Re: [Amc-list] disk brake hack

[Tom Jennings <tomj@xxxxxxx>]

On Thu, 2007-07-19 at 12:54 -0700, d stohler wrote:
> so, i got the MUCH bigger, better, more responsive
> master cylinder on. still have rear brake lock up
> first. i have the little 9x2 rear brakes with the
> little wheel cylinders. does anybody have a heavy duty
> 9x2.5 rear brake set up with the big wheel cylinders
> they would be willing part with? i would love to
> upgrade to disks back there also, but i dont have the
> money for that right now. any help would be great.

Just swapping parts around will probably make things WORSE. If the rear
is grabby now, putting bigger brakes in it will make it grabbier.

All you need to do is change out rear wheel cylinders to get the
balance. If it's just a bit grabby, switch to a 1/16" smaller; if it's
dangerously grabby in the rear, try 1/8" smaller.

Conversely, you go put a BIGGER wheel cylinder in the front, to make the
fronts grab faster than the rears (assuing you have drums in front). If
you have disks up front you're pretty much stuck with adjusting the
rears to match.



The hydraulic balance thing isn't hard to understand -- for a given
master cylinder, when you make a wheel cylinder bore larger that brake
grabs sooner and harder. 

What I would do is, find some AMC car that's close in weight and
distribution (eg. Gremlin vs. station wagon) and start with wheel
cylinder ratios from that car. Then go plus and minus.

Wheel cyls are like $10 - $30 each, and all you gotta do afterwards is
bleed at the wheel. Easy and relatively cheap.


When you have front to rear balance OK, THEN fiddle the master cylinder.
Changing it WILL NOT change balance (see note) only overall pressure.
It's a waste of tim to fiddle that first.



NOTE: Some wagner master cylinders allegedly have different bores for
front and rear brakes but I never found one in a TSM or aftermarket
catalog.


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