M35A2 brakes soft on initial startup

[plym49]

Hi, 1970 Kaiser-Willys Deuce. All stock.

On first startup, with air pressure built up and engine idling for five minutes as it should, the brake pedal will about go down to the floor with no brakes. They then pump up and work about as well as any Deuce I remember.

There are no fluid leaks. There are no air leaks. There is no moisture in the air tank. I do not think there is air in the lines. Compressor properly tightened. Ebrake is released. If you've been driving a while and shut it down, the brakes are fine. It's only when it has been sitting - say a day or more.

The only other brake issue is occasional sticky pads, also after sitting. I don't think the two items are related.

What should I be looking for? Air booster/master? Bleed system and go from there?

TIA.

 

[Mullaney]

Hi, 1970 Kaiser-Willys Deuce. All stock.

On first startup, with air pressure built up and engine idling for five minutes as it should, the brake pedal will about go down to the floor with no brakes. They then pump up and work about as well as any Deuce I remember.

There are no fluid leaks. There are no air leaks. There is no moisture in the air tank. I do not think there is air in the lines. Compressor properly tightened. Ebrake is released. If you've been driving a while and shut it down, the brakes are fine. It's only when it has been sitting - say a day or more.

The only other brake issue is occasional sticky pads, also after sitting. I don't think the two items are related.

What should I be looking for? Air booster/master? Bleed system and go from there?

TIA.

.
Is it possible that the shoes need to be adjusted to the drums? There are 4 adjusters on each wheel. There is a hole that you slip a feeler gauge in to and if I remember .015 is a workable number. The bottom two are cams - and you can go the wrong way. The TM's (Technical Manuals) will help with "doing the job right".

The Deuce TMs

M35, M35A1, M35A2, M35A2C, M109A3, exc. Find TM's related to the M35 series trucks in this forum. - No posting of threads

www.steelsoldiers.com

AND, if you want the quickie version of how to adjust the brakes there is a short version attached below.
Thanks to TommyG45 way back in 2008

Also take a look at the adjusters in this post.
It shows the 1 1/8th inch nut (wrench size) on the bottom cams that I mentioned earlier

Proper Wrenches for Seized Brake Adjustment Jam Nut

I ran into a bit of a problem with the 1 1/8 anchor pin jam nuts. I am getting ready to adjust brakes. I have two TM's that mention different ways to loosen and tighten them. One TM says to tighten to 80-110 ft lbs which requires using a socket, while the other TM says to use a box end wrench to...

www.steelsoldiers.com

.

 

[gringeltaube]

What should I be looking for?

Brake shoe return springs rusty & weak? Linings worn down, allowing for excessive shoe travel? Brake hoses old, with possible restriction or swollen, so that fluid will only return very slowly?

 

[plym49]

Brake shoe return springs rusty & weak? Linings worn down, allowing for excessive shoe travel? Brake hoses old, with possible restriction or swollen, so that fluid will only return very slowly?

Good points to check for sticky brakes. But they only stick on a 'cold' start, and that is also when the pedal goes almost all the way to the floor. After that everything is OK. Agree that it's a good idea to adjust the brakes but why do they pump up?

 

[GopherHill]

I second the above advice. Look at the -10 manual and perform a major brake adjustment. Check the brake flexible hoses carefully. If cracked or dry rotted , replace them.

 

[plym49]

I second the above advice. Look at the -10 manual and perform a major brake adjustment. Check the brake flexible hoses carefully. If cracked or dry rotted , replace them.

Understood. However I am not understanding how that would make the brake pedal go to the floor on the first stop, and not afterwards. Because if the brakes are not adjusted then aren't they so all the time? Apologies if I am missing something.

 

[cattlerepairman]

I would add "air in the lines" to the list. Probably the second thing I would do after verifying brake adjustment is to simply re-bleed the brakes (including air pack!) and then re-assess. It is a long truck with loooong brake lines and air bubbles can hide away for a long time.

 

[Mullaney]

Understood. However I am not understanding how that would make the brake pedal go to the floor on the first stop, and not afterwards. Because if the brakes are not adjusted then aren't they so all the time? Apologies if I am missing something.

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I am kinda of the opinion that "all of the above" could have a lot to do with the peddle "pumping up" with time. Air bubbles could get chased further down the line, the shoe springs could be getting weak over the years (slow shoe return), a little rust on the pivot cams down on the bottom of the drums would cause a slower than normal return on the shoe movement too. A bunch of little things that might total up to the brake peddle going almost to the floor on the first press.

All of us are guessing, but if you wanted to start with adjusting the front axle shoes first you will know something. AND you only have to remove 2 tires rather than 8. When you check those first two - If the shoes measure out at .015 in all four positions - we need to talk some more before you do the other 4 drums (two axles).

Badly worn drums with a lip might be difficult to measure too.
You almost need to pull at least one drum to see what is going on inside the drum...

 

[davidb56]

my Guess would be air in the line, then master cylinder needing rebuilt/replaced .

 

[plym49]

Thank you for the replies so far. Really good advice. I will need for the weather to break a bit until I can get into it. Will keep the thread updated with what I find.

 

[Mullaney]

Thank you for the replies so far. Really good advice. I will need for the weather to break a bit until I can get into it. Will keep the thread updated with what I find.

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Good Deal!
Looking forward to what you find.
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