Honda CRX brakes

[ddewhurst]

Someone crashed a Honda CRX big time this past weeekend suposedly because of a brake issue. No facts just idle talk/guess by people at the track. The driver is mostly ok to my knowledge.

It was stated that the Honda CRX OEM brakes work with one master cylinder for one front brake & one diagonally opposite rear brake. Is this statement true?

Have Fun http://Forums.ImprovedTouring.com/it/wink.gif
David

[Greg Gauper]

I know the first gens have diagonal braking systems and I think 2nd gens are the same. The LF and RR are connected to one master cylinder line and the RF and LR are connected to the other master cylinder line. Under normal circumstances, when you step on the brakes, equal pressure is applied to both master cylinder lines. When you push on the pedal, the fluid pressure between the two pistons is applied to one brake line and also applies an equal force on the second (front) piston which in turn applies the same pressure to the other brake line. In the event of a failure in the first brake line, the first piston can't develope any pressure because of the leak and there for bottoms out against the second piston. Once it bottoms out, the second piston can then continue to apply pressure to the unaffected line to provide emergency braking for street use. This is a very simple, very reliable method of providing emergency braking for street use, which is why most OEM braking systems use it. Unfortunately for racing, where you are already braking at the limit of the cars potential, any upset in the braking system is going to get ugly. Having suffered a similar failure as Tony did in the exact same spot (turn 12 at Road America) because I forgot to put the $.02 ty-wrap on the brake line clamp to keep it from rubbing against the wheel, I vividly remember the pedal going to the floor and having it register in my brain "You just suffered brake failure!!!" in that split second before I flew off the road into the pea gravel.....with the car just starting to yaw from the diagonal effect as I skipped and bounced over it.

The other common problem with some FWD cars (Honda's and VW's come to mine) is when you have a front hub failure, the brake rotor which normally floats on the hub suddenly shifts and the pedal will go to the floor because that calper piston no longer has anything to push against. You're screwed no matter what.

BTW, Fernadez in the SSC Neon suffered a LF hub failure going into turn 3 at the Sprints. He was lucky. If it happened at 1, 10, or the Kink, it would have been real ugly. Most FWD cars replace their hubs after X number of races.

[pavis]

Front hub failure requires use of the emergency brake to slow down (speaking from experience!)

Not to derail this thread but anybody know what CRX front rotors are the lightest? (i.e. OEM vs aftermarket). The aftermarket one's I just purchased weigh 2 lbs more than the (cracked) ones that are coming off.

[ddewhurst]

Greg, I apprectate your knowledgable technical response. (My OEM race car brake system is one mastyer cylinder front, one master cylinder rear.)

With the diagonal OEM system which has an end result of braking yaw, why in your judgement in the interest of safety dosen't the SCCA rules specify that replumbing is required with systems that have diagonal systems? (granted I don't know the cylinder sizes & so on but this diagonal system is an accident waiting to happen.)

Have Fun http://Forums.ImprovedTouring.com/it/wink.gif
David

[This message has been edited by ddewhurst (edited June 24, 2003).]

[Greg Gauper]

My gut instinct is that it won't make any difference. If you are committed to braking as deep as possible, anything that suddenly upsets the car i.e. loosing the fronts or the rears or diagonally, it's going to be ugly no matter what. Since the fronts do about 70%-80% of the braking on a front wheel drive car, loosing both fronts is probably just as bad as loosing one side. Even a true dual master cylinder arrangement with balance bar ala formula or GT cars can have a problem if they don't put some form of stop to limit travel. There was a post by Randy Canfield on the old H-Prod site about this.

You are permitted to change the plumbing on an IT car and add proportional valves, etc as you see fit. But the cylinder areas might become screwed up if you plumb one line to the fronts and one two the rears.

Either way your screwed. You just don't have time to react and do anything in any type brake failure period!

[Junktech]

What track did this happen at?

[ddewhurst]

Greg, sometimes I look at the reality of the overall situation. This diagonal stuff adds another contributor to a major safety failure. & it all adds to another question. What are anyones thoughts on why the Honda diagonal OEM brake system is designed as it is?

Junktech, (David ?) at Road America T 12 a sharp 90* right hander at the end of the fastest part of the track.

Have Fun http://Forums.ImprovedTouring.com/it/wink.gif
David

[Geezer]

The dual circuit braking system is a safety feature. For a street car, where the brakes aren't generally used that hard, it's much easier to come to a straight stop with one front and one rear brake working on opposite sides. You have this option if either circuit fails. If you set it up with one circuit for front and one for rear, you'd have a 50% chance of losing your front brakes, which would be a greater reduction of stopping power, and (on non-abs cars) give a better chance of locking the rears and spinning.

I'm not sure that there would be any better way to set up a race car. One circuit on each side would be worse for straight line stability. One front and one back would still leave you with a 50% chance of losing the fronts and either snap spinning when the rears locked up going in with way too much speed to turn. A four circuit system would be expensive.

I'd guess the best thing to do is to pull maintenance on your brakes frequently, and make sure you have everything tight before you go out.

[Paul]

Mark up this cheap, single line, single piston. floating caliper b.s. to economy by the manufacturers these days. Check out the 140 Volvos sometime. A true dual X system. Four pistons on each front caliper and two on each rear. On each front caliper, one pair of pistons is independent of the other such that one half of the master cylinder operates half of both front calipers and one rear caliper. Where can one find that these days? Maybe on one of those $50k ITS cars?
Just an observation.
Paul

[Greg Gauper]

As I stated before, if you are using your brakes at their maximum limit and suffer any failure, whether it uses a diagonal braking system of not, your screwed. David, picture yourself at IRP and loosing your front or rear brakes on your RX7 entering turn 15. Or having a tire fail in turns 1/2. Get the picture? The real issue is not what the OEM manufacturers or SCCA should do to solve an alledged problem on a 10-20 year old car that is no longer in production.....

The real issue is that this is a stark reminder that this sport we all love and enjoy is a hazardous one. A mechanical failure or driver error of any type can occur unexpectedly, and seeing it happen makes you want to consider putting as much safety in the car as possible, i.e. building the best cage, having the best seat, wearing the best helmet, etc.

This same weekend at the Sprints, an E-Prod Mazda clobbered the wall at the kink and the driver had to be transported to the hospital but was okay. Several of the welds on the cage failed due to lack of full penetration! The car was from out of division. Several tech inspectors stated that they would have never issued a log book if the car was presented to them.

Don't skimp on a cage design!!!!!! Have it built by a reputable person. You can never tell when it might have to do its job.


[This message has been edited by Greg Gauper (edited June 24, 2003).]

[ddewhurst]

We each have what we have on our cars for a brake system. My car has a master cylinder for the front & a second master cylinder for the rear. I will take loosing either the front or back knowing that at failure time the car even tho under braked in theory will go in a predictable straight line. No unknown whip diagonal right of left that is totally unknown & uncontrolled by the system.

Thanks for each of your comments http://Forums.ImprovedTouring.com/it/wink.gif
David

[uscrew96]

the brakes were fine the hubs were fine. not sure what happen the A piller, and floor are fine. :confused

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Mike Machi crew chief USGUYS RACING

[ddewhurst]

Mike, on the USGUYS RACING car are the brakes diagonal as some have suggested ?

Were some eariler models diagonal & later models separate front & separate rear MC's.



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Have Fun ;)
David Dewhurst
CenDiv Milwaukee Region
Spec-7 #14

[USGUYS]

As USCREW says, we did not find anything wrong with the brakes. at any of the wheels. The crash was probably caused by locking up the brakes on the oil of a Spitfire that blew coming into 12 at Road America. The car turn 90 degrees and hit the wall at about the 2 1/2 marker.
The system is split diagonally at a fixture on the right inner fender, above the transmission. Two lines in, four lines out. This is different from VW which splits it at the MC.
Check this photo #64 and 65, http://tobinschuster.gotdns.com:8080/2003/...rints/index.htm (http://tobinschuster.gotdns.com:8080/2003/2003JuneSprints/index.htm)

[ITC Racer]

The diagonal plumbing also has to do with the different volume requirement of the rear drum/front disc brake setup, specifically on cars with such a setup (1st gen CRX and early 2 gen CRX) and how the two outputs of the master cylinder a biased. If both outputs have a similar output (50/50 biasing) if you plumb two calipers to one output and two drum wheel cylinders to a different one, your biasing will be hosed, so to speak.

This will be somewhat different on a 4 wheel disc brake car but may still be an issue due to different size caliper pistons.

Hope this helps.
Devin