Brake Pads

Leseee, lap record at Summit Point in GTL is ~5.5 secs faster than HP. Better brakes will get maybe .5 secs of that, no doubt I can get the other 5 secs by adding more cage tubing..... Great idea, Kyle, thanks!! What a pal!
 
Harold: Is the .060" clearance on the can .030" on each side or .060" on each side?

Jay: What is a "counterbored disc brake piston insulator?" Sounds pretty sophisticated for a hillbilly from Walhalla!

Thanks guys. You all make me think!

I know braking is one of my weak points as a driver. Maybe I can do something about it this year: get good brakes and learn to use them.

John
 
Still find it curious no body is addressing brake bias! The initial car was a VW FWD car. The conversation has drawn in others, and RWD.

Using differering brake compounds, on the front and rear will influence brake bias.

How do you identify when your brake bias is well balanced? If it is heavily biased to the front, you may be locking one, or both of them first. But, are you simply braking earlier and releasing the brake sooner - to avoid lock-up?? Driving around the problem.....

If you have too much rear brake bias, you may come in saying "the rear is too loose!!" and chasing chassis or tire issues.

Try using a pyrometer on the discs when you come in. Difficult, because they will have cooled down on your cool down lap. Apply some temperature sensitive paint or welders tape to identify the temp to the rotor hubs.

Do your front pads wear out significantly faster than the rear? Use some more rear bias, and spread the work load to the rear.

Remote Brake Bias Adjusters are designed to attach to brake balance bars, at the master cylinders. If you are still using stock master cylinder bores, without a Tilton style brake bias setup on the master cylinders, I don't think adding a brake proportioning valve to the rear brake line will allow MORE pressure to the rear bias. The balance bars will effectively increase or decrease rear line pressure, over what a proportioning valve will allow.

A simple test, is to put the car on jackstands, in the shop. with clean, rust free discs. Have someone apply light brake pressure as you try to rotate the front tire. As you reach the point where the front tire is getting too difficult to rotate, ask the brake man in the car to hold that position and pressure. Compare the effort now required to rotate the rear tire. If they are similar, you are probalbly in the ball park. If the rear is much easier to rotate, you are on your way to discovering how to measure and correct the problem. It is not a scientific or precise method, but it gets the point across. Under actual braking on the track, you transfer weight to the front and somewhat negate this test. But I have used this test for years to quickly help, at least initially, diagnose the problem, without a lot of test equipment, pressure gauges, or track time available.
 
Bias on my car is set 1 click on the adjuster knob forward from where the rear end locks on corner entry and kills the engine.
I'll fiddle with it a click or two either way during a race, but I've pretty much left it alone the last few practice days and am able to brake late enough that I scare the people behind me.

I use a lot more rear pad than the front, but I'm still running 300ZX calipers and rotors on the back w/ Wilwood Superlites up front. (Wilwood brake pedal setup and bias adjuster as well.) The car comes off the track with rear rotors blue-black and smoking, but the fronts (with much larger 2-pc rotors) are cool enough I can yank off the car with leather gloves.

As for upping rear brake pressures, there's not much you can do with a stock master cylinder. I have seen people install a tilton bias lever on the front brakes, but that's a poor solution, as you're reducing the max pressure available to the fronts. I think you would be better off going with different pad compounds if they can take the heat. get one with less friction on the front and more on the rear, then dial down the rear pressures if you have rear brake lockup.
 
My car has an inline proportioning valve for the rear brakes. As noted it cannot INCREASE the rear brake force, only decrease it.

I keep it somewhere midrange, so on the surface it's doing it's job.

Having said that, you've made me think a bit.....

I race mostly at Summit Point, and the first thing I notice when shifting the bias rearward is rear lockup, not usually on braking for 1 but rather for 5. The issue there is (for those who don't know the track) is that you need to brake for a slow corner (5) just as you are exiting, downhill, a very fast sweeper (4, or the Chute). So it's easy, especially on a front-heavy FWD car w/ high rear roll stiffness bias, to get rear wheel lock on the inside wheel.

So maybe I'm using too-far-forward brake bias as a patch for a driving issue.....???

I had actually thought about cycling the bias between two positions each lap but dismissed this as too complex for my overworked brain.....
 
In order to set rear bias (without DAQ) you need an observer and white shoe polish. Mark a 3" wide strip on the front and rear tires on whichever side your observer will be located. Get the brakes HOT on track. Come in to pits and set the bias heavily front biased. ID a safe spot to make medium speed stops in a straight line and locate the observer there. Get up to say 80 mph and using older tire make heavy stops. A radio is helpful. Keep increasing rear pressure until the vehicle is slightly frontish and it is possible to lock ALL of the front and rear brakes with additional pedal effort.

Hard to do unless on a test day but mandatory to get bias right. We always used Nelson Ledges for this kind of thing as well as shock scans.........since a test day was so cheap. There is no substitute for 1) the courage to change stuff even if you know most of it won't work......at least you learn what the car feels like with a malady 2) test days without the pressure of trying to race
 
My experience with lighter fwd VW race cars is that there is so little weight on the rear axle, that the best setting for a prop valve is almost always full front. With a heavy front weight bias, and effective front brakes - the amount of available friction that the rear tires can contribute goes way down when you brake hard.
 
Two years ago I installed brake pressure sensors F&R. Last winter I installed wheel speed sensors on all four wheels. I can now see which end of the car is slowing/locking first and adjust from there. I can also see the pressure bias and pressure change through the braking event. Very interesting stuff.

You also have to consider brake timing, or which end of the car is seeing pressure first. This can confuse things a bit. The compromise of having a larger rear master and smaller rear caliper pistons causes the rears to see pressure first. You'd think that the bias bar design would prevent this, but it doesn't entirely eliminate it.

Al, if you need some DAQ tips, feel free to give me a call! :twisted: :twisted:

-kyle
 
Al, after 5 pages of suggestions, have you considered that your decrease in braking performance indicated by the data logginger is just because of all the other prod cars leaking oil on the track?
 
Now now.. We can't let logic and common sense intervene! The problem is the car needs to go faster. It's nothing to do with environmental conditions or driving habits.
 
I thought the leaking oil issue was why the wanted a class just for English cars!

I've owned enough of them, and the bikes...
And oil dry in drip pans...... ;-)

And at my age, I'm starting to leak more than I care to!!!
 
I was going to throw in a jab about age, but since you've been racing longer than I've been alive, I'll keep it to myself. 8)
 
For the guy with the Rock 1, Try slotting the pads. You have too much gas off. Also run more air. The rules say you can source from the head light hole and the lower valence.

Your goal should be to reduce the rotor temp . wheel fans, more air.etc

Water mister?? Works on the Chumper and I used them on the IT cars before it was
un- approved.

I dont see any mention of water on the brakes today. MM
 
mg_john":1eb9nprw said:
Most of you won't support this (reason soon obvious) but a #303 can (yes a 15oz green bean can from the pantry) is the perfect size to make a cheap cooling can for 3" OD hose.. Just weld on bolt flange to attach to the knuckle, cut the appropriate slot for the rotor, attach hose. I actuall ran tin can ducts on my Hcar for 5 years with no problem.

Admittedly........... they were a little hillbillyish looking
Click to expand...
.

Jay:

My kind of modification! Cheap and effective! And maybe I can get someone to make me a green bean casserole!

And, living in Walhalla, SC hillbilly fits right in.

Thanks,

John
Click to expand...


John, I always had brake cans I made myself on my Spridget race cars and believed to be huge help, I always had my competitors look at them and want me to make them for them, but I was never interested due to all the different ideas on supsensions. On the square body Spridget, you have wasted grille opening space, even with the VW radiators, so I would get a couple of the plastic duct, trim them a little to fit in behind the outer edges of the grille, it worked well and didn't creat any more openings for the brake duct, but used what was already there, so no more drag created. AS far as jay's refernce to using food can, i didn't but i'm sure it would work fine, I used exhaust tubing, it's fairly thin (about .060") , light and obviously made to hols to heat, i then made two attachment point, one being the dust shield mouting place in the spindle, the other being where the king pin zerk fitting went, and I still used the zerk fitting, as well, the attachment leg, were just simple steel flat bar, I think I use 3/4", they didn't end up even weighting a pound when I got done with them. I'll be making some for the vintage MGB race car soon.
 
Thank you for the pics. OK, you guys actually meant soup cans, I was thinking something possibly more elaborate.

On a non-vented disc is it best to duct air directly to the caliper (at a 90 degree angle or so the air passes through and over the pads) or perpendicular to the rotor (like loop’s pics) or toward the hub?

The number of companies who make performance pads for my car are limited. Does or has anyone used EBC? How do they perform?

Thank you,
L
 
On a non-vented system, you're looking at two main areas to cool - surface of the disc and caliper.

Surface of the disc (ie soup can) will take heat away from the disc and by one remove the surface of the pads. Caliper cooling will take heat away from "boiling the fluid".

In my case, I'm having pad fade but (knock on wood) no "pedal to floor" so I'm concentrating on cooling the rotor surface. If I upgrade pad materials (and thus can brake harder/longer) I could indeed boil the fluid and thus need to start cooling the caliper. Or running higher boiling point fluid, or insulating/venting the pistons as has been suggested here.....

So (I'm thinking) if one had a solid disc system and ran two air hoses, one would be to a can and one blowing on the caliper.

Hope that helps...

Al Seim
HP VW Scirocco
 
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