Another afternoon awash with brake fluid today. Kev came up from the South Coast again & brought the stripped, checked, lubricated & rebuilt front calipers with him. We fitted them, bled them, bled them again. Still not right. Bugger.
When the brake pedal's pushed, the caliper pistons are moving freely, but the caliper body's actually flexing the mounting bracket. That ain't right.
The truck's sat on axle stands with all 4 wheels off the ground, so we checked how far the pedal had to travel to apply the brakes. Fronts should lock up first. Yup, that's good. About an inch of pedal travel & very little effort required. Great. Now the backs. Spin the rear drum, push the pedal ...nothing. Huh? Push harder. Still nothing. Push the pedal almost to the floor & they finally lock up. What's going on?
We adjusted the brake shoes to reduce their travel inside the drum. No difference.
Seems there's no fluid getting to the drums. The brake cylinders aren't moving when they should. Kev confirmed this by switching the ignition on & pushing the pedal. There should be over 500 pounds of pressure in there. The brake light switch only needs 15 pounds to work, but the lights aren't coming on till the pedal's almost at full travel. Following a process of elimination, either there's a huge air-lock in the pipes somewhere, or the master cylinder isn't pumping fluid to the rear. We've pressure bled & manually bled everything a million times today & we're sure there's no air in there.
So it has to be the master cylinder. It's a dual circuit cylinder, so has 2 pistons inside, one behind the other. When you press the pedal, the first piston is moved, supplying fluid to the front brakes. That's followed by the second piston, supplying the rears. It looks like the second piston's stuck at the far end of the cylinder, so no fluid's going to the back end. The front caliper mounts are flexing because we're practically standing on the pedal, so they're getting the full force of the pressure that should be split between fronts & rears.
We called it a day at that point, but Kev's coming back tomorrow & is confident we're on the right track now. Gawd I hope so!
I should say a huge Thank you to Chris, ("Poprodder"), by the way, who packaged up & posted his Triumph Spitfire front calipers to us. They arrived safely this morning, all the way from Norfolk -22 quid postage! They're our Plan B, but with luck, we won't need them. Thanks Chris.
3 days left till the test!
