brake line valve

Faro

Faro

Junior Member
'48 Merc 4 dr Mod 114 (Canadian model) Drum brakes

brakes heating up, seems to move around wheel to wheel currently left rear wheel. When I say moving around, its after each garage (2) works his magic, it goes to a different wheel after approx. 100 miles. Usually when I'm in a city with frequent stops.
Subsequent conversations with well meaning people center around something called a defective residual valve.
My question; situation seems to imply drum brake springs not doing their job?
Or, psi too high on residual valve?

What is there now seems to be an original part, located under the car, close to frame.
 
try adjusting the master cylinder rod --it needs to be loose or rattle when the pedal has been released, this adjustment allows the brake fluid to return to the MC. is there a good return spring on the pedal?
 
Will check that out tomorrow am; keep you posted
tks and regards
F

PS will also check movement of brake pads on all 4 wheels to see if brake springs are working.
 
Last edited:
Faro, is the brake system modified from original? That will make a lot of difference in the answer.
 
Original braking system on this round back treasure of mine. Other stuff has been modified, eg shocks, exhaust, 12 volts. This is a Merc but restored using a Canadian Ford as a donner car.
 
The Lockheed master cylinders on U.S. built '39-'48 Fords and Mercs used an internal residual valve, also common on most other master cylinder manufacturers. If your car has an external residual, it may not be original, but the very low 10-20 psi rating of residuals cannot overcome the much stronger drum brake return springs.
Make sure there is about 1/32"-1/16' clearance between the push rod and master cylinder when the pedal is fully returned against it's stop and with it's own return spring.
 
I can confirm Canadian built models also used the same ''internal'' system. I found no valve under the car. Line from the MC goes to an frame attachment, out the other side to a 3 pt joint with lines going to each back wheel. Line to the front wheels comes directly from the MC, using another 3 pt joint for each wheel. There is about 1'' very easy movement on the brake pedal. Will check further this PM, closer to the MC for movement there.

More relevant, I think, I checked left front wheel brakes, and found the spring there is not functioning very well. Jerky, and difficult unsymmetrical movements of the 2 pads. Had to rubber hammer the pads back in position to re-install the wheel. Its my unexperienced opinion that I should re-establish easy movement of these pads, on all 4 wheels, using some sort of lub, and avoiding the pads and inside the drum casings.
Unfortunately, I developed a brake fluid leak at the wheel cylinder while doing all this. But, thats another story.
 
Last edited:
Sometimes the shoes will wear grooves in the backing plates that keep the shoes from completely retracting. Good backing plates or a little welding and grinding will solve the problem. You might want to disassemble the brakes and check for wear.
 
Your first post stated


"Subsequent conversations with well meaning people center around something called a defective residual valve.
My question; situation seems to imply drum brake springs not doing their job?
Or, psi too high on residual valve?

What is there now seems to be an original part, located under the car, close to frame"


....which led me to think you found an external residual under the car.


I think you next need to check and/or rebuild the wheel cylinders, as one or more seem to be stuck.
 
I don't see 'history' of system mentioned... Have the wheel cylinders been 'refreshed' recently? What if it's old and cruddy? What if the wheel cylinders were assembled using brake fluid as an 'assembly' fluid? Aren't these things that would contribute to sticking pistons, and not allowing the shoes to back off, normally, as they should? Personally, I like to start out with known conditions on cars that I work on. And, that is, master cylinder refreshed with a new kit. Assembled using 'assembly fluid'. Then, all lines and hoses blown out (and verified with fresh brake fluid showing at the entrance to each wheel cylinder). Brake lines and hoses replaced or refreshed as necessary. All wheel cylinders refreshed with new kits, and assembled using assembly fluid. And, of course, check for 'free-play' of rod at master cylinder. And, of course, all springs (shoes and pedal return) doing the job they are supposed to do. Then, when all of the system is checked, I generally don't have further problems. One of the biggest problems that I have seen recently, is that I'm finding stuck, or sticky, wheel cylinder pistons. Generally from old age, and probably assembled with brake fluid, and severe corrosion due to moisture reacting. My recent experience is with three Willys from the 40's and 50's , and a 38 Plymouth, all of which have been sitting out, exposed, for decades. And, one 47 Ford, which has been in service, but horribly assembled using wrong front wheel cylinders, and wrong front shoes. Using the outline above, paying attention to the details, all of these cars have been returned to having well-functioning brakes. In the case of your car, I'd be starting from square one, using the above outline. Obviously just opinion.
 
I would start by making sure the return port in the master was clear. It is a small hole in the bottom of the resivoure right below the filler cap. they can rust over or become plugged by debris. When I had the same symptoms as you this was the cause. hope this helps.
 
Same questions at bobH:

I don't see 'history' of system mentioned... Have the wheel cylinders been 'refreshed' recently? What if it's old and cruddy? What if the wheel cylinders were assembled using brake fluid as an 'assembly' fluid?
 
Thanks to all, getting valuable input here. Checking piston clearance on MC tomorrow. Also the pin hole on reservoir.
What I've seen here so far, is a refreshed system. Wheel cylinders, have only witnessed 2, appear to be new, as well as some line attachements.
But, previous work does not seem to include a manual ''massage'' of working parts, shoes & springs. Just cleaned and a few parts replaced. Final decision here is to completely review all 4 wheels for proper functioning system, by my friendly mechanic.
Your support is greatly appreciated, keep you posted.
PS; how do I attach a picture to a post?
 
Hoses are cheap. You can have a problem where a hose collapses internally and acts like a one way valve, holding pressure downstream. If one front or both rear wheels bind after a good solid brake application then the hoses could be suspect. New hoses will help.
 
Good point. This case, the heating up, with eventual binding, occurs on in-town drives with frequent start and stops. Not so much, hard stops, but frequent stops.
I've decided to overhaul the brakes on all four wheels to make sure all shoes are moving easily. Yesterday's inspection of a front wheel revealed a situation where the shoes were jerky in their movement.
Also, checking breather hole on MC reservoir makes a lot of sense.
TKS for the input, update on this coming after next week's appointment with my garage.
 
Note to pistonbroke; did not find small hole on MC reservoir. Below the cover, nor on the cover. Must be clogged. Will have this looked at wed. next week.
There is looseness with the piston into the MC, which, I'm told is necessary to prevent residual pressure in brake lines, and which also probably confirms an interior residual valve within this MC.
 
You must log in or register to reply here.
Back
Top