I'm working on the final analysis for Cale Kastanek's accident and I'm a little confused about the S2000's brake system. It's my understanding that the S2000 has a dual diagonal brake system. The right front and left rear are on a completely separate hydraulic system (other than the reservoir) than the left front and right rear. If brake pressure is lost in one circuit, the other two wheels should still have full braking and even ABS.

If this is true then why is it that the brake pedal goes from rock solit to full soft by simply opening one caliper bleeder? This implies that a brake line failure would allow the pedal to go to the floor with little to no braking. That doesn't sound like a safe, dual diagonal brake system to me. It seems the brake pedal should still have some resistance with one bleeder open.

I had a brake caliper piston seal fail on me on the track and the pedal did go to the floor and it felt like a complete brake failure. I have it on video and it appears that engine braking may have been all that I had. I was in third gear at high RPM coming into a third gear corner so no downshift was required.

Can someone enlighten me on the S2000's brake system design?

Rob Robinette

 

FYI...the ABS is not diagonal on the the AP1...it is a 3-channel system. The AP2 is 4-channel. So not sure if ABS would work on the rear if either rear side lost hydraulic pressure.

 

John over on the Mid-Atlantic forum found the answer for me. Here's a Lexus brake article that details how modern master cylinders work:

http://www.autoshop101.com/forms/brake02.pdf

The explanation and diagrams of "Leakage in the Primary/Secondary Circuit" makes it clear why the pedal goes soft when a leak occurs. When either circuit fails, much of the brake pedal stroke is used to compress the failed circuit's piston return spring.

Here's a quote that I can verify, "Stopping distance is increased signigicantly, however, when operating on only one circuit."

 

The service manual suggests my MY00 S2k has a mix between diagonal and split system, one piston in the master is for one front caliper and the two rear calipers, the other piston is for the other front caliper and again for the two rear calipers.
There is a Proportioning Control Valve (PCV) in the rear brake lines.
They also state the ABS is Quote is from a MY00-03 service manual.

By looking at the drawings in the PDF I think my MY00 S2k has a primary port-less piston, as there is a pin through the piston just like in the drawings and a conventional secondairy piston (no pin).

Thanks for finding the PDF

So if I understand it correctly, while bleeding one of the front brakes, one should be not able to turn the other front wheel when the pedal is forced to the floor.

 

Hey Spitty...can you tell me the page or section where you pulled that quote? I want to show it to an AP2 buddy who convinced me that 4-channel was only on the AP2s.

 

[QUOTE=negcamber,Dec 22 2008, 12:53 PM] Hey Spitty...can you tell me the page or section where you pulled that quote?

 

negcamber Posted on Dec 22 2008, 10:53 PM
Its taken from the online available MY00-03 service manual in PDF format, it looks like to be a scan / photocopy of a paper version.
Its on page 19-44, Chapter ABS Components / System Description (cont'd) / ABS Modulator.
In the drawing following the text you can see that every caliper has its own valve system inside the ABS modulator unit to reduce, retain and intensify hydraulic pressure.
I can't find any mentioning of the two rear sensors working together, it all works independant according to the descriptions.

I also have a Dutch Honda ESM (Electronic Service Manual), and in there is the same quote - in Dutch.

Anyway... I don't know why it happened today but it happened: driving home the driver side rear piston decided it didn't want to retract, maybe because the pads are still new so the piston is all the way in making it easier to get stuck or something so I had to work on it this evening.
The disk & wheel were hot enough to not let it be.
With the caliper taken apart - the official way by removing the 2 bolts from the sliding pins - I was turning the piston even further in to pump the brake pedal to make it come out (to get it moving again)
Pressing the brake pedal it felt like going to the floor but it wasn't, especially the second pump action I felt pressure build-up in the non leaking system.
I guess that when it happens unexpected one doesn't notice the pressure build-up because the extra long stroke in the pedal gets all the attention.
In situations like that its worth it to pump the pedal again.

 

Thanks Spitty...found it in my legal Helms copy too. hehehe

Mike...page 19-42 in my MY00-02 Helms. Same quote.

Another AP1 vs AP2 myth busted.

 

It gets even better.

Look at your page 19-43, the ABS Control Unit / Main Control.
The drawing explaines the wheel speed is detected per wheel, vehicle speed is calculated based on the wheel speed (all 4).
For the 2 rear wheels there is a selection of the "slowest wheel".
Slip rate is determined on (or by) the 2 rears together and seperate for the fronts.
ABS control is the same: the 2 rears together and the fronts seperately.
(Does this mean it is 3-channel?)
All wheels DO have their own ABS solenoid.
(Does all wheels having their own solenoid means its 4-channel?)

Myth not busted... yet.

Warning!
Lots of debate possible here!
Warning!

 

Like I said. It's a three-channel ABS system. Each of the fronts is independent, but the rears are controlled together.