if it is in the long tube or one side or the other.
 
If Joe at Sierra Designs did your MC, you certainly won't need to send it back. His re-sleeving work is fantastic. The brass-sleeved MCs should outlast any of us by quite a bit.
He did my bugeye and the slaves for the Austin front end, all beautiful work.

I like that bleeder trick. Smart and easy. Thanks for posting that.

Glen Byrns
 
Mike,
If you need a hand give me a call I'm in town this weekend.
I'll throw on a parka and drive SPOT down i could pump the peddle drink a pint!
 
You could always was the very lowtech method that I use if I have air in the system, I buy about 15 feet of 3/16" ID clear plastic tubing (Tygon), plug the tube into one of the (very well cleaned) rear brake bleeders nipples and put the other end into the master cylinder resorvoir. Pump the heck out of it (while someone watches the fluid level so that it coesn't get low) and the bubbles seem to disappear. Has worked many times.
Bill
PS: DOT3 will pretty much destroy the tubing so don't plan to use it much after this, it will harden in a few days.
 
I really like the bleeder nipple at the MC. Old dog, new trick.
 
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