Had a leaking master cylinder...
There was a trail of brake fluid coming from the back of the m/c and running down the front of the brake booster.
There was brake fluid in the front m/c reservoir but none in the rear.
I HAD JUST DISMANTLED THE MASTER CYLINDER AND REPLACED THE PISTON CUPS - DAMN.
So I carefully removed the master cylinder, put it in a vice and looked at the rear of the m/c, there was brake fluid at the back of the m/c, but after a real close look, there was no fluid around the circlip that holds the piston in the m/c bore.
There was some brake fluid on the outside of the m/c reservoir at the rear of the tin lid.
Got the old tin lid rubber gasket (original gmh) and checked the thickness with the new one - it was the same.
So I put the tin lid back on the m/c without the rubber gasket and put the hold-down clip back into the closed/locked position - there was a lot of space between the clip and the tin lid.
I removed the clip and then after 7 or 8 times of slightly bending the ends of the clip, it just touched the tin lid clip grooves (front and rear) as I swung it over the top of the tin lid.
I put the rubber gasket back on the tin lid, put the tin lid back on the master cylinder reservoir and locked the clip back into position. It was a much firmer fit now.
Hasn't leaked a drop.
I think what happened was; when the brake pedal was released, a shot of brake fluid shoots back out of the bottom of the reservoir, hits the underside of the tin lid, then escapes between the tin lid rubber gasket and the m/c reservoir sealing surface. Runs down the back of he m/c reservoir and then down the front of the brake booster - you'd swear it was a leaking m/c.
It's so important to find the problem before buying parts - I nearly ordered a new m/c 'cause I thought the bore must've been stuffed.
"Do you know what Thought, thought. Thought thought he had shit himself, but he hadn't!"
P.S. it was a 1978 HZ 202 ute 190,000km
P.P.S. I had trouble bleeding and had to
1). remove the piston stop bolt and the rear piston
2). bleed the front half of the m/c
3). replace the piston stop bolt and the rear piston
4). bleed the rear half of the m/c
to get rid of all the air.
I also used rubber fuel line clamped over the flared end of the m/c brake line and directed the bled brake fluid back into the m/c reservoir. (held finger over the end of the hose when the piston was returning).
hz mc.jpg 46.57K
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