Power booster push rod to master cylinder piston clearance ??? - Team Camaro Tech
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post #1 of 15 (permalink) Old Dec 28th, 16, 10:39 AM Thread Starter
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Power booster push rod to master cylinder piston clearance ???

How much, if any, clearance should there be between the push rod of the power brake booster and the end of the pocket in the master cylinder piston with the master cylinder bolted tightly to the power brake booster?

It is the original power brake booster with it's original push rod (the long style). I have a new master cylinder and when I push it as far as it will go on to the booster, the mounting flange of the master cylinder will not sit tight to the mounting surface of the booster. There is a 1/16 to 1/8 inch gap. I can rock the master cylinder side to side. It's pivoting on the push rod.

If I tightened the mounting bolts, the pushrod would push the piston in that 1/16 to 1/8 inch......By the way, the old master cylinder that I took off (not the original) fits tight to the booster so apparently, the piston pocket is a little deeper in that one.

I am probably not going to be using this new master cylinder and getting another one for reasons I won't go into here but I am still curious as to what the proper fit of the push rod and piston should be.

Thanks......Dave

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #2 of 15 (permalink) Old Dec 28th, 16, 12:25 PM
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Re: Power booster push rod to master cylinder piston clearance ???

You'll want to file away some of the rod, then. It shouldn't push on it at all but, rather, be just snug.

Try tightening up the bolts, start the car, push the brakes a couple times, jack it up and spin the wheels. Did the brakes loosen back up or are the dragging? If they're dragging the rod is too long.

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post #3 of 15 (permalink) Old Dec 28th, 16, 03:43 PM Thread Starter
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Re: Power booster push rod to master cylinder piston clearance ???

Thanks for the reply.

So there should be no pressure being put on the piston in the master cylinder just by tightening the master cylinder to the booster?......I didn't think there should be but wanted to be sure.

Like I said, I'll probably be getting another master cylinder. I'll see how that one fits before doing any filing the push rod.

I am just getting the braking system together now. The car is not running yet and I still have to install the brake lines so it will be a while before I could perform the test you mentioned.

Thanks.....Dave

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #4 of 15 (permalink) Old Dec 28th, 16, 05:00 PM
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Re: Power booster push rod to master cylinder piston clearance ???

I agree that there's something up with the master cylinder. Send it back and get a new one....you shouldn't have to make modifications to the rod if all the components match properly.

69 SS, 350/300 h.p., M-20, 12 bolt, matching numbers.


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post #5 of 15 (permalink) Old Dec 28th, 16, 05:47 PM
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Re: Power booster push rod to master cylinder piston clearance ???

Just out of curiosity did you make sure there wasn't a spacer in the master?

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post #6 of 15 (permalink) Old Dec 28th, 16, 06:11 PM
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Re: Power booster push rod to master cylinder piston clearance ???

Been discussed countless times. Zero freeplay is not correct, and you do not need the tool here for verification: Diagnosing and fixing a soft pedal | Booster pin to master cylinder gap | Master Power Brakes

Call for restoration and custom paint scheduling:
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post #7 of 15 (permalink) Old Dec 28th, 16, 06:52 PM
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Re: Power booster push rod to master cylinder piston clearance ???

The procedure is in the Chassis Service Manual to adjust the clearance for the pushrod to master cylinder piston. The pedal need 1/16" - 1/4" of free travel before push rod contacts the piston in the MC. Loosen the jam nut at the clevis where it pin to the pedal and adjust the rod till you have the proper free pedal movement. You should not have to grind the rod for clearance.

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Jeff


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post #8 of 15 (permalink) Old Dec 28th, 16, 09:09 PM Thread Starter
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Re: Power booster push rod to master cylinder piston clearance ???

Thanks for all of the replies.

So there should be a .02 inch gap between the push rod and the piston as specified in the article that Scott provided the link to. That's really what I needed to know.

By the way, I probably should have clarified but the booster is not even in the car. I just the threw the master cylinder on it to see if it fit OK. The push rod is not threaded. It just slides in and is at the end of it's travel. To the best of my knowledge there's nothing to adjust on it.

The old parts store master cylinder that came off of the car does not have this clearance problem so I'm guessing the problem is with the new master cylinder. I'm not going to use this new master cylinder anyhow but now I know when I get another one that there should be the .02 inch clearance.

Thanks.....Dave

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #9 of 15 (permalink) Old Dec 29th, 16, 11:22 AM
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Re: Power booster push rod to master cylinder piston clearance ???

Quote:
Originally Posted by Gbauer View Post
You'll want to file away some of the rod, then. It shouldn't push on it at all but, rather, be just snug.

Try tightening up the bolts, start the car, push the brakes a couple times, jack it up and spin the wheels. Did the brakes loosen back up or are the dragging? If they're dragging the rod is too long.



^^^^


Common problem. Place washers in the two m/c bolts and try what is stated above. This will give you an idea of how much to shave off the rods if they are too long.
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post #10 of 15 (permalink) Old Jan 3rd, 17, 12:48 PM
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Re: Power booster push rod to master cylinder piston clearance ???

Quote:
Originally Posted by 69&76 View Post
^^^^


Common problem. Place washers in the two m/c bolts and try what is stated above. This will give you an idea of how much to shave off the rods if they are too long.
x2. (or just leave the washers as I've done for the past 5 years. Nobody sees them anyway)

'67 rs - ordered new by my Grandfather
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post #11 of 15 (permalink) Old Jan 3rd, 17, 03:38 PM
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Re: Power booster push rod to master cylinder piston clearance ???

Hi Dave
I too had allot of Problems, I bought the Replacement Power Booster and Master Cylinder from Ground Up and they were from The Right Stuff Mfg.

See my Post # 4 from this Post, might give you a little more Info -

https://www.camaros.net/forums/16-bra...my-brakes.html

I went back to Ground Up, we opened several M/C and Brake Boosters, All had the Same Issue, I'm sure they get them from the Same Mfg too.

I could not Bleed my Brakes as because the "Nub" of the Booster stuck out Fwd, it Pushed the Master Cylinder Piston Forward when I bolted it up to the Booster, which now made the Piston Seals past the Port where the Fluid would get Sucked In while Pumping the Pedal.

There should be a small amount of Clearance between the Brake Rod and Master Cylinder Piston.

Timmy

1969 SS/RS Coupe 427BB 700R4 12 Bolt 4:11 A/C, High School Resto Mod

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post #12 of 15 (permalink) Old Jan 3rd, 17, 03:42 PM Thread Starter
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Re: Power booster push rod to master cylinder piston clearance ???

I have another master cylinder on the way and we'll see how that one fits. (I'm replacing it for reasons that have nothing to do with the push rod clearance.)

Just out of curiosity, has anyone ever taken a drill bit and removed a slight amount of material from the end of pocket in the piston to solve the clearance problem?

This is the original booster and push rod. Up to this point, there has only been the assembly line installed and two parts store master cylinders on this car and none have had a clearance problem. I'm not sure I want to be grinding that push rod just to fit one particular off the shelf repro master cylinder. If that master cylinder needed to be replaced for some reason in the future, the push rod might be to short for the one that replaces it.......I think I like the idea of the spacer washers better.

But like I said I have another master cylinder that should be here in a couple days and hopefully there will be no clearance issues with it. If there is, I'll figure out what route I'll take then.

Thanks.......Dave

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #13 of 15 (permalink) Old Jan 3rd, 17, 10:55 PM
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Re: Power booster push rod to master cylinder piston clearance ???

You can shim the master cyl forward at the bolts. Easiest way is to grind the rod, it just pulls out. If I had an original booster & pushrod, I would not feel good about having to grind the rod. You might be able to drill the MC piston a tiny bit deeper. up to 1/8" max. I don't know if the bit would grab and just spin the piston around but it might be OK. Use a little wd40 for lube and don't push too hard and maybe it'll work ok for you.

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post #14 of 15 (permalink) Old Jan 4th, 17, 04:50 AM
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Re: Power booster push rod to master cylinder piston clearance ???

It's just going to swing the piston. You won't be able to do it.

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Offy intake
Holley 390 CFM carb
Langdon split header to a 2.5" exhaust
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post #15 of 15 (permalink) Old Jan 5th, 17, 10:17 AM
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Re: Power booster push rod to master cylinder piston clearance ???

It's easy to remove the piston, but take care not to damage it.

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