Re: 4kq brake master cyl upgrade

["Doug Johnson" <ur-quattro@msn.com>]

----- Original Message -----
From: Gerry Snow <gsnow@iea.com>

> Is anyone aware of a good upgrade to the brake master cylinder on my 84
> 4000q?  I have heard something about fitting a larger piston bore master
> cylinder from a 5kq, 200, or maybe from an 80/90.
> I want to achieve a shorter pedal stroke and a harder
> pedal for better heal and toe use on the race track.


You're correct about a larger diameter master cylinder providing a shorter
throw at he pedal, because the volume of fluid displaced to move the caliper
pistons (hence, the distance the caliperr pistons move) remains unchaged.
Your proposed diameter increase will result in a decrease in required travel
for the same braking effect.  However, the force you will need to impart
upon the brake pedal (with your leg!) is proportional to the master cylinder
diameter.  So, if your new master cyllinder is _twice_ as large as the
original, you will need _twice_ the force from your leg to achieve the same
braking effect.   Again, this doubled force will only move the pedal _half_
as far, but it is worth pondering before swapping master cylinders (could
get tiring on the streets, or maybe _dangerous_ if someone special to you
drives your car and is not ready for (forgets?) how your brakes respond...

Would a shorter pedal throw not leave the brake and accelerator pedals
_futher_ apart than they are now, and _tougher_ to heel-and-toe?

> I am also searching the archives on this.  If anyone can point me to any
> threads on this, I would appreciate it.  If I learn something new, I'll
post
> it.
>
> Best Regards,
>
> Gerry Snow
> Spokane, Washington, USA
>
>
FWIW,

Doug
Renton, Washington USA
'87 4kcsq - 181k
'83 Ur-q - 69k (up on blocks)
http://members.tripod.com/ur-q/inreno.jpg