Urgent - AP Racing Brake Kit Issues

Y

Yohan87

Guest
Afternoon all,

Although not an Audi S3 8L, please bare with me.

I have a 2000 (X) Registered Volkswagen Bora V6 4motion with an Audi S3 1.8T engine fitted.

I bought an AP Racing Kit from a member on this forum, the same as this one: - AP Racing Kit - AUDI S3 1999- 4 Pot 330 mm disc 7.5x17 inch wheel

The garage who have fitted the kit (Motorsport Specialists) are having problems getting a pedal on it and this is the latest feedback from them.

"Do you know and have checked the sizes of the pistons in calipers are suitable for the master cylinder? My current thinking is that the master cylinder is too small for the piston area of the calipers as the pedal is just crap and hits the floor, regardless of how many times or methods you use to try bleed it. Been trying all morning with bleeding it and now it’s just getting silly. There is no air coming out of the system so fairly confident that its clear. "

Can anybody help shed some light on the matter?

Does the ABS pump need bled through VCDS?

Many thanks,

John
 
<tuffty/> said:
Bled the master cylinder?

<tuffty/>
Click to expand...

I believe they have, both nipples as well.

<tuffty/> said:
http://www.audi-sport.net/vb/a3-s3-...l-a3-s3-owners-other-golf4-platform-cars.html

ABS pump generally only needs to be cycled if replaced as there is already fluid in the system and if its getting to the bleed nipples its passing through the ABS unit fine... fitting a new unit can trap air bubbles occasionally so cycling it agitates them out..

<tuffty/>
Click to expand...


Thanks tuffy, I shall pass the information on.

The ABS unit is original, master cylinder was replaced a few months back when it was on the stock 312's and the system bled fine.
 
badger5 said:
If CP5040 series
pistons
Piston Sizes - mm- Ø38.1mm x / - Ø41.3

http://www.apracing.com/product_details/race_car/brake_calipers/pro_5000_range/4_piston_caliper_families/cp5040-2/-3/-4/-5-152mm_centres.aspx

Same as I run in my ibiza on 25mm mc no problem.. good firm short pedal
not bleeding m/c is a common issue

confirm how yours measure up to these
Click to expand...

Thanks Bill,

I believe mine are from the 5200 family.

http://www.apracing.com/product_det...-152mm_mounting_centres-16.8mm_thick_pad.aspx

I was sure that the Bora V6 master cylinder was good for it.
 
Yeah bet they haven't bled the master cylinder.I had similar size brakes on my 4mo bora with no issues
 
These are the calipers by the looks..
http://www.apracing.com/product_det...-152mm_mounting_centres-16.8mm_thick_pad.aspx

They look to be the same piston sizes as the CP6600 calipers I have which would give a slightly longer pedal but not one thats on the deck...

Its plausible they have flipped the seal in the MC... I don't know how they bled them but if they have used a traditional 2 man/pump pedal method at all then I suspect the issue could be this...

<tuffty/>
 
Thanks for all the quick replies guys.

Would there be any other symptoms from flipping the MC seal?

If the calipers had been lying in my garage unused for a few months could that contribute if they are seized?
 
if mc seal is damaged you can pump up a hard pedal evenatually (engine off) but sustained pedal pressure and it sinks to the ground.. unless its very fecked in which it just wont pump up...

to islolate calipers from hydraulics, clamp the hoses to calipers and pedal should pump up hard and confrim hydraulics ok, but system volume @ caliper too much for the mc

those calipers remort 38mm/41mm pistons which is same as mine..
25mm mc on mine... whats on yours? same I would imagine

i suspect summat else is amiss

badly sized the other way, porka rears, is very hard pedal with poor clamping... shyte install.
 
Latest update.

"Your car only has a 23mm master cylinder, the rs3 uses a 25mm, same as the bloke below with his Ibiza. This will def give a difference in pedal. The pedal still isn’t amazing. The new calipers have a piston area of more than double the single pot caliper. Harvey has had it along the road and says he is happy with it now, so I guess the best thing is to give it a try and see how you feel with it."

I guess all I can do is try and see.
 
I have also used the same piston/calipers in a mk2 golf, on 23mm mc... no pedal issues.
the fact the pedal has come better must be its bled out some entrapped air.. The pistons wont have changed size ;)
 
Update 2

"Yeah no problem. Have just come back from having a run in it myself and once bit of heat into the pads the brakes are great. :) Thankfully. Took a while but got there."
 
They are indeed.

They were bedded in using that procedure that Bill posted online somewhere.
 
First impressions: -

The pedal feels as long as it did before, only this time there is more bite once the brakes do engage. I don't see what I can do to make it harder and it had about 12L of fluid bled through it yesterday.

The master cylinder is a few months old and a genuine VW part. When the car is off the pedal is very firm.

I'm now wondering if it's to do with the plumbing of my brake vacuum pipe. Maybe a valve the wrong way round?

This is the only picture I have at the moment so I'll take a close up tonight.

P1020030.jpg


I definitely don't have any boost/vacuum leaks but if that one way valve was the wrong way round, how would it affect the pedal?
 
Hard pedal is normal when the engines not running... gets harder as you pump as the servo loses vacuum... pedal will sink again when the engine is started

<tuffty/>
 
there's still a lot going on in that bay bud :happy:
 
<tuffty/> said:
Hard pedal is normal when the engines not running... gets harder as you pump as the servo loses vacuum... pedal will sink again when the engine is started

<tuffty/>
Click to expand...

Agreed. But I was wondering that if I had that check valve the wrong way round if that would affect the pedal feel?

olethalb said:
there's still a lot going on in that bay bud
happy.gif
Click to expand...

Tell me about it.

I need another car for a month so I can take this one off the road and tidy it up. Unless you fancy a road trip up North to blitz it one weekend :p
 
Just to provide a conclusion to this thread, it appears the issue has been solved.

Car went in for an MOT yesterday and the tester noticed that the connection between the front right brake hose / caliper wasn't as tight as it should've been and fluid was leaking out.

He tightened it up and the pedal is definitely a lot firmer this morning, and that's without any re-bleeding of the system.

Doesn't appear to have lost much fluid looking at the reservoir but perhaps one final bleed would be worthwhile now that the leak has been spotted.
 
its always the ****** simplest things that go unnoticed
 
Right I'm bringing this one back because I'm still not happy with the brakes.

I have changed the following in an attempt to improve it: -


  1. New Master Cylinder
  2. New Rotors
  3. New Pads
  4. Rebled the system multiple times with varying time/mileage delays in between bleeds
  5. Replaced brake booster vacuum hose from the inlet manifold to the servo

I still can’t even get the wheels to lock up with them!

Does an ABS pump bleed via VCDS make any difference and is it worth trying?
 
Have you tried fitting a std set of calipers/discs back on? it just might be that the calipers are unsuitable?

You could try cycling the ABS pump but have not had to do this on brake installs normally...

Does pumping the brakes make them more effective? maybe getting pad knock off some how?

<tuffty/>
 
That's my next plan tuffty. Still got my stock 312mm setup so will pop them back on and see if I can get a firm pedal.
 
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