brakes not locking

[vandit]

we had tough time last year in australia 05 event during brake test, the wheels never locked...after returning from event we replaced our bike master cylinders to a mid size car master cylinder as we found out that req pressure was not there with bike mc's....the braking improved a little but still it's not able to lock the wheels properly....any reasons or thoughts?

[SeanM]

Check your motion ratios in the pedal, I believe they should be 1:1 not 100% sure on that so don't quote me. i know last year we had a bad motion ratio in our pedal so that gave us a hard time in locking the brakes

[Matt Gignac]

A mechanical advantage of 1:1 would probably not be ideal if you're having trouble locking the brakes. The higher the mech adv., the more force you exert on the pushrod, and thus higher forces on the calipers. However, this means you need more overall travel, but with the kind of distances we want the caliper to travel, it shouldn't be too bad.

Assume coefficients of friction for the tire/road and disc/pad interfaces, figure out what kind of clamping force you need on the disc to achieve the brake torque you want, and then work back to the pedal to see what kind of force you want. It may be that your calipers are too big in relation to your master cylinders, or maybe you have bubbles in the fluid.

Matt Gignac
McGill Racing Team

[Eric Schieb]

Does the pedal go to the stop or is the effort just too high?

How many wheels are locking?

Eric Schieb

[Ryan Boysen]

Have you considered walking through the equations? Maybe your wheel to rotor diameter ratio is too high..

[drivetrainUW-Platt]

Originally posted by Ryan Boysen:
Have you considered walking through the equations? Maybe your wheel to rotor diameter ratio is too high..

YES, you need to do brake calculations, there are a number of spreadsheets floating around this site, dont just assume components will work together, it shot us in the foot in 04, we never did get things working at competition

[Ryan Boysen]

YES, you need to do brake calculations, there are a number of spreadsheets floating around this site, dont just assume components will work together, it shot us in the foot in 04, we never did get things working at competition

I have a pretty solid algebriac Spread Sheet if you would like..

send me your email if you want it.

[Wright D]

Did you bleed the brakes really really well? We had loads of trouble locking the wheels till we got a descent bleed job. Willwood has some good write-usp on proper bleeding methods, fallow them and you will have no troubles.

[Steve Yao]

1) Is pedal actuation firm or 'squishy'?

2) As Eric asked, are you sure you are not hitting the pedal stops or End-of-Travel?

3) How many lbf from the driver does your system require per G's of braking achieved?

[vandit]

thanx guys for all different areas to look into....but hav already checked some of them like about the calculation part... i followed backward method to figure out mc size assuming 33kg of force by driver...regarding pedal travel...it's travelling full...i mean the push rod is giving full stroke length...now whether that's good or bad i really dont know...and pedal actuation is pretty losse...u dont feel any pressure until u travel half of it...and regarding coefficient of friction i assumed .4 between pad and disc...
the problem what i think is that putting the rims we found out that we hav bigger disc then req...so we just turned them up to smaller size...and thats where our braking area on disc got reduced....what do u say????
and one more thing i want to ask that is it sensible to use car mc with bike calipers....i mean are bike calipers designed to retain that much amount of pressure....
plz fill me up on this discussion everybody???
and yes RYAN i would be thanfull if u can provide that calcultion spreadsheet...my id is "vandit_goyal@yahoo.com"

[Didier Beaudoin]

If your MCs travel their full stroke, I would think your problem is

a) Your MCs bore is too small for the calipers' piston(s);
b) There is some air in the brake lines.

[LSU Dave]

From your statement that you don't feel any pressure until you push halfway, it seems like you must have some air in your brake lines or you've got a massive air gap in between your pads and rotor.

1) Which calipers/MCs are you using?
2) What is your brake line setup? - any residual valves etc?
3) Bleed those brakes!

[vandit]

i think the only probable reason might be air in lines....will re bleed and get back to u guys ... thanx..

[Bill Kunst]

Ahh, the old air gap. If you made the wonderful decision to use wilwoods karting caliper, it sucks back big time (in karting you want no drag, if possible) and if you have not designed for this volume, u r screwed. I don't know how many brakes are designed for this, but keep this in the back of your mind.
Bill

[Belo]

are you using only flexible braided hose? Solid brake hose will not make your wheels lock but they might give you that little extra pressure needed to achieve wheel locking. If you made a a close design you maybe can<t afford a small pressure drop due to hose expension...
I would suggest

good bleeding
less flexible hose possible
if it doesnt work you might want to review your calculations

[Mexellent]

Make sure that youre calipers and discs are aligned properly.

[RiNaZ]

i read the rules and i dont find anything in the rules that required the car to be have a full lock up on all 4 tyres.

And ive been to the competitions for several years now and i dont think they have a brake test on the car.

So is it a requirement to get the car locking up for the competition?

[jdstuff]

Originally posted by RiNaZ:
i read the rules and i dont find anything in the rules that required the car to be have a full lock up on all 4 tyres.

And ive been to the competitions for several years now and i dont think they have a brake test on the car.

So is it a requirement to get the car locking up for the competition?


Read them again. Have you ever been through tech with one of your cars??? No brake lock, no tech sticker....it's kinda hard to miss.

"4.2.4 Inspection Process
Part 3 – Noise, Master Switch, and Brake Tests
Noise will be tested by the specified method (Rule 3.5.5.3). If the vehicle passes
the noise test then its master switches (see Rule 3.4.9) will be tested. If the
vehicle passes both the noise and master switch tests then its brakes will be tested.
Each vehicle must be able to lock all 4 wheels after an acceleration run."

[RiNaZ]

hey thanks jason ... wonder how i missed reading that.

No i havent gone thru tech with my own car. This year will be my first. I started going to the competition since 2000, and ive been watching tech inspection all the time, that's how i made the assumption. I guess, i should've paid more attention.

Thanks again.

[jdstuff]

no prob....best of luck this year!

[Steve Yao]

Rinaz,
You should realize that besides the couple of stewards who scrutinize your car in a static setting, there are are two more 'dynamic' test in order to pass tech. One is the tilt test where they angle the car up 60 deg from horizontal and the other is brakes/noise test. Noise of course requiring <110 dB, and brakes requiring that you lock all four wheels simultaneously.

...and as far as UTA taking a few tries to get thru brakes; it looked more like driver error than a problem with the car.

[RiNaZ]

thanks steve ... i started off with formula, but then got heavily into baja 2 years ago, and now i got mixed up with all the rules http://fsae.com/groupee_common/emoticons/icon_smile.gif.

And i keep on forgetting that rules changed every year too http://fsae.com/groupee_common/emoticons/icon_smile.gif.