Brake problems

Got a problem with my M35A2 brakes. After sitting for a long while, I started getting it ready for the upcoming parades. It started great, runs great and has no brakes. The pedal went to the floor without resistance. I checked the reservoir, no fluid. Added fluid then started bleeding the system. As an aside, I only use DOT 5 in my trucks. First wheel, yellow fluid came out of the fitting with a bunch of air. Not very much came out. Not good! Why is there (presumably) DOT 3 in my system?!?! Okay, take a deep breath and try another wheel. Same thing, yellow fluid, not very much and full of air. The master cylinder fluid level did not drop. I’ve had this truck for 10 plus years and never had a broblem with my brakes.
I can only assume at this stage there’s something messed up between the reservoir/master cylinder. Can any of the M35 Gurus recommend which, where, what I should do next?

Dot 5 can turn yellow with age. Did you bleed up by the air pack before going to the wheel?

Elk1111 said:

Dot 5 can turn yellow with age. Did you bleed up by the air pack before going to the wheel?

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No, that’s what I’m doing next. Usually (every time I’ve bled truck brakes) I start at the cylinders. I’ve never seen this before. Best bet would be moving to the air pack before I do anything else?

jeffhuey1n said:

No, that’s what I’m doing next. Usually (every time I’ve bled truck brakes) I start at the cylinders. I’ve never seen this before. Best bet would be moving to the air pack before I do anything else?

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You need to bleed the air pack to master cylinder first then move to the wheel cylinders.

Your fluid went somewhere look around and you should see where it is leaking, if you get it bleed out hold the pedal down hard if it creeps slowly down you have a leak it is unsafe to drive!!!
Big Tom

Welder1 said:

You need to bleed the air pack to master cylinder first then move to the wheel cylinders.

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Thank you. I’ve had these trucks for 10+ years and this is a first for me.

It may not be a wheel cyl. It could be the master bleeding into the airpac

You didn’t see any brake fluid leaks anywhere?

Bleed the master cylinder then the hydrovac. After that, go to the farthest wheel cylinder away then work your way back to the next farthest, then the next farthest, and finally the closest. You may need to repeat to fet

Tip: do not pump the brakes more than twice prior to bleeding. Pumping up brakes or vigorously pumping them caused air bubbles to form and those bubbles will eventually group into a big bubble.

Brake bleeders work pretty good but I’m old fashioned and do it the messy way.

It would not hurt to check the brake shoe adjustment on each wheel. I think the shoe to drum gap is 0.010 and 0.020.

Thanks to all, I was able to get a handle on this problem. The air pack was full of air. Once I got it purged, I started getting some resistance on the brake pedal. Now it’s just matter of purging the rest of the wheel cylinders.
Not sure where the brake fluid went. There’s some oil leakage but it doesn’t appear to be coming from the brake lines. None of the wheel cylinders show any leakage either. A short test drive around my property went well. Brakes work as advertised and no visual fluid loss.
Hopefully it’ll behave until Cheyenne Frontier Days is over.

jeffhuey1n said:

Thanks to all, I was able to get a handle on this problem. The air pack was full of air. Once I got it purged, I started getting some resistance on the brake pedal. Now it’s just matter of purging the rest of the wheel cylinders.
Not sure where the brake fluid went. There’s some oil leakage but it doesn’t appear to be coming from the brake lines. None of the wheel cylinders show any leakage either. A short test drive around my property went well. Brakes work as advertised and no visual fluid loss.
Hopefully it’ll behave until Cheyenne Frontier Days is over.

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Check your brake booster vent line. If your leaking fluid from the booster that is the first place to look.

rustystud said:

Check your brake booster vent line. If your leaking fluid from the booster that is the first place to look.

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Okay, will do. So far brakes are working as advertised but I give Murphy plenty of leeway.

rustystud said:

Check your brake booster vent line. If your leaking fluid from the booster that is the first place to look.

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Where is the vent line?

SETOYOTA said:

Where is the vent line?

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.
Most of the time the vent is on the top of all three axles. About the size of one of those "fat pencils" that we used in first and second grade (about the size of your little finger). Maybe 3/4" tall - normally on the wide side of a Deuce axle. If you see a rubber line coming up toward to top of the truck (on the axle) - somebody may have created a deep water vent.

@SETOYOTA was asking about the brake booster vent line but thank you.

Duh Huh is about all I can say.
(Tim Mullaney)

SETOYOTA said:

Where is the vent line?

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Usually the brake booster vent line is on the firewall on the left (correction right) side, but you never know anymore. Who knows who did what with it. So I would trace it from the booster itself.
Had to correct my mistake. I wasn't thinking from the driver's seat which all directions come from in a vehicle.

Mullaney said:

.
Most of the time the vent is on the top of all three axles. About the size of one of those "fat pencils" that we used in first and second grade (about the size of your little finger). Maybe 3/4" tall - normally on the wide side of a Deuce axle. If you see a rubber line coming up toward to top of the truck (on the axle) - somebody may have created a deep water vent.

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I was asking about the brake booster vent line but thank you