Finally got the brakes to work at the track

[DavidSalama]

If you are like me, that is, enjoy driving your Ultima to the limit at the track, then you may have experienced the same braking issues I have. The first time I tracked my car, the car snapped around unpredictably under braking. I noticed rear brake wear, but only minimal front brake wear. I fully adjusted the balance bar to the front brake, but this did little to nothing. The throw of the master cylinder feeding the front brakes, located on the left side of the pedal, is longer compared to the short throw rear brake. I fully adjusted the master cylinder throw rod on the front brake, but the car was still unstable with too much rear bias. I then installed an adjustable bias valve in line with the rear brakes. Despite completely minimizing the rear brake line pressure, there was still poor braking and too much rear bias. I then experimented with running street pads at the rear, and race pads up front. This actually helped with the feel, but the rear brakes overcooked under hard track driving.

Since I like to heel and toe, I tend to lean on the right side of the brake as I roll into the throttle. Since the right side of the brake is the rear brakes, I decided to swap master cylinders. I disconnected the front and rear lines and swapped them at the master cylinders. My next track event was in the rain, and the car had total front brake bias. It was stable in the rain, but in the dry, I was experiencing front brake lock up. At this point I had race pads at all 4 corners. I completely opened the bias valve in the rear line, and adjusted the balance bar towards the rear. Still I had ineffective braking and front brake lock up.

Now the fix!! I moved my adjustable bias valve to the front line, keeping the swapped master cylinders for the front and rear. I adjusted the bias valve 5 half turns from open. I just got back from Lowes Motor Speedway in Charlotte, NC. The brakes were phenominal. I was able to outbrake Porsche GT3 cups cars, Porsche GT2s, and every other track vehicle. My car was the fastest car at the track. My confidence improved greatly under braking, always fearing the snap turn around. I also feared overheating of the brakes. Nothing bad happened all weekend.

The pads are Hawk DTC70s, with the AP racing rotors. Hoosier tires with 285/18 front and 335/18 rear.

My Ultima is now a great track car. I couldn't be happier.

[GTRCLIVE]

Question what you doing with a Bias Value on the car at all ??? Should be able to
balance the Brakes with the Balancing Pedal bar.... and yes I believe the smaller cylinder should be on the front no the rear.....

The setup for the balance Bar is very critical, and could cause allot of difference in
balance if you don't get the travels you need....

Have you got a 3/4" and a 5/8" cyclinders ???

[Rusti Evo]

Great report!

Do you have any clearance problems with the 285s up front?

[GreenV8S]

GTRCLIVE said:

Question what you doing with a Bias Value on the car at all ??? Should be able to
balance the Brakes with the Balancing Pedal bar.

I disagree. A balance bar will set the static balance but not the dynamic balance. Put another way, with the balance bar you can get the balance correct under light braking, or heavy braking, but not both.

You need to get the front/rear rotor sizes roughly matched to the heat output, set the hydraulic/mechanical f/r leverage ratio to achieve the static balance and then set the bias valve to compensate for weight transfer.

[deadscoob]

I think Clive probably means if the master cylinders and everything else is correct then there's no need for a bias controller on a road car. Unless I'm reading that incorrectly.

[GreenV8S]

DavidSalama said:

I moved my adjustable bias valve to the front line

DavidSalama said:

My Ultima is now a great track car. I couldn't be happier.

You might be happy with it, but putting a bias valve in the front circuit is absolutely and fundamentally wrong. It sounds as if you are using the bias valve to overcome some design flaw in the system. It has a specific purpose, which is to compensate for weight transfer under braking. You can have the car set up completely wrong and still have a car that happens to have the right balance under heavy braking in the dry. That doesn't mean that it's right, or safe, just that it happens to work OK under those particular conditions. I suggest you have another look at the problem because there's something seriously wrong with the system you're describing. Is there any chance that you've mixed up which are the front and rear brake lines?

[San Diego GTR]

What again is the factory suggested setup for the balance bar? Isn't it 21mm or something like that from the pedal?
Paul

Edited by San Diego GTR on Thursday 10th July 14:46

[DavidSalama]

First, I am surprised that none of you have experienced a similar problem. The fundamental problem with the design is that the front and rear calipers are the same size. Front should be larger. Also, the rear had a shorter throw compared to the front which has a longer throw. I agree that this can be balanced statically or for street driving, but at the track with repeated threshold braking, it doesn't work. As I mentioned, it is exagerated for those of us who heel and toe because we lean on the right side of the brake pedal.

No, I did not mix up my lines because I double and triple checked it and the results were predictable.

The only clearance problems I have with the 285s is that I cannot have the same small turning radius. Turning the steering wheel 3/4 away around causes rub on the inside. It also rubbed on the outer rear lip of the body and a bit on the inner edge of the the wheel well. All of these problems have been corrected with some fiberglass work. Now I have no issues except when turning into a tight parking space. These are only my track tires anyway, so no issue.

When I say I am happy with the brakes now, I speak from quite a bit of experience. I am a PCA national Drivers Ed instructor. I have tracked different cars for 19 years, including a Porsche GT3, 944 Turbo with Big Red brake upgrade, a Lotus Elise, and a Toyota MR2 Turbo.

I agree that fundamentally the front should not have the bias valve. It works only due to the design quirks. I can lean on the right side of the pedal, and the bias valve stops the front line from getting so much line pressure that it would lock up.

The next step if this were to be a problem would be to change the front calipers to something larger, and to match the two master cylinder volumes so that static and dynamic application of the brakes will track one another in a linear fashion.

[GreenV8S]

DavidSalama said:

When I say I am happy with the brakes now, I speak from quite a bit of experience. I am a PCA national Drivers Ed instructor. I have tracked different cars for 19 years, including a Porsche GT3, 944 Turbo with Big Red brake upgrade, a Lotus Elise, and a Toyota MR2 Turbo.

I don't know what all that experience means, but I presume you know what you're doing behind the wheel. do suggest you keep looking at the problem because there is something very wrong with the setup you're describing. Perhaps the balance bar is locking up, or you got supplied the wrong m/c sizes (I assume front m/c is smaller bore than the rear) or fitted them the wrong way round. But there's definitely something wrong somewhere.

[DavidSalama]

Perhaps there is a problem. I did not build my car. My rear M/C was on the right and is smaller than the front. Is this correct? Can anyone confirm proper M/C size and location?

Thanks.

[738 driver]

I was going to ask you the same question about having self built the car.
I understand lots of UK Ultimas go on the track and have minor brake tweeks, pad choice etc but it would appear the current system does generally work okay.
I would have thought if the standard system were wildly out of bias it would not get SVA approval?
Also, I'd have to confirm that during a recent factory test the car was pushed to the point of just starting to lock the fronts first whilst still holding its line perfectly around a fairly tight, narrow bend.
Could you not get the original factory brake system spec for your particular model and start with a clean sheet!

[GreenV8S]

DavidSalama said:

My rear M/C was on the right and is smaller than the front. Is this correct?

I don't know enough about the rest of that braking system to say for sure. You would need to know the weight distribution, front/rear caliper piston areas and mechanical leverage of the caliper to say with any confidence. The line pressure goes up as the piston area goes down so you would normally put the smaller bore m/c on the circuit that needs the higher pressure. You would need to look at the factors I mentioned above to work out which this was. (Or better, ask somebody who knows.)

[GTRCLIVE]

GreenV8S said:

GTRCLIVE said:

Question what you doing with a Bias Value on the car at all ??? Should be able to
balance the Brakes with the Balancing Pedal bar.

I disagree. A balance bar will set the static balance but not the dynamic balance. Put another way, with the balance bar you can get the balance correct under light braking, or heavy braking, but not both.

You need to get the front/rear rotor sizes roughly matched to the heat output, set the hydraulic/mechanical f/r leverage ratio to achieve the static balance and then set the bias valve to compensate for weight transfer.

I have never seen a Balance bar setup that recommends a Pressure reduction valve as well !!!

Ps if you get any differences then that's what the remote balance bar adjusters for, Road/Track conditions is it not ???

I agree with why the hell do you need identical brakes on the front and rear. You will find it hard to match the front and rear brake temperatures on a track with that kind of system, and Pad Temperature has a great effect of some types of brake material, front could be hot and increasing stopping power while rears are still cool and less effective. There fore creating a front lock up..... How much difference between front and rear I not sure, but at least some... Maybe 6 pot front on 360mm and 4 pot rears on 330mm... That's what I'm trying next...

[GTRCLIVE]

http://bp2.blogger.com/_dGrsGySHr9s/SHd5zO-NRWI/AA...

As you can see the front cylinder moves a greater distance, and therefore must have a smaller Diameter (cylinder with least resistance) and therefore creates a larger pressure (most fluid movement). But for reason I never figured out the factory still recommend the great pressure goes to the rear ??? and please don't anyone say that rear engined cars needs more pressure to the rear than the front... as that's just stupid...

For the full setup guide look here..

http://www.wilwood.com/Products/005-PedalAssemblie...

[deadscoob]

Don't Stealths have same size front and rear?

[GreenV8S]

GTRCLIVE said:

GreenV8S said:

GTRCLIVE said:

Question what you doing with a Bias Value on the car at all ??? Should be able to
balance the Brakes with the Balancing Pedal bar.

I disagree. A balance bar will set the static balance but not the dynamic balance. Put another way, with the balance bar you can get the balance correct under light braking, or heavy braking, but not both.

You need to get the front/rear rotor sizes roughly matched to the heat output, set the hydraulic/mechanical f/r leverage ratio to achieve the static balance and then set the bias valve to compensate for weight transfer.

I have never seen a Balance bar setup that recommends a Pressure reduction valve as well !!!

Ps if you get any differences then that's what the remote balance bar adjusters for, Road/Track conditions is it not ???

I agree with why the hell do you need identical brakes on the front and rear. You will find it hard to match the front and rear brake temperatures on a track with that kind of system, and Pad Temperature has a great effect of some types of brake material, front could be hot and increasing stopping power while rears are still cool and less effective. There fore creating a front lock up..... How much difference between front and rear I not sure, but at least some... Maybe 6 pot front on 360mm and 4 pot rears on 330mm... That's what I'm trying next...

The balance bar and bias valve serve different functions and you need both of them.

The balance bar adjusts the static brake balance i.e. the ratio of front versus rear effort under light braking. This might need to be adjusted as brake or tyre temperatures change or the weight distribution changes as fuel is consumed. It can also be used to vary the handling balance of the car under braking to suit the preferences of the driver. You don't need an adjustable balance bar to set the static balance, you can do it just as well by choosing the right mechanical and hydraulic leverages. A balance bar is a nice convenient way to do it though.

Having got the static balance right you also need to set the dynamic balance so that the ratio between front and rear varies correctly to account for weight transfer under braking. The balance bar is no use at all for this; you need a bias valve. A brake system which does not have the correct dynamic behaviour can be correctly balanced under light braking, or heavy braking, but not both. This is why every single type approved road car without exception will use a bias valve; they are fundamentally essential to produce a properly set up brake system which is correctly balanced.

[GreenV8S]

GTRCLIVE said:

As you can see the front cylinder moves a greater distance, and therefore must have a smaller Diameter (cylinder with least resistance) and therefore creates a larger pressure (most fluid movement). But for reason I never figured out the factory still recommend the great pressure goes to the rear ??? and please don't anyone say that rear engined cars needs more pressure to the rear than the front... as that's just stupid...

There's no universal rule that says rear engined cars need more pressure to the back, or anything like that. The master cylinder size is one of the factors that determines the static balance. The overall mechanical and hydraulic leverage through the pedal, balance bar, master cylinder(s), calipers, pads, rotors and wheels/tyres will ultimately need match the static weight distribution. If you have a car with most of the weight on the rear it wouldn't be surprising to see the rear brakes run at higher line pressure than the fronts.

[rduart]

Sorry for asking this question. Its a little off the topic but related. The following statement is copied directly from the GTR build manual.

"The ¾” master cylinder is for the front brakes and the 5/8” version is for the rear brake circuit."

Is this correct? I am asking because it is currently how I have my GTR setup. I am still building and have not tested anything.

Randy

[GTRCLIVE]

GreenV8S said:

GTRCLIVE said:

As you can see the front cylinder moves a greater distance, and therefore must have a smaller Diameter (cylinder with least resistance) and therefore creates a larger pressure (most fluid movement). But for reason I never figured out the factory still recommend the great pressure goes to the rear ??? and please don't anyone say that rear engined cars needs more pressure to the rear than the front... as that's just stupid...

There's no universal rule that says rear engined cars need more pressure to the back, or anything like that. The master cylinder size is one of the factors that determines the static balance. The overall mechanical and hydraulic leverage through the pedal, balance bar, master cylinder(s), calipers, pads, rotors and wheels/tyres will ultimately need match the static weight distribution. If you have a car with most of the weight on the rear it wouldn't be surprising to see the rear brakes run at higher line pressure than the fronts.

So your telling me that a car with Identical brakes front and rear might have more braking at the rear.... Poppycock.....

Weight transfer will always go to the front even under the stiffest suspension....

Ok will have to research the Bias valve more but that's a new one for me.... But then again I have never raced in competition. But I know a few men who have, will get back to you on that....

[GreenV8S]

GTRCLIVE said:

So your telling me that a car with Identical brakes front and rear might have more braking at the rear.... Poppycock.....

Weight transfer will always go to the front even under the stiffest suspension....

I'm not clear what part of my post you think is poppycock. If by 'identical brakes' you mean identical calipers and rotors, yes of course a car with the same calipers and rotors front and back could have different amounts of braking front versus back. Why else do you suppose we play games with balance bars and master cylinder sizes?

Weight transfer under braking is irrelevant when you're setting up the static balance since this is only concerned with the static weight distribution and static brake distribution. You only need to consider weight transfer when you move on to the dynamic brake balance. Even here the suspension characteristics don't play a big part in the design since the steady state weight transfer is determined by the CoG position and vehicle pitch doesn't really come into it.