brakes

[honeaj]

Morning all. I have a '51 PW with brake problems. When we go for a drive, the brakes work well at first. As the drive continues the brake pedal gets hard and the brakes begin to drag to the point they finally get so tight you cannot go on. I posted this problem once before but got no response, so I have decided to replace the master cylinder. I can find the one ton MC easily but it is for disc/drum combinations. I cannot find a proportioning valve for drum brakes only. I do not intend to go to disc brakes. My questions are, Do I really need the proportioning valve, and if so, will the one for front disc/rear drums work? My truck has all drums. Thanks in advance for any insight, information, or advice. Jerry

[Gsmith]

What is the condition of the rubber brake hoses? I know people have had those go bad and cause a blockage where the wheel cylinders can't release, or release very slowly as it leaks back.

[honeaj]

brakes

Thanks Gsmith, I should have further stated that I have replaced all rubber hoses and all four wheel cylinders. I also rebuilt the master cylinder with a rebuild kit off of e-bay. It wasn't exactly like the original but was very close. I read on another thread where someone said something about not pushing the brake all the way to the floor while bleeding the brakes as this ruined the cups. That was done. Could that cause a brake lockup such as this? Thanks again, Jerry

[Tom Petroff]

Check the pedal pushrod at the MC. Should have a little free play. so the piston releases all the way.
TGP

[Gordon Maney]

If a particular one of the two ports in the floor of the reservoir is plugged you will get that symptom. I have had it happen on hydraulic clutch applications, too.

[honeaj]

brakes

Thanks Tom and Gordon, I will check those two things out. It is frustrating to have a good running M37 and not being able to take her out. Thanks again, Jerry

[Charles Talbert]

The better option

Pedal rod free travel not correctly adjusted is your most likely issue for the symptom you described, if everything else is functioning as it should be, however

Rebuilding the M/C was not a wise move, especially with a will fit kit that isn't exactly like the original parts, who knows what may be going on with that? The best thing to do is replace the M/C, not expensive and a much better option. In most used M/C's, rust pits are prevalent in the cylinder bore and must be honed out in order to get a good rebuild. In the majority of cases, by the time you hone out enough material to get back smooth and round, the bore is larger than the max spec allowable and is unserviceable. No rebuild kit will work in an out of spec bore. Since a new unit is only $72, it's a good investment, leak free, and will give years of trouble free service.

If you do choose to rebuild anyway, assuming you have an original equipment type M/C, the correct kit is available locally at NAPA, United brake parts kit #1 is the part#.

We have any brake components needed for M37 on the shelf.

A proportioning valve is not necessary on the stock drum system. We use both adjustable proportioning valves and residual check valves on some of our various custom M37 and PW power boosted brake systems. These components are readily available without issue. Just general information, residual pressure check valves in a disc system should be rated at 2 PSI, in a drum system, they should be rated at 16 PSI. None of these components are necessary with the non-boosted stock system used on an M37. It is simply not a wise expendature to invest in these components with the stock system. If the system is not functioning properly, other issues exist and adding these components will be to no avail.

[honeaj]

brakes

Thanks Charles, I was hoping you would weigh in on this. The master cylinder I rebuilt was only 7 years old and did not seem to have any pits. I think pushing the petal to the floor when bleeding the brakes may have damaged the cups. Nonetheless, I would still like to put a double reservoir MC on this truck. Am I understanding correctly that I can put one of the one ton chevy master cylinders designed for front disc brakes on my truck with straight drum brakes without a proportioning valve? Do I need any other parts? Thanks again. Jerry

[saburke17]

Hey charley do you still have wheel cylinders in stock?

Sean

[Charles Talbert]

Hey charley do you still have wheel cylinders in stock?

Sean

I have new wheel cylinders in stock, I try to keep them on the shelf all the time.