What Disc Size.

[bilko0795]

I am about to embark on a rear Porsche brake conversion the calipers i am fitting are normally fitted to the fronts of our cars part no's 425/426 and not the 421/422 ones with the 312mm disc these use i believe a 323mm disc so i am wondering if these same diameter discs can be fitted to the rear of my car or can i still get away with using the S4 300mm x 30mm ones from the B5 S4.

[andy10v]

Have you worked out the piston sizes before you fit them?

If you have front calipers front and rear I think you might have a lot of pedal travel unless you change the master cylinder, also interesting bias.

[bilko0795]

Have you worked out the piston sizes before you fit them?

If you have front calipers front and rear I think you might have a lot of pedal travel unless you change the master cylinder, also interesting bias.

Good question and no i havn't worked the piston sizes out but i shall find out.

[GazzaG60]

piston on the rears and accepted disc width for the gt2 6 pot front and 4 pot rear was a lot less as was the piston size.

if you must have the 4 pots on the rear id get some smaller rear calipers.

if not id go with one of the other conversions and put the cash into 6 pots up front.

[bilko0795]

Right i got a bit confused with these calipers they are in fact 996-352-425/426 and not the 351's fitted to the front's so can i still use the S4 disc's 300 x 30 or do i have to go bigger.

[Rusty]

So those are designed to be used with the 429 430s you are selling.

Don't bother with upgrading the rear brakes so much if you're only running 323s up front.

My 314mm conversion with stock callipers is too much with 314mm fronts... Don't forget an S2 is front front heavy and the 911 is very rear heavy, so you'll need a bias valve.

Carrera is 330x28 front, just search Porsche parts store for rear sizes.

[Error404]

As above that's a bloody big caliper for the rear Ray, are you going for 380mm rotors and 8 pots up front?
I would go so far as to say there is no point in having a multi-piston rear caliper on these cars at all unless you are able to get better weight distribution. With factory weight distribution you need to dial the bias down that much there is no point in having them. They do look cool though

[bilko0795]

As above that's a bloody big caliper for the rear Ray, are you going for 380mm rotors and 8 pots up front?
I would go so far as to say there is no point in having a multi-piston rear caliper on these cars at all unless you are able to get better weight distribution. With factory weight distribution you need to dial the bias down that much there is no point in having them. They do look cool though

Yes they do look the biz, i have had them for about three years now they came with the fronts i have fitted along with 330x32 disc's from a merc e320 and when i read john's thread on the rear upgrade i thought they do look nice and would improve the breaking thing is i have got everything now apart from the handbrake calipers which i have ordered so i am now in a bit of a what to do now situation i mite as well get them fitted just for the bling factor

[Error404]

Personally I'd sell them and fit the smallest piston size mono-blocks you can from a 2.5 or 2.7 Boxster, also fit them on a small diameter disc, I'd be looking at the S4 300x22 disc or RS4 2 piece rotor 312x22. This will reduce the rear brake force significantly and also help reduce the rather large amount of unsprung weight you will have on the rear.

IIRC the Boxster rear calipers are 986-352-421 & 986-352-422 and have 25 & 27mm pistons - even then you have ~ 2 x the piston area on the rear over standard.

[bilko0795]

Personally I'd sell them and fit the smallest piston size mono-blocks you can from a 2.5 or 2.7 Boxster, also fit them on a small diameter disc, I'd be looking at the S4 300x22 disc or RS4 2 piece rotor 312x22. This will reduce the rear brake force significantly and also help reduce the rather large amount of unsprung weight you will have on the rear.

IIRC the Boxster rear calipers are 986-352-421 & 986-352-422 and have 25 & 27mm pistons - even then you have ~ 2 x the piston area on the rear over standard.

They mite prove hard to sell same as the fronts as most bods on here have already done this upgrade. any idea what size pistons are on these they do look a bit small.

[Error404]

28 & 30mm IIRC.

[bilko0795]

Would these be suitable for a golf front upgrade as my son knows someone who might be interested.

[bilko0795]

28 & 30mm IIRC.

Just messured these and they are 20mm and 25mm.

[Error404]

You need to measure the piston O/D or the piston bore not the top of the piston where the dust boot lip is, as that is a smaller diameter

[bilko0795]

If they are 28mm/30mm then they are the same size as the Rs2/996 rears which are fitted to johns upgrade i know this is a bore but im just trying to justify fitting them or sell them, i have e.mailed a porsche guy for the rear disc size as im getting two sizes on searching 299x24 and 330x28 both fitted to the 996 but different years.