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Reaction Disk


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I'm pretty sure my reaction disk has slipped, this is based on reseaching on the site. I have a question, Do I have to take the brake booster off to try and repair or can I attempt to fix with it still on the car. It's a 73 240

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You can pull the master cylinder off then pull out the seal and push rod with the booster on the car.

Try to fish around inside on the bottom of the booster to get the reaction disk. It may be difficult with the internal spring. If you can't get it,either use a disc from another booster or take the booster apart.

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post-7641-1415081932967_thumb.jpg

Edited by Blue
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Sorry Beerman but I don't agree. Give me one reason why grease is better than super glue. I had to pull my push rod out to adjust the rod recently (it was so tight, I had to put it in a vise). It was so nice not to have to have someone hold the brake pedal down so I wouldn't drop the disc again.....came out as a unit.....went back as a unit.

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Sorry Beerman but I don't agree. Give me one reason why grease is better than super glue. I had to pull my push rod out to adjust the rod recently (it was so tight, I had to put it in a vise). It was so nice not to have to have someone hold the brake pedal down so I wouldn't drop the disc again.....came out as a unit.....went back as a unit.

My primary concern is how the rubber will react to the adhesive. If it has a bad reaction the rubber could change. The reaction disk is a spring and is part of what determines how the Master-Vac reacts to pedal pressure. If the rubber changes the assist curve will change and change the feel of the brakes. Beyond that it is only the formality of following the factory's instructions.

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  • 2 weeks later...

Ok I left the booster on the car and got the pushrod out, no reaction disk but when I feel inside the hole where the rod goes it feels like a rubber disk is in the chamber where the rod goes. When the brake pedal is pushed it moves forward and back. Is it possible it was glued to the other end? I don't want to remove the booster from the firewall unless it becomes a last resort. I'm a big guy and have trouble getting in there to remove. Is there another rubber piece in the booster or do you think it is my disc.

does anyone have a reaction disc they would be willing to sell me. please PM.

thanks

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I suggest pulling the booster. I had to do it my race car with a race seat roll cage in the way. I didn't want to do it but it turned out to be not such a bad job and didn't take long. I don't think it's a good idea to install another disc with the old one still in there...somewhere.

Chuck

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Success, I left the booster on the car, Found the disc. It was in the chamber where the push rod goes. Got it out, glued to the push rod and solved my problem. Thanks for eveyones help. Blue the pictures helped alot. I would recomend everyone try this fix while the booster is on the car first. You can always remove it if this does not work.

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  • 3 years later...

Old thread but it's a good one... I doubt Manny will read this three years later but if anyone can comment I'd appreciate it. After you removed the push rod was the seal still in good shape and reusable? Is there any place to source a new seal if necessary? I didn't see anything from MSA or from a generic Google search.

Any tips in general regarding removing the push rod or is it pretty self explanatory once I get in there? Thanks guys.

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  • 4 years later...

Reviving an old thread.

I have a 1973 240z with 48,000 miles that has been off the road for 7 years. (I pulled the engine to reseal it and it has sat since then.)  I am now working to put it back together this year and enjoy driving it again.

One of the issues I had with this car was the brakes never felt good. Almost as if the booster wasn't working. However, I recall doing the standard brake booster test back then and determining that it indeed work.

I pulled the master cylinder last night to check for the presence of the reaction. While it did not come out attached to the push rod, I think it is still in place at the back as it is black and feels rubbery.

Does it matter if it is attached to the pushrod for it to work?

Thanks!

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Poke it, inside, with a screwdriver.  If you feel metal it fell out.  If it's rubbery it's still there.  As long it's between the rod and the diaphragm seat when assembled it doesn't matter where it started.

I don't know why they cal it a "reaction" disc.  It should be called a damper or something similar.  

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Zed Head, thanks for the reply. It definitely is rubbery, I could feel it with my finger.

When the car is back up and running I will try new pads and rotors. Maybe my problem is as simple as old pads.

 

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