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**chancha** · 7 November 2004, 15:36

forgot to say.........

something else I rememebered.......when I disengage the abs, I cannot however hard i try, manage to get the fronts to lock up.......... although the back will under severe provocation.............

**dan_b** · 7 November 2004, 16:00

You will have less relative servo assistance now: don't forget that the internal fluid volumes of those whopping 4-pot calipers is much larger than your previous 2-potters, and there are more pistons to move. The servo was designed for less pistons and less total fluid, so you'll now need more force with your right boot to move it all.

Have you checked your brake fluid levels - you may be low on total fluid in the system?

You might have an air lock in the system I suppose, or you might have some old fluid still in the sytem - what order did you bleed the brakes in? Right rear, left rear, front left (both bleed valves, outside first), then front right (both valves, outside first)

**Doug_RS2** · 7 November 2004, 17:24

I drove this car today and the pedal is hard but it takes a lot of leg power to stop the car - I couldn't get the car to lock up - even after getting some heat into the brakes.

**chancha** · 7 November 2004, 18:03

hi again......

Bled the brakes, rear right, rear left, front right then front left......but when the fronts were done I bled both nipples at the same time not outer first then inner.........

**chancha** · 7 November 2004, 18:04

from what I remember also, the originals did not feel as if there was much in the way of assistance either...........

**twoqu** · 7 November 2004, 18:29

Hi!,

If you don't have a spongey pedal, i.e. one that pumps up, then its probably not air in the system. I think other "experts" recommend bleeding with the pedal down using an easibleed or other pressure system. Look on Phil Payne's site. I think I remember something being on there.

It might be you are experiencing one of the benefits of an upgrade. Increased pedal feel. I guess you had the twin pot G60's. With these you have to virtually bury your foot through the bulkhead. It was a common complaint that they were difficult to modulate due to the travel. Now of course the pedal is near the top!

Not sure its a valid test, but if you put your foot on the brake and start the car, the pedal should sink indicating the servo is providing assistance.

Other than that, you will need to examine master cylinder sizes. As a rule of thumb, if you have a hard pedal that fails to stop the car adequately, you need to either decrease m/cyl bore or increase caliper piston sizes.

Arrgh! Going back to your first post. You aren't using 996 rear calipers are you? I believe these have small pistons and are all the same size. The fronts have larger differental bore pistons! Get the p/n of the caliper and maybe we can cross reference to be sure!

**twoqu** · 7 November 2004, 18:41

Hi,

This is the link I was thinking of.
http://www.isham-research.com/quattr..._bleeding.html
Hope that's of some help!

**chancha** · 7 November 2004, 19:04

hi......

Thanks for the advice. For what it's worth, the claipers supplied were 996 but they are rear calipers....... there are two different sized pistons on both.............

**twoqu** · 7 November 2004, 19:14

Originally posted by chancha

Thanks for the advice. For what it's worth, the claipers supplied were 996 but they are rear calipers....... there are two different sized pistons on both.............

Hi!,

Well I guess that is the problem. I havent heard anybody else complain with their upgrade. I guess the RR isn't a lot different to the S2 brake set up. The pistons on rear calipers are significantly smaller than those of the equivelent front caliper. The only way to rectify the problem according to the info I have is to either change the master cylinder for a smaller bore one or increase the piston size of the caliper. Thats what made me think that you have used rears not front.
If I get some time later, I will look for the piston size difference. It is considerable. I think the fronts have 44/38mm and the rears have 28mm or something.

**newsh** · 7 November 2004, 19:28

I can't believe Corey would have sold you rear calipers..

My 996-A8 setup felt a bit "wooden" for the first few hundred miles untill the discs and pads had bedded in, I was dissapointed at first, now I love them, good feel, good bite, good power. No complaints at all.

I take it you washed the discs off before fitting them?

**twoqu** · 7 November 2004, 19:56

Originally posted by newsh

I can't believe Corey would have sold you rear calipers..

My 996-A8 setup felt a bit "wooden" for the first few hundred miles untill the discs and pads had bedded in, I was dissapointed at first, now I love them, good feel, good bite, good power. No complaints at all.

I take it you washed the discs off before fitting them?

It's always handy to have someone who has done something similar comment.
Have you used the front 996 caliper. If so, that would support my argument.
As for not selling rears. Well it seems he was quite happy to supply "odd" calipers i.e. not a pair!
The only info I have found is that most of the porsche front calipers seem to have 36/44mm pistons, whilst the GT3 rear has 26/28mm. That is assuming these are the ones you have. Dosen't sound like a big difference but in terms of area it is quite a difference! Get the caliper p/n so we can identify what you have. Some listers have the Porsche electronic catalogue for reference.

**newsh** · 7 November 2004, 20:06

Mine are the black 996 - Boxter S calipers.

Copied from a previous post:

"996.351.425.11 Left Front, 996.351.426.11 Right Front (as far as I know the last 2 digits refer to the colour)"

**newsh** · 7 November 2004, 20:08

IIRC you can identify the rear calipers by a lump cast into the body, there's pics on here somewhere.

**chancha** · 7 November 2004, 20:19

thanks agian.........

Thanks again guys.......I have the part number for one of the calipers,
996 352 421........ the pistons are definitely differnet sizes because I had to replace one of the seals and had to order from my local porsche dealer. The piston size was 28mm...........just had the car out and to be honest it does brake, no fade, it's just effort required is more than Iwould have anticipated.
As to the argument for front or rears remember that my standard wheel size is 15 inch. Perhaps the fronts would be too big for the wheel.......In coreys defence he did ask me to send the kit back when I told hime the brackets did not fit but he obviously does not know there is a dfiferent offset for black and reds....... and to boot it cost me an extra Â£90 to have to the red noe painted.......... you live and learn I suppose

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Brake upgrade issue......

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