ok so on friday i put new s13 brakes on the front of my ute and also a new 3/4 master cylinder. Yesterday i was driving along and they locked up and the pedal went hard right at the top of the stroke ... So i pulled them apart and pulled the anti-squeal shims out and it was fine ... But now the pedal is starting to get harder higher in the stroke and i'm worried its going to happen again ... Any ideas as to what the problem is?

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Adelaide monthly meet

Is the piston releasing completely? Can you adjust the push rod so that there is a slight gap between it and the piston when the pedal is released? It sounds like it's not releasing completely, and letting all the fluid out of the M/C. I had something similar on a clutch cylinder, and that was the problem. Also had the same on a brake M/cyl but that was an old M/C and the springs inside were out of whack, so that both pistons weren't uncovering the fluid return hole when the brakes were released.

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They have drifting in forests now?
What will they think of next?

there is no adjustment on the small bar that goes into the back of the master cyl, btw i am not running a booster

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Adelaide monthly meet

Does not matter about a booster. As the other guy said the piston in the master must fully return. If its not you either need to shorten the push rod or go to your local brake guru who should have a bucket of old rods that are adjustable. you need at least 10mm freeplay on your pedal. Also if the piston does not return by itself you need to remedy that.

well ive had a think about it and when you put the rod into the mc there is a washer that sits there as well so maybe that is also the problem along with the dome on the end of the rod being too large so looks like i get to pull the bastard apart tomorrow which means bleed all the brakes again grrrrr

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Adelaide monthly meet

BAH! so i pulled it out and modified the dome and got an adjustable rod and its still friken happening!!! if it was the m/c piston wouldnt i have a problem when i go to bleed the brakes because it wouldnt take any new fluid and wouldnt flow out of the bleeder valve on the caliper?

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Adelaide monthly meet

if the master cylinder you are using was meant for drum brakes on the front circuit you will need to remove the residual pressure valve (it is a small rubber bung with a spring attached) that is found beneath the large nut into which you screw the brake pipe for the front circuit. the problem you describe is usually caused by this valve retaining pressure in the lines that is necessary to keep shoes close to the drum on drum brakes but upsets discs as you have described.

even if the master cylinder was not meant for drums it is worth a check

yea well i gotta pull it apart again tomorrow grrr ... i might put my old M/c on just to see if thats the problem

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Adelaide monthly meet

Haha, welcome to my saturday afternoon tow truck ride in my 1200

Sounds like exactly the same problem I am currently facing!

My car is a 1200 coupe with a completely standard braking system (Std disk brake front end, drums rear, no booster).

My original tockico master cyl was leaking so I bought a shiny new "Protek" brand one and poped it in the car, bled the brakes for hours on end and was then pretty pleased with myself, until I got to take it for a reasonably long drive after getting it back on the road (approx 20mins).

Cruising down the road, had used the brakes about 2 mins earlier and they were fine, just touched the brake pedal and it was then rock hard with no brakes, and front brakes started grabbing!

Tried limping it home, got nowhere (though initiated a nice smoke show from the front pads!)

Towed it home, checked it next morning in the garage and everything appears fine, except the front brakes are dragging a little.

Don;t know where to next other than getting another master and trying again...

Did you try the trick above, looking for the residual pressure valve? I might try that next...

Cheers

Matt

Sounds like the rod is preloading on the back piston
You need to have about 0.5-1.0mm clearance

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1969 Datsun 1000 wagon (Daily)
1969 Datsun 1000 coupe (Next project)
1969 Datsun 1000 coupe (Long term project)
1974 L34 Torana replica (In the build)
1976 SS Torana hatchback (Restoration project)
1976 Cadillac sedan deville (Pimp cruiser)

have you guys fixed the problem? i had this problem, all fixed now though

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Speed safely