The Stovebolt Site Forums The Parking Lot Big Bolts Brake Pedal Travel

Well, I've finally got the brakes finished at long last on my '57 6400. I'm not sure that I've got everything as it should be, though. The pedal has a lot of travel. It will go down to within 4" of the floor. The hydraulics are in perfect condition and they are well bled. When it does develop pressure, the pedal is nice and firm and doesn't drift down. It will have a higher pedal on the second stroke, so that tells me that it's taking up mechanical slack some place. I've carefully adjusted all the shoes per the manual and I really don't think I can snug them up any more without causing a serious drag. I've also got the free travel on the master set at about a 1/4". Is there anything I'm missing or is this typical on these old trucks? I really don't have any point of reference as the brakes never did work right when I got the truck. I haven't driven it or had it running yet either, so things may change a bit once the HydroVac comes into play. With 4 big 'ole wheel cylinders out back and two little ones in the front, I guess it would take some piston travel in that one little master to supply them all with fluid. The manual says it's time for adjustment when the pedal goes to within 2" of the floor, so maybe it's just me. I'm probably just spoiled by the high pedal on the more modern cars. Any thoughts?

the hydrovac will make a definite difference from regular brakes, hard as a rock, but if you can pump it up there's air in the system, "mechanical slack" will affect the travel on the first push [lower pedal] ... if the hydrovac is hooked up, have you bled that? could be air in that part of the system .... all those wheel cylinders are fulla fluid all the time, all the master has to do is move them a quarter inch or so

Bill

I should have been clearer.


This is what I'm referring to. The pedal is hard on the first push, but it will go down to within 4" of the floor. On the second push, it will be considerably higher. More than two pushes doesn't make any more difference. That's what leads me to believe that the excessive travel is from the hydraulic system taking up mechanical slack. The hydrovac is in fact hooked up and has just been rebuilt. I did bleed it per the manual (twice) and I'm pretty sure that there's no air in it or anywhere else in the system. I dunno. Maybe I just need to get a fire lit in the powerplant again and drive her around a bit. Maybe once everything seats in I can get things adjusted a little better.

Once the Hydrovac gets into the act, you should have plenty of pedal. Right now, you've got about the same situation as any other power brake without vacuum assist, having to push the fluid through the system with no boost. The hydrovac is actually a second master cylinder operated by the vacuum chamber, which uses the main master cylinder as a trigger unit. In case of a loss of vacuum, you have to push both master cylinders with foot pressure, which will lower the pedal considerably. Get it running, and I think you'll be pleasantly surprised with the difference in pedal height.
Jerry