Why Are M37 Brakes So Bad?

[w30bob]

Hi Guys,

Have you ever noticed that many of the M37s you see for sale have brake problems? I keep an eye out for M's for sale and the common thread in all the adds seems to be "needs brake work". So I pulled out a new wheel cylinder to look at it. Seems simple enough in design. So what is it about those cylinders that make them so prone to leaking? I looked at some other cylinders I had on hand, mostly GM stuff, but I'm not seeing the design flaw in the M37's wheel cylinders.

Is it just because these trucks tend to sit unused for long periods of time, and brake fluid is corrosive, or is it something else about the cylinders that makes them so failure prone? Let me know what you think.

thanks,
bob

[ashyers]

My guess is it's a combination of sitting, harsh environments, and outer seals that are somewhat floppy where they meet up with the shoes allowing nasties to get in and start corrosion. I have never seen any brakes as bad as the brakes on the M we are rehabilitating. They looked like they had been residing in a swamp, of course I'm not sure that was not their last stop!

[Cal_Gary]

Brakes were the first project I tackled on mine, 11 years ago: MC and wheel cylinders (couldn't afford shoes or turning the drums back then). Last year I did the shoes and drums then expected good brakes; however, one of the wheel cylinders I replaced 11 years ago ended up pitted and leaking right at the rubber cup edge due to non-use most likely.

Gotta keep driving them to keep them working I suppose.
Gary

[w30bob]

Hi Guys,

So would a stainless steel liner in the wheel cylinder solve all the brake woes?
Just a thought.

regards,
bob

[RMS]

stainless would be good. I will be installing brass sleeved wheel cylinder in my 265 truck. all the trucks that I have seen with leaky pitted cylinders all had one thing in common: a broken or absent breather line. i've also got in the habit of sucking out the old dot 3 with a vacuum pump every spring and renewing.

[sturmtyger380]

Not just our trucks buy any of the hard core restorers and collectors flush out their brake lines at least every other year or some each year to remove water that accumulates.

I built a pressure bleeder and last year filled it with new brake fluid and went around bleeding the wheel cylinders on my M38A1. So far so good. I wish I had done that one in silicone.

I plan on doing the M37 in silicone.

Alan

[Kaegi]

its any old car that sits around. like others said they need to be driven. and M37s tend to be used in offroad conditions which ads more dirt and moisture into the shoe area. go on CL and look for 1950s chevy or ford trucks and they all have brake problems form sitting around as well. Another thing is the aluminum pistons in replacement wheel cylinders cause corrosion. always clean and re use the original cast iron pistons if you still have them.

[Theosaf66]

I've add a vacum brake assist from a M601 and u can't imagine the difference.

[MSeriesRebuild]

Several answers apply to your question.
Sitting idle certainly affects everything, including brakes. Most wheel cylinders have aluminum pistons in a cast housing; dissimilar metals cause corrosion over time. Yes it would be better if this choice of materials could change; however not cost effective for manufacturers looking to make an item at a price low enough to have a saleable product. In general, buyers go for the cheaper stuff; just remember there is always a common reason why items are cheaper. If you are one who browses the web looking for that item that someone has for a few $ less than other sellers; you could well be selling yourself short. Most sellers who genuinely make an effort to offer the better quality items will do so with an explanation detailing why their product is of higher quality. Be careful there also; of course there are some that pedal the cheaper stuff while representing it as something more.

Badly worn or out of round drums is another issue, with no new ones available; there isn't much you can do about this one. Even if you do find a new one; remember they are many years old, if they have not been stored properly, you will find that new drum is still out-of-round; thus no good.

Something we see a lot on trucks that come in our shop with complaints of inferior brakes is the shoes not properly adjusted to the drums. Most people seemingly don't have a clue how to adjust these types of systems correctly. Many times owners go to modern automotive shops where techs are clueless; I guess the reason they go there is because they themselves are clueless, and so on the story goes. Shoes MUST be adjusted so that when they are activated, the WHOLE length of the lining contacts the drum interior surface. We have seen many with linings worn out on half or less of the shoe length. This offers only half the braking ability that one could have had if adjustment was correct.

A booster in the system does make a huge difference; it is WELL WORTH the few hundred $$$ it cost to add one to your system, whether you are running a drum or disc system; with single or dual fluid circuit.

Be careful with silicone fluid, most components are not built with internal parts that are compatible with silicone fluid; I've seen silicone fluid cause total system failure very soon after total rebuilds in a few cases. Most component instructions will specify whether silicone fluid is permissible. If instructions don't say using silicone is ok; the smart thing to do is not use it. Never just assume it is ok.

[w30bob]

Theo.........how about some pics! Sounds interesting.

thanks,
bob