Thread: Unusual Brake problem, need advice

Originally Posted by Tank

Replaced my Brake Vacuum booster and master cylinder with a known good working system (Non ABS).
First up had trouble getting the pushrod yoke onto brake pedal arm.
fitted Master cylinder and bled brakes.
Went for a test run, I actually had brakes that would lock up when applied hard, before it was hard pressed to stop at all.
About 2 k's into test and front right and rear left brakes started grabbing, pulled over with smoking brakes and released both front and rear brake bleed nipples and was OK to get back home, no more grabbing.
This morning replaced new booster with old leaving the "new Master cylinder in place.
Same test, same distance (almost to the metre) and same brakes are grabbing again.
Before I pull the master cylinder (the original was leaking out front seal, minutely) and rebuild would like to hear any opinions/advice.
Also noted that alloy spacer between booster and firewall was the same thickness as the new booster, but the master cylinder pushrod in the old booster was adjusted to about 1/8" longer, why the difference, anyone, Regards Frank.

The master cylinder is being kept on, you need to adjust the push rod length to have zero pressure on your master cylinder main piston. With the piston slightly forward the transfer port to the reservoir is being covered.

I figured as much, problem is which way do I adjust, do I shorten or lengthen it.
With the (new) master cylinder and booster, which came from a working system and the same thickness spacer the brake arm push rod was too tight a fit and had trouble getting the clevis pin and joint to line up.
I'm now thinking it might be easier to fit a rebuild kit to the original master cylinder back onto the old booster which is back on, will try and adjust or maybe swap the adjustable pushrod over as well, Regards Frank.

Originally Posted by bee utey

The master cylinder is being kept on, you need to adjust the push rod length to have zero pressure on your master cylinder main piston. With the piston slightly forward the transfer port to the reservoir is being covered.

Originally Posted by bee utey

The master cylinder is being kept on, you need to adjust the push rod length to have zero pressure on your master cylinder main piston. With the piston slightly forward the transfer port to the reservoir is being covered.

If I can't wiggle the rod with my fingers it's too tight. Pat

Pat how do you get to the rod? It is completely enclosed inside the booster with the Master cylinder in place, Regards Frank.

Originally Posted by PAT303

If I can't wiggle the rod with my fingers it's too tight. Pat

Originally Posted by Tank

Pat how do you get to the rod? It is completely enclosed inside the booster with the Master cylinder in place, Regards Frank.

I think the only way to do this is to manually do the measurements with a depth guage and ruller. Would be fiddly but you should be able to do this with booster in situ.


Tom.

Originally Posted by Tank

Pat how do you get to the rod? It is completely enclosed inside the booster with the Master cylinder in place, Regards Frank.

On the clevis to the peddle. Pat

OH! I was talking about the adjustable rod inside the booster which you can only get at with the M/C off, it is the only adjustable part.
Found some info on the adjustment of that rod, it is supposed to be 26.5mm from the tip to the surface of the booster, thanks for the help, I'll let you know the outcome, Regards Frank

Originally Posted by PAT303

On the clevis to the peddle. Pat

Don't take that to the bank Frank,I've tried it and it's yes or no.With the M/C pipes off see how much travel you have with the peddle before it pumps fluid,I worked on a Tojo tray back once that needed the shaft out of the old M/C before it worked,they were the same length even,stuffed how that works. Pat