northiam

I am wondering about the effectiveness of the brakes on my XA 351
It has XC booster, master cylinder and rear 9inch discs, Front has XF callipers.
The wheels do not lock up under heaving braking no matter how hard the push, do I have a problem? Should the wheels lock up?
Thanks

reece1

well sort of yes in a way. what sort of engine vacuum do you have to start with? what pads are you using?

northiam

11 inches of vaccum with standard pads

reece1

tha vacuum is your problem, i would say without looking at the vehicle. the booster to work at its best requires a text book 17-21" of vauum. does your booster hold vacuum when car is not running? is your one way valve working? with this amount of vacuum you will probably never get your car to lock up at all. you would be better off with drums on the rear as they dont require a booster they are self energizing.
my enginner is requiring me to run disc on the rear as well, i have explained to him this point when using a low vac engine. but the guidelines set out require this upgrade(downgrade) and it is not correct for the application intended.
you can use a vac tank to increase your booster storage, but this will not help it will only give a few more applications before recovery time. if you use one of these also make sure there is a one-way valve between tank and manifold port.

northiam

Yes the booster holds vacuum for a longtime after the engine is off. So do all modded engine cars have this problem?

reece1

pretty much sadly. i will check tomorrow i forgot today if you change the reactionary disc pad in the booster, this may give you a bit better pedal feel. i am pretty sure it wont help though. the vac is low does it have a large cam. what sort of timing is in it iniataly is it set up correct? i know it probably is. note where your timing is at, at idle and put vac gauge on and advance dizzy and see if vac reading goes up or not.

Henry's XAGT

With regards to manifold vacuum pressure, where is a good location on the cleveland to tap this from?

thanks

northiam

Depends on the manifold you have but generally at the base of the carb or booster connection you have vacuum.


I'm looking into a vacuum pump system as a min 16" vac is required for proper booster operation.

Which lends me to wonder! Whats the point in huge brake upgrades 4 pot capilers etc if you dont have the vacuum, the brakes will never perform to their potential!

atec77

Give serious thought to adding a small vacuum tank and you might have some advantage changing the booster pad .