Help with my brake problem

[rick3216]

Just bought my 1954 M37,very original truck. Previous owner told me that one brake cylinder was sticking. I put truck on jack stands and found right front wheel hanging-up when rotated.

Installed two new front wheel cylinders and flex lines and bled brakes - everything turned free. Drove three miles and stopped to get gas. Started truck after gas stop and I felt brakes dragging slightly. Headed back home and pedal got very stiff and brakes dragging more. Finally stopped and both front wheels/brakes were smoking. Brake pedal hard as a rock with no free play. No apparent problem with rear brakes. MC is original single pot style.

Checked MC vent and valve is open. I know valve works because I pressure bled brakes and forgot to turn off valve and had brake fluid venting out of air intake elbow. Used 7/16 wrench and cracked bleed screws on front brakes. Lots of pressure released and fluid shot out and zero brake drag. Drove the remaining 1 mile back home and by the time I got there brakes were starting to drag again and pedal stiff again. I'm going to let it set and check brakes after they completely cool off.

Any thoughts???

[Cav Trooper]

I had the same problem after trying to adjust the brakes up on my M37. After I adjusted them, I found out that one brake was dragging slightly and the heat would build up and expand the brake fluid to the point it boils and locks up the brakes. I ended up backing off the adjustments to where they didn't drag at all, had a lot of pedal travel though and not good braking. I found that the previous owner had replaces all the brakes, including lines, wheel cylinders, master cyl. and turned the drums. He had also used Silicone brake fluid. Trouble was, the shoes were not fitted/re-arced to the drums which no one evidently can do anymore and brake surface is only 1/4 or less of the shoe to drum. I finally replaced the front drums with calipers and the rear ones are slowly wearing in and getting better.

[Cal_Gary]

Rick,
You didn't mention turning back the top side 3/4 wrench sized adjusters that have the D-rings inside, nor the bottom cam adjusters. I'd check the D-ring adjusters up top first, backing them off to see if the wheel turns freely, then snugging them just enough to get some drag back on the drum.
Try that then let us know, thanks,
Gary

[just me]

Sounds like master cylinder issue. If the pushrod is adjusted too lkng or the orifice in the MC is plugged, the fluid can't return to the reservoir and the brakes won't release.

[Elwood]

...the shoes were not fitted/re-arced to the drums which no one evidently can do anymore and brake surface is only 1/4 or less of the shoe to drum.

There are still some shops that can do this work, as long as they have the right tool, such as an Aamco brake shoe truing machine. Or, if someone wants to do their own shoes, these machines are available used on ebay and from used machinery dealers.

[RMS]

I have had two residual pressure valves fail causing the brakes to "pack up". the valve is located in the MC. the diaphragm got hard on one causing higher pressure and the other was packed with crud. packing can also happen if the mc is put together incorrectly. check petal free play and inspect the mc guts.

[rick3216]

UPDATE
I did use the cam adjusters (top and bottom) to adjust the shoes per Charles (from Mseriesrebuilder) write-up where he explains to use the view port on the hub to visually adjust the top and bottom of each shoe so that they are visibly just shy of touching the hub. I thought that was a great idea and felt good about the adjustment.

I do believe it is a MC problem. I took the hubs off again today and could not rotate the hubs until I relieved hydraulic pressure by bleeding some brake fluid out. I took the hubs off, removed the dust and reinstalled the hubs. I checked my shoe adjustment again via Charles technique and everything looked great. Got in truck and pumped brake pedal 10 times and pedal got stiffer with each pump until the hubs were locked again against the shoes.

I already wanted to rebuild the MC and actually have the parts on the way. I'll keep you posted

Thanks for all the input guys

[Kaegi]

I think either pushrod too tight on master or failed brake hose at the frame. if the rears are not locking up then the hose from frame to axle is bad or both front left and right are bad, or all 3

[MSeriesRebuild]

Could well be hose interior lining is coming apart. It will allow fluid to be forced by with a brake application; then flops closed acting like a check valve not letting fluid return, thus locking the wheel cylinders after a few applications.

As mentioned, there must be a slight amount of brake pedal free travel. This insures that the M/C push rod is NOT contacting the end of the piston at all when pedal is released. The push rod is adjustable. Do you have the pedal pull back spring in place; if not the weight of the pedal and push rod will keep slight pressure on the piston 100% of the time. Either of these scenarios will cause the problem you have. I highly doubt that rebuilding the M/C will do any good at all. We never rebuild a M/C or a wheel cylinder. It is basically useless, as most are rust pitted to the point they can't be honed large enough to remove all pitting before they become to large to accept the kit components. Installing a new kit without removing all pits or any out-of-round condition is worthless. My assessment is buying kits and tooling to hone properly is money that could have been much better spent on replacing the bad parts which are readily available at reasonable prices. Again I strongly suspect your issue is either bad hoses, bad or missing pull back spring, or push rod adjustment, with stronger emphasis on the latter. A 5 minute adjustment won't cost anything and very well could correct your issue.

We also offer shoe relining service and have equipment to radius the linings so they fit turned drums correctly. I'll give you some good advice on that too; it is impossible to radius a lining correctly unless you have the drum so the lining can be fitted correctly to it. You can cut that radius all day long; but it will never be exactly right unless properly fitted to the drum it will be run against. Then there is the issue of turned drums most likely being no good anyway.

[rick3216]

Thanks for all the great advice. I will replace the flex lines and check the free play in the plunger rod. I do have the return spring installed.

Regarding the MC rebuild. Since I have the kit I thought I would give it a go. Here is a photo of my rebuild parts lined-up in order of install into the bore. I'm not sure where the rubber washer goes (top of photo). I think it is the first thing that goes into the bore when reassembling. Any thoughts?

mc parts.JPG (125.26 KiB) Viewed 2052 times

[RMS]

first in

[rick3216]

Thanks. Is the valve positioned correctly with the radiused side of the valve inside of the spring? I'm referring to the second part that goes into the bore which is on the right side of the spring in the photo. I have it shown with the radiused side of the valve facing the spring and part of the valve being inside of the spring.

[RMS]

the orientation of the residual pressure valve seems to be correct in your pic.

were your brake lights staying on ?

if not, its probably as Charles suggested, a bad hose.

[rick3216]

UPDATE - not sure if the brake lights were on or not.

The MC rebuild did not resolve the problem. With all new wheel cylinders and flex lines, ample free play at the brake pedal, shoes adjusted just shy of contacting the drums - I still had the packing problem as described in the initial post. Installed new MC and problem solved. I guess there was some passage blocked in the MC. Thanks for all the help. Case Closed!

[MSeriesRebuild]

UPDATE - not sure if the brake lights were on or not.

The MC rebuild did not resolve the problem. With all new wheel cylinders and flex lines, ample free play at the brake pedal, shoes adjusted just shy of contacting the drums - I still had the packing problem as described in the initial post. Installed new MC and problem solved. I guess there was some passage blocked in the MC. Thanks for all the help. Case Closed!

It should always be common procedure to check and completely clear all small fluid passages in the M/C at the time of a rebuild. A rebuild kit should never be installed without honing the cylinder bore. This creates fine particles that can clog small passages; so a thorough cleaning is necessary after honing. This is rarely a problem except after honing without cleaning well or foreign matter has gotten into the M/C; dirty fluid poured in, etc. You did the best thing by replacing it; likely you also headed off other problems that would have shown up soon as well.