# porsche boxster brake install....help!!!!!!!



## xdoktor (Feb 4, 2005)

ok so last weekend i did 312mm rotors, porsche boxster calipers and stainless lines. i had g60 brakes previous. i bled them out nooooooo air. drove the car and expected to stand it on it nose. brakes no better than what i had, maybe worse. hrad braking produces an under the dash npise that sound like a whistle. a shrill noise.......what is up? anyone else have similar problems? oh yeah the car is a 1991 b3 wagon. help SoWo is weeks away and i have waaaay more to do. thanks!!!!!! US129 will win if i dont fix it, damnit!


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## xdoktor (Feb 4, 2005)

well?


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## Chickenman35 (Jul 28, 2006)

1: Which Porsche Boxster calipers did you get.. front or rear? Fronts have a 36m and 40 mm piston ( Differential bore ). Rears have smaller pistons with proportionally less clamping force.

2: Brake pads and bedding. What brake pads are you using? They may not be properly bedded yet. *New pads on new rotors can easily take 500 to 750 miles of stop and go CITY driving before they are properly bedded.* New pads on old rotors can take even longer as the old pad material deposits have to be worn off. Braking force will be dramatically reduced until pads are properly bedded.

3: Bleeding. Pressure bleed the system while rapidly tapping the calipers with a Plastic Mallet. This will set up vibrations that will dislodge any trapped air bubbles in passage ways. Multi-piston calipers have more end runs that can trap bubbles. 6 piston calipers are even worse that 4 piston calipers for this issue.


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## petethepug (May 25, 2001)

Need to know if you have ABS. If not, are you running the stock master cyl?
Need to know what Porsche calipers you installed.
Pictures always help. Love to see how they turned out.


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## xdoktor (Feb 4, 2005)

*brake help*

they were listed as rear calipers, not sure about the pads brand/type but they look new or close to it. no abs, stock master cylinder, used 312 mm rotors.


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## Chickenman35 (Jul 28, 2006)

xdoktor said:


> they were listed as rear calipers, not sure about the pads brand/type but they look new or close to it. no abs, stock master cylinder, used 312 mm rotors.


Seems a lot of people are making this mistake lately. You usually cannot use rear calipers for ANY front application on ANY car. The rear caliper piston diameter and volume is too small. Caliper piston volume is directly proportional to clamping force. Reduce the clamping force and you reduce braking force.

See my posts in the following thread, particularly Post #14:

http://forums.vwvortex.com/showthread.php?7003812-Porsche-caliper-issue&p=85916297&viewfull=1#post85916297

Here's a cut and paste of what your issue is:



> _
> 
> 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.
> 
> ...


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## petethepug (May 25, 2001)

OK ...

B3 / 1991 Passat Wagon. There's a lot missing still, especially pics ... If you have a 91 Passat the only option was the 1.8 16v in the States. Have you made changes to the drive train?

How did you upgrade your 4x100 hubs to 5x100 for 312 rotors?
Did you re-drill the Passat hubs or swap to a VR6 K frame?
What adapters are you using to mount the Porsche calipers on the spindles? What spindles are on the car right now?

Regardless of all the info above, if you have Porsche rear calipers you prolly have 28 & 30mm pistons in the calipers from the rear of a Porsche. 
Your car had Girling 54 (Corrado) calipers up front when it was new, Only the discs were different with 254x20mm rotors. If you upgraded to g60 parts you'd have the same calipers but the discs would be 280x22mm.

Once the rest of the missing info is identified you're simply left with swap'g from a single ATE 54 mm caliper piston .... over to a Porsche 28x30 4 pot caliper. It takes a larger master cylinder to push more fluid to four pistons. The surface area of all 4 pistons pushing on the disc is slightly larger than OE. A larger (thicker) rotor is being used and I'm not sure how to calculate that into the equation or if that's even important.

Regardless if you have the oe mater cylinder using Porsche 4 pot calipers *you will *have to get a larger master cylinder. I'd go with the 25.4mm (441 611 021). You'll get your oe pedal travel back from the larger m/c. *Keep in mind you may have a vacuum leak on your booster*. Prolly not, but check anyway. Always look for the easiest fixes 1st. If you're travels take you through a junk yard check out the newer VAG cars for a larger brake booster that will fit in your bay. It will lessen the braking effort. It's common for the Mk I owners to use Mk III & IV boosters. The larger A4 booster may be a bolt on if your lucky.

Don't throw big $$ out for one of these m/c. Shop for it online as a "90-91 V8 Quattro master cylinder bore size 1" or 25.4mm", You'll save $100's. 
https://www.rockauto.com/dbphp/x,ca..._AUDI_V8_QUATTRO_3.6L_V8_Master_Cylinder.html



Slytle said:


> The answer is YES! I am using the 25.4mm Audi master cylinder on my Mk2 with Audi Dual Piston calipers and factory rear disk brakes.
> When I upgraded to the dual piston calipers, I found that the 22mm master was inadequate. The pedal felt mushy and pedal travel was so excessive that it almost hit the floor under hard braking.
> 
> With the 25.4mm master the pedal is VERY firm and pedal travel is decreased significantly. The firmness is an obvious tradeoff for the decrease in pedal travel. The shorter travel allows for more braking modulation, however, more effort is required to lock up the wheels. I greatly prefer the firmer feel and heavier pedal.
> ...





silvervdubs99 said:


> here is what i have found::
> the "old style wide mount MC and brake booster can use these I BELIEVE, not 100%:
> 447 611 021 25.4mm
> 443 611 021 23.8mm [SUP](what a 91 16v got at the factory)[/SUP]
> ...


Check your brake booster hose for vacuum leaks!!


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## petethepug (May 25, 2001)

Added this info from other Porsche caliper threads since Porsche decided to share the same part #'s on calipers using 20 & 25 mm discs :banghead:

*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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## xdoktor (Feb 4, 2005)

*brakes*

my spindles, corrado vr hubs, g60 calipers. and redrilled g60 rotors to 5 x 100. made my own adaptors. yeah im thinking because its the original mc its time for a new one. would love to do a newer mk iv booster and master cylinder, not sure if it will fit. if anybody knows what newer mc/booster will work lmk. ill try to post pics of the stuff its not on the car now.........thanks for all the help and input!


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## Chickenman35 (Jul 28, 2006)

^ Read all of my posts in this forum regarding Porsche rear calipers. :beer:opcorn:


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## petethepug (May 25, 2001)

Size your OE brake booster. Look to see if another VAG has a larger one that will bolt on and fit. It's just a little research and tenacity. In the end it's all worth it.

This Bimmer dude just jumped into his project and got it right the first time with a Subie booster.

http://www.e30tech.com/forum/showthread.php?p=1281855

This Vanagon Syncro guy got it right with a Bimmer booster. This might be the one for you.

http://www.thesamba.com/vw/forum/viewtopic.php?t=401822

It may be easiest to research via pictures

https://www.google.com/search?q=vw+...%2Fforum%2Fviewtopic.php%3Ft%3D401822;640;480


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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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## xdoktor (Feb 4, 2005)

*brakes*

the calipers i have are 996 352 422 so thats the problem im guessing.


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## petethepug (May 25, 2001)

Unfortunately yes. 

Big Kudos to chickenman35. All the info is available now to properly size your calipers.
It's a bummer that simultaneously, two or three had posted on the brake forum that the Porsche rear calipers were having issues on the front axles. 
One of the biggest issues was that Creations Motorsport put out an add stating that Porsche rear calipers would work on the front axles of VAG cars in the thread below. It taught me the difference between a product ad and a product review.

Porsche caliper issue


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## Guyver96 (Jan 17, 2007)

I'd love to know why in the calculator your putting 2 calipers per axle? the site says multiply by 2 but that's for the end is it not? I've messed with mk4 calipers several times and never have I seen 2 pistons or 2 calipers per axle. Its one caliper with a single 54mm piston... So why say 2?


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## jettag60 (Nov 2, 2005)

can anyone confirm that the 986.351.421/422 calipers will work for a corrado g60?


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