Front / rear braking percentages? Is it equal, or does weight distribustion / brake dive mean most of hte braking is done in front?

If so, and one plans on taking their beloved A4 to the track one day, could one save a few bucks and get cross drilled rotors in front, and slotted in rear.

Also all you guys with slotted or cross drilled rotors - Any reduction in wet braking problems? Archives: some yes and some no.

Slack
99.5 2.8M

And there isn't a proportioning valve. The fronts do most of the work, so yes you can and should go with the superior brake setup in front. Try searching Cathleen's postings under Alcon. She has done a very serious brake setup, including changing pads for the track (which is a good idea). Are you just upgrading rotors, or going with 4 pot calipers too? Good luck and keep us posted on the results.

Regards,
Rodney

'99 A4 1.8tqms

I have had cross drilled rotors on my car for the past 32K miles. First I had the
Brembo rotors...and now I have the Zimmerman (both cross drilled). I read somewhere
that 80-85 percent of braking is done with the front brakes....so I only replaced the
fronts (both times). Most of us that play with our brakes only do the fronts. The Brembo
"BIG" brake kit is ONLY for the front. I dunno...that is my 2 cents worth.

If anything...the cross drilled rotors slightly helped in the rain. And, I have been on
track with cross drilled rotors...IN THE RAIN.

Steve S.
97 2.8QM

Yes, there is a proportioning valve. With our abs series there is active proportioning front to rear to reduce brake dive. We still get some, but it is nothing compared to older cars. As to the actual ratios allowed by this system I don't know.

As Steve mentioned, the work is all done by the fronts (70-85%), so changes there will have the greatest impact. However, for serious use I would definitely upgrade the rears to the S4 kit. For track use on a low budget get some Ferodo pads (ds3k) or porterfield R4's, something that doesn't go off at high temps, and some Dot 4 or 5.1 spec fluid. If you stick to the stock brakes, run some ducting to to the brakes. It doesn't have to be fancy, once the stocks get hot they stay hot and boil the fluid.

Only stupid people who ask questions. ;-)

There is? Is it manually adjustable? I was under the impression that we could not adjust the proportioning in the stock system. What does the S4 brake kit involve? I am under the impression that going to 4 pot calipers all around would also necessitate upgrading the master cylinder. Thougths?

Regards,
Rodney

'99 A4 1.8tqms

actually, given that I just read that the RS4 has duals, I am sure

from what I have heard from the Porsche grapevine, and I think it is also the case for Audi's, don't buy drilled rotors unless the rotors were made for drilling. Just drilling holes in a std. rotor will lead to very rapid rotor cracking between the holes. Both my old '84 Porsche Carrera and present '95 Porsche 993 have factory drilled rotors, and they still crack after about two years (before the rotors warp or wear too thin).

The recommendation for cars that have non-drilled or non-slotted rotors is to install the slotted ones. They provide similar benefits as drilled and last longer. Supposedly, the helical-cut are better than the straight-cut from what I have heard..

I'll go along with EricR on his fluid and ducts recommendations.

an electronic rear pressure regulation. Audis in the past have used a "height sensing proportional valve" which reads wheel position versus body position or spring compression to determine how heavily the rear end is loaded. This also compensates for brake dive. As the rears are unloaded, the pressure to them is reduced. The new electronic valve is probably an improved version of the old mechanical valve which had a tendency to stick. Front to rear pressure often runs in the 75/25% range. Upgrades to your brakes should be as follows. Pads, Slotted rotors (front), cooling ducts, rear pads. If you want serious brakes upgrade to an S4 set up. Nobody does it like the factory. And yes the S4 setup would likely require a larger diameter master cylinder to match the twin pot front brakes.

Good Luck.

mac 99.5 1.8QMS

I have yet to see an S4. We don't get much for cars here regardless. Steve S. tells me that the fronts are 4 puck (2 on each side of the caliper) and the rears are single puck (as I remember it). The only problem according to an Audi tech is that the whole front hub is different (aluminum, new bearing system). So no go there unless I have a lot of money. The rears sound much more likely for a retro fit. And, yes, Audi states that they have at least 1 and likelier several, new master cyl. in 2000 for the A4 and now for the S4.

1)"Nobody does it like the factory."

The S4 brakes, judging by the resultant numbers, are not significantly better in performance than the A4 brakes. Remember, it's what market will bear and when mass marketing, they have to keep in line with competitor pricing and performance. They could not possibly put the "best" brakes on the car and make any money. The "best" brakes for that car ARE available via aftermarket and do cost what they are worth in performance. The best brakes for those cars were on the Audi A4 Touring Cars.

2) "And yes the S4 setup would likely require a larger diameter master cylinder to match the twin pot front brakes."

NOT SO. Many big brake upgrades using the Brembo/Porsche twin turbo (a.k.a. Big Red) 4-pot calipers and also the Alcon B-type (a.k.a. Audi touring car calipers) have been done using the stock A4 master cylinder. These have been track tested and have phenomenal performance numbers. You don't need to graduate to a larger master cylinder until you go to a 4-pot caliper/big brake upgrade in the rears.
If you need more info, give Todd or Greg a call at Vortrag. and they have done extensive research and development and can give you all you need to know about the brake systems.
-Cathleen *modified A4qm including Alcon B-types 4-piston calipers/13" Coleman rotors up front and Alcon R-types/11.9" OEM front rotors in rear.<ul><li><a href="http://www.vortrag.com">Vortrag Motorsports, Inc.</a></li></ul>

See what happens when you read the last post first! I didn't have the whole story, sorry.
I didn't get the impression from your post about the S4 front brakes being used in the rear, until I read the posts underneath yours. I should be more thorough.
Anyway....One notable item. Cameron (fellow A4.org'r) has 4-piston Alcons all the way around. He has Vortrag kit/Alcon 4 piston B-Types up front and Alcon 4-piston H-types in the rear. This necessitated a larger master cylinder for the fluid demands.
As an interesting side note. I happen to know a fellow Quattro Club member who did a DIY 4 piston brake upgrade both front and rear on an older Audi. Not the safest looking stuff, IMO. In addition, he was still using a stock master. At Blackhawk Farms Raceway, this summer, his brakes kept failing because they could not keep up with the fluid demand. It was a bad story. IMO, this is not an area to skimp on if people are serious about performance and want to get in to track events.
Regards,
-Cathleen