The Stovebolt Site Forums The Parking Lot Big Bolts Brake question 55 2nd 6500

Last summer I purchased a 55 2nd 6500 dump and it finally arrived last fall. Upon receiving I went through the entire brake system, pulled all wheels and replaced master cyl. I bench bled the MC and followed the bleeding process for Hydro vac and wheel cyl. Brakes worked great so I drove it about 2 miles to my brothers building and parked it. This past Sunday was the first time I've had a chance to take it out since last fall and when I got in the brakes went to the floor. I opened the MC and it was empty. I looked under the truck and at each wheel but there was no fluid anywhere. I pulled each wheel and checked for fluid in the drums, there was none. I then pulled the plug in the Hydro vac and there was no fluid there.
I filled the MC back up with fluid and began the bleeding process. I was able to get some brake back but ran out of time to do the job completely. Where could the fluid have gone? Could I still have had enough air in the lines that the fluid in the MC gradually worked its way into those pockets of air?
Thanks in advance for your help.
Brian M
55 6500
59 1/2 ton Napco
59 3/4 ton Napco.

Perhaps a leaking hydrovac and the brake fluid was consumed by the engine? I generally understand how the hydrovac works but not sure if that's a possible failure mode?

Grigg

Grigg,
I was wondering about that too. Since I haven't run/driven it that much I don't know much about the motor and I certainly don't know much about the Hydro vac system. Hopefully someone can help. When I started it and ran it for a little while it seemed to smoke an awful lot. When I first had it delivered and finally got it running, it smoked because of the crap that was stashed in the exhaust pipe. Acorns were shooting out when I reved the engine and it smelled like firewood burning. It seemed to lessen the more I ran it. The truck was used on a farm in Sacramento and only has 20,000 miles on it. I guess the top end probably could use a rebuild. The other bad thing is that to take it to someone to repair I have to go down my brothers steep, 1/2 mile driveway with brakes I don't trust.
Looking for help.

Hy BrianM, there should be a drain plug in the steel cover of the Hydrovac, remove that and see if you find any brake fluid, hope that helps.

Pulled Hydro vac plug again and no fluid. Could it be sucked into motor and burned? I don't fully understand system.
Brian M

The HydroVAC works on engine/manifold vacuum, theoretically the brake fluid if leaking internally might be sucked up and ingested by the engine.. Again not sure if that's actually going to happen, worth looking into though. Check your service manual for a cutaway picture of a hydrovac.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0530.htm

Look here too
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0536.htm


Grigg

If you're checking the Hydrovac for brake fluid by removing the small plug on the back of the piston can you're looking on the wrong side of the piston. That side is the fresh air side and the vacuum side is between the piston and the hydraulic cylinder so the fluid may be trapped and the piston seal is keeping it out of the fresh air side. If the vacuum side has fluid in it the engine will smoke as it sucks it up the vacuum hose. Remove the hose at the engine and see if it's wet on the inside.

Mike B

Thanks Mike. I assume if the hose is wet the Hydro Vac needs rebuilt? If so what cost am I looking at?
Brian M

I removed the vacuum hose to the intake manifold and the one to the valve cover. It doesn't appear to be any fluid in the hoses. I plan on replacing the hoses, since they apparently are original, and see that the hoses have a plastic sleeve or lining. Is this hose something that needs to be a specialty item?

Finally removed Hydrovac from truck. When I removed the bottom vacuum line that runs up to valve on firewall and then into intake, a considerable amount of fluid ran out of hydrovac. I then tried to blow into that line and I could easily blow through it. When I tried sucking on line there was nothing. I assume that means the valve is operating correctly. Two weeks ago I found someone who can rebuild the unit here in Pittsburgh and he told me to use that method to check valve.
I guess that explains the excessive smoke. The cost to rebuild is $340.00 I assume that's about right? Brian M

Sounds reasonable.
Compare to the exchange or rebuild listed in some of the usuall suppliers like Jim Carters.

Glad you figured out the issue.

Grigg

Check with NAPA, they might be cheaper.

Mike B

Finally installed my rebuilt Hydro Vac and vacuum lines. Had Midwest Power Products do the work. With shipping and a new main return spring the cost came to 342.00. After a few rounds of bleeding process the brakes are good and firm. Changed the oil, started the truck and the smoke has all disappeared.
Once again, thanks for the help.
Brian M
55 - 6500
59 - 1/2 ton Napco
59 - 3/4 ton Napco

Yep, Midwest is sort of a one-man operation. He sold me a NEW Hydro for about the same price. (didn't even know you could get new ones, but the one he sent definately was.)
He does the rebuilding for the guys in Pittsburg, then in turn everyone gets them from Cardone. But we cannot buy from them unless you have a parts buisness.
It was for my 57 GMC 370. Got great brakes now, after new lines, all wheel cyls. and a MC rebuild. Used the same shoes, since they had about 1/2" left on them. Just figure $1000 to have brakes on these Big Bolts.