Anti-knock-off springs.

[Spac]

OK, so I keep hearing about these, but can't seem to find any good details...

As I understand it, they are springs that go inside the caliper, and push the piston onto the disc with a light pressure in an attempt to combat knock-off.

Is that right?

Anyone know what sort of rate they should be?

Obviously they would be harder on discs and pads - so should I go to a higher temp pad (DS2500s to DS3000s is what I'm thinking). Disc life is not really an issue - as long as they last for a whole rally, I have enough spare discs to outlast the car...

Car is a RX-5 rally car, using standard brake hardware. The old one stopped pretty well with Metal Kings, but knock-off was a real hassle. I figure some DS2500s will give it enough stopping power, but only if I can deal with the knock-off.

Cheers.

[dbasteve]

Yep, they are a conical wound spring that sits behind each piston. Most AP Racing calipers come with these fitted.
I believe they range from 4lb up to 7lb each.
http://www.apracing.com/car/caliper/springs.htm

I doubt these springs are available for most O.E calipers so it may be worth looking into adapting these AP springs.
A lot of EVO's and WRX's run these springs in O.E calipers.

Too much spring pressure can have an adverse effect on braking too so don't go overboard. Continuous rubbing of the pad can distort the rotor and cause fade which puts you back where you started.

[Spac]

Awesome, thanks! :)

Those three paragraphs gave me more useful info that I've found in three years of asking people (and there was a couple of tries on here before today!).

[dattoman1000]

We have modded subaru pistons for this purpose before on rally cars.
You need to machine a section at the bottom of each piston to accomodate the spring at full compression.
We have had a local springworks turn the springs up for us in 7lb for the local formula ford guys.

Another way to cheat if you have a master cylinder with a screw on cap is to fit a tyre shrader valve into the lid.....and before each rally you put a few pounds of air pressure into the resi which in turn pressurises the whole brake system and has the same effect. You only need 5 or so pounds so don't get carried away.

[Spac]

Any suggestions on which is the better method? The air-pressure system would be easier to set up...

[Rob]

Hey Spac

We've been using a Willwood residual pressure valve in the rear brake circuit of the Escort. Holds a constant 2psi in the rear lines which helped the knock off problem a lot.