Why GL Deuces have no Brakes

[stumps]

What could be a more common event? Go to GL to pick up your new deuce, and its brake pedal has no resistance all the way to the floor. It happened to me, and I would bet it has happened to more than a few of you.

So, you pull out your patented SS Garden Sprayer Brake Bleeder, bleed the brakes, and everything seems fine for the trip home. Everything seems fine for the next several weeks, or maybe even months... until you let your deuce sit unused for an extended period of time, and then once again you step on the pedal and find your brakes are deadlined. Bother!

When it happened to me, and I got tired of bleeding the brakes, I tore down the offending axle, and tried to figure out why:

1) the wheel cylinder was brand new... shiny even.
2) the rubber parts were USA made, and were perfect.
3) the boots were USA made, and perfect too.

But in spite of everything looking great, the boots were full of leaked DOT 5.

On inspecting the parts from the bad wheel cylinder, one very big thing became evident immediately: The spring was totally wrong for a brake wheel cylinder. It was square shouldered, and didn't have expander coils on the ends to expand out the piston cups. I have attached a photo to show what I mean.

Here is what I think happened:

As the deuce reached its end-of-line with the active units, the DOD started to get more aggressive in beating down the prices on parts needed to keep the trucks running. Somewhere along the way, they found a vendor of loaded wheel cylinders that was willing to shave a few cents to make a cheaper unit. They substituted common square shouldered springs for the more complicated expander springs that should be in wheel cylinders... probably betting that nobody important would take a loaded wheel cylinder apart and look. I'd say they won the bet.

Why does it matter?

Most of the time it doesn't. If the truck is used regularly, the brakes will stay pumped up, and the DOT5 will keep the piston cup expanded just from regular use. But if the truck sits on the lot for months at a time without use, a different problem starts to show up.

The master cylinder on most deuces has a one-way vent (bobble head) that lets excess air pressure out of the reservoir, but won't let water (or air) back in. This is a good idea if the deuce ever happens to ford 3 feet of water, but otherwise, maybe not so much so.

When air gets hot, it expands, and so it happens in the reservoir of the deuce master cylinder. The pressure caused by this expansion makes the one-way air vent burp the air out. But when it gets cold again, the air contracts, and sucks on the one-way air vent. Because the vent is one-way, the suction cannot be relieved through the vent, so it is reflected through the DOT5, and draws in the wheel cylinders instead.

Wheel cylinders are by design, great at sealing against pressure from the fluid side... the hydraulic pressure pushes the lip on the piston cup tight against the cylinder wall.... But suction is the wrong way. Absent the expander coils, the piston cup lip deflects inward, and air passes into the wheel cylinder. When that happens, the highly compressible air lets your pedal go to the floor... once again.

Any comments?

-Chuck

 

[XanRa]

your a genius my friend

 

[91W350]

I just looked at five deuces with no brakes today. The trend continues... Thanks for the great post. Glen

 

[Bob H]

I'll buy that

 

[hndrsonj]

So here's a question, what does the new star wheel cylinder have. South Korea still uses the Kia M35's there. Is that where the bad ones are coming from?

 

[stumps]

So here's a question, what does the new star wheel cylinder have. South Korea still uses the Kia M35's there. Is that where the bad ones are coming from?

The NewStar wheel cylinder kits that I got from OD Iron have USA rubber parts, and the correct spring. I don't have any of the NewStar loaded wheel cylinders. It would certainly be easy enough for someone that has one to check.

-Chuck

 

[Speddmon]

I deduced the same thing about the air sucking into the wheel cylinders a few months ago...So, I'm thinking of changing my MC cap vent. And IMHO, just as easy of a fix if not easier is to replace the vent on the master cylinder with a piece of plastic tubing and a swivel fitting. Then route the tubing up into the engine compartment. I also put a breather vent on the end of the tubing to keep spiders and such from crawling up in there and plugging up your new vent line (don't ask me how I found that they do things like that).

 

[flyxpl]

previewed two dueces a while back , both brake pedals went to the floor with absolutly no resistance at all .

 

[O.D. Fever]

Both of my dueces have been sitting for a month so I guess I better take a run and pump my brakes.... Too busy playing with the 5 ton.

 

[jasonjc]

I just open up a South Korea wheel cyc it has the bad springs in it,see pic's. I don't think it's a new star though. All the new star stuff I have gotten have labels with the dealers name. This wheel cyc has a label with a NSN and bar code. I have 10-15 new star kits from a few years back and they all have the good springs. And you can see how they would work better.

I also have pic's of old springs taken out of a deuce that I got stright from GL. They all have the bad springs,some of the rubber parts have made in USA some do not. The do nots, don't show any country at all.

 

[hndrsonj]

The good rebuild kits from OD iron are $6.88 ea.

 

[197thhhc]

This is great information. I am dragging a deuce home tomorrow with absolutely no brakes. Now I know where to start looking.

 

[DieselBob]

I just replaced all 6 of my wheel cylinders. All 6 had the boots full of BFS. 2 had started leaking into the drum assembly. All 6 were full of crud. All 6 had the straight cut springs. Never had any problem with low / soft brake pedal even when I picked it up from Jefferson City GL lot. I do agree that these straight cut springs are at least part of the issue.

 

[agtblank]

Sounds like someone active duty needs to blow the whistle. I think there is a reward program for finds like this.

 

[hndrsonj]

Sounds like someone active duty needs to blow the whistle. I think there is a reward program for finds like this.

All the M35A2's are out of active duty. I believe only a couple are still in the Reserve units, and they are supposed to turn them in.

 

[stumps]

Sounds like someone active duty needs to blow the whistle. I think there is a reward program for finds like this.

It is probably way too late to blow that whistle.

First we would have to show that the government was in some way harmed by this "problem" ... that would involve extensive study of repair records, collision reports, product specifications, and of course, interviewing mechanics, contracting officers... very expensive to do.

Then, there is the statute of limitations. Only a finding of intentional fraud would extend beyond the short window of the SOL.

It might not be fraud, it could have been a reasonable decision by some faceless government official to trade some longevity for reduced cost, or it could have been a simple mistake on the part of some shift worker.... Back in the days of yor, square shouldered springs were used with separate little stamped metal expanders. Perhaps some shift, acting through ignorance, simply forgot to include the expanders in a few runs of wheel cylinders, and we were the lucky ones that got them?

I think our best course is to return any defective loaded wheel cylinders we have bought, to the vendor (with explanation), and to check our trucks for this potential problem whenever we do brake work.

-Chuck

 

[cbvet]

Not trying to argue, but the master cylinder shouldn't have a "one way" vent on it. Air has to be able to get in & out.
And I'm not at all sure the shape of the springs means anything. We used an awful lot of the so-called "wrong" springs for a long time.

 

[stumps]

Hi Eric,

You certainly won't get any argument from me about the vent. It is a very wrong idea. I think it fits in the category of: When all you have is a hammer, everything is a nail. They had tons of the little bobble head vents from the axles, T-cases, and transmissions, so when they needed a vent for the master cylinder, that wouldn't let in water, they just used a bobble head. The bobble headed vents are wrong for transmissions, T-cases, and axles too, as they also need two way air passage.... but I digress.

The square spring without an expander is a completely new one for me. I have been turning wrenches since about 1970, and back then square shouldered springs were used almost exclusively, but always with a little stamped sheet metal spreader to expand the rubber piston cup. I have included a picture of the NewStar instruction sheet that came with the wheel cylinder kits, and it definitely shows a square shouldered spring with the separate cup expanders.... Even though the kit came with the expander springs...

I suspect that what happened is the manufacturer of the loaded wheel cylinders got caught between two eras: the old days with the separate sheet metal expanders, and the more recent design with the expander type spring.... Somewhere in the transition, they deleted the expanders, and used up their stock of the old style springs where they should have used the new style expander springs.

Clearly the square shouldered springs, used without the little sheet metal expanders, can work, but not without sacrificing some safety inherent in the design.

-Chuck

 

[televisionman007]

wow ive bought 5 dueces from gl and not one problem other then a set of batteries once

 

[cbvet]

You're right Stumps. I forgot all about those stamped metal "expanders". I've got you beat on "time turning wrenches", but you win on memory.
Eric