We have an F600 dump truck with duals. It runs fine except for the brakes. The brake pedal will not move at all -- only three wheels get a dribble of brake fluid; one of the front wheels gets no fluid at all. Someone told us it was an airlock in the brake fluid. Anyway, if there is someone out there familiar with this braking system and willing to talk about it by phone with my husband, please contact me. Or, if not that, I'll try to type out the messages for him. Obviously I know next to nothing about this (but then neither have the three brake places we've tried). Thanks

 

 

[updated:LAST EDITED ON 13-Jun-02 AT 11:09 PM (EST)]I could be wrong but I don't think an air lock would cause the brake peddle to be stuck. I'd be suspicious of the master cylindar. Might be time to rebuild. You could always disconnect the break lines at all four corners and see what happens when you pump the peddle but then you'll have to bleed the system. I mite be a clogged line. But the truck would stop sort of with three brakes. I'd start with a thorough clean up including blowing out the lines and closely inspecting the master and the linkage. But the more I think about it 3 dribbles and a nothing makes me real suspicios of the master cyclindar. Good luck

Maybe you should post this message over at the ATHS site. One of the old time big truckers mite be able to help.

 

thanks for taking the time to help. I didn't know where to post but I will add a plea on the big truck site. He did last weekend replace the master cylinder with no change. A couple of years ago he replaced two wheel cylinders. Had to pump the brakes but they eventually worked until this latest twist. Bleeding never helped. If I stand on the brake pedal with both feet, it goes down about 1/8" inch

 

Check the linkage. If ok, disconnect the brake lines at the master cylinder and see what happens. The only reason why the peddle would not depress normally under normal operation is that the lines are full and the wheel cylinders (all of them) are stuck open or closed and the fluid is not moving. Probably a good time to put the truck up on jack stands (heavy duty jack stands) pull the wheels and drums and and go thru the whole system. Also, that vehicle should have a booster on the brake system, either vacuum or hydraulic, and you might want to inspect that as well.

By the way, the reason you had to pump the brakes was because the system needed bleeding. Good luck

 

bleeding never helped. It has a vacuum booster so have wondered whether the pumping action somehow builds up the vacuum. Thanks for the info. I'll pass it on to my resident mechanic (who is actually a carpenter who hates doing mechanical work). He's only working on it because the three brake places we've taken it to have just rolled their eyes and said no thanks.

 

Maybe the booster is toast; it'll have some kind of hydraulic cylinder in it, and if that has sat for a long time it could have seized or corroded. Or the vacuum boost thingy could have failed somehow.

If the brake lines on the truck are original, it's a really really good idea to replace them. I can tell you it is not a good feeling at all when a brake line springs a leak because of rust. Especially since it only bursts when you're stomping on the brake hard for a good reason.

 

How right you are! We finally pushed a wire up the connector hose and out came bits of rubber and lots of rust. So, changed all the hoses, put in new brake fluid, bled it and brakes worked but the part that connects to the vacuum assist is now leaking (someone in the past cobbled it up with some bad welds) so when we replace that we should be ready to roll.