72 with Power Brakes Question

[rn2fine]

Regarding 72's or other years with power brakes has anyone had any experience with either using or not using a spacer (looks like a bullet) fitting into the rear of a master cylinder piston. Have all new brake parts, entire system, and pedal goes to floor. A local classic Chevy parts store gave me a spacer to put into the back of the master cylinder. Just wondering if anyone has used the same. Thanks.

[TBONE1964]

I have never heard of such a thing. Did you replace the power brake booster? If not, there should be no reason to have a spacer. If you need a spacer then you probably have the wrong master cylinder. is there any resistance on the peddle as it goes to the floor or is it just floppy? Does the peddle move freely and then has some resistance?

It sounds like you still have air in the system. Did you blled the master on the bench before you installed it? You will never get all the air out of a master unless you bench bleed it first. When bleeding, always start with the farthest wheel away from the master, RR, LR, RF then LF. make sure the pedal is not released even a fraction of an inch while bleeders are open or you will suck air back in the system. What is the method you are using to bleed the brakes?

[luvbowties]

Originally Posted by rn2fine

Regarding 72's or other years with power brakes has anyone had any experience with either using or not using a spacer (looks like a bullet) fitting into the rear of a master cylinder piston. Have all new brake parts, entire system, and pedal goes to floor. A local classic Chevy parts store gave me a spacer to put into the back of the master cylinder. Just wondering if anyone has used the same. Thanks.

Hey, rn2fine, when updating the brakes to a dual line m/c and power brakes(on a '66 with the old and dangerous single-outlet m/c system), I used available good used parts from donors I already owned. They were mis-matched, and I ran into a low-pedal situation.

I realized the booster pushrod--non-removable and non-adjustable--was going into a hollow-ended piston on the m/c and "using up some of the stroke" from each pedal-pump. I made a 'bullet', as you called it, from the unthreaded shank of a bolt whose head and threads I cut off. Ground one end to a bullet-shape to mate into hollow-bottom of the m/c-piston; shaped outer end to resemble the piston end of a m/c that had no hollow, just an indentation; length was about 1.25 inch, iirc. I first used a round wooden rod as it was easy to shape and shorten, just for a pattern. (I actually drove it with the wooden rod pattern, very carefully, a few blocks to ensure it would work as I theorized!)

My home-made spacer, slightly smaller than the bore of the m/c's hollow piston, took up the slack and is still doing well three years later. Since then, I have seen a couple of pics--very vague--of mfg'd spacers with some m/cylinder-kits advertised on the i'net, but the spacers are barely mentioned in the ads, if at all.

The bullet end of mine resembles the wheel cylinder end of the rod that connects a wheel cylinder to its brake shoes. I think(only think, not sure)that more drum brake m/c's have the hollow piston, and disc brake m/c's tend to have a flat ended piston with just an indentation. If the same situation were to arise again, I don't know where I could buy a mfg'd spacer. But at least we now know a home-made cure for the problem!

[oklalawnboy]

Originally Posted by TBONE1964

I have never heard of such a thing. Did you replace the power brake booster? If not, there should be no reason to have a spacer. If you need a spacer then you probably have the wrong master cylinder. is there any resistance on the peddle as it goes to the floor or is it just floppy? Does the peddle move freely and then has some resistance?

It sounds like you still have air in the system. Did you blled the master on the bench before you installed it? You will never get all the air out of a master unless you bench bleed it first. When bleeding, always start with the farthest wheel away from the master, RR, LR, RF then LF. make sure the pedal is not released even a fraction of an inch while bleeders are open or you will suck air back in the system. What is the method you are using to bleed the brakes?

My thoughts too.

[luvbowties]

Originally Posted by rn2fine

Regarding 72's or other years with power brakes has anyone had any experience with either using or not using a spacer (looks like a bullet) fitting into the rear of a master cylinder piston. Have all new brake parts, entire system, and pedal goes to floor. A local classic Chevy parts store gave me a spacer to put into the back of the master cylinder. Just wondering if anyone has used the same. Thanks.

See pics: one has a void! Just for interesting information: A company called getdiscbrakes.com makes a plug(their part #MCBUL01), kinda shaped like a bullet, to fill this void. I've actually never seen a mfg'd one, as we had already learned to make them, to go between wrongly-paired booster-and-m/c, for several years before I knew anybody actually made such an animal. We made them simply, using the non-threaded portion of a bolt, and grinding-and-shaping to loosely reside in the void/pocket. BUT I'D ADVISE TO NOT USE A PLUG FOR PEDAL-TO-MC--BUT ONLY FOR BOOSTER-TO-MC, AS NOTHING MUCH WOULD ENSURE ITS REMAINING IN PLACE IF POSITIONED BETWEEN BR-PEDAL AND MC!!!
HTH,
sam

[LSUMurse]

I am not trying to insult you, but are you talking about the pushrod between the booster and master cylinder? The reason I ask is because the one that came out of the one I just replaced sort of look like a bullet. It's brass in color, 3/8" thick, and about 3" long.

If that's missing then your pedal would go down to the floor, I would guess.

EDIT: I see that is what was being discussed in the response above.