aaddpp

After bench bleeding / installing my new clutch hydraulics, I reinstalled the brake booster, and brake master. I haven't bled the brakes yet (I still have some lines I want to change), but I did install the shaft that connects the brake pedal to the booster (aka brake pressure rod). Following the WSM I made a simple tool to set the brake pressure rod length to the 158mm +/- 2mm. I also marked the larger section of the brake pressure rod to indicate its center, with two additional lines for the +/- 2mm settings.

My question is about the play that's supposed to be in the brake pedal, and how critical / meticulous you need to be when setting it up (its my first time doing this). WSM specifies 10mm of play - with a bled system and stopped engine. I've noticed that the even before bleeding, the pin that joins the brake pressure rod to the pedal allows for around 3-4mm of play, b/c the pin changes angle and allows forward movement of the brake pedal w/o advancing the brake pressure rod. I'm wondering if this pin movement is normal and its part of the 10mm, or if something might be worn (plastic bushings), or if this is just the way things work, and the pin play will be absorbed once the system is bled and holds a vacuum.

Sorry for what probably sounds like a really nit-pick question, but sloppy brake pedals irritate me to no end...and its an area I'm definitely willing to invest some time to get it right.

Thanks, Dave


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Don Carter

Don't have any answers to your question, but have a related question... Does this adjustment effect brake pedal resting position? I've noticed that the brake pedal on my 86.5 is about 2" closer to the height of the gas pedal than my 89. It's somewhat annoying going from one car to the other, but haven't had time yet to see if it's adjustable (lower the 89 pedal to be closer to the gas pedal height)

WallyP

There are apparently two reasons for the 10mm free play spec.
- To ensure that the tiny hole in the master cylinder is not covered when the pedal is released. This hole, sometimes called the compensation port, allows passage of fluid from the master cylinder to/from the reservoir. If it is blocked, the brakes can be self-applying as they get warmer.
- To ensure that the cruise control is killed before the brakes are applied, which is not normally a very important factor.

As long as you make certain that the port isn't blocked, you can probably reduce the free-play slightly...

aaddpp

Thanks Wally, thats an excellent explanation. With this, I at least know what I am working toward. Much appreciated - Dave

aaddpp

Don, the height of the brake pedal can be adjusted to a certain degree by rotating the solid piece of aluminum (the one I marked with three lines), though the WSM specifies pretty tight limits regarding its length. 2" seems like a lot, and it appears to be more than I would be able to achieve. First photo below is my setup before I disassembled it. I marked the exposed threads with a blue paint pen prior to disassembly so I had a record of what the initial set up was - looks like there might be around 1cm worth of distance to move the pedal forward, though if I did, I would goes this would probably be outside WSM stated parameters. Let me caution that I'm not sure if the setup I found in my car was correct give that there have been a number of things what were not done properly on my car in the past, and I didn't take the 158mm measurement prior to pulling it all apart.

Also worth noting is that when the aluminum block is adjusted, the brake light plunger also needs to be adjusted accordingly. WSM has specific numbers on this, but I don't recall them off hand right now. WSM also lists some figures for the height of the brake pedal relative to the clutch if you have a manual gear box.

One more thing I learned...next time I do this, the front driver seat is coming out so I can lay on my back while working under the dash, in comfort, with my legs up. A beer would probably help things along too

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brutus

There is a lot of adjument for pedal height. Sometimes people lower the brake pedal so they can "heal and toe" easier.

WallyP

The throttle pedal is adjustable.

For working under the dash...
Go to Home Depot/Lowes/etc. and buy a good 8' 1x12.
Measure from the floor to the top of the door sill. Add 1/8" and cut that much from one end of the 1x12.
Screw and glue the two pieces together to make an L. Add a couple of pieces of scrap to brace the L.
Talk the lady at your place out of an old throw rug or bath mat. Put most of it on top of the L, put a small piece over the door sill to protect it.
End of the L on the floor, stick the long part thru the door.. Lay down on the top and work away.

jpitman2

Assuming the 'free play' is a measure of how far the push rod is from actually moving the piston in the brake booster when the pedal is at rest, to ensure the m/cyl return port is not blocked, 10mm is a LOT. Despite the pedal return spring, you should be able to feel the difference when the rod contacts the piston and starts to move it - it may take a few test pushes to establish what you are feeling, but you should be able to detect it by foot. To me, free play here should be a round 1mm.....Porsche's free play must be something different.
jp 83 Euro S AT 54k

WallyP

I have alway interpreted the 10mm as pedal movement. Still seems like a lot, which is why I suggested that the OP could carefully adjust to less. I test with my hand - it seems to be more sensitive than my foot.