Why need rear proportioning valves??

[ali_baba]

I've been told that when you upgrade your Mk1 to Mk3 rear disc brakes that you would need rear proportioning valves to adjust for the bias. Why is this?.

I know a couple people who didn't use these and they have not complained about their switch yet.

[Jarred]

under hard braking the back can overtake the front! (due to increased stopping power at the rear)

[Stuwey]

THIS is why!

YouTube - Park Like a Boss

[GRN_VAGN]

THIS is why!

YouTube - Park Like a Boss

BWHAHAHAHA that is awesome!!

[huss]

under hard braking the back can overtake the front! (due to increased stopping power at the rear)

But how hard do you need to brake?? normal street braking or racing ??

[Stuwey]

How hard do you intend on braking behind the next car?

Old Minis are bad for this too, when you do a disc brake upgrade. Can make for some "interesting" stops at the lights!

[Peter Jones]

You need them on the street especially in the wet or when braking downhill.

Back will lock up and you'll go sideways into the intersection.

Another option is to replumb the brakes and use a wilwood prop valve or grab the self adjusting unit on the back axle of a MK3 and intall that with the lever fixed in place.

[h100vw]

VW didn't go to the trouble of fitting them for the good of their health.

They also compensate for changes in load, ie when you have 4 people on board, there's a change in bias to keep the car inline when you brake.

Seized up ones were a nightmare in the UK.

Gavin

[WABIT]

indeed you need them, i had the same thoughts untill i started the car and rolled up the newly layed driveway locking up 1 wheel easy as pie.... spend the time, pay the cash and you wont spin out and potentially crash your car your obviously building..... over 2 proportioning valves?

dom

[huss]

You guys make a strong case. They sound hard to install, I'd rather stick with larger drums after reading this.