Brake pedal feel

[sambb]

vacuum relief regulator. type 2 in this link. purely mechanical. they look to cost as much as a master cyl if you paid someone to do it too! so dont know if it'd be worth it. Basically it like a 'blow-in' valve for vacuum ie opposite to a blow-off valve for capping over-pressure.

How Equilibar Vacuum Regulators Work | Equilibar Precision Control

[sambb]

Controlling brake assist with a vacuum regulator - NASIOC

looks like these guys have played with the idea.

[sambb]

so it seems that Prodrive made a thing called a brake servo spacer.
STI Brake Servo Spacer

It was developed for rally cars that were running anti lag. Anti lag means you dont have inlet mani vacuum long enough to build vacuum in a booster so you can end up with an impossible pedal if running anti lag and a booster. This kit was a way to ditch the booster entirely, fit it in and then run boosterless. Dont know how that would work given that it appears to be a closed system.

[JTop]

What about ignoring the VW system and applying an electric brake option?
Seen this being used in a lot of older vehicles to combat their ancient brake systems
Power Brake - Cruisin Automotive - Dream It Build It Drive It
Just a thought for the pond

[simon k]

It wouldn't be hard to put in an elevtric vacuum pump (various VWs have them, 02 Pass at is one) button run the stock booster but it'd still need a vacuum switch to turn the pump off. Not much different to a switch and a valve..

I'm still digging for a bigger bore MC

[Sydneykid]

Sorry in advance, I'm not very good at road brake pads, I really only concern myself with what we use in the various race cars. My go to brake pad supplier is Hawk, as follows;

DTC80, they are new and I haven't used them as yet, supposedly even higher coefficient of friction and faster bite than the DTC70.

DTC70, what we use in the front of Formula cars and cars with downforce (eg; sports sedans) as they have a high CoF and very quick bite.

DTC60, what we use in the rear of Formula cars and the front of cars with a little bit of downforce, plus FWD cars with LSD's, they also have a high coefficient of friction (CoF) but the initial bite is slightly more forgiving.

DTC50, I have never used these, they are a bit of an orphan for our uses.

All 4 of the above need a driver with the skill to modulate the brake pedal to mitigate the propensity to lock the wheels. The DTC60 works OK on the front of cars with ABS. I wouldn't use the DTC80/70/50 on a car that gets used on the road (or hillclimbs), their minimum operating temperature is too high.

HT10, the pad that I use front and rear, good all rounder, works OK at low temperatures, tolerant of fairly high temps, good release (handy for drivers not that great at modulation), can be used on the road, not noisy, average dust (which would be next to no dust compared to Euro pads).

Blue, the original, Hawk have tried a few times to discontinue this compound but the demand just won't go away. Much like the HT10 but with slightly lower operating temps.

HP Plus, their combo road and track pad, OK for supersprints, hillclimbs and maybe time attack in a zero downforce car with no ABS. Rather dusty and they squeal, well they did in the Evo.

That's a summary, any questions just ask and I will try and answer them as best I can.

FWIW, when I have a pad shape that I can't get from Hawk I simply choose a pad that is the closest shape but slightly bigger and then I cut them to size using the band saw. Hawk pads have high tensile backers, so a hack saw is not recommended (your arms will fall off).


Cheers
Gary

[simon k]

Thanks Gary, I'll keep going on the MC path for now because the pedal is poor when the car isn't moving, so unless the pads are made out of cardboard it shouldn't matter what's in there, the pedal should be firm.

Dude at brakesdirect made some suggestions about MC which I'll chase down, SEAT Leon Cupra R may be the same but 2mm bigger bore

[sambb]

dont want to highjack......somewhat related, but Gav do you know what the stock Polo rear calipers have in them. Is it a 34 or 38mm piston. I'm finding both listed on UK websites. I suspect its the 1.4's,1.6's and maybe the diesels that had the 34's and the Gti that had the 38mm but I'm finding both sizes lisetd for the Gti. Just trying to find out for sure because I'm thinking maybe there's a couple of different rear calipers with different sized pistons getting around on the Polo's which might change the brake feel.
There's different ring gears, boot locks, airbag on/off switches in glove boxes, seat belt chimes, resonators etc. Just thinking calipers might have varied too.

[h100vw]

Would expect 38mm. But not sure

[sambb]

Gary when you say some pads are not ok for abs use, is that because they are inclined to locking as they bite abruptly
And can throw the car into premature abs intervention OR some other factor?

[Sydneykid]

Gary when you say some pads are not ok for abs use, is that because they are inclined to locking as they bite abruptly And can throw the car into premature abs intervention OR some other factor?

The reverse Sam, there are some pads that I wouldn't use in a car with limited downforce UNLESS it had ABS. Too high an effective operating temperature is the only reason not to use any "race" oriented pad in a road car, ABS or not.

Cheers
Gary

[Sydneykid]

This is a bit rudimentary but maybe worth a try. Many years ago I had an argument with a guy about how much a brake calliper expands when we stand on the brake pedal. To convince him I used a set of verniers and measured the width across the calliper without brake pressure applied and then measured it with. The difference was mm's and that's the vagueness he was feeling in the pedal. As they age and go through millions of heat cycles brake callipers get "softer" and expand more. Even high quality race callipers suffer the same, as they age they get less rigid and the pedal gets longer and harder to modulate.

Cheers
Gary

[simon k]

This is a bit rudimentary but maybe worth a try. Many years ago I had an argument with a guy about how much a brake calliper expands when we stand on the brake pedal. To convince him I used a set of verniers and measured the width across the calliper without brake pressure applied and then measured it with. The difference was mm's and that's the vagueness he was feeling in the pedal. As they age and go through millions of heat cycles brake callipers get "softer" and expand more. Even high quality race callipers suffer the same, as they age they get less rigid and the pedal gets longer and harder to modulate.

Cheers
Gary

I was thinking about calipers too, but I was looking at the guide pins and apparently they have rubber bushes that go hard and are better replaced with bronze

Our calipers are all about the same age so might have the same symptoms

ECS tuning etc. sell them in kits

I can definitely check for expansion though..

[sambb]

yeah thats the ECS caliper stiffener kit I think I mentioned to you in a PM Simon. My Audi TT calipers have that kit on them. ECS dont do it for the Polo caliper but they do do it for a Golf Mk4 Gti caliper which I believe bolts onto our hub and uses a bigger pad with more options.... I think. Hayden can you help us with that, is that true?
Hey while you're checking caliper expansion, any chance you could dial gauge the firewall at the master. I'd be super curious to see if that does in fact move when you stand on the pedal.

[simon k]

yeah thats the ECS caliper stiffener kit I think I mentioned to you in a PM Simon. My Audi TT calipers have that kit on them. ECS dont do it for the Polo caliper but they do do it for a Golf Mk4 Gti caliper which I believe bolts onto our hub and uses a bigger pad with more options.... I think. Hayden can you help us with that, is that true?
Hey while you're checking caliper expansion, any chance you could dial gauge the firewall at the master. I'd be super curious to see if that does in fact move when you stand on the pedal.

Yep, checking the flex is on the to do list. I was looking for braces on the weekend