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3.2 Brake Refurb and Upgrade


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I have had new front and rear disks and a pair of front Boxster callipers with adaptor blocks sitting on the shelf for a while and as my brakes were sticking a bit through lack of use over the winter, I thought I would fit them before this year’s MOT.

 

Kept it standard at the rear except for some paint, with rebuilt callipers over new discs.

DSCN3459.jpg

 

Made some block off rings out of thin tinplate to block the gaps in the front hubs and direct air into the vents in the disks.

DSCN3466.jpg

 

As the Boxster callipers are used rotated from the Boxster’s trailing location to the 911’s leading location (keeping the orientation of the smaller piston leading) they end up upside down. So they can be bleed, you have to swap the connecting pipes over to the new lower position on the opposite calliper and the bleed nipples into the new upper locations. The swap over is done in this picture (pipe in location A came from location D, pipe in location C came from location B).

DSCN3464x.jpg

 

A longer brake pipe was needed (380mm) to connect the calliper to flexible line pipe.

DSCN3467.jpg

DSCN3468.jpg

 

Took the opportunity of comparing the weights:

One 3.2 calliper complete with pads, locating pins etc = 5.5kg

One Boxster calliper complete with pads, locating pin etc, with adaptor block bolted up = 4.0kg

 

For reference, the Boxster calliper used are from a 97 to 04 Boxster (not an S) and the part numbers are Left 968-351-421-03 and Right 968-351-422-03

 

As the Proportioning valve is not needed with this set up...

DSCN3463.jpg

 

... so I deactivated it by removing the spring (S) and valve (V) from inside.

DSCN3462x.jpg

 

I used EBC red stuff ceramic pads back and front. I know some on here do not rate them highly, but I got a very good deal that made them very much worth a try.

 

Welded a couple of tabs onto each A-arm and fitted the 993 air scoops.

DSCN3471.jpg

 

After bleeding, I did a 70 mile drive to bed everything in.

 

Initial impression is that there is a lot more stopping power and that I have to learn to be more light footed!

 

Took it for the MOT and passed with flying colours, but it got wet in the rain.

letmein.jpg

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love the last photo

 

I don't normally park it there and when I saw it it looked just like it was peaking in the window asking to come in out of the rain. Maybe I had sniffed too much brake fluid.

 

Mark

 

where did you get the adaptor blocks from and how much?

 

I got them off ebay for about 75, about a year ago.

 

Mark

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  • 3 years later...

Old topic now I know, but as rear adapters are way more money than fronts, i am thinking of replacing fronts only. Did you calculate that bias valve would need removing or was it a guesstimate? After a few miles by now is the bias about right?

 

Chris.

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Did you calculate that bias valve would need removing or was it a guesstimate? After a few miles by now is the bias about right?

Not a guesstimate, there was a lot of data, experience and calculations on Pelican and so after some research I went with their recommendation.

 

Having covered a lot of road miles and a number of track days since the swap I can confirm the recommendation. I find the bias spot on in all conditions.

 

Mark

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Mark,

 

Many thanks for your reply, spot on!

 

So that's it, boxster fronts, stock rears or if cash allows 'S' style alloy rear callipers and no bias valve.

 

Thank you! Chris.

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So that's it, boxster fronts, stock rears or if cash allows 'S' style alloy rear callipers and no bias valve.

Chris, I thought alloy "S" callipers were front callipers for use over 282mm x 20mm disks.

 

Are you doing this on an SC or a 3.2?

 

My comments and the recommendation are based on having the "wide M" callipers over 290mm x 24mm disks, i.e. standard 3.2 fitment, on the rear and Boxster callipers over 282mm x 24mm disks up front.

 

The front/rear hydraulic ratios are as follows (numbers cribbed from Pelican)...

 

SC & earlier IBs 1.596

3.2 1.306 (rear calliper piston diameter was increased from the earlier 38mm to 42mm, why a proportioning valve was needed)

Boxster front and SC rear 2.006

Boxster front and 3.2 rear 1.642

Boxster front and rear 1.720

 

Mark

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Hi Mark,

 

It' an 3.2. I started looking for the brackets and found some from rebel racing in the USA. their top recommendation is to use boxster callipers all around and standard bias valve or boxster fronts and their own alloy 'S' callipers at the rear. As they have 48mm pistons they are only an upgrade as they are lighter not any better. I strongly suspect I'll stick with the standard ones and save $500 for just a 2kg penalty. They are also as you say for 20mm discs, but as I was thinking of changing them anyway that is no bother and I would probably save another 2kg too.

 

Here 's what they say;

 

 

Brembo Aluminum Calipers w/ 3.0" Bolt Spacing

 

These are the very rare Brembo aluminum calipers with 3.0 inch bolt spacing and 48mm pistons. Essentially

these are an "S" caliper with the smaller 3.0 inch bolt spacing. Direct bolt on for 356 front (w/ disc brakes),

65-77 911 front/rear, 78-89 911 rear w/ 20mm wide rotors. Completely refurbished with new pistons, seals,

and bleeders. Sold in pairs (right and left side), pad springs and pins included. Weight is 4 lbs. each. Please

specify for solid or vented rotors when ordering. Extremely popular for rear spec 911 racing applications

when used with Boxter front conversions listed above. Rotor discs are available as an option. All 356,

911/912 (65-68) rotors are solid. 911 (69-89) rotors are vented, cross drilled, and have directional spiraled

vanes (left and right specific). All rotors offered below are high quality German made, sold in pairs.

 

As always, thanks for your help and advice. Chris.

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Not a guesstimate, there was a lot of data, experience and calculations on Pelican and so after some research I went with their recommendation.

 

Having covered a lot of road miles and a number of track days since the swap I can confirm the recommendation. I find the bias spot on in all conditions.

 

Mark

 

Interesting - I changed to boxster fronts 4 or 5 years ago and have been driving it daily since then. I didn't do anything with the bias at all (through ignorance that anything would be needed). What does the change do and why do they consider it needed?

 

Is that (from your quoted figures) there was too much rear braking on the stock setup so they added the valve in to push more to the front - so when you switch to boxsters this adjustment is no longer required?

 

Thanks for any info or links

 

Cheers

 

Mark

Edited by sladey
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Is that (from your quoted figures) there was too much rear braking on the stock setup so they added the valve in to push more to the front - so when you switch to boxsters this adjustment is no longer required?

That is about it, but not too much rear bias in all circumstances.

 

The standard 3.2 has a much higher rearward hydraulic ratio than earlier cars, but the proportioning valve limits the total hydraulic pressure that can be applied to the rear circuit. This means that under lighter pressure on the brake pedal there is more rear braking bias, but under higher brake pedal pressure the braking bias moves to the front.

 

I would surmise that this was done in conjunction with the increased under-steer to make the cars "safer" to drive for the average buyer.

 

As the Boxster callipers increase the forward hydraulic ratio, giving a hydraulic ration very close to the pre-3.2 cars, leaving the proportioning valve in place would mean not enough rearward brake bias, especially under heavy braking.

 

Mark

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  • 6 months later...
  • 2 years later...

Update to this older thread on Boxster front calliper conversion.

 

Although fine on the road, I was not so comfortable with the length of pedal travel at the Oulton Park track day a couple of weeks back and so will be trying this out.

IMAG1757_zpsvdi6m5uu.jpg

 

A Turbo 23mm master cylinder instead of the standard 19mm one.

 

The original 19mm one always felt fine on the track with the Boxster front callipers and removed proportioning valve, but a new 19mm replacement (a URO one rather than ATE) I fitted a while ago seems to give a longer travel than the original and this does not feel so good on track.

 

I will post up some pictures and report back next week when it is on.

 

Mark

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Got the boxster / 3.2 setup with the 930 master cylinder on mine.

On the road the pedal feels a bit wooden but once you re-calibrate your legs/feet to the feel it works well on the track.

The cams, carbs and inlet manifolds have also removed 50% of the servo efficiency which takes a bit of getting used to but provides better modulation and control.

With the brackets and discs installed, everything just bolts up. The only bespoke part is the short length of rigid pipe that connects to the flexible line. After trying with several short lengths of pipe and bending to suit I decided to incorporate a banjo and bolt at the calliper end. This provided a very neat solution.

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Any chance of a pic of that last bit please?

Here is a picture of mine.

IMAG1758_zpsz6q8f1zr.jpg

 

I used a custom length of brake pipe between calliper and flexi, bent by hand to fit. I can't remember the length, but I will measure it later. The black wire clipped to the pipe is the unused pad wear sensor (no sensor hole in the DS2500 pads) kept out of harms way.

 

 

Got the master cylinder swapped over, which is just doable without taking the servo right off, but not bled them yet.

IMAG1762_zpsu9fmsos1.jpg

 

I also dispensed with the gutted proportioning valve as I found there was just enough length in the rear brake pipe to reach the master cylinder without it.

 

 

Mark

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Ben, I have a boxster conversion on my 3.2 which currently has no wheels etc and is on a ramp for easy access. Come over later today or tomorrow if you want a look and measure those pipes. My local DIY store can make them for you while you wait for pennies.

 

Chris.

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