brake booster

[Ted Z.]

Changed my master cylinder on a 1972 Corvette. I took hold of the push rod and noticed it came out of the booster completely. I reinstalled it with the master cylinder on but felt bothered by the idea That would come completely out. It seems that it would fall out of alignment from the pedal side . I merely centered it pushed it back in and hooked up the master the master. I now have a pedal that seems to travel to the floor which may be related to the master cylinder and not to push rod.. Can someone please help me.. Do those push rods come completely out? On illustrations I see a Push rod seal Is near the face of the booster, But I do not see a seal anywhere near the pushrod. The rod did seem to stay in position and sticks out 2" from booster and fit nicely into the master cylinder. But I'm not comfortable with the rod not being attached on the inside. if it does need to be attached, how to I get it in position.

[Mark E.]

Re: brake booster

With manual brakes there's a single push rod threaded into a clevis that's attached directly to the brake pedal. A locking nut provides pedal height adjustment.

With power brakes there are two rods. There's a rod between the back of the booster and the brake pedal that's threaded to a clevis and attached to the pedal like manual brakes. There's a second "hydraulic rod" between the master cylinder and booster that just fits into the booster.

When removing the MS you're seeing the hydraulic rod which just pushes into the booster.

[Mark E.]

Re: brake booster

I found this website with photos: https://www.corvette-restoration.com...oster-removal/

[Ted Z.]

Re: brake booster

Thanks Mark. The push rod has a golf tee shape at the end that goes into booster (not threaded). It is threaded with acorn nut on the end that goes into MC.
As you can imagine, there is no way to look into booster while boster is installed. perhaps the rod slides into a cylinder and bottoms out at proper depth. the booster is not the orig. but looks correct. When I search boosters, there seems to be a rubber seal mounted on MC side of booster. Mine has no seal for the rod to be centered. Fyi, rod length appears correct, no prob getting MC to bolt on.

[Mark E.]

Re: brake booster

Correct, the hydraulic rod slides into the booster as you say. It sounds like you're fine.

[Ted Z.]

Re: brake booster

Man, I hope youre are correct. Tbis brae wirk has not been fun on this old man. It just seems inappropriate for the rod to have a little free play inside booster. Also, Mark, looking at the push rod opening, i dont see a vavuum seal. I'll hunt for one. on another site, iheard Booster Dewey can help. there are not gaskets or seals between MC and booster. Perhaps this is factory correct.
Thanks you sir, Ted

[Larry M.]

Re: brake booster

Ted:

There is also a critical clearance between the booster pushrod tip and inside the master cylinder pushrod cavity. It is about 1/32 to 1/16 inch free clearance. If you are over or under this number, brake pedal travel or brake performance will suffer. There is a special tool that can be purchased to set this clearance. About $30. Available from CSSBInc. or others.

I purchased one to assist my friend in setting up his 69 car brake system. It is easy to use........and it works.

Larry

[Ted Z.]

Re: brake booster

Thanks for tech tip. I didnt get rod ool but i did meaure depth of master cylinder bore until it bottomed. it showed 2". i then meaured push rod from face of booster to tip of acorn nut. came to 2". if rod is too long, you cant install MC. the inner seals and pistons in MC will not budge. also if too long, you might see brake lights on, or, brakes would be partially iengaged. Too short an adjustment and pedal play would be deeper before brakes engage.

My worry for the moment is lack of front vacuum seal which centers push rod. ive checked 2 vette vendors and cand find one. im still wondering if it had one in'72. my booster is only about7 years old from PO.
appreciate feedback, Ted

[Larry M.]

Re: brake booster

Thanks for tech tip. I didnt get rod ool but i did meaure depth of master cylinder bore until it bottomed. it showed 2". i then meaured push rod from face of booster to tip of acorn nut. came to 2". if rod is too long, you cant install MC. the inner seals and pistons in MC will not budge. also if too long, you might see brake lights on, or, brakes would be partially iengaged. Too short an adjustment and pedal play would be deeper before brakes engage.

My worry for the moment is lack of front vacuum seal which centers push rod. ive checked 2 vette vendors and cand find one. im still wondering if it had one in'72. my booster is only about7 years old from PO.
appreciate feedback, Ted

Ted:

Check with Booster Dewey or perhaps CSSB, Inc. regarding the seal.

If the pushrod is too long, the MC WILL push in a bit when it is mounted to the booster. When it does, it can/will cover the release port in the MC. Then the brake hose/ caliper pressure cannot release once applied. So be careful here with the booster pushrod setting.

Larry

[Patrick H.]

Re: brake booster

Yes, there is a seal, but apparently it is not critical to operation of the system. The original was just foam, and often poorly installed.
There are no correct/exact reproductions. The only versions I have seen are just a large O-ring, so I have just reused the original if available.
Most diagrams and installation instructions don’t show the seal at all.

[Ted Z.]

Re: brake booster

Many thanks Patrick. I found new pin, seal, and washer sold by ecklers and CSSB. the seal sets about 1" inside the booster on MC side and the rod comes thru center. Ted