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Vehicle: 1953 M37, all original with straight 6.

Ok guys...I have a head scratcher here. My left front brake shoes were "dragging" and over-heating at my last Veterans Day Parade outing (sounds like an adjustment problem, right?...nope). After some field adjustments of the lower cams to get through the event and avoiding the use of the pedal...I pulled the drum and cleaned/checked everything at the wheel. Shoes and drum all looked good...even "clean" (no leaks). In the process, I discovered that the pads were not retracting after letting up on the pedal (even with applying some "squeeze" on the wheel cylinder pistons). By cracking the bleed screw, the pads quickly retracted.

Another similar thread on this forum suggested that the pedal/piston rod was not allowing the MC to clear the pressure relief port...or that the port was clogged. So I pulled the brake pedal rod and the MC boot and checked that the piston was returning all the way forward (all good there)...still had the problem. So...assuming I had a clogged MC port, I backed off the fitting at the back of the brake MC to allow any pressure in the line to relieve itself there (got a little dripping...but no flow). Still no dice...I had to crack the bleeder at the wheel for the shoes (piston) to retract properly.

Now I know the next step is to start replacing brake lines...but I don't have any leaks and have never seen clogged lines acting like a check valve.
Has anyone seen dirty/old steel brake lines act like a one way a check valve? I hate to pull and replace all the brake lines if I don't have to...but that is the only thing left to check. I plan to flush the lines really well to try and blow any sediment out. Any other ideas/tips?

Note: I've not yet pulled the right front drum to see if am having the same problem there. I will update here as I continue to troubleshoot this problem.

Cheers!

Keyslammer

I would check the rubber line.

First thing would be the rubber lines.

When the rubber lines fail they act JUST like check valves. Ran into this on my carryall. All the lines were old/bad and they all did exactly that.

-jim lee

Guys! Great feedback as usual. I will replace the front left flex line and let y'all know the result. Thanks!

KEYSLAMMER

Do yourself a favor. Replace them all. If one is bad, all are bad. Doing one is false economy since they are not expensive anyway.

Replacing them all is not only good advice, but the whole process will allow you to replace all the brake fluid, which is something that (IMHO) probably doesn’t happen often enough with these rigs (and cars and trucks in general).
Go for it, you’ll be glad you did.
Also, it looks like you are a new member here. Welcome aboard! Here you are dealing with a great bunch of knowledgeable guys!

Very common problem with old rubber brake lines, Like the others have said, replace them all. They are probably the original 60 plus year old lines.

When I recently replaced my rubber lines, I also made up all new brake/vent/fuel lines with tubing and parts from FedHill. I suggest getting a supply of new bleeder screws and extra special copper washers for attaching the new rubber lines to your wheel cylinders. My old bleeders were a bit rusty, and all is well with replacement new ones. I suggest getting extra washers. By the way, i measured my washers, and tried to find them on assorted parts sites, and even though some of the auto parts store's web sites claimed to have them via order, I couldn't get them. Suggest also you avoid ancient, OEM rubber lines, get new ones. The new ones are usually made overseas, and of possibly dubious quality, so try to get US ones. I eventually ordered my rubber lines and washers and bleeders from one of the major vendors for our trucks. As for bleeding, I have a Motive pressure bleeder, so bought a NPT plug with a nipple on it, screwed it into my master's fill plug, and then easily pressurized and bled my entire new lines easily. I chose to not use Silicone fluid, but Valvoline fluid, and keep some under my truck's seat, along with the tools to add more if necessary to my master cylinder out on the road. I will try to post a picture of my pressure bleed system. JEGS and Summit have ever possible hose fitting you will ever need.

NAM VET
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Ditto on the full-line replacements, and power bleeding. I also have the Motive jug and got a ton more pedal using it than the old "pump it up and crack the bleeder" method. Also, I wondered if your brake shoes are moving freely on the lower cams? You might try some Blaster or other lubricant to ensure they're not stubborn and sticking due to lack of movement over the years.
Gary

Thanks for all the tips...I have a Motive Power Bleeder on the way...good price off of FleaBay. I now have all my brake shoes adjusted nicely and all my flex lines have been replaced. I have no leaks (thankfully for the old fittings). However, I now have a new problem and I am about to embark on a replacement of the MC and all the wheel cylinders; my pedal goes all the way to the floor before the brakes start to engage. (aaargh) After pumping the brake pedal one time, I have a firm pedal about 3" off the deck. Just to test the boundary of my problem, I adjusted all the brake shoes "tight" in the drums (no brake shoe travel). The pedal goes to about 2" off the floor before I get a firm stop.

Background
My brake pedal push-rod into the MC is adjusted properly...the brakes are all adjusted (with a feeler gauge)...there are no leaks. I've run almost 2 quarts of fluid through the brakes...no bubbles (with somebody operating the "down/up/down" exercise from the cockpit). The pedal (after one pump) is firm (not spongy). I am wondering if I've washed some of the old crap out of the MC and the plunger isn't establishing pressure until it is halfway through the stroke.

I ordered the Power Bleeder after my 2nd quart of fluid and having my kids operate the brake pedal.

Has anybody else seen this issue?

Craig

It is entirely possible that the cup on the piston has gotten hard over the years and is bypassing fluid until you actually force the issue by adding sheer volume to it and then it comes out. sounds like a master cylinder is a good choice. You can save the old one for a rebuild.

Craig,
If I understand the last bit of your post, I had a similar problem. I'm stubborn and decided to bleed the brakes w/o a pressure bleeder. After way too much monkey motion and wasting a bit of fluid I pressure bled the system to get a good pedal quickly. I no longer attempt manual bleeding on the M37 .

Andy

Pressure bleeders work great but to me are too fiddly to use. I use a vacuum eductor and pull the fluid and air out at the bleeders. Either way has enough fluid velocity to carry trapped air out of the system .

I tried a vacuum bleeder and it was a complete disaster. I think there was a tiny leak somewhere in a brake line and the vacuum pulled air into the enture system. Turned all my brake fluid to milk. I guess if everything is perfectly sealed it should work fine. But the smallest leak and your just hosed.

-jim lee