Imprezer

Hey guys,

I have recently installed this huge Brembo brakes with 338x38mm rotors and silver 4 pot indy calipers on MY02 US WRX.

My pedal is soft. The brakes don't "bite". During the recent test, they stopped my car only 2ft better than the stock brakes. I almost cried.

What is going on? Too street of a pad? Stock master cylinder too small? Anyone?

TIA,

Alex

Dave T-S

They are probably not run in yet. How many miles have you done on them?

Imprezer

~1000 miles maybe.

firefox

Alex..

It will be interesting to see how well the disks/rotors go... most people suffered from warping when running brembo rotors.

I assume you have re-bled the brakes again ?

Changed the fluid ?

Check your ICQ

J.

Imprezer

Thats all the responses I got? I thought most of our guys have upgraded bigger brakes.

Stef

Alex.
The main beneift of big brakes is not purely to reduce stopping distance, but also to increase the number of times which they can consistently stop without fade.

Stef.

Pete Croney

Rather than the master cylinder being too small, it may be that your caliper cylinders are too big.

I once drove a car fitted with W*****od calipers (how ya doing Dan ) and the pedal went almost all the way to the floor before anything happened. Very scary It had huge pistons and just required too much fluid transfer before doing anything.

Ideally, a total piston surface area of around 4250mm2 per caliper is about right.

Imprezer

Pete, well, I would say you are as right as I am, hehe.

My problem is that I already have the brakes and I would much rather change the master cylinder than change the brakes (we are talking $2k+ here).

I am taking a little brake from my car, but I will be getting back to it in about 5 days. This is what I am planning on doing:

1. Re-inspect my installation to make sure that everything is installed properly.
2. Re-bleed/Flush the braking system.
3. Look up Brembo caliper piston surface area.

What else should I do? I am a novice when it comes to brakes.

Thanks,

-Alex

MRK

Alex have you changed and uprated the rear pads. Becuase when I put a new huge front brake set-up on mine I initially had the same problem. but I changed my standard rear pads for fast road pads as I assumed they were cooked due to numerous track days (standard Scooby pads are crap and they go like bricks after seriuos pounding).

And OOPPPAAALLLAAHHH the brakes were transformed, the fronts started to bite my braking was seriuosly excellent and I have a firm pedal, just like I had expected

Hope that helps.

M

Imprezer

I did some more research and here is what I found out:

1. My brake kit is the "F40" style kit for Impreza
2. The caliper is P4 38/44
3. They use 332x32mm disks

In the manual it says: Quantity of Pistons/Diameter: 4 pistons ø 38x44 (part #'s are 20486205 and 20486206)

http://hp.brembo.com/mproduct.asp?EC...ponentPage=yes

I guess this means that there are 2 pairs of 2 diff pistons. 2 38mm ones and 2 44mm ones. If this is correct, then the total surface area of all 4 pistons on each caliper is ~5308mm^2. I am over what Pete suggested.

Here is another question, what pads do the kits come from the Brembo? Are those good pads or are they "OEM-like"?

I am very close to set my car on fire if I don't figure this problem out soon. Please, help.

I was also thinking, that having OEM rubber hoses in the rear doesn't help in my situation, or does it not matter?

Does anyone run this setup? The F40/332x32mm kit?

AAAaaaa!

-Alex

MRK

Hey Alex


READ MY PREVIOUS POST. And let us know if it makes any difference.


M

DARREN

Have you tried adjusting the link rod between the pedal and the master cyl

Darren

Scoob on I-Club

Be careful with a full system bleed Alex. You'll be meesing with the ABS unit too. The last you want to do is get air trapped in there.

If you have a special pressure bleeder, then you could do it, but not manually.

When some cars are filled at the factory, they are either pressure filled, or the ABS unit is supplied to the line ready filled. If this is done in production to avoid end of line problems, imagine the problems doing in your garage!

Just a word of caution.... I'll PM you on I-Club too...

Grant Swan

Brake Problems Bring you car to A W D Motorsport we will sort that out
Ask for Scott

Puff The Magic Wagon!

iTrader: (2)

Daftie question time...

One would presume that you changed your brake hoses to steel braided or the like & not just kept the OE rubber cr@p????

& that includes the rears as well as the fronts...

Also, I, who have Brembo/AP setup also find that on an immediate (& therefore cold) application of the brakes, then there seems to be a period of time (like micro seconds) when you think your brakes aren't going to do the job Then they bite & all is well

As Stef says, the main purpose of Big Brakes is to stop you time after time (45 min track session no worries ) & it is only after they warm up that they will come to maximum efficiency Try the same emergency stop test after they are warm/hot & you may lose a further few feet...

That any help m8??

chiark

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Puff The Magic Wagon!:
<B>One would presume that you changed your brake hoses to steel braided or the like & not just kept the OE rubber cr@p????[/quote]

Just thinking out loud, but Prodrive say "don't bother" with respect to braided hoses.

Regarding piston sizes, this has me intrigued:

Looking at the AP 6-pot calipers, they use 27, 31.75 and 38.1 diameter pistons - this gives around 5000mm2 of piston per caliper. These would appear to be OK for the Impreza, but 5300 is just a bit too much...

What would be the effect of putting, say, a caliper using 22, 25 and 29mm pistons on, giving around 3260mm2 of piston - is that too small for the Impreza?

Also, and this is a *really* dumb question, do different calipers require different travel on the piston, such as in order to take up "slack" - or is that just too stupid to answer?

Finally, where did the magic figure of 4250 come from - is there a formula to calculate this? (based on disc size/weight/inside leg measurement?)

Pete Croney

Alex

Those pistons are too big and will require a lot of fluid movement to activate them... hence all the pedal travel/sponginess.

chiark

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Grant Swan:
<B>Brake Problems Bring you car to A W D Motorsport we will sort that out
Ask for Scott [/quote]

Are you near San Rafael in California then???

RON

I'm no genius, bur surely if you use a caliper that has a lesser piston area, you'll get a firmer pedal, and some odd braking effect at the rear.
I would guess the 'magic' number was worked out from measuring the original calipers.
Ron

gregh

&gt;&gt; but Prodrive say "don't bother" with respect to braided hoses.


Where do they say that? Loads of people swear by them as an excellent part of a brake upgrade!

greg

chiark

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by gregh:
<B>&gt;&gt; but Prodrive say "don't bother" with respect to braided hoses.


Where do they say that? Loads of people swear by them as an excellent part of a brake upgrade!
[/quote]

I know and realise that, but Prodrive say don't bother for their 6-pot upgrade...