1983 M35A2C Brake Fluid Disappears

[ballencd]

My truck has recently started leaking brake fluid but I can't find out where it is coming from. I had a very small leak for a few years but only enough to need more fluid every year or so. For those who are going to yell SAFETY!!!!......I use it in my yard only and I have never had any trouble stopping. Just reservoir would go partial low and I would fill it. I don't see any fluid leaking anywhere. Lately I find that it goes empty after a 5-10 days of use....I only use it to move dirt about 300' and hardly need the brake anyway but do like to be sure I can stop.

When I fill the reservoir the brakes harden up quickly after maybe 20 pumps and seem to work fine. No puddles or wet spots under the truck, at wheels or on axles...???

Any idea where to start looking?

Thanks

 

[BEASTMASTER]

my 5 ton has had the disappearing brake fluid since I bought it 17 yrs. ago. I put some in it every couple weeks to keep it from running dry. and I check it before I take it for the usual coffee run on sat and sun. never did find the problem and got tired of looking.

 

[98G]

Most likely leaking internally into the air pack.

 

[ballencd]

Beastmaster: I like your attitude. Ive ignored mine for a long time but it is now needing a fix as it goes to the floor fairly quickly and i'm needing to move some dirt.

98G: If into the air pack where is the fluid going? Just stays in there? Any way to verify this is where it is? I have never had any trouble with the brakes (other then the missing fluid) and have had it for about 20-21 years. Seems like it would fill it up and stop leaking after awhile? : )

 

[m38inmaine]

If it is still vented to the air cleaner check your air cleaner, if I recall if the air pack is bad it will vent fluid.

 

[ballencd]

I will look and see. The truck has not been modified other then bobbing it and adding a dump kit so it will probably still be connected to the air cleaner if that was the way it was built. If vented there, I would guess, it could get sucked into the engine and burn, without me knowing about it. Thanks for the direction.

 

[exhogflyer]

Only a few places it can go, if it’s a line or wheel cylinder it’s visible. Master cylinder or Airpac is my guess .

 

[ballencd]

I'm thinking airpac since I don't see any fluid. I'm not really sure where the airspace is or what it does but I will figure it out. If it was at the MC it would stay full or leak somewhere and be visible, would it not? The brakes work fine until I am out of fluid and when I fill it back up and pump it some they come back with no apparent need to bleed them.

Hopefully I will have some time to look at it soon. Kids and wife are about done with school and summer comes immediately after that. They expect to go on some sort of vacation too! And they keep wanting to eat.

 

[frank8003]

Not modified?
" The truck has not been modified other then bobbing it and adding a dump kit"

 

[ballencd]

Not modified that much I guess. It's a lot easier to steer this way.

 

[Floridianson]

If it was at the MC it would stay full or leak somewhere and be visible, would it not?


The master cylinder boot can hold a lot of fluid. I check my master boot sometimes by sticking a small flat blade screw driver under the lip on the rod end of the boot and pull down just a bit. If the master is leaking you can get a face full so watch you splash zone. If that's dry then air pack. If the wheel cylinders leak they drip on the inside of the backing plate / drum.

 

[98G]

Beastmaster: I like your attitude. Ive ignored mine for a long time but it is now needing a fix as it goes to the floor fairly quickly and i'm needing to move some dirt.

98G: If into the air pack where is the fluid going? Just stays in there? Any way to verify this is where it is? I have never had any trouble with the brakes (other then the missing fluid) and have had it for about 20-21 years. Seems like it would fill it up and stop leaking after awhile? : )

Air cleaner or under the hood on the right side just in front of the firewall.

 

[ballencd]

OK so I did find a leak in a brake line and replaced it and have had no trouble since. That was a few years ago.