9n3 polo brake pedal / master cylinder

[simon k]

Hi, I have a 9n3 polo GTI, had it for 3 years and I've never been able to get a firm brake pedal while the engine is running. With the engine not running the pedal is firm with minimal travel, as soon as I start the engine the pedal sinks past half way to the floor. I've spent a significant amount of time pressure bleeding with VCDS and I'm 99% sure there is no air in the system. I've spoken to other Polo owners in Aus and they all say the same thing. I drive the car daily plus compete in circuit sprints every month or two. The car stops OK, but the brake pedal just doesn't inspire confidence

I know 9n3 Polos were raced in South Africa and I wonder what they did to the brakes (if anything)

One thing they might have done is fit a bigger bore master cylinder out of some other VW

Any ideas or suggestions ?

Thanks

[Callum229]

Sounds like you leaking vacuum to your brake master. I've driven polos and they have firm pedal feel, especially the GTIs.

Check vacuum lines to the brake master and check if your brake master has a leak. It might be slight.

Upgrade brake fluid, maybe it is boiling?

Either then that I would say upgrade to racing brakes and pads.

[simon k]

The pedal is soft from cold, when the car isn't even moving so it's not pads or fluid, I have high temp fluid, quality pads/rotors etc. anyway.

I've checked the vacuum line and booster, I don't think it's leaking but it seems more like the booster is working too well rather than not well enough. A few people out here have said that VWs are often over boosted, hence wondering about a bigger bore MC

[Howie-WP]

I know 9n3 Polos were raced in South Africa and I wonder what they did to the brakes (if anything)

Many remove the booster as they prefer unassisted pedal (I don't and still have my booster, Mk1 Citi though, with bigger master cylnder)