# 315mm REAR brake upgrade



## [email protected] (Jul 2, 2006)

*315mm REAR brake MK4 upgrade*

Anyone ever tied to convert a OEM TT 315mm mm disc to rear brakes ?
Ive seen a bunch of 288 here in europe ,,,but never 315mm
I got R32 kit on the front brakes and got a bunch of stuff over from other projects and im thinking of making a custom braket .
But ....will the 315mm + TT rear caliper fit under 17" ??


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## 01 Wolfsburg (May 7, 2003)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*

What do you hope to accomplish with that giant rotor at the rear?


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## elRey (May 15, 2001)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*

custom 12" REAR brake setup.... almost 
If you can make the brakets yourself, let me know. I can send you a CAD file if you make a set for me also.


_Modified by elRey at 1:15 AM 7-26-2006_


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## [email protected] (Jul 2, 2006)

*Re: 315mm REAR brake MK4 upgrade (01 Wolfsburg)*

190mph + = Thats why









I want to get rid of the small ugly R32 stopper that i have mounted as rear brakes .


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## 01 Wolfsburg (May 7, 2003)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*


_Quote, originally posted by *[email protected]* »_190mph + = Thats why























http://****************.com/smile/emthup.gif


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## [email protected] (Jul 2, 2006)

*Re: 315mm REAR brake MK4 upgrade (01 Wolfsburg)*

But i might get the same problem as the guy in the post above .
17" wont be able to swallow the 315mm TT discs


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## elRey (May 15, 2001)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*


_Quote, originally posted by *[email protected]* »_But i might get the same problem as the guy in the post above .
17" wont be able to swallow the 315mm TT discs









Not that I would suggest wheel spacers for anything performance, but
with my 17.5mm spacers the Long Beaches clear.
Rey


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## [email protected] (Jul 2, 2006)

*Re: 315mm REAR brake MK4 upgrade (elRey)*

R32 in fornt and 312s rear on under my 17" wheels
























http://****************.com/smile/emthup.gif


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## elRey (May 15, 2001)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*


_Quote, originally posted by *foff[email protected]* »_R32 in fornt and 312s rear on under my 17" wheels








http://****************.com/smile/emthup.gif 

Details!!!


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## [email protected] (Jul 2, 2006)

*Re: 315mm REAR brake MK4 upgrade (elRey)*

easy install and easy 20min fabrication the bracket .
The disc actually ONLY got 0.5 Inch thats noy reached by the caliper








i will post a drawing tomorrow


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## [email protected] (Jul 2, 2006)

*Re: 315mm REAR brake MK4 upgrade ([email protected])*

Better pics of the brakes .
Sick ass hell!
I even got a "low oil" signal today because of the damn crazy brakes .
My external aftermarket sensor went nut when i tried em new brakes really hard
















And ive created a new custom software today .$$$$$$$$$ but works good .
Street 16psi right now .
Last step to 25-26psi next friday


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## claudefrog (Aug 17, 2006)

any pictures of how you done this?
pics of the rear of the caliper?
also, how did you work it that your handbrake still works?


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## Pete_S4 (Aug 14, 2003)

*What the brake bias!!!*

Careful guys. Going too large in the rear will cause the rear to lock up before the fronts. Your rear end will become very loose and cause your car to be very unstable.
There are other factors at play here such as caliper clamping force and the brake pad friction coefficient. But radically increasing the rear's rotor size relative to the front and keeping the stock calipers and similar brake pads all around needs to be approached with caution. 
Just remember the fronts always whould be more effective than the rears in most front engined street cars. This is especially true of FWD cars since most of the weight is in the front. Take a look at you average RWD BMW and you'll notice that the rotor sizes are almost always very similar.


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## collins_tc (Dec 19, 2000)

*Re: What the brake bias!!! (Pete_S4)*

A couple of things here:
1. What good are the rear brakes with huge rotors if the pad is still contacting the same amount of surface area? Even with the added mechanical advantage of the caliper being further out from the hub, you're still not gaining a full benefit.
2. Running R32 calipers in the rear with the same size rotors and calipers in the front is going to make your braking bias *WAY* out of line. You're going to cause some serious oversteer if you ever attempt to trail brake in a turn.
3. I would **really** like to know how you're going to get a MkIV to 190mph. You can build up the engine, but aerodynamically, the car would be so unstable at that speed, no matter what brakes you have on it, you're not going to be able to control the car. And with the setup you're proposing, the bias is going to be so far out-of-whack that I wouldn't even want to be watching you, much less in the driver's seat.
4. Realistically, I would say maybe 150mph is about what you should be looking to achieve. And for that the braking system you should be looking for is something that keeps the brake bias close to 70% front and 30% rear, and some serious race-spec pads and fluid.
To me, the original poster doesn't understand ANY of the forces involved with cars that go over 150mph. And that they are trying to go faster than that is really quite scary...










_Modified by collins_tc at 1:28 PM 8-17-2006_


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## Pete_S4 (Aug 14, 2003)

*Re: What the brake bias!!! (collins_tc)*

http://****************.com/smile/emthup.gif 

_Quote, originally posted by *collins_tc* »_
1. What good are the rear brakes with huge rotors if the pad is still contacting the same amount of surface area? Even with the added mechanical advantage of the caliper being further out from the hub, you're still not gaining a full benefit.


You do gain added cooling and thermal mass by going to a larger rotor. That will keep the pad temps in a more reasonable range for at least a little longer.


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## [email protected] (Jul 2, 2006)

*Re: What the brake bias!!! (collins_tc)*

. What good are the rear brakes with huge rotors if the pad is still contacting the same amount of surface area? Even with the added mechanical advantage of the caliper being further out from the hub, you're still not gaining a full benefit.
*Grabbing furter out WILL ALWAYS use less clamp force =better efficiency*
2. Running R32 calipers in the rear with the same size rotors and calipers in the front is going to make your braking bias *WAY* out of line. You're going to cause some serious oversteer if you ever attempt to trail brake in a turn.
*No probs yet*
3. I would *really* like to know how you're going to get a MkIV to 190mph. You can build up the engine, but aerodynamically, the car would be so unstable at that speed, no matter what brakes you have on it, you're not going to be able to control the car. And with the setup you're proposing, the bias is going to be so far out-of-whack that I wouldn't even want to be watching you, much less in the driver's seat.
*Worlds fastest Jetta MK4 ....Highest HP Street Jetta MK4 ..thats how *
4. Realistically, I would say maybe 150mph is about what you should be looking to achieve. And for that the braking system you should be looking for is something that keeps the brake bias close to 70% front and 30% rear, and some serious race-spec pads and fluid.
To me, the original poster doesn't understand ANY of the forces involved with cars that go over 150mph. And that they are trying to go faster than that is really quite scar


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## collins_tc (Dec 19, 2000)

*Re: What the brake bias!!! ([email protected])*


_Quote, originally posted by *[email protected]* »_Grabbing further out WILL ALWAYS use less clamp force =better efficiency
No probs yet
Worlds fastest Jetta MK4 ....Highest HP Street Jetta MK4 ..thats how


I understand mechanical advantage. I have larger rear rotors on my car - I know how it all works. With what you have now and what you're proposing, my point is two-fold: First, you are currently running huge front rotors in the rear with the much smaller rear pads. Right now, you're running a lot of extra rotating mass, but other than that, other than looking kinda dumb, there's not really a problem. However, and my second point, when you switch to running the front calipers in the back, and thus making full use of the rotor's surface area with pad and caliper force, your "no probs yet" is going to change to "fine as long as I don't mind the rear wheels locking up everytime I touch the brake pedal".
Don't take my tone the wrong way, I think you've got an awesome car and you should be very proud of making the thing work so well considering you've really gone against the grain of what everyone else does with their MkIV (more or less cookie-cutter turbo kits). I know you do a lot of drag race events from what I can tell. Have you ever taken this thing on a road course? If you have, you would know the imprtance of brake bias. I track my car a lot, and with my current set up, the car feels well-balanced when braking heavily from 120mph. I can't imagine how horribly scary (and not in a good way) your braking is going to be with the bias thrown so far backwards. The rears will always lock up and the back end will always want to wander around. NOT a good thing at high speeds. For how well thought out your engine stuff is, I think you're totally missing the mark with the brakes. Get a nice ECS Stage 2v2 or 3 kit with Stage 1R rears (or a StopTech or Brembo kit) and get full race-spec pads, braided lines and some Motul RBF600. That's about as good as you can do.
Best of luck... http://****************.com/smile/emthup.gif


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## [email protected] (Jul 2, 2006)

*Re: What the brake bias!!! (collins_tc)*

Sorry if i sounded "angry"
This is not my native language 
Something strange is that it feels much better








Compared to
Stage 1 = oem 280ish with CD disc size int hte rear
Stage 2 = OEM TT kit front 315 and rear 254s
stage 3 = R32 front + R32 254 rear

My home town is my track









Ill give you new updates if this setup feels "strange"
but ....for now i dont have any problems with it exept it got some SICK efficiency compared to TT oem and R32 oem


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## collins_tc (Dec 19, 2000)

*Re: What the brake bias!!! ([email protected])*

Believe me, I didn't think you were yelling or anything, the internet makes it tough to discern someone's "attitude". It's all good! http://****************.com/smile/emthup.gif 
I think right now it feels better because the rear brakes have more mechanical advantage by being further away from the hub. I think that feeling will change once you throw the front calipers and pads onto the rears. I predict that's when all heck is going to break loose back there (no pun intended).
I'm just worried that you're going to find out the hard way that too much rear braking bias on our cars is a VERY bad thing.
PS...Don't make me preach to you about the dangers of street racing. Take it to the track!


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## elRey (May 15, 2001)

*Re: What the brake bias!!! (collins_tc)*


_Quote, originally posted by *collins_tc* »_...when you switch to running the front calipers in the back, and thus making full use of the rotor's surface area with pad and caliper force, your "no probs yet" is going to change to "fine as long as I don't mind the rear wheels locking up everytime I touch the brake pedal".
....

I may have missed it, but I don't think he plans to "switch" rear calipers with front calipers. I he swapped stock MK4 rear calipers with stock R32 *rear *calipers.

_Modified by elRey at 6:15 PM 8-17-2006_


_Modified by elRey at 6:15 PM 8-17-2006_


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## Mohudsolo (Feb 25, 2004)

*Re: What the brake bias!!! (elRey)*

Given that the stock setup from the factory has the proportioning already screwed up with too much rear bias, I'm thinking that the ABS sytstem is capable of dealing with the funky brake sizes. However, I think the car would be more stable and easier to drive at speed with correctly sized brakes. It's probably OKish due to pulsing the rear brakes while the fronts have plenty of tire grip left, allowing decent steering even with ABS working. The couple of times I've run my car on track or autocross I found it was very unhappy with trail braking if a rear tire was in the air and just went into ice mode. I had to brake earlier while in a fully straight line to keep the brakes happy. If that's the balance he's working with, it may be OK.
For myself, I would also add front brake until the brakes were better balanced so I could get max efficiency out of the heavily loaded front tires. I''ve found with any front drive car that getting enough front brake really shortens the stopping distance while reducing the dependence on ABS.


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