M-817 Brake fluid

[PeteNora]

Need some advice on my M-817 brake fluid. I am in the process of planning to drive this truck to my camp once the snow goes. I know little about it and I can not get any answers from the seller. I have not tried the brakes. I was told they worked. The red flag to me was the quart bottle of dot 3 in the truck cab about 3/4's of it gone. I can only speculate that it could of been put in this trucks system. Reading the TM'S here I believe these trucks were all converted to dot 5 silicone based fluid. I don't know this for a fact am just asking for advice on what I should do to avoid problems. So I would appreciate what the guru's here think on my situation.

 

[porkysplace]

The military uses DOT 5 , you probably need to drain (or suck some out of the MC) some brake fluid and test it


[h=1]Brake fluid -how to tell which kind you have DOT 3 or DOT 5[/h]

 

[Floridianson]

The red flag to me was the quart bottle of dot 3 in the truck cab about 3/4's of it gone. I can only speculate that it could of been put in this trucks system.

Ruh-Roh

 

[dmetalmiki]

Pull some brake fluid from the master cylinder with an Eye dropper or such, And then squeeze some drops into a shallow dish or saucer of water, If it mixes it is hygroscopic And is a dot three four or 5.1.
If it does not mix it will be a hydrophobic silicone brake fluid which is DOT.5. Fluid.
If it appears to be discoloured multicoloured or messy, It has been (Wrongly!) Mixed.
Now you will have to decide whether to go with the expensive Silicone DOT.5 or the cheaper (DOT 3 - 4 or 5.1). brake fluid.
BUT, You WILL have to completely flush the brake system out in that case.
With either option (And before driving any distance) CHECK the braking (And system) of the truck first.
I have always run my trucks on DOT-4 Brake fluid.

 

[PeteNora]

Thanks for the advice. When I go Saturday I will pull a sample, test it and decide what to put in the system. I have both dot 5 and dot 3 fluid to take. I have to drive it about 60 miles and want to be somewhat safe. The good side is I only need to run maybe 5 miles of highway and can take the back roads to camp. Once there I can flush the system. Can it be fluid flushed till its one fluid coming out or does it need to be chemically flushed? I think I can borrow a friends pressure bleeder. In hind sight I think I should of passed on this truck.

 

[porkysplace]

Thanks for the advice. When I go Saturday I will pull a sample, test it and decide what to put in the system. I have both dot 5 and dot 3 fluid to take. I have to drive it about 60 miles and want to be somewhat safe. The good side is I only need to run maybe 5 miles of highway and can take the back roads to camp. Once there I can flush the system. Can it be fluid flushed till its one fluid coming out or does it need to be chemically flushed? I think I can borrow a friends pressure bleeder. In hind sight I think I should of passed on this truck.

You can also build a power bleeder fairly cheap .
[h=1]Deuce Power Bleeder R4x4 Style[/h]

 

[PeteNora]

You can also build a power bleeder fairly cheap .
Deuce Power Bleeder R4x4 Style

That's an idea. I believe the master cap has a breather vent. Does the vent screw into the cap? If so what pipe thread would it be?

 

[98G]

These trucks have single circuit air over hydraulic brakes. This means one broken line or one good leak and you have no brakes. Frequently without warning...

Stomp on the brakes repeatedly in the parking lot to stress test the lines before you start the drive home. Far better to have the line rupture at low speed controlled conditions than when you really need them. Subsequently treat every stop as if the brake pedal may suddenly go to the floor.

 

[Floridianson]

Could I ask you what your plans are for the truck? Stays on you property or on road use. The only trucks I have ever bought were from the government and had about 30 of them. Now every one that I serviced I found that the axles needed service. That is new seals and bearing repacked. Then when in there replace, check or clean out the wheel cylinders real well. That way you know what you have got axle wise. Then comes the air pack and master. I made the mistake once of doing a axle service once on a Deuce and wheel cylinders were not leaking. Put on a new master cylinder and popped a wheel cylinder. That bright side I have a wheel dolly and the bearings are fresh repack. So pull wheels/hubs and just replace wheel cylinders.

 

[DeucesWild11]

These trucks have single circuit air over hydraulic brakes. This means one broken line or one good leak and you have no brakes. Frequently without warning...

Stomp on the brakes repeatedly in the parking lot to stress test the lines before you start the drive home. Far better to have the line rupture at low speed controlled conditions than when you really need them. Subsequently treat every stop as if the brake pedal may suddenly go to the floor.

I did that unintentionally trying to get something to slide out of my bed, brakeline hose broke and I instantly had NO BRAKES!! I had to cut the engine out to stop it, thank god I was in my driveway. I think I'm going to work that into my SOP every few months or so. On another note I use Dot 3 and bleed out about once a year to get any water out of the fluid, it's cheap enough to do so.

 

[PeteNora]

The guy that sold me the truck added dot 5 and said he had a brake pedal. I went up there today and the master was about 1/2 full. Visual inspection shows the master has a slight leak where the push rod goes in. The truck did start and I do have brakes. When I apply pressure there is an air leak underneath and the air pressure will drop off fairly fast. I assume it is from the air slave unit. It wors good enough to get it to camp. I have to ask is there any easy fixes here? I was by myself so I could not locate the leak and with the rain and mud today was not a good day to crawl underneath.