70 replies to this topic

[TheRealVXed]

Thinking about this a bit more.....
The brembo doubling issue applies when considering MC bore BUT not for when comparing brake caliper cylinder areas front to back (at least that's how it works in my head.

WRT the cylinder; have you tried taking the numbers off the side of the OEM cylinder into a generic shop to look in their catalogues at options? The other thing you could do is get a second one and get it over bored and a new piston made by an engineering co.

 

The single piston in the brembo needs to move twice as far as each piston in the 2 pot APs, as it needs to pull the floating side in and push the piston side pad as well.  Each piston on the 2 pots only needs to push 1 pad.  The cylinder area is the indication of the displacement and therefore you would need to times by 2 in order to match it with a 2 pot caliper.

 

I was thinking about that second option of getting a second hand MC bored out to say 28 or 29mm, but I would need to look and see if there is enough available material first.

 

On over boring the rears, what exactly are you referring to?  The last thing I want to do is increase the fluid capacity of the calipers any further with the same MC as this would make the issue I face worse surely?

[FLD]

I am talking about boring the caliper and sleeving the piston to give you a larger piston area. This will restore some balance F-R in your system so you won't lock fronts so easily. It will increase pedal travel and make it more sensitive.

[FLD]

The single piston in the brembo needs to move twice as far as each piston in the 2 pot APs, as it needs to pull the floating side in and push the piston side pad as well.  Each piston on the 2 pots only needs to push 1 pad.  The cylinder area is the indication of the displacement and therefore you would need to times by 2 in order to match it with a 2 pot caliper.

This thought process works when you are considering swept volume for the MC and calipers but not when you are considering piston area for brake balance F-R in the system. It's a real mind-fcuk

[siztenboots]

so in summary , don't bother?

[TheRealVXed]

so in summary , don't bother?

 

I wouldn't say that yet, but I think the sellers need to be more transparent about these changes and supply a "kit" including any necessary MC changes required.

 

If you go for the smaller 4 pots and maintain the rear brembos it should be a plug and play though as you only increase the piston area on the front and the rear stays the same. (6079mmsq >> 7699mmsq = ~25% increase), so shouldn't affect the pedal travel and feel as much.

 

The issue with moving the 2 pots to the rear and the larger 4s on the front is that the piston area has increased by 50% across the entire system, meaning that the smaller MC has to travel that much further to fill the pistons in the calipers.  Effectively with the same pedal effort you get increase clamping on the discs reducing feel and increasing braking torque = easy lock up.

 

Larger MC should reduce this as the pedal effort would increase for the same clamping force on the discs.

[FLD]

It all depends what you're trying to achieve.  I have the lotus "upgrade" 4-pots on mine just because I like how it looks.  Are these an upgrade on their own?  Probably unlikely but I imagine most people do it for the same reason I have done and find an excuse.  4 pots must be better than 2 right?   It shifts the bias forwards which may give the feel of better braking but the reality is likely to be a slight reduction in retardation without adjustment of the rear to match.  The OEM bias is already slightly forward of the 60:40 which is 'ideal' in the dry.  Obviously they are catering for wet roads etc.  You could conclude that 'big brake' conversions are aesthetic rather than a performance upgrade. 

 

There is the likely scenario that replacing non-maintained OEM parts with new parts gives a greater performance as you're swapping out worn or seized parts.  This gives the perception of 'better'.  An overhaul may do the same job. 

 

For those actually wanting an increase in performance consideration of the whole needs to be taken into account.  The big brakes do give a greater pad area which can deal with heat better but also has friction issues.  This will deal with fade and overheating a little better but obviously fooks your bias.  The best retardation will occur with a balanced set up.  Considering the whole system allows for consideration of bias and also for pedal feel.  Big brakes will give a long pedal with less pressure on the same MC.  I'd think that MC choice is then down to personal preference. 

 

Just my brain fart

[Exmantaa]

For real heavy track braking (the 180° after the straight at Zandvoort f.i.), my experience is that the VX can use a bit more rear bias. Therefore I fitted slightly more aggressive pads on the rear with the std. calipers/system.

 

And the sliding rear Brembo is not the best choice for performance braking (it flexes...), so a fixed caliper there would be a nice upgrade. But keeping the right F/R bias...

 

 

[joshua]

To fit the Subaru master cylinder the servo is turned 45° and I machined an adapter between the piston and actuator rod.
I have a decent proportioning valve but to the front calipers.
Also the abs has a hydraulic bypass circuit and can be hydraulically isolated and switched off or back in circuit and switched on.
Unlike with the FTE cylinder the brake pedal takes up straight away and is solid.
I’ll dig out some photos of the master cylinder fitted.

[TheRealVXed]

To fit the Subaru master cylinder the servo is turned 45° and I machined an adapter between the piston and actuator rod.
I have a decent proportioning valve but to the front calipers.
Also the abs has a hydraulic bypass circuit and can be hydraulically isolated and switched off or back in circuit and switched on.
Unlike with the FTE cylinder the brake pedal takes up straight away and is solid.
I’ll dig out some photos of the master cylinder fitted.

 

Thanks Joshua!  That would be really useful if you had a picture.  I have a Cayenne MC, so am going to see if that will fit, or maybe explore the possibility of boring out the VX one, but would be good to see what you have done on this side.  

 

Forgive my ignorance though, what do you mean by "FTE"?

 

Thanks

VXed

[FLD]

https://www.fte-auto...ftermarket.html

[TheRealVXed]

https://www.fte-auto...ftermarket.html

 

[FLD]

How are you getting on?

[JohnTurbo]

I've said a lot about brakes in the past - some of which was quoted above.

 

The main point is made by FLD above - you can't change part of the system without considering all of the system.

 

 

In the end I didn't do Joshua's 28mm master cylinder conversion but went for the MGF AP conversion (including a lot of machining) whereby the piston sizes were much better suited to the car. (Twin 30mm or 32mm pistons, I forget) I probably still have a M/C somewhere.

These calipers were eventually sold on the continent somewhere I gather!

 

Why the "lotus" 4 pots didn't have the smaller pistons (making the part a direct swap) will eternally be a mystery to me! - The original suggestion by lotus being to fit higher COF rear pads to compensate! Madness.

 

 

 

 

 

Edited by JohnTurbo, 28 May 2019 - 11:06 AM.

[TheRealVXed]

How are you getting on?

 

So the Cayenne's master cylinder doesn't fit on the bolts on the servo (can't say I'm surprised), however the brakes are a lot better now the pads have bedded in.  Still far too sensitive for my taste, but infinitely less snatchy than before.

 

I'm in two minds here.  Ideally, I want to up the MC and re-align the ratio (approx 1.5:1) of increased piston size, to have increased the whole system and restore the pedal to stock feel (at least that is the theory!).

 

My next port of call is going to be to find a second hand VX MC, have it bored to 27mm and use the Cayenne internals... But, none of that will be done before the national, so looks like I'll have to terrorise you all in my bright yellow Clio

[Exmantaa]

Search for Subaru 26401AC190 (26.99mm):
Ebay, or
https://www.autodoc..../oem/26401ac190

[NOSBandit]

Did everything else fit right apart from the mounting bolts with the cayenne master cylinder?

Sent from my SM-G935F using Tapatalk

[NOSBandit]

Just to let you know, the cayenne master cylinder fits nicely after a few minor mods.

Sent from my SM-G935F using Tapatalk

[Exmantaa]

Please post the needed modifications + part nr. Cayenne cylinder here for future reference & searches.

[TheRealVXed]

Just to let you know, the cayenne master cylinder fits nicely after a few minor mods.

Sent from my SM-G935F using Tapatalk

 

Awesome! Can you please let me know what the modifications were?  Are they just to the base plate to fit it to the servo?

[TheRealVXed]

Please post the needed modifications + part nr. Cayenne cylinder here for future reference & searches.

 

Exmantaa, I got the part numbers from this thread http://www.vx220.org...t-the-vx/page-2

 

You have to make sure you buy a RHD version though otherwise the brake lines come out of the wrong side of the MC I believe.  Also the MY you need is 2003 - 2007 (the one I have came off a Turbo S)

 

VXed

Edited by TheRealVXed, 13 June 2019 - 02:12 PM.