Hi gang

So been cruising about in my bus which is now looking pretty good. Did a run over the weekend which was about 220 miles. Got there all good then on the way back the brakes decided to seize up. It's totally weird as I had this problem before and assumed it was the old single circuit master cylinder so I replaced it about a month ago with a brand new dual circuit system and replaced some of the lines. She is running all drum brakes with a straigh axle kit from t2d on the rear. All the brakes locked on and the pedal locks in the upper most position. The pedal can be depressed ever so slightly like a few mm but that's only through a lot of pressing. I went round each wheel cylinder and released the pressure and All was back to normal.

Does anyone have any clues what could be up? I could understand if it was either front or rear but it's all 4. The master cyl is brand new and It wasn't catching on somthing as when I released the pressure from all the cylinders the pedal worked as normal and has been fine for the rest of the 90 mile journey home.

I'm puzzled!

Is the pushrod adjusted correctly at the master cylinder,correct amount of freeplay?

^^^^ bet it isn't.

Ahh

Quite possibly not. Where should the free play be? Between the plunger and the piston?

What should it be set to..?

Thank you!

Yip ,can't remember the exact figure,but 1-2mm is a safe bet.

Just to explain why this happens, dual circuit master cylinders have a couple of small ports in front of the pistons, which have to be uncovered to release the pressure in the system after braking. If there is no free play (2mm is OK) the ports remain covered when the pedal returns so residual pressure stays in the system and the brakes lock up. I fixed exactly this problem on a friend's Kramer front loader/digger after some 'engineers' had replaced the M/C and forgot to readjust the pushrod. Bit scary when brakes lock up on a 3 tonne machine carrying a tonne of sand down a muddy slope