Audi UR Q brake master cylinder options....???

[speedfr38ky]

Hi guys,

My car has a vacuum brake conversion done on it. I have also recently had my brakes upgraded to an AP Racing kit but am not at all happy with the feel of the pedal nor the braking performance once I hit the pedal. The pedal gives no feel or consistency making braking distances hard to judge and the braking is poor to say the least. To describe it best its like hitting a load of pedal slack followed by a wooden block under the pedal and theres just no bite. The car feels like its got glazed discs (which it hasnt). Its not right and the brakes should make your eyeballs ache.

I suspect its the master cylinder and reservoir which just dont work with these calipers. Am wondering what alternative options there are instead of a 20v RR brake master cylinder and reservoir? There is no air or leaks in the system.

Thanks for your help...
Adam.

[Error404]

What MC do you have? The stock S2 1" cylinder should be fine if its in good order and the system is properly bled & discs & pads in good order.
Only when you start going to really big calipers like the RS4/6 8 pot do you ideally need a larger MC.
TBH compared to modern cars with tandem boosters, the brakes do require a lot more effort but there is normally good pedal feel to go with it.

If you have a lot of pedal travel I'd say you have air in the system or some issue with the pads wearing unevenly/disc run-out.

[adam g]

Have you bled the air out-of the nipple on the master cylinder under the reservoir.

Sent from my D5803 using Tapatalk

[speedfr38ky]

Alex, the system is all new mate. Even the mc is new for a 20v RR bought from Pete Reeve. All new calis pads n discs. Car hasnt been driven in anger yet. I agree there needs to be more effort put in when braking but this has no feel nor stoppage. Something defo isnt right, as I say these should warrant four point harnesses. But think you are right its gotto be air in there. It feels like it from my experience....

Adam, I was unaware about there being a bleed nipple under the mc....it could well be this. I didnt see martin bleed from anywhere other than the calipers when the kit was fitted. I will investigate. Thanks.

[steverrquattro]

Its VERY important that you bleed them in this order....................

Master cylinder.
Proportioning valve (check for leaks on the front of the valve).
Rear right caliper.
Rear left caliper.
Front right caliper.
Front left caliper.
At least 500ml of brake fluid must pass down each line.

Also, when was the Brake Accumulator last changed?

[speedfr38ky]

Hi Steve, yes thanks for the advice. I dont think Martin did anything other than bleed at the calipers. So sounds like thats it.
Im not sure when the accumilator was changed but will find out. Cheers.

[terrybullwon]

Hi guys,

The car feels like its got glazed discs (which it hasnt). Its not right and the brakes should make your eyeballs ache.

All new calis pads n discs.

Daft question maybe... But you have bedded your discs and pads?

[LHD_Kid]

Does it still have an accumulator as it's been converted to vacuum?

[steverrquattro]

Does it still have an accumulator as it's been converted to vacuum?

Correct and I should know as I converted mine on the SWB car

[speedfr38ky]

Yeah sorry guys. Brake bomb has been deleted as its vacuum now.

And yes Terry, they should be bedded in by now. I've driven it about 400 miles and done the bedding in from the off. Plenty of brake dust on the rims. Whether or not the way in which the brakes have felt have affected the bedding in process or not I couldn't tell you, as it just feels the same, little feel, bite or stoppage power even with a heavy foot. however the discs aren't glazed and look fine.

Like as has been said, I don't recollect bleeding them from anywhere other than at the calipers so strong possibility that there is still a little air in there if the MC hasn't been bled.

[Pirvu Eugen]

where is connected the vacuum hose for the booster?
Straight in the intake?

[Pirvu Eugen]

with engine stopped...press pedal few times then, keep the foot on the pedal and start engine. You should feel the pedal going down, as the servo is doing the job.
is doing this?

[speedfr38ky]

Pirvu, I couldnt tell you if this is the case because the car is off the road now and has a new engine being built. So for the timebeing I cant start it or anything at the moment. This is something that was playing on my mind shortly before the engine needed to be replaced (which is an altogether different story of epic misfortune).

[quattro-nick]

maybe a stupid question but have you checked that the bleed nipples on your front and rear calipers facing upwards? air always sits on the highest point!

[speedfr38ky]

yeah thanks Quattro Nick I will get that checked when they are bled.