S2 / RS2 brakes specs etc

Started by wilco, January 19, 2009, 11:18:00 AM

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wilco

OK, I'm at a bit of a roadblock with my brakes on my Coupe quattro.

After the A8 rear calipers went on I have lots more pedal travel.  Both my wof guy and me think its too much.  You can feel the pedal pushing through the rear stroke into the hard of the front piston in the master cylinder.
I've been told that yes if you increase the rear caliper piston size by only a wee bit the pedal travel increases a lot, despite being able to fit pretty much anything onto the front.

What I want to know is (and I've looked around a lot to date without answers..)
1. how did Audi do it on the RS2 with respect to having the 4-pots on the rear (must have much more fluid displacement than stock)?
2. what master cylinder specs the RS2 has, same as 3B and ABY S2 I understand but what is it?  Might be different than a std B4.  The local brake master suggests the stroke ratio on disc/disc cars doesn't vary much, ever. Master cylinder diameter changes give more push but the ratio remains much the same I think.
3. Are there any Audi or VW models that used a rear caliper with a 38mm piston and vented rear rotors?

The A8/S8 used 20mm vented rotors but with a 43mm caliper piston.  I can just squeeze the std 38mm caliper over the rotors but need to use nearly worn-out pads to fit the reduced gap.

Any (useful!) ideas out there?

W.



typ53

The Fleet:
Orange Roughy:'90 16v Corrado
'89 Carrera 4. 
'12 330d Touring
Still trying to figure out how to get 'em all to fit in a single garage....

wilco

Duh, how did I miss that?  Thanks 53 that gives me some of the answer - the different stroke lengths of course. I had thought maybe they'd used a stepped bore like the 944 et al. Just need to confirm which are front/rear, ie the 13/22.5...
Gives me something to explore. Thanks.

typ53

They look to be fairly common,  the Audi 200 quattros have them, as do late 100 quattros with AAD/AAR/AAH/ABC/AAN engines have them, as do the later coupe quattros from '89 on (KV/NG/NM/7A/3B/ABY/AAH/ABC) and the last of the 80 quattros also (late '92 on with ABK/6A/ACE/NG/AAH/ABC/ABY).  So you shouldn't have too much trouble finding one to fit.

Vagcat is such a good tool.
The Fleet:
Orange Roughy:'90 16v Corrado
'89 Carrera 4. 
'12 330d Touring
Still trying to figure out how to get 'em all to fit in a single garage....

wilco

Yeah not bad. I see the A8 has an 18/18 stroke which might put it all awry.
Now I know what the differences are meant to be I can measure the stroke easy enough.  I have a 25.4mm, 23.81mm x 2 and the original 22.2mm master cylinder that I can play with.  Hopefully I already have one that will work.  I'm hoping one of the 23.81 ones will be ok as one is from a car that had G60's and 38mm rears as opposed to the Lucas 57mm/38mm rear.
Fluid dynamics eh?

W.