Need Advice on how to test and tune brakes

[RebekahsZ]

I just completed a disc brake conversion on my LS2/240z. It has stock front calipers and rotors and 1984 Maxima rear calipers on either 280sx or 300zx non-vented rear rotors. Car has Porterfield R4S pads on all 4 corners. Master cylinder is 15/16" with rear drum brake check valve removed. Cockpit adjustable proportion valve is Willwood. New DOT3 fluid.

 

Please describe the steps or exercises I need to put car thru and the tests and measurements I need to perform to validate (test and tune) that the system is working maximally with the highest reliability. My dad just had me stomp the brakes, and if the car stopped and didn't yank the steering wheel out of you hands it was good enough. I'd like to be more thorough and precise than Dad was.

 

Right now, I have one caliper that is heating its pad more than the others (tested with a laser pyrometer-or whatever you call the $39 laser guided thermometer that looks like a little pistol). I have ordered some SSBC caliper gauges that screw into the bleeder screws, but I'm not sure how I am supposed to bleed the caliper after installing them. Once my brake sysem has been validated, I will move to other aspects of the build.

 

Thanks for any advice you can give.

[EMWHYR0HEN]

First thing I always do with new pads/rotors is bedding in the brakes.

 

How to

[johnc]

Here's how I setup braking system balance:

 

1. Find a race track that's having an open test day - NOT an open track day because you'll piss off the organizers and the other participants.

2. If you can't do number 1, find an open stretch of lightly used straight road (3am to 5am is a good time) where you can repeatedly accelerate to 80mph and brake at the limit.

3. Put four good tire on the car, same brand, model, and size. Set air pressures to 30 psi all around cold.

4. Make sure your pads and rotors have been properly bedded, make sure the brakes are properly bled, and everything in the braking system is perfect.

5. Set the rear prop valve and/or balance bar to the middle of its adjustment range.

6. Accelerate to 60 mph and perform a moderately hard stop. Watch for tire lockup and immediately release the brakes if that happens.

7. Repeat step 6 five times in quick succession making sure you don't lock the brakes.

8. Accelerate to 60 mph and brake hard enough to lock a tire. Immediately release the brakes note which tire (front or rear).

9. Reverse direction and repeat 8 (only if testing on the street - don't reverse direction on a race track).

10. If the fronts are locking, increase bias towards the rear and repeat 8 and 9.

11. If the rears are locking, decrease bias towards the rear and repeat 8 and 9.

12. Continue this cycle until the fronts just lock before the rears.

13. Accelerate to 80mph and go back to step 8 using 80mph as your new number.

14. If at any time you get a big lockup on a tire, your testing is done. Go home, get new tires, and try again.

15. If at anytime you experience any brake fade, let the brakes cool and go back to step 6.

 

Be very careful. Hard rear lockup will throw the car sideways. Be ready for it.

[thehelix112]

I'd love the above as a sticky. That's great info, thanks John. One question would be how important is it to have tyres the same as you want to actually use? The scale of the forces involved I'd imagine would be important to control their effects on weight distribution, but I couldn't afford to be flat spotting a set of semi slicks..

 

I guess you could always unflat spot them? >

 

Dave

[johnc]

Its pretty important to set the balance with the tires you intend to use. Expected load transfer is important. If you test with 400 treadwear tires and then race on 40 treadwear tires you'll get a lot more load transfer forward and will most likely have a big rear bias problem. Testing and setup costs money and can sometimes costs a lot of money.

[RebekahsZ]

Thanks SOOO much! I will look over ALL the suggestions in depth. Mostly, I wanted to see if temperature testing played a role in diagnosing problems or tuning. Sounds like I will need to really heat up the system to see. Then when I have a muffler, I'll start going thru these recommendations and post result. Car is too loud to really get on it repeatedly. I will follow this cherished advice.

 

I find it interesting that no one has suggested testing the fluid pressure at the calipers - I guess that was another wasted $80! Add it to the pile.

Edited March 19, 2012 by RebekahsZ

[johnc]

You can test fluid pressure at the calipers, but that is just one part of brake balance. And do you know what pressure numbers to shoot for? If not, then you have to do the testing I outline above and then check the pressure numbers after you're all done.

[EMWHYR0HEN]

Here's my experience with brake tuning : brake bias tuning

 

Good luck!

[RebekahsZ]

Thanks johnc (and everybody else!). I wasn't really concerned with achieving a particular pressure (I have the sense to know that it will vary with my foot pressure)! I just wasn't sure if I should spend time getting the pressure/temperatures equal on the left and right sides before working on the front to rear bias. Gauges haven't arrived yet, so we'll see which I get to first. I really can't be doing a lot of accel/decel maneuvers until car is quieter. I'm gonna consider this question answered. I've got a friend who is doing a Toyota front brake "upgrade." I've had enough with "upgrades" for a while and am going to focus on enjoying what I have!