Static Leak of Wheel Cylinders

SofaKing

SofaKing

Well-known member
I am looking for a solution to leaking wheel cylinders. They weep when the car is sitting. They are USA, NOS parts. They weep with new USA cups and the original USA cups which appear to be in remarkable shape. I cleaned the old packing fluid/ grease from the bores and seals and lubed everything with a light coat of new brake fluid.

I used the technique Dick Spadaro quoted in an old thread to clamp the pistons in place, all 4, and then bleed the system. I was also very careful to install the shoes in a balanced fashion so as not to displace the seals/pistons past the ports and induce a leak. It took several days but I find the new cylinders are leaking exactly like the old ones I replaced. The vehicle, 39 pu, has not moved since install. I am using Dot 3.

Before I ruin another day of my life I'd like to know if there is some other trick to getting these to work. Thanks.
 
Even without moving the PU I would (after bleeding) work the brakes with a bit of 'real time' vigor. This would allow the rubber cups, and the spring 'end cage? socket?' to marry-up under pressure and create a good square stance within the cylinder bore. If the job is a leaker you'll know right away. If the seal is tight today (and all was clean inside - surely it was - ) there ought to be no leak in three days. Good Luck.
 
What A bones said. If it is still leaking then you need to take them apart, hone them, clean them and put them back together. Something didn't get together correctly if they are leaking.
 
JSeery said:
What A bones said. If it is still leaking then you need to take them apart, hone them, clean them and put them back together. Something didn't get together correctly if they are leaking.
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I agree. There is no reason there should be any leaks.
I like the fact SofaKing is using USA parts. We've all heard horror stories in regard to the foreign made cylinders. Still, USA or not, defects happen and NOS does not necessarily mean the parts were properly manufactured.

When I do a complete brake job, I power bleed the system and leave the pressure, set at 20#, on the system overnight. I expect to see 20# the next day. Only then am I satisfied the system is free of leaks.

I would be 100% certain the new USA cups are the correct size. Seriously... I have experienced 1" cups that were not 1".
If I were a betting man, I'd say the cups are the issue. The odds of all cylinders being defective has to be low.
 
JSeery said:
What A bones said. If it is still leaking then you need to take them apart, hone them, clean them and put them back together. Something didn't get together correctly if they are leaking.
Click to expand...

Correct, and thank you!
 
Original cylinders had a small bleed hole maybe 1/16 and the vent in some cases are 1/4 ,if you have thicker linings backed of and maybe new drums it will cause the cups to straddle the hole and leak , Ted
 
My thoughts are like Richard.
Is there a line pressure valve in the master cylinder?
This keeps a regulated low pressure in the lines. This residual pressure in the lines keeps the seal lips pushed against the bores.
If you already have one, I understand they are available in 2 pressure levels.
Lastly, what about expanders behind the cups?
 
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A bones said:
Even without moving the PU I would (after bleeding) work the brakes with a bit of 'real time' vigor. This would allow the rubber cups, and the spring 'end cage? socket?' to marry-up under pressure and create a good square stance within the cylinder bore. If the job is a leaker you'll know right away. If the seal is tight today (and all was clean inside - surely it was - ) there ought to be no leak in three days. Good Luck.
Click to expand...
I will try exercising them more to get them to seat after I disassemble and inspect them, again.

Kube said:
When I do a complete brake job, I power bleed the system and leave the pressure, set at 20#, on the system overnight. I expect to see 20# the next day. Only then am I satisfied the system is free of leaks.

I like this idea but will have to improvise as I don't have a bleeder that will hold pressure as described.

I would be 100% certain the new USA cups are the correct size. Seriously... I have experienced 1" cups that were not 1".
If I were a betting man, I'd say the cups are the issue. The odds of all cylinders being defective has to be low.
Click to expand...

I will measure the face. They went together well, no obvious defects. I installed the cups just barely in the cylinder and then squared it by pushing them in with the pistons.

richard crow said:
if the check valve in the master cyl is not working they will leak.
Click to expand...

Where is the check valve? I did not see anything that looked like a check valve when I resealed the original MC and the replacement Cardone brand MC appears identical to the OEM.

FlatheadTed said:
Original cylinders had a small bleed hole maybe 1/16 and the vent in some cases are 1/4 ,if you have thicker linings backed of and maybe new drums it will cause the cups to straddle the hole and leak , Ted
Click to expand...

The feed and bleed holes were not 1/4" but I do recall on a couple cylinders one of the holes was oblong. How thick is too thick? Mine are all in the .220-230" range but I have nothing to compare that with, the drums are old, used.

I am reluctant to hone them, they have a very smooth finish. When I honed the last set the finish was nothing close to being this smooth, almost polished, and I cannot duplicate what I have now. Thanks everyone for the suggestions.
 
I think you guys have brought up a valid point in regard to the "check valve" in the master cylinder. Yes, if the rod is adjusted too tight, the pressure will not be allowed to release very well and will keep some pressure within the wheel cylinders.
I'd like to know if the pedal stays hard after a short drive. If not, the master is not the cause.
As I'd noted previously, I place a constant 20# on the hydraulic system for at minimum a full 24 hours. No leaks... to me, that says there is an issue with the original posters cylinders.
 
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When you replaced the master, did you adjust the rod?
When you drive the car, does the pedal get harder after multiple uses? If so, does it stay hard for a bit?

The "check valve" is located at the bottom of the master reservoir. If the rod is adjusted "too tight", the piston is not allowed to return far enough and as such will block the "check valve" and subsequently the fluid can't return to the master. This leaves a hard brake pedal and some pressure remaining on your hydraulic system.

If you can pump the pedal and it gets hard but goes back to "normal" right away, the master is not the issue.
 
I remember check valves were behind the brass seat where the brake line connects. When you rebuild, you pull the seat by threading a sheet metal screw in the hole and pry it out. Maybe old Fords are different. In your case, try putting a small drill bit in backwards or something in the hole and feel for a spring loaded device.
 
The "check valve" is actually called a "residual valve" , it is the second piece you install in your clean master cylinder when assembling it. The first is a rubber washer that it seats on in the end of M/C. Third is the spring The purpose of the residual valve is to hold slight line pressure keeping the wheel cylinder seals seated against the W/Cylinder bores. Without the rubber washer or residual valve your wheel cylinders will probably leak just sitting & not being used .Good Luck !
Cheers
Tony
 
You can also add external residual valves.
 

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Kube said:
When you replaced the master, did you adjust the rod?
When you drive the car, does the pedal get harder after multiple uses? If so, does it stay hard for a bit?

The "check valve" is located at the bottom of the master reservoir. If the rod is adjusted "too tight", the piston is not allowed to return far enough and as such will block the "check valve" and subsequently the fluid can't return to the master. This leaves a hard brake pedal and some pressure remaining on your hydraulic system.

If you can pump the pedal and it gets hard but goes back to "normal" right away, the master is not the issue.
Click to expand...

I am at a disadvantage in answering your questions as the car does not currently drive, has never been driveable during my ownership and I have never driven a vehicle from this time period, nothing to compare. I bought it as a basket case. That said, the new master cylinder gives a firm pedal when depressed. Prolonged pressure does not cause any perceptible bleed down. Releasing the pedal and reapplying pressure there is nothing abnormal, it is not stiff but gradually builds pressure as expected. Repeatedly pumping the pedal does not change anything, maybe a slight change after the first cycle but very minor if at all.
The brake rod is adjusted so it has a small amount of freeplay in the linkage, a slight amount of pedal travel before any pressure build-up. To me the MC is working normally. When I get back to the brakes, I will hang a cinderblock from the pedal to simulate brake pressure to replicate your suggestion and seat the cups.
 
You will never be able to tell if it has it correct residual valve or rubber washer from pushing pedal , the master cyl. will operate perfect !
The sole purpose of the residual valve is as I explained above.
 
It will be the large end of the cylinder that has the hole in it (front ) .I had to grind 1/16 of the end of the shoe bit that enters the cylinder ,not ideal but after trying several . It could be the piston that's larger ,
As well as the residual valve the tension from the cups sealing against the wall should be enough on there own to seal ,If you do a carful inspection of the cylinders you may find that piston is fully retracted over the oblong hole ,Ted

The feed and bleed holes were not 1/4" but I do recall on a couple cylinders one of the holes was oblong. How thick is too thick? Mine are all in the .220-230" range but I have nothing to compare that with, the drums are old, used.

I am reluctant to hone them, they have a very smooth finish. When I honed the last set the finish was nothing close to being this smooth, almost polished, and I cannot duplicate what I have now. Thanks everyone for the suggestions.
 
We were having a similar problem with the large bore side leaking on the front wheel cylinders.

Discovered the same problem as described by Flathead Ted; after measuring everything we found the large piston was thicker than the original; so we milled the slot that contacts the shoe a little deeper as a correction.

No more leaks.
 
FlatheadTed said:
It will be the large end of the cylinder that has the hole in it (front ) .I had to grind 1/16 of the end of the shoe bit that enters the cylinder ,not ideal but after trying several . It could be the piston that's larger ,
As well as the residual valve the tension from the cups sealing against the wall should be enough on there own to seal ,If you do a carful inspection of the cylinders you may find that piston is fully retracted over the oblong hole ,Ted

Thanks, clearly I will have to start measuring and verifying the design, something I did not expect would be required, especially with NOS parts.
Click to expand...
 
I recall that in my case the piston all measured up correctly ,it was all caused by the oval hole that intruded into the cup zone .On one we had to take more than 1/16 and there was not enough thickness on the piston to do this . Ted
 
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