C-65 Brakes

I have a C-65 grain truck with hydraulic brakes. I'm losing brake fluid, but I can't find any leaks in the lines. I can pump up the brake three times with the master cylinder full and have brakes. The only thing I can think of is a wheel cylinder is leaking. Are C-60 an C-65 wheel cylinder the same. Local parts store takes a month of sundays to look something up and can't find a lot for a C-65. Is there anything I'm over looking in the brake system. Thanks for the input Andy

If it has power brakes with a vacuum pack it could be a bad master cylinder and the brake fluid is being sucked into the engine and burn off. I have sen that happen in both cars and trucks

(quoted from post at 08:48:32 10/10/19) I have a C-65 grain truck with hydraulic brakes. I'm losing brake fluid, but I can't find any leaks in the lines. I can pump up the brake three times with the master cylinder full and have brakes. The only thing I can think of is a wheel cylinder is leaking. Are C-60 an C-65 wheel cylinder the same. Local parts store takes a month of sundays to look something up and can't find a lot for a C-65. Is there anything I'm over looking in the brake system. Thanks for the input Andy

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First off, if you need to pump the brakes 3 times to get brakes, first bleed EVERYTHING, then set up all the brakes, 'cause it's certainly unsafe to drive that way!

If you have a wheel cylinder leaking, the brake backing plate on that wheel will be wet and/or stained from the leaked fluid.

If no sign of that and the truck has a frame-mounted brake booster ("Hydrovac"), likely it's leaking internally and the brake fluid is being sucked into the engine intake manifold and burned.

If you have been working with it lately and it's been losing fluid that way, there should be signs of brake fluid in the vacuum hose from the hydrovac to the intake manifold. If you need to replace it, and are lucky, there will be a steel tag dangling from the bolt in the big clamp that holds the diaphragm area together, this is the number you need to order one.

If you need to deal with a wheel cylinder the only way to figure out what you need is to get it apart and check for casting numbers on the cylinder and measure it's bore diameter, as even cylinders with the same casting numbers may have different bore sizes.

Not only is it likely that wheel cylinders are different between C60 and C65, there are many, many possible differences within the same series, depending upon what axles and brakes were originally "spec'ed" on your specific truck.

GOOD LUCK, and hope you have a big checkbook, getting into the brakes on an old medium-duty truck is typically NOT cheap!

Are you talking about the Hydro Vac brake booster under the floor board?

Yes if it has a vacuum hose that goes to the intake the brake fluid can be sucked into the intake and burned off in the engine

Thanks for all the help But not all wheel cylinders leave stains or will be wet. Just change the back ones on my little truck

Our fire department had one of these trucks. Same problems. It was/is leaking into the vacuum system and burning out through the engine.

Fixing it is going to be pricey and will depend on how much you really like this one. We decided to sell the truck and upgrade. It was a 1978 model.

We found that rebuilt units were expensive and not all that reliable.

3 pumps the brakes are out of adjustment
missing fluid? If not wet at a backside of a wheel
then master or booster leaking

master can leak around firewall and booster into engine

Vander Haags is on the internet, several locations in Iowa, they have rebuilt everything for those older trucks, last hydrovac I bought from them a couple of years ago was less than $200 exchange and shipping.

They was not installing the kit for the vacuum to vent the crankcase gasses off and it was eating the diaphragm in the booster,, old gasoline did not bother them much, something in "todays" fuels,, eats them seen it more times than I think when they sell you a rebuilt booster but not the kit,,

If the booster is leaking into the engine the vacuum hose will be wet with B fluid inside!! Jim

Whatever parts you buy, look for a number specific to the part.

As said, many different possibilities depending on the axle option. Everything must match internally, not just if it will bolt on.

The booster should have a metal tag, the master and wheel cylinders will have casting numbers.

My C-70 has 2 cylinders per wheel. After sitting for a year, my master cylinder does go down.

I bought a 75 C65 grain truck a few years ago and had to go through the brakes. I replaced the master cylinder, hydrovac unit under the cab and both wheel cylinders in the left front and right rear wheels. I got all my parts from Napa but you might find some online if you know part numbers.

Not only do you have to bleed it well starting at the master cylinder, then at the hydro unit then at each wheel, you also need to jack up each wheel and turn the little star adjusters to get the shoes as close as you can to the drums w/o dragging. This reduces the amount of fluid the master cylinder has to push to get braking action. I have brakes on the first push but it's close to the floor even after fixing and adjusting. 2nd pump I have a full firm pedal.

The standard master cylinder has a 1.5" piston if I remember right. I remember looking around on Rock Auto and finding an optional master cylinder with a 1.75" piston that looked like it would fit. That larger piston would move more fluid when pushed the pedal and might help eliminate some of the pumping.

I also have a 74 C60 and it doesn't have the same mushy pedal issue...go figure...I just think think there is enough give in all the tolerences in the system that it takes a LOT of adjustment to get really good brakes on these old trucks...some harder to get than others.

(quoted from post at 13:55:33 10/10/19) Thanks for all the help [b:a4b0e05e95]But not all wheel cylinders leave stains or will be wet. [/b:a4b0e05e95]Just change the back ones on my little truck

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If they are leaking they will be.

GM made some really good wagons. Put a tongue in it and pull with the tractor.