I am having a problem with brakes, ( 74 w/ drums around ), I have to put so much pressure on the pedal my arss comes off the seat. Everything but the drums have been replaced. I know discs are better but I'd rather keep it original. I read somewhere that residual valves are required with an all drum system, and that they are not built into aftermarket master cylinders. Are these residual valves in the fluid dispursing block on the inside fender? If so, my problem is in another area. Help!! ******************************************************* IF IT'S GOT BOOBS OR WHEELS IT'S GONNA COST YA!
Have you bled the brakes and removed all the air from the system??? What kind of Master cyl are you useing and did you bench bleed it or bleed it on the car after install???
***************************************************** I always bench bleed and I've bled the system 3 times since installing a Bendix 1645. I didn't have the drums turned because they didn't look glazed or burnt. But with new shoes it shouldn't make that much difference. Have you heard anything at all about residual valves? ******************************************************* IF IT'S GOT BOOBS OR WHEELS IT'S GONNA COST YA!
Residual valves are only used if the Master cylinder is below or even with the wheel cylinders. These just keep the fluid from flowing back to the master cylinder. If used on one where the cylinder is above the brakes all it will do is keep pressure on the brakes. Sounds like you may have a power brake cylinder.
Did you put a replacement M/C on the car or did you put something that was not original equipement on it.I ask becuase if it is not original equipement style its possible it does not have a residual press valve built into it...this will cause a mushy pedal.Residual valves are used to keep a small amount of line pressure in the system so you dont have a mushy pedal.Other possibility is the master is bad...or you need to adjust the brakes up more so you have a bit of drag on the drums.Did you replace your flexible brake hoses as well??? bad ones can cause a mushy pedal also.
I try to always use a reman if possible, I've had a lot of problems with new replacements, yes this is a reman. I never thought of replacing the hoses, DUH. This is the information I was referring to about the residual valves:. "Since drum brakes require the use of residual pressure valves the original drum master cylinders had residual valves built into the outlets. Later model aftermarket units DO NOT HAVE THESE VALVES and they must be installed in the lines externally. Failure to incorporate residual valves will cause spongy brakes. 10# valves ( 2 ) for drum brake applications, installed as close to the master cylinder as possible."
If it is a factory replacement style...It will have the valve built into the M/C...But...Re-mans tend to be hit or miss for a good one.You may have a bad one.Are your brakes adjusted properly??? you will have a soft pedal with lots of travel if they arent.I was going to say something else but just lost the thought......It will come back...I hope...
It looks just like the one I took out, but I don't know if that one was the original or a transplant. I've bled till I bled and adjusted till I cried. Yes 11645 oops! ******************************************************* IF IT'S GOT BOOBS OR WHEELS IT'S GONNA COST YA!
Residual pressure valves maintain a small amount of pressure in the brake system to keep the wheel cylinder lip seals for collapsing. it is used in all drum brake systems. i don't see how not having it would make it harder to brake but it could cause a little farther pedal travel, cause it has to make just a little more pressure with out it. with out one the wheel cly seals will leak over time. the residual pressure valve keeps 8-16 lbs of pressure in the lines at all times. ld say you have the wrong master cly though
Thanks for the input fellas. I think I'll try another brand of master cylinder and have the drums turned ( if there's room ). ******************************************************* IF IT'S GOT BOOBS OR WHEELS IT'S GONNA COST YA!
Yep these guys have been there. Dont trust a rebuilt master. I wouldnt install one on my vehicles. Seen too many fail out of the box and shortly after install.
same problem i had, after replacing all the brake cylinders it ended up requiring a new master cylinder. Fix and works great now.
First i want to imput on turning the drums, Brake shoes are made to fit a specific diameter hole. If you open up the drum the brake shoes no longer can make contact in the whole circle. Therefore you have in effect cut your braking in half. Have you ever took off a brake drum and the shoes be worn only in the middle, Thats because the drum is worn past the limit of the original hole size. Most drums have a max limit stamped on the drum and it not much more than when the drum was new. The only way to use a drum with a bigger diameter would be to get over sized shoes, They do make these for ATVs but have never saw them on cars. Second is the residual valves, I'm not going to say they never had them because they may have at one time,I know my 74 has never had it, although it does have front disc with rear drums. But they would have no effect on pedal effort. I work on drum brakes daily on big trucks and school buses, They do not have the valves. So i would see no need to have the valves on anything if the master cylinder was above the wheel cylinders as gravity will keep the fluid from backing up. I have one Maverick with drums and it has no valve, The master cylinder could have been changed i cant say it hasn't. I also have a 55 model jeep that has drums and I'm pretty sure it never had the valve, I know it doesn't now. On drag cars or round track the master cylinder is sometimes below the wheel cylinders, Therefore they do require the valves. As always this is just my opinion.
I work at an old NAPA store and there is a machine back in the shop made by Ammco to fix this problem. Basically, you mount the brake shoe to it and an abrasive drum removes some lining material from the middle of the shoe so it will mate correctly with the turned drum. Its adjustable to what ever oversize the drum was turned to. I have never seen this used in my 6 years there and judging by the amount of dust and junk piled on it, it hasn't seen use in decades. Probably illegal now, but it worked. BTW, the max oversize for most brake drums is .060".
