Improving 247mm brakes

[Flynn]

Continuing on from the other thread that sort of got off the original topic, I wanted to continue our discussion about the 247mm brake setup. This is the setup I currently have and rather than invest in heavier calipers and discs I would like to see what effects can be had from fine tuning this setup, without things that are beyond the layman's capabilities like Rippthrough's flower shaped discs (before anyone mentions his setup, albeit in a tongue in cheek manor).

I guess the main thing that I don't like about the 247mm setup is the lack of initial 'bite' which is not very confidence inspiring, I like to press the pedal and feel instant feedback. Although once warmed up, they do a reasonable job of stopping the car, but they always seem to lack bite whether cold or hot. I currently am running Mintex discs, standard pads and fresh brake fluid through braided hoses. There is no air in the system this is confirmed by a solid brake pedal.

From what I read I thought the larger 23mm master cylinder would provide the feedback I was looking for, although Rippthrough has advised that this is not the case, citing the fact that it would provide less braking force, I am not sure of the details but feel free to explain it in this thread. Also I am not sure what role the rear brakes play in the overall feel of the braking, could it be that old rear shoes cause the brakes to feel less positive? I must say, the braided hoses have made a good difference, I was planning the larger master cylinder as my next step, but from what Ripp has said I am not sure what to do now.

[cully]

if you take the pads out rough them with sand paper they will work better for about 5 mins

oh oh 1 hour 20mins to i blow up our neighbourhood

[Flynn]

Yeah I roughened them up with sandpaper before putting the new discs on and yes they did feel better for awhile but it quickly went as the surface smoothed out again.

[Daniel306]

Gti6 master cylinder wont really work because its a larger piston working on a smaller piston meaning you would need to push the pedal harder to get the same force as with the original, im not even sure i want to put in on my car with the 6 disks, http://science.howstuffworks.com/transpo...aulic1.htm

[Eeyore]

Just get bigger brakes and disc rear beam... its the best way to do it instead of trying to 'make shit shine'

[Rippthrough]

My wavy discs aren't 247mm anyway

You said in the other thread that you have a lot of pedal travel before the brakes engage, so that would be my first port of call - either the rear brake shoes aren't autoadjusting properly (or the shoes are worn), or the pedal pivot has some play in it, or the linkage from the servo to the master cylinder isn't adjusted for proper clearance, all 3 of those make a big difference to pedal feel and bite. Smaller effect would be from discs not running true on the hub or drums ovalled slightly pushing the pads/shoes back when the pedal is released.

Do you have the assymetrical Bendix brake pads up front?

[Flynn]

Hello Rippthrough, thank you for your input. The front setup is the ATE setup which has benefitted from new discs and pads. I think you might be right about the brake shoes, I have never adjusted them myself and stories are common about the adjustors sticking. The shoes are also quite old, they've been on since I've had the car since 2009. You raise an interesting point about the servo rod, when the servo is on the pedal does have to travel a fair way before it is firm. I would certainly prefer if that same firmness could be experienced almost instantly. I have checked the Haynes and getting to the servo appears to be a pig of a job. Perhaps I will get KrisB to do it, haha!

Daniel306, thanks for the link, so in that article the smaller longer piston is the 19mm master cylinder and the wider shorter piston is the 23mm master cylinder.

[Rippthrough]

You just need to whip the master cylinder off to get to the servo rod. Don't adjust it too tight thought as the brakes will bind on after a few miles.

[Flynn]

Is it possible to take it off without undoing it from the brake lines? Many thanks.

[Rippthrough]

Yeah, you can can unclip them from the bulkhead and move it enough usually.

[Flynn]

Well I was going to do this this weekend although on a final check of the Haynes it says you need a new O ring, is this true? Edit: To ask two questions with one stone (can't remember the exact phrase) I have found a picture of a servo with the cylinder off:



What is the bit that needs adjusting and how does one go about it? Thanks.