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View Full Version : Downgrading my Brembo GT Kit


NewfoundlandDude
07-16-2009, 06:50 AM
I'm considering downgrading my Brembo GT front brake kit. I'm all about useable power, useable mods, and useable braking power, and I just don't utilize the kit 100%. The brakes are large, and I'm sure are designed to withstand full day track events without fading, but realistically I won't be doing that any time soon.

Right now, I push the car hardest at AutoX every weekend. I've been playing with some of the setup, and I've seen some improvements that I need to make with the car. The front brakes however are more than the car needs to perform at its best, so I'm thinking about trying another setup.

Right now, I run into the problem of the front inside wheel locking up with minimal pedal pressure on the track during heavy braking. My problem is that I can't hear them locking up, and usually can't feel it, as they don't fully lock into a slide when this happens. The wheel locks for a second and it smokes the tire a little entering the corner, costing me time and r-comps....lol. I have noticed, even on the street sometimes, that when I get into the brakes, they can fully lock up pretty easily if I don't modulate correctly.

I've bled the brakes a bunch of times and went back to the "stock" Brembo pads from the Endless Blue track pads, but the brakes are just way overpowered compared to the rears. I don't have ABS, but this is happening at minimal peddle pressure, so there's more going on than just driver error.....i.e. I'm not mashing the brakes. I'm probably not the best driver out there, but I do have enough seat time to know how to brake properly.

I haven't tried any brake bias valves, and I have no experience with them, so if anyone can school me a little on their effectiveness, I'd love to hear it. I obviously understand what they do, but I just wonder if it's the bias that's causing my issues or just too much braking power. If I were to guess, I'd say that a little rear bias wouldn't hurt my overall braking setup, but even with the adjustment, the GT kit may be more than I need.

What are your guys thoughts on some of the popular brake upgrades for the 240SX. I used J30 calipers and Cobra rotors last year with my Maxima, and I liked that setup a lot. It was a great improvement over stock, and didn't overpower the rears a whole lot. It was "just right" for that car. I have some Z32 rears and the 300zx MC, maybe some Z32 fronts would do the trick. I haven't ever used the Q45 brakes either.

What are some of your setups, and your opinions of them? Maybe getting a set of bias valves for the front lines, and re-installing the ABS system will help out a little. I'd like to hear any experiences using proportioning valves on our cars, and any advice.

I guess if all else fails, I could sell these brakes and try out something smaller. Although at an MSRP of $3195.00 US, I'm not sure I'd find a lot of people willing to pick them up right away.....http://www.son240sx.org/forums/images/smilies/icon_razz.gif

NewfoundlandDude
07-16-2009, 06:51 AM
So about installing a proportioning valve.......everything that I've read up on is basically for cars that have undergone rear drum to disc conversions, and have too much rear bias. The valve will then dial down the rear pressure for a better front bias.

The problem that I'm having is exactly the opposite, I need less front pressure. I think that our front brakes have two separate lines coming from the oem "bias or combination valve" no? The obvious thing to say is install two proportioning valves in these lines, but I've also read that you should never install a proportioning valve in the front lines.

I don't see why you couldn't install dual front proportioning valves, the only problem I can see is tuning them to both react with the same pressures, which may be difficult. It would be great to hear from someone who has done this, and see what they say about it.

Am I incorrect in saying that our cars would need dual valves, is there another place in the line that would capture both fronts and not bump down the rears?

WhiteGLX
07-16-2009, 11:36 AM
what size r-comps are you using? what pressures do you run them at hot? how much experience do you have on track? what is your rear brake setup? what speeds are you getting up to before heavy braking zones? do you have any video to help us see what you are doing on track and maybe that will help diagnose the issue?

Om1kron
07-16-2009, 11:46 AM
I would get the proportioning valve. Or get 6piston brakes up front rather than the brembo gt's

NewfoundlandDude
07-16-2009, 12:35 PM
what size r-comps are you using?

245/40/R17 BFG G-force R1's
I know that they're not ideal, an AutoX compound such as an A6 or V710 would be a bit better, but these came almost new with the RPF-1's that I bought, so I'm using them for this year.
To be honest, they are well suited to my needs this year, it's the first year that I've ran r-comps, and I'm teaching someone to drive on them as well, so they are more resilient than something like an A6.

To note, this happens both with the r-comps and with my street tires. (225/35/R18 Contisport Contact 3's). It seems that the passenger side tire likes to smoke the majority of the time, if it happens in a straight line.

This might happen a few times throughout the course of a full day of racing, and it happens at hot and cold tire temperatures. I don't think it's an underperforming tire issue?


what pressures do you run them at hot?

My fronts get up to about 38psi and the rears get up to about 35ish.
I basically started below this and slowly worked up to it over the span of a few events. At these pressures, you see the tread patch go right to the sidewall and not over, so it seems to be the ideal pressures for the higher speed tracks.


how much experience do you have on track?

By track, I mean AutoX course set up on an airstrip or parking lot, but I have 2 years competition experience, and I tend to finish near the top or at the top at most events. I ran a supercharged Maxima last year, and the brakes were J30 calipers on Cobra rotors.....I had no problems with them, they were dialed in about perfectly.


what is your rear brake setup?

Z32 rears and a 300ZX BMC.


what speeds are you getting up to before heavy braking zones?

Speeds before the braking zone get up to about 90-100 km/h max (about 60mph), I'd say the average is more around 70 km/h. I find that I get a slight lockup AFTER the speed decreases to where I'm about to turn though.


do you have any video to help us see what you are doing on track and maybe that will help diagnose the issue?

I do have one video here, this is the FTD from an event a few weeks ago.
I was 2nd going into this run, and I was pushing hard to get the win, so I went into the end pin too hot at 0:48 and smoke the passenger side front. Honestly that's probably the worst that I've seen it lock up, as I just got on the brakes too late. Driver error.

However, at 1:05 you'll see exactly what I'm talking about. I take a right hand sweep at a decent speed, and the passenger side again just barely smokes before the turn. I barely even touched the brakes at that point, but that passenger side seems to like to lock rather easily. I really don't tend to get on the brakes hard when this happens, which is why I want less from braking torque to mitigate the quick lock-ups.

Event #4 Bell Island - Run 4 FTD - June 20, 2009 on Vimeo (http://www.vimeo.com/5427716)

p.s. Any idea where I can get some 5-lug ABS rings. I've never had ABS since I bought the car, but only the rings are missing, so I thought I might try it out.

NewfoundlandDude
07-16-2009, 12:39 PM
I would get the proportioning valve. Or get 6piston brakes up front rather than the brembo gt's

Have you used a proportioning valve before on a 240?
Where in the system did you install it?

I took a look this morning, and it seems that from the bmc, 2 lines run to the combination valve (term?), then form there 3 lines exit, one to the rear and 2 to the front. Before that, I had only seen the 2 fronts with 3rd rear, and was thinking I'd need 2 valves for the fronts. Now that I looked closer, it seems that one may do on the line leaving the bmc.

I'd still like to hear at least one account of this from a 240 owner, where it cured a similar problem, and hear some feedback.

WhiteGLX
07-16-2009, 01:27 PM
i dont think anything more than Z32 fronts would be needed at all. I say step the whole setup down and dont waste time making it super complicated with proportioning valves.

No need to reinvent the wheel, just make use with what work and have fun without worrying about flat spotting tires.

I use Z32 calipers up front on my track car (road racing) with very aggressive pads, her is a vid where in the beginning i get up to about 140mph and slow down fairly aggressively in the braking zone.

Summit Main Trackdaze 7/09 on Vimeo (http://www.vimeo.com/5622126)

NewfoundlandDude
07-16-2009, 01:35 PM
I agree.
The thing about being in Newfoundland is that the closest "car scene" is in Ontario, and it's not even large there.
Finding a Z32 setup and then finding someone to buy the setup I have for a reasonable price is going to get hairy.
Any "ballers" on this site I wonder?

brokeAs240sx
07-22-2009, 10:50 AM
You already know what you need to do, you answered it in your own post:

- Remove the Brembo brakes and go w/ 300zx brakes; looks like the Brembo GT's aren't built for the stock 300zx BMC setup.

Anything else you do is a band-aid. That being said, looks like you are running an s14, which has the thicker smaller brake booster (compared to the s13 manual). You may want to try running a manual s13 brake booster, which will give you a little more brake pedal play.

You can also adjust the brake sensitivity/engagement knob that is between the bmc & the brake booster.

Going proportioning valve would work; however, as you said in your own post, you have no experience w/ it, so you could actually make things worse. If you want to go that route, I would find someone else @ autox who has experience setting these up.

Another suggestion: although you have 2 years competition experience, have you tried getting a better driver (national competitor, regional champ) to drive your car a couple laps & see their inputs just to verify? Not being critical, but I have 5 years autox experience & I still learn something every time I have someone drive my car.

slider2828
07-22-2009, 11:01 AM
Get better pads, or change pads setup with Z32, WhiteGLX and people who actually run full track have no problems with Z32's at all....

Cobalt, or Porterfields, will stop you on a dime. If you are skidding, your suspension setup might nto be setup right....

zads
07-29-2009, 12:33 AM
I did a lot of messing around with my S13 (though I'm assuming you have a S14)..
Maybe it will give you some extra ideas..

1. I started off by going with a S13 manual M/C with Z32 brakes front and rear,
converted all my brake lines to SS lines and AN- fittings,
then added in a lever-type Wilwood proportioning valve on the rear lines to balance the car out.
Allows quick in-cockpit adjustment as well- I had one optimal setting for high grip surface and tires,
another optimal setting for street tire autocross and looser surfaces, and one setting for rain.

2. Switched to Ford Cobra front rotors with Z32 calipers, then couldn't get enough rear brake even on the most rear biased setting.

3. Switched M/C to Wilwood 260-8556, bias fixed.
Bolts up to brake booster, just adjust the booster inner rod to fit.
S14 may have some issues using this M/C to the shock tower, I don't remember if I actually tried it or if I just eyeballed it on my S14.
http://www.wilwood.com/Products/006-MasterCylinders/009-ATCMC/webMC8555_500.jpg