# Porsche caliper issue



## 20v master (May 7, 2009)

I have installed Porsche calipers 996.352.425/6 calipers on the front of my MK1 TT with stock sized 12.3" discs with Hawk HPS pads and SS lines. I have the calipers in correct orientation (smaller piston leading, crossover tubes on bottom, bleeder screws pointed up), they bled fine, the pedal is firm, and the car stops fine in daily driving and the pedal though firm, is easy to modulate. From my research, the calipers are 996TT/C4S rear calipers. The issue I'm having is that I can't engage ABS. There is clamping and the car stops aggressively, but at full pedal pressure from 80mph, I get smooth stable deceleration but no ABS intervention, with the pedal on the floor. Obviously I haven't done back to back brake testing, but I have a feeling the OEM two piece single piston calipers would stop shorter than these Porsche four piston fixed calipers. It "feels" like there is a fluid restriction that doesn't allow full line pressure to reach the pistons, almost like there is a pressure reducing orifice built into the calipers. Anyone ever experience anything like this or know of a solution? I'll ditch the calipers if they aren't the proper application or can't be made to work, as I bought them cheap off a friend that needed cash. Thanks in advance.


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## Chickenman35 (Jul 28, 2006)

How many miles on the Hawk HPS pads? They may not be bedded properly to the rotors yet. New rotors an take up to 500 to 750 miles of stop and go city driving to bed in properly. Old rotors may have material deposits on them that require really aggressive bedding to bed in. Until pads are bedded to rotors properly, braking force can be greatly reduced.

Juts noticed you used REAR calipers? Do you know the piston size? Piston size directly affects clamping force. Front Boxster and Boxster S calipers use 36mm and 40mm pistons. With the proper pads you should have know problem actuating the ABS. I have front Boxster calipers on my , and I can engage the ABS with factory ATE semi-metallic pads.The HPS pads when bedded properly should have no problem with sufficient braking.

I suspect it is a piston sizing issue.

Edit: Post up the piston sizes and I'll work out the piston volume for you. I know the volumes on stock A4's and TT's and also the volumes on Boxster and 17Z calipers. The 17Z calipers have about the maximum volume that you can get away witha. Any more piston volume and you can run into Master Cylinder travel issues.


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## Chickenman35 (Jul 28, 2006)

Juts another thought. Are those are 6 piston calipers ( I haven't bothered to check )? 6 piston calipers ( Such as the 17Z and 18Z and others ) have a bad tendency to trap air bubbles in passage end runs. You can bleed and bleed until next Sunday..but you they remain trapped. Steve ( Spartiati ) ran into this problem.

Solution is to pressure bleed while tapping the caliper with a Plastic Mallet. The tapping sets up vibrations that release the trapped air bubbles. This made a huge difference to Steves 17Z setup. He thought he had all the air out, but the tapping method released a bunch more ).


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## 20v master (May 7, 2009)

No, they aren't six piston, only four. I don't think Porsche puts any six pots on rear brakes, but I could be wrong. I'll see if I can find the piston sizes and report back. These were not recently installed, so they have plenty of miles on them to not be bedded in.


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## 20v master (May 7, 2009)

I'm a little confused at this point. :laugh: I'm wondering if the same caliper casting is used with different size pistons on different models. The part number of my calipers comes up as being used on:
02-05 C4S
01-05 Turbo/GT2
03-05 GT3
There are two digits on the end of the part number that are different for each of the above applications, but these two digits aren't on my calipers. So according to this, since my calipers mount radially, the pistons are 30mm/28mm, aka small, so seems like these calipers need to find their way into someone's hands that can use them.


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## Chickenman35 (Jul 28, 2006)

20v master said:


> I'm a little confused at this point. :laugh: I'm wondering if the same caliper casting is used with different size pistons on different models. The part number of my calipers comes up as being used on:
> 02-05 C4S
> 01-05 Turbo/GT2
> 03-05 GT3
> There are two digits on the end of the part number that are different for each of the above applications, but these two digits aren't on my calipers. So according to this, since my calipers mount radially, the pistons are 30mm/28mm, aka small, so seems like these calipers need to find their way into someone's hands that can use them.


Yep.. that'll do it. Pistons are too small.


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## 20v master (May 7, 2009)

Chickenman35 said:


> Yep.. that'll do it. Pistons are too small.


 Under heavy braking, would this cause excessive/higher pressure to the OEM rear calipers?


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## Chickenman35 (Jul 28, 2006)

20v master said:


> Under heavy braking, would this cause excessive/higher pressure to the OEM rear calipers?


Yes and No. Depends on how you look at it.

With your situation you have reduced the Front Caliper piston volume, compared to stock ( or the Boxster front calipers ). You haven't altered the " System Operating Pressure " ( Input ) but you have altered the Front Brake clamping pressure ( Output ). For a given System pressure ( Lets say 1,200 PSI in a Panic stop ) the rear brakes will still generate the same clamping force, but the Front brakes will generate less ( due to the undersized caliper pistons ). Thus, you overall braking distance would increase. 

Edit: I'm having difficulty putting my thoughts clearly into words. This article by Stop-Tech explains the correlation between Line or System pressures and Caliper clamping force ( Piston Area ).

http://www.stoptech.com/technical-support/technical-white-papers/brake-system-and-upgrade-selection


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## petethepug (May 25, 2001)

Those Porsche calipers are 996 turbo rear
(996.352.425 & 996.352.426)
[SUP]*(updated/edited)*[/SUP]

Your 225 Mk I TT has those 312x*25* (12.3") up front.

The *Cupra *that uses those Porsche calipers in place of the OE 4 pots uses *305mm x 28mm *discs. 
Those same Cupra discs are used with the *Brembo's GT Junior Big Brake Kit*. It uses *323x28mm* rotors.
The *Porsche discs *that use those calipers are *<strike>318</strike> 330x28* with pot diameters of ..........................................................28 & 30 mm [SUP]*(updated/edited) *[/SUP] *vs. the oe TT 180 54mm ATE single piston calipers
*
The discs on your car are a full 3mm/1.5 ea side smaller than the calipers were designed for. Now that I think of it, the Girling 60 calipers running on my Corrado g60 are exactly the same. When new, the g60 rotors are 1mm beyond the wear limit designated of the thicker Audi V8 rotor it replaces. There goes my theory of your rotors being too narrow.:banghead:

You should have the perfect set up. Those calipers are spec'd fine for those rotors. It's a common swap. I'd start with the easiest fix. Let the pads bed in. If that doesn't work. bleed the brakes again. My BBK felt strange after it was installed. It was because the pads had not bed in yet. It took about of week of normal dd driving before I had the pedal feel I knew from before. Brembo makes a 323x28 disc that bolts up to the Mk I TT. Upgrade to it when it's time to replace the discs. It's the disc supplied in the GT junior brake kit. Brembo # 1A4.6007a (solid) 1A5.6007a drilled

The same disc is also available as the Seat Leon Cupra R (turbo) 1.8T 323x28 in the UK and EU 2002-2005.


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## Chickenman35 (Jul 28, 2006)

petethepug said:


> Those Porsche calipers are off the fronts of the 996/Cayman/Boxster/S
> (996.351.425/996.351.426) [Snip... ]


Except OP stated he has 996.*352*.425 calipers which come up as REAR calipers according to various Porsche sources. .


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## jonpwn (Aug 13, 2010)

I did crazy research on this topic before buying and have the numbers. For the user who wanted piston sizes:

986.351.422/421 = porsche boxster fronts
1997-2008 base boxster 2.5 or 2.7L
36/40mm pistons (i rebuilt mine and measured, so these are exact diameters)
These fit the stock 312mm rotor setup (i did a mock setup but couldn't mount my wheels so took them off, reverted back to my GLI carriers setup)

996.352.422/421 = porsche 911 (996 gen) rears
28/30mm piston and cannot fit >25mm caliper

sources:
http://www.briskoda.net/forums/topic/261760-the-brake-thread/
http://www.clubgti.com/showthread.php?237256-Porsche-Brakes-for-my-Golf-with-16-quot-rims/page2


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## FastAndFurious (Feb 2, 2002)

im actually going to be doing 

996/352422/421 on front and rear of a beetle with mk4 r32 rear caliper for handbrake, lets see how it works out


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## petethepug (May 25, 2001)

Chickenman35 said:


> Except OP stated he has 996.*352*.425 calipers which come up as REAR calipers according to various Porsche sources. .


Thanks for catching my copy/paste errors. I updated the info on the rear Porsche calipers. Let them bed in and you should be fine. Look into the 323x28 disc if your pedal feel doesn't change. It's VAG part # 1ML615301
http://www.partsbase.org/seat/leon-leon-4-le-eu-2002-61536-disc-brake-for-rim/

http://www.ebay.co.uk/sch/i.html?_o...t+Leon+1.8T+turbo+Cupra+323x28+discs&_sacat=0

Don't get confused with the Ibizia Cupra discs that are the same size but 4x100. You want the Seat Leon Cupra 1.8T Turbo listed in the fine print


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## Chickenman35 (Jul 28, 2006)

petethepug said:


> Thanks for catching my copy/paste errors. I updated the info on the rear Porsche calipers. Let them bed in and you should be fine. [SNIP]


Adam mentioned in Post #4 that rotor and pads have plenty of miles on them and that bedding is not the issue. What is the issue is that the piston size of these calipers is too small ( 28mm and 30 mm ). This dramatically reduces the clamping forces which dramatically reduces total braking force. It's basic Hydraulics 101.

In a different thread, another member mentioned that he had talked to Apikol about using 996/986 rear calipers for his front BBK on his TT. He was advised against it because the the piston bore size was too small. 

Ideally you want to keep front piston volume to within *Plus 10 to 15 percent of stock* to keep the hydraulic ratio within balance. Go too big on front piston volume and you can have excessive front brake bias and a long pedal travel. Go too small in front piston volume and braking performance is decreased. WilWood, Alcon, Brembo and Stoptech all have articles on this. I'll see if I can dig up some links later..but right now I have other work that I need to get done.

Edit: Here is a link to a Piston Volume calculator:

http://brakepower.com/help_abc_27_PAC_t.htm

Plugging in dimensions for Boxster Front Calipers ( 36mm/40mm ) we get an axle volume of *14.08 sq/in* ( 7.04 sq/in per caliper )

Plug in dimensions for Adams' calipers ( 28mm/30mm ) we get an axle volume of *8.2 sq/in* ( 4.1 sq/in per caliper )

You've reduced your comparative Piston volume by 41.5% !!!. Well THERE"S your problem as the Heineman would say... :beer:


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## petethepug (May 25, 2001)

TT 225 Q have ATE 54mm single piston calipers up front. If he's moved up to 4 pot 28 & 30mm pistons. Isn't he actually over his OE piston area of 54mm vs. the new 58mm (28+30mm)? The numbers show he's over the OE piston area by 14.5%.

I'm using logic from my Girling 54 single piston swap to Girling 60 calipers with dual 40 & 45mm pistons. With my OE 54mm pistons vs. the new Girling 60 with 85mm (40+45mm) there's a new, increased piston area that's 36% larger. We're both at that 10-15% of stock that's being referenced. Both of us are using our OE rotors. Both of us are using the factory ABS. 

Using the rear Porsche calipers (996.352.421 and 996.352.422) on the front axle of a lot of VAG cars is common, accepted and has worked well for owners in UK & EU. Not really sure why they've had success with selling the adapters and kits if there were issues like what's occurring here. I say get the man to stand on the brakes with a punch the pedal like a baby carriage ran out from a cross walk. See what happens. I'm sure the ABS will kick in. 

Ironically I couldn't get the ABS to engage on a TT at an Audi event in San Diego. The instructor yelled and scared the $hit out of me. It got me to fire off the ABS while entering a slalom at full brake from at 80.


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## petethepug (May 25, 2001)

*You've got the right Porsche calipers (Carrera 2/4 rears)

 IF 

they're wide enough to fit over your 25mm brake rotor. The next step is to find the adapters others have used. 

The pic & add I copied in the previous post from Creations Motorsport shows Porsche calipers (996.352.421 & 422 ) will work. HOWEVER, I don't think they're aware that Porsche used the same part number on calipers for the 20mm wide discs as well as the 25mm wide disc calipers *



BySeaByLand said:


> The calipers I have are for the 996/boxster s and may be the rear calipers. Part number is *996.352.422*. I thought I found someone who made these work on a mk 6 for front fitment.
> 
> Sent from my SPH-L710 using Tapatalk
> 
> ...


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## Chickenman35 (Jul 28, 2006)

petethepug said:


> TT 225 Q have ATE 54mm single piston calipers up front. If he's moved up to 4 pot 28 & 30mm pistons. Isn't he actually over his OE piston area of 54mm vs. the new 58mm (28+30mm)? The numbers show he's over the OE piston area by 14.5%.
> 
> I'm using logic from my Girling 54 single piston swap to Girling 60 calipers with dual 40 & 45mm pistons. With my OE 54mm pistons vs. the new Girling 60 with 85mm (40+45mm) there's a new, increased piston area that's 36% larger. We're both at that 10-15% of stock that's being referenced. Both of us are using our OE rotors. Both of us are using the factory ABS.
> 
> ...


Haven't had time to reply by now but you have made a *basic mathematical miscalculation* from what I see. Did you read the supplied link CAREFULLY before you calculated piston areas? If you did you would see that fixed mount and floating mount calipers have piston areas calculated differently. *With floating mount calipers you have to take the calculated volume and MULTIPLY by two.* This is stated several times throughout the article. It is CRITICAL that you understand this difference in mechanical/hydraulic advantage between Floating calipers over Fixed Mount calipers. 

This is why Boxster front Calipers are recommended.

1: Stock A4 or TT caliper piston diameter = 54mm or 2.125".

Plug the numbers into the online calculator and you get a sub-total of 7.09 sq/in. But... and this is critical.. you have to take that value and double it with a FLOATING caliper. So that brings the front piston area of a stock TT or A4 to 14.18sq/in per axle ( 7.09 sq/in per caliper ).

2: Plug in Boxster front caliper dimensions. 36mm/40mm = 1.417"/1.574" . Using the calculator and we see that Boxster front calipers give a piston area of 14.08 sq per axle ( 7.04 sq/in per caliper ) Nearly and exact match to the stock caliper volume, but you can see that the Boxster front calipers have slightly LESS effective area than the stock 54mm single piston FLOATING calipers. 

3: Plug in the numbers for the Rear calipers with the smaller pistons. 28mm/30mm = 1.102"/1.181" , using the calculator we see that the Boxster rear calipers give a piston area of 8.19 sq/in per axle ( 4.08 sq/in per caliper ).

So using the rear Boxster calipers on the front equates to a *42.2% REDUCTION* in effective piston area over the Stock single piston 54mm floating caliper using these equations. . ( Not a 14.5% increase as you erroneously calculated ). If you keep the same size brake rotor, that is going to result in a dramatic REDUCTION in braking force.

I will include the pertinent section in a post below.

Edit: BTW, WilWood simplifies the design difference in Floating calipers and Fixed mount calipers by calculating the piston area of only *one side of a caliper*. It's in their Tech section and FAQ. This method seems to be less confusing to the average lay person. :beer:


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## Chickenman35 (Jul 28, 2006)

Text from the online calculator provided. Note the importance of DOUBLING the calculation for FLOATING calipers:

http://brakepower.com/help_abc_27_PAC_t.htm



> *Total area of caliper pistons per axle in case of FIXED MOUNT calipers.*
> 
> This is the area of one piston, multiplied by the number of pistons in one caliper, multiplied by the number of calipers on that axle.
> 
> ...


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## Chickenman35 (Jul 28, 2006)

I would also like to add that I speak from personal experience on running Boxster front calipers on my Audi Quattro. I teach HPDE at a very brake intensive track Mission Raceways BC ) and needed a bit more brake than stock. 

I upgraded to A8 312 mm rotors ( stock = 288mm ) and TT carriers and stock calipers at first. Pagid semi-metallic pads. This was adequate for Autocross and HPDE but I did get a fair amount of pad taper after track sessions. However, I could get the ABS chattering at 100mph stops with Hankook EVO RS1 tires. A fairly sticky tire. BTW. this required a fairly darned hard push on the ol' Brake Pedal. I happen to like it that way, but I have driven Race cars that required BOTH feet on the pedal and your eyes bugging out to stop the danged things. Those car required a lot more clamping force !!! 

I later switched to the Porsche Boxster front calipers as they were much stiffer and this eliminated the pad taper. However, even though the pedal was firmer due to less caliper flex ( SS lines on both setups ), I could brake no deeper that with the stock single piston floating caliper. Pads were similar. ATE Euro spec semi-metallic ( Porsche Brembo pads ). This make sense as the effective piston area ( 54mm single piston floating caliper = 14.18 sq/in per axle vs Boxster 4 piston front = 14.08 sq/in ) and thus effective clamping pressures are nearly identical. If I had used Porsche rear calipers ( 28/30 mm ) up front then I would have had a significant REDUCTION in clamping forces from the stock calipers or the Boxster fronts....and probably have needed BOTH feet on the brake pedal :thumbdown: 

I hope this clarifies things for people. All in the name of providing accurate info. Cheers :beer: :wave:


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## petethepug (May 25, 2001)

Hey Richard (Chickenman35),

Nice read you posted as well as links to the sites that allowed me to wrap my head around hydraulic theory. 









This has been x posted to the other recent Porsche caliper posts to clarify that PORSCHE BOXSTER REAR CALIPERS WONT CUT IT AS FRONT CALIPERS ON 99% OF THE CARS OUT THERE. 

*This fact along with Porsche uses identical part #'s for the smaller rear Boxster calipers (with thinner discs) as well as the calipers on the Porsche 996 C2/C4 rears with (thicker discs). Niether of these options will work because their pistons are too small at 28 & 30mm.* The only exception seen for using Porsche rear calipers is the 993 C2/C4 rears that run 34 & 30mm (1.34 & 1.18") pistons, BUT AT 10.02in[SUP]2[/SUP] they're still sized too small.

So the rule with using Porsche calipers on your ride is .... Don't use *rear *Porsche calipers on the front of your ride.



I'm only about 75% there on grasping the basics but the rest will come with time and application. I had a nice flashback to instructors teaching thermal dynamics from my apprentice days. I'll memorialize the rest, mostly for myself, since I wont remember most of this because I have so many irons in the fire right now.

Porsche uses FIXED calipers, mounted as RADIAL except earlier versions.

(below) Early *AXIAL *mounted *FIXED *calipers from the Porsche 944.










(below) Later *RADIAL *mounted *FIXED *calipers from the Porsche 996. You can see these need adapter brackets to mount on our VW/Audi cars.









So, moving on to Piston area of our calipers. Thank god for the piston area calculators at BrakePower.com. I put some screen shots in since it's easier to show how to plug the numbers in than explain it.
http://brakepower.com/help_abc_27_PAC_t.htm

VW uses *FLOATING *calipers, mounted as *AXIAL*

Mk I tt 54mm front Girling Axial floating caliper. 
As Richard stated, with floating calipers the final number is doubled. 







The OE Mk I TT Girling 54 front caliper has *14.18"* on the piston are NOT the 7.09" shown on the calculator.



Porsche Boxster *front *FIXED, RADIAL calipers
4 pot piston
2 @ 36mm or 1.417”
2 @ 40mm or 1.574”












Porsche Boxster *rear *FIXED, RADIAL calipers
4 pots per caliper
2 @ 28mm or 1.102”
2 @ 30mm or 1.181”


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## 20v master (May 7, 2009)

petethepug said:


> Using the rear Porsche calipers (996.352.421 and 996.352.422) on the front axle of a lot of VAG cars is common, accepted and has worked well for owners in UK & EU. Not really sure why they've had success with selling the adapters and kits if there were issues like what's occurring here. I say get the man to stand on the brakes with a punch the pedal like a baby carriage ran out from a cross walk. See what happens. I'm sure the ABS will kick in.


You may be sure of it, but you'd be WRONG. While it works, and I'm able to drive the car without incident, it's obvious something is wrong when you put the brake pedal to the floor as hard and as quickly as possible from *120 MPH* and ABS doesn't engage. Please do not insist that there is something I'm doing wrong, when the obvious conclusion was reached a long time ago in this thread, and subsequently proven mathematically, that the pistons are too small on these calipers to be used on the front of my car. :thumbdown:


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## petethepug (May 25, 2001)

Didn't Richard just point out I was incorrect?
Didn't I just redact my speculation in the last thread?
Did I not post the same links Richard did as well as visual examples using the piston surface area calculator? 
I've got no issues stating my assumptions were exactly that, assumptions.

I'm sorry you're having issues with the Porsche caliper install on your TT. Richard did a great job sharing engineering stats and resolving that another companies big brake kit (similar to what you installed) wont cut it using *rear *Porsche calipers. It's great that the advertised rear Porsche caliper conversion from Creations Motorsport I stood behind (as a reliable conversion) got debunked as severely under engineered. 

This one ...

http://www.creationsmotorsport.com/product-detail.php?pid=131









Thank you for correcting the 1st post letting us know the car was traveling at 120mph and not 80 when the ABS didn't kick in. Richard graciously spoon fed (both of us) facts and hydraulic theory. *After all the information listed below *


How and where to calculate brake piston diameters.
Porsche uses the same part number on two different calipers. 
Creations Motorsport sells a bracket to use rear Porsche Boxster calipers that will never work.
The rear Boxster calipers installed on the front axle of your Mk I TT proves Richard was correct and Creation Motorsport made a mistake.
Petethepug was incorrect in backing up Creation Motorsports product and corrected his calculations.
Petethepug, with Richard's help discovered the post from Vortex user,* christianrojas* posted data showing that 996 Carrera 2/4 Rear calipers work on VW front axles is incorrect too.

*was conveyed and clarified in petethepug's last post, there's only one matter that's not clear. *


Why are you insisting you're being told that you're doing something wrong?
Why are you changing your initial travel speed from 80 to 120 mph but expect the suggestion from the first speed you gave to also applies to your speed that's 50% faster?
As soon as Petethepug erred on the brake formulation, discovered that other users/vendors had flawed references/products, he set it straight.

BTW, thanks for being so cool and supplying all the facts Chickenman35. Hey 20v master, I'm not out to get ya. What happened? Did you not see the post I made clearing everything up before you posted?


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## 20v master (May 7, 2009)

petethepug said:


> Hey 20v master, I'm not out to get ya. What happened? Did you not see the post I made clearing everything up before you posted?



What happend was after I got the conclusive data on 07/11, is you continued the thread with rampant speculation about disc sizes, aftermarket brake "kits" that are nothing more than adapters, and referring to yourself in third person, and somehow don't see where I feel people are saying I'm doing something wrong (and you had me doubting myself, as I went out and did an emergency stop from 120mph, AFTER having previously attempted to engage ABS from 80mph, I am still driving the car with the small piston calipers on it, so I'm not sure why you pointing out the two speeds matters)....when in fact it was *YOU* suggesting more bed in was required as seen in your quote that was posted on 07/15, which was 4 days after we knew the calipers aren't a good application for this chassis.



petethepug said:


> I say get the man to stand on the brakes with a punch the pedal like a baby carriage ran out from a cross walk. See what happens. I'm sure the ABS will kick in.


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## petethepug (May 25, 2001)

It all true, I did all of that. Anyway, what's your plan to remedy the rear Porsche calipers on the front that are sized too small? Going back to oe or Porsche front calipers, aftermarket?


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## Chickenman35 (Jul 28, 2006)

Porsche 986 Boxster ( Non S model ) front and rear calipers share the same mounting dimensions, as do several other Porsche calipers. Some rear calipers will clear 25mm thick rotors. However the piston size is wrong as proven.

Boxster S front calipers are physically larger than the Boxster non-S and take the larger 996 pads. Piston size is the same ( 36mm/40mm ) but the caliper mounting is different. Some companies, like Apikol, are now providing conversion mounting brackets to fit either Boxster non-S or Boxster S calipers. 

There's not any more significant braking advantage to be gained with the larger Boxster S pads, but Pad life will be extended somewhat. Some people prefer the look of " Big Reds ".


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## bgcarter1 (Sep 22, 2013)

just picked myself up a set of Non-S Boxster Front callipers and thats the only thing that is worrying me; the lifespan of the pads and discs...


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## Chickenman35 (Jul 28, 2006)

^ as long as you picked up Quality pads and rotors life span is of no concern. Pad size and thickness is more than adequate.

I have Bendix/Zimmerman rotors and stock ATE/Brembo SM pads and pound the living s**t out of the brakes on Track Days and HPDE ( instructor ). Other than a bit of fade after about 6 laps of HARD braking I've had zero issues. Pad life and condition is still excellent. European Semi-Metallic pads are pretty darned good

I should be using a full on Race Pad for Track Days, but my Audi A4 is a DD and I just don't need to bother changing pads. HPDE are not races so I just back off for a couple of laps if I feel some fade creeping in. 

Funny story. Local track has a particular Marshal who apparently does not know that brake rotors will glow and throw sparks when a driver is braking really, really hard. I've been called in on more than one occasion because she thought my brakes were on fire :screwy:


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## Guyver96 (Jan 17, 2007)

Sorry to bring this back buy concerned since I bought rear s calipers... I did the calculator thingie as per instructions the stock piston of 54mm gave me a total of 4578.12 and the Porsche rear calipers with the 2x mm and 30mm pistons gave me 5xxx.06... So isn't that more braking power? Can't recall the exact Porsche numbers right now... So hows it work the higher the number the less braking power?

As far as I've seen the mk4 golf and bugs have one single piston per axle.. Multiplied by 2.. Gets me 7.1 the Porsche has 4 pistons 28 n 30 and brings it to 8.2... 


Oh also isn't the abs supposed to kick in if and only if the wheels lock up and car keeps moving toward? Anti lock? I say find a dirt road where you'll e all alone and not hit anything then bring it to 30 and slam the brakes... If abs doesn't kick in then yea there is def and issue.. Also brake fluid and air in the lines could cause horrible braking.. I know this cause that's how I'm driving now braking sucks! Abs wont kick in unless its really slipping.....


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## Guyver96 (Jan 17, 2007)

So I tried again... 

1 caliper per axle
Sized 2.12598425in (54mm)
1 piston
=3.5in sq x 2 
=7.1 now that's per axle! 

So left and right =14.3 total!


Now Porsche 

2 calipers per axle
Sized 1.18110236 (30mm) x2 & 1.1023622 (28mm) x2
4 piston
=8.2 per axle!

So left and right =16.4 total

That's a 15% increase in braking power no?

But if I try to understand and say its per side.. That's still 7% more or 7.5% more clamping force compared to the 54mm single piston only now your getting a fixed more evenly spread surface of force on the rotor there for theoretically better stopping.. 

Copied from website.. 

Clamping force can only be increased either by increasing the line pressure or by increasing the diameter of the caliper piston(s). Increasing the size of the pads will not increase clamping force. Any increase in caliper piston area alone will be accompanied by an increase in pedal travel. The effectiveness of a caliper is also affected by the stiffness of the caliper body and its mountings. It is therefore possible to reduce piston size while increasing caliper stiffness and realize a net increase in clamping force applied. This would typically improve pedal feel.

Only increasing the effective radius of the disc, the caliper piston area, the line pressure, or the coefficient of friction can increase brake torque. Increasing the pad area will decrease pad wear and improve the fade characteristics of the pads but it will not increase the brake torque.


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## Ephry73 (Feb 18, 2002)

Bump because I will be doing this upgrade in a few weeks


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## jettag60 (Nov 2, 2005)

can anyone help clarify which calipers will work for me on a corrado g60 with 11" calipers...

996.352.421 & 422
or the 986.351.421 & 422


https://www.youtube.com/watch?v=9A0b9uZuRt0

this guys is saying the 986 calipers are the ones to go with, and these adaptors

https://epytec.de/en/brake-system/a...m-brake-caliper-adapter-for-front-axle?c=2047


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## Butcher (Jan 31, 2001)

jettag60 said:


> can anyone help clarify which calipers will work for me on a corrado g60 with 11" calipers...


Maybe you need to reread that again. It makes no sense what so ever.


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## jettag60 (Nov 2, 2005)

rotors man, rotors.

thanks for the useful input.


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## kirk_augustin (Jul 21, 2012)

You could always let a machinist split the calipers and machine them out for the larger front piston size?

Don't worry about no ABS, as ABS should always be disabled anyway.

If you also reduced the rear caliber volume, then you could go with a narrower master cylinder, in which case you would get more leverage by a longer throw, which has a nice feel in my opinion.


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## jettag60 (Nov 2, 2005)

i've removed my calipers and dropped them of at a media blasting place and they've cleaned up them and are painting them today.

I have a rebuilt kit and will go with that for now.

Lots of other expenses getting my swap done so if i can save $1000 (canadian) by no buying the wilwoods I'm going to start with that


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