8E0 Rear Brake Upgrade

[John B]

Will this brake me?

Hi Greg, Well countless brain cells have been sacrificed on this particular conumdrum. I haven't had time to write it up yet but I have photos, measurements and rough drawings on my proposed set up for the rear, which is (IMHO) an elegant solution that does not involve the 8EO set up but something rather more juicy....here's my train of thought in later posts.

[John B]

Floating v fixed calipers

Having re-furbished the S2 standard rear calipers due to binding brakes and doing the same to other sets of floating calipers over the years, I got to thinking that floating calipers are fundamentally flawed in that they rely totally on the guide pin mechanism working perfectly all of the time. As soon as this process is thwarted e.g. the pin surface gets worn or a gaiter splits (common) and dirt gets in, the caliper will begin to stick and not centre laterally on the disc. In this and other regards fixed calipers are far superior to floating calipers IMO. High-end performance cars have fixed calipers front and rear e.g. most Porsche models. My view is that floating calipers are employed largely on cost reduction grounds.

[Greg_S]

Sounds intriging, are you using porker calipers or something?

[John B]

Brake balance

As most will know, the standard upgrade on the front is the Boxster/996 C2/C4 caliper and RS2 caliper carrier. The front brakes on the RS2 use the 993 caliper and a 304x32mm disc and the rear brakes use a 944S2 rear caliper and a 299x24mm disc. The master cylinder on the RS2 is the same as the S2.

This got me to thinking about brake balance with the standard S2 upgrade:

Discs
We use 323x30mm front discs from the first generation S8 (or 314x30mm). Why not use 280x22mm rear discs also from the first generation S8? Yes, I know these are smaller than the 300x22mm discs on the 8E0 conversion but we already know that the S2 coupe cannot have the standard 8E0 conversion and has to run with discs shaved to 280x22mm because of the handbrake issue. Anyway bear with my logic for now.

Calipers
We use front brakes from the 996 (part numbers 996 351 425 11 and 996 351 426 11). Why not use the rear brakes from the 996 (part numbers 996 352 421 11 and 996 352 422 11)? Ignoring the handbrake issue (which is not insignificant), the hydraulic balance between the calipers appeared to be ok and the discs on which they brake are broadly similar (299x24mm v 280x22mm)

Caliper carriers
Herein begins the crux of the problem in that we need a carrier (sometimes called an adapter) that will cope with the 996 calipers and potentially the handbrake (see later posts). Anyway, my logic went that if the RS2 caliper carriers worked for the front calipers (they have a 130mm bolt spacing from caliper to carrier) then they should work for the rears (they also have a 130mm bolt spacing from caliper to carrier) or at least be a good starting point for a solution.

Handbrake
I won't spoil the intrigue of this tale by spilling all up front (sounds familiar!) but my thoughts at this point consisted of 3 options: -

1) A similar set up to the RS2 (and BMWs, Subarus etc) where a drum brake exists inside the rear disc
2) A separate mechanical handbrake device that fitted to the 996 caliper to allow the caliper to act as a hydraulic foot brake and separately as a mechanical handbrake
3) A separate mechanical handbrake attached to the caliper carrier or otherwise to the car similar to the R8 / Lambo Gallardo / Jaguar XKR

Please bear with me as I post my voyage of discovery (which is not yet finished, I hasten to add and may yet come to a complete dead-end) and share you good folks tall tales of braking componentry.....

[S2central.net]

I have no doubt that a technically superior solution is available, but cost is going to be the tricky bit.

[John B]

Cost

Hi Paul, not decrying the copious amount of work you put in to develop the 8E0 solution: far from it. Being of the bean-counter-type I too have an eye on costs and am aiming to get this li'l project within reach of the 8E0 cost. I felt it was time to give somet (as we say in Cumbria) back to the Forum that may be of use and collect together some of the threads that are spread far and wide on this subject. Cheers, JB

[S2central.net]

Go for it - not trying to dampen your enthusiasm one bit...

[John B]

996 rear calipers

OK....so you have been tempted?!

This is the end result (almost but not quite). Excuse the rusty bolts!


And here is a close up. Black is the way to go with these upgrades. Understated yet powerful IMHO.


Still interested?.....

[S2central.net]

Spill the beans matey... all of them

[John B]

Discs

I'll introduce you to the stars of the show one by one. Remember because I ain't finished yet, this show may be a block buster or a tragedy....or possibly a comedy where you guys can all have a laff at all that has not been achieved!

Anyway here is the first member of the cast (LoL cast iron), the humble first generation (96-03) S8 disc bought from Brakeparts for the princely sum of £17.25 per disc + VAT + delivery.

The is the outer face: -

tn_DSC01373.JPG

The disc is actually made by Apec. Not quite EBC but I'm keeping the cost low in the name of research!

This is the inner face: -

tn_DSC01376.JPG

Usual 5x112 PCD etc but this view shows more of interest: -

tn_DSC01378.JPG

Here you can clearly see the tapered insde face of the disc from the hub interface towards the inside of the vents. Now the other feature that is important is the width of the surface that runs around the inside of the vents for a potential drum in disc handbrake solution (see above and later posts on this)

Anyway this fella is a star of the show albeit he is a bit on the hefty side!

[S2central.net]

Thate the 280x22mm disc rfrom A8/S8 - right ?

[John B]

996 rear calipers

Now you've met the rookie star-to-be, here is the anchor man (ha ha). This is Mr. dependable otherwise known as the 996 rear caliper from the Brembo stable. Now this is how my second-hand calipers arrived (dind't think i'd buy new or did you?): -

tn_DSC01257.jpg

Thanks to Porsch-Apart for these black beauties. I bought my fronts and rears from them. They can be contacted via
www.porsch-apart.co.uk/

....and the best bit was that they cost £220+delivery+VAT (£266.80) delivered to my door. That included the original Jurid pads (yeah I know they are not Ferodo but hey that is what Porsche supply) and the pad anti-rattle shims. Here's my attempt at a clean up (no marigolds here!)

tn_DSC01263.JPG


And the end result was fairly pleasing: -

tn_DSC01282.JPG

Other notable features are that these are built to accept 24mm wide discs and so 22mm are not a problem as regards the pad guide pins, unlike the front where the calipers are only designed for 28mm wide Porsche discs and we ask them to fit round a 30mm wide S8 disc, hence the filing of the guide pins by ~1mm each side on the front. Also the anti-rattle plates are separate for each piston in each side unlike the fronts where each shim plate has two of the springs attached. By the way, just like the front calipers, the pistons in each side are different diameters such that the pad is applied to the disc in a slightly angled way to avoid squeal and give progressive applications.

Anyway that's enough for now...time for some shut-eye...TTFN

[CliveH]

cant wait for the next instalment...!!

[S2central.net]

Lets see the custom brackets then, but more importantly - a handbrake !!!!!!!

[John B]

Rear Discs

Just grabbed a few moments at lunch to write up this on discs. Hope this answers your question on disc size, Paul: I am not privy to the family album and cannot confirm the part number though.

Pictures are courtesy of Brakeparts and I'm probably breaching their copyright but this is in the interests of research and potential future sales, so hopefully they won't mind!

Here is the original (puny IMO) 245x10mm original disc fitted, which looks embarrassingly small compared to the S8 discs up front: -

S2 Original Rear Disc (245x10mm).jpg

The important dimension here is the hat height or measurement C in the diagram, (which is 39.8mm in this case) as this determines where the caliper needs to sit in relation to the hub face.

Now look at the Neu S4 rear 300x22mm disc, which is machined down to 280mm for the Coupe 8E0 conversion: -

Neu S4 Rear Disc (300x22mm) conversion.jpg

Here the hat height is lower at 36.4mm.

Finally, look at the proposed S8 rear 280x22mm disc: -

S8 Rear Disc (280x22mm) for 996 rear conversion.jpg

This time the hat height is 46.2mm.

The upshot of the measurements that I took (you'll see these in later posts with pictures) is that in order to accommodate the 996 rear caliper on the strut using the RS2 bracket (modified), is that the disc needs a longer hat height i.e. the disc surface sits further inboard than either the standard or the 8EO set up.

Just to assuage your thirst for knowledge here is peek of what is to come: -

tn_DSC01369.jpg

Will post more when I can....