drove my bec (mk indy 490KG) yesterday and the brakes are bad:

-long travel
-poor decelleration
-cant get front brakes to lock


setup is as follows:
-system bled over and over
-280 mm brakes solid 9mm
-wilwood dynalite 4 pots 1,75"
-dual master cylinder with bias bar
-AP racing mastercylinder 0.875" front ( tried 0.7" before)
-girling mastercylinder 0,7" rear
-sierra rear brakes
-wilwood proportionong valve
-ferodo DS2500 pads front
-car has only done +/- 10 miles

what to do?
- smaller cylinder ( = even longer pedal but higher brakepressure)

advice needed urgently ....... :-(

koen
WWW.ZX12R-INDY.TK

I have 0.625 FRONTS and 0.7 REAR.
Try swapping your master cylinders
My car is not a 7 though. You will also need time for the pads to bed in.


Description



[Edited on 9/4/2007 by nitram38]

@nitram38

do you use the wilwood brake-calipers?
(4pot 1,75" )

koen

[Edited on 9/4/07 by bikkel]

No but I am assuming you have larger ones at the front?

front = wilwood 4 piston with 1,75" pistons

combined with the 0.875" master cylinder AP

Are the rear ones smaller?
You should still have the smaller master cylinder going to the larger front brakes.
It looks like you went the wrong way with your choice of front cylinder.
Smaller bore cylinders have less volume when you press the pedal but have greater pressure on the caliper.
If you use a 0.625 cylinder on the fronts, you will have a firmer pedal and the fronts will grip more than the rears.

[Edited on 9/4/2007 by nitram38]

you have bleed the brakes fully?

As it can take some time, if you batter the pedal does it start to get firmer? if so then there's air in the pipes. First thing I'd check.

system fully bled ( pressure bleeder)

i used a bigger size front master cylinder
because :

-tried a 070 before (also bad) and figured out that my 1,75" pistons need more fluid displaced , hence the bigger bore cylinder)

i would like to know what else may be wrong before buying another 0,625 bore AP cylinder ( € 150) :-(

koen

put standard pads in the front and see what happens

unfortunately there are no std pads for wilwood


koen

First step is to try applying some logic to it all.

Get rid of the proportioning valve you don't need it.

The car is way over braked on the font axle but you can fix that with the balance bar.

A 0.875" master cylinder is way too big put the 0.7" back in. 0.7" dia master cylinders on both front and rear is a good starting point.

Next step is to bleed the system trace where the excessive lost motion is coming from.

(1) You say you have standard Sierra rear brakes - do you mean disks or drums ? With Sierra rear discs on Locosts there is a well known problem bleeding them because the bleed nipples is in the wrong postion when fitted --- unbolt the caliper and tilt so the bleed nipple is higher than the caliper piston when bleeding.
(2) With either rear discs or drums if the hand brake cable is too tight it will prevent he self-adjusters from working which can give a spongey pedal.
(3) when bleeding brakes don't open the bleed nipples to far. Even with a pressure bleeder get someone to pump the pedal a couple of times when bleeding and also to press and hold the pedal too the floor when the nipple is closed.

(4) Check the front calipers are sitting 100% true to the disc surface (in both axis), if they are sitting even at a slight angle to the disc it will give a very spongey pedal.

(5) Check the mastercylinder pedal box is not flexing when the pedal is pressed.



[Edited on 9/4/07 by britishtrident]

thx britishtrident

rear = discs + calipers mounted reversed L/R --> bleed nipple up

will try to bleed some more with he rear of the car jacked up


koen