[Diy_efi] OT: ABS retrofit into older car...

[Tom Sharpe]

You seem to be in the know.  Are those pressure surge tanks that go in the brake
lines to "modulate" pressure any good?  Their hype seems incredible.

"Amenson Scott (AC/ESC4)" wrote:

> Scott,
> Did you get any responses to your post?  If so, will you forward them to
> me...I am interested to see what their recommendations were.
>
> Now for my input...it is a very bad idea.  No, it is a very, very bad idea.
> Why???
>
> ABS systems use vehicle models and calibration settings to determine how to
> optimize the braking process in panic situations.  These models/settings are
> very specific to a particular vehicle.  Even if you can find a system from a
> vehicle which seems to be "similar" to your target vehicle (and get it
> working), things like caliper volume, GVW, shock/spring rates, CG,
> tires....will be different enough to cause bad things to happen.  These bad
> things are listed below, least to most severe (and for the most part, least
> to most likely):
>
> Rough Control/Over Brake:  The very best thing that could happen is that the
> ABS control would be rough.  In this situation the system would hold
> pressure on the wheels too long causing them to lock (over brake) and slide.
> Locked wheels do not generating the maximum amount of deceleration.  The
> degree to which this happens will influence how badly your stopping distance
> is affected.  Best case (not all that likely) is that the abs system would
> stop the car in the same distance that a semi skilled driver could achieve
> with non ABS brakes, nothing better, probably worse.  The worst case of this
> would be locking the rear wheels before the front...which would cause the
> car to oversteer and spin while turning (cool if you are a rally driver).
>
> Under brake: This is not so good.  The way ABS works is by determining the
> approximate road friction and then setting target wheel slips which optimize
> braking performance in that situation.  It does this by HOLDING or RELEASING
> the braking force that you are trying to apply to the calipers.  If this
> slip target is calculated to be lower than what is actually possible...you
> will not decelerate as well as you could because the system limits the
> pressure going to the wheels.  Stopping distance increases and you run into
> whatever it is that you are trying to avoid.  A hard pedal is the worst case
> of under braking.
>
> Hard Pedal:  The name explains the situation...you press on the pedal and it
> is hard, very hard.  This occurs when the ABS system thinks that the tires
> are rotating much slower (slipping) than what they should be and tries to
> decrees the slipping by blocking most/all pressure from going to the brakes.
> This situation is quite scary and very dangerous.  There is minimal if any
> braking force and thus no deceleration...that is until you run into whatever
> is in front of you.
>
> Changing only a master cylinder or upgrading calipers without adding and
> properly tuning a proportioning valve will usually negatively affect braking
> performance/balance.  Adding a control system not specifically setup for a
> vehicle will earn you an Honorable Mention in the Darwin Awards.  If you
> want to brake better, go to a performance driving school and learn how to
> threshold brake.
>
> How do I know???  Look at my email address.
>
> More technical information concerning the operation of ABS systems was
> posted by one of my colleagues at the following link:
> http://www.fiero.nl/forum/Forum2/HTML/028643.html
>
> Please do not try it,
>
> Scott S. Amenson
> AC/ESC4 (ESP, ABS, TCS Development)
> > Robert Bosch Corporation
> scott.amenson at us.bosch.com
>
> Message: 2
> Date: Tue, 19 Nov 2002 20:51:36 -0500
> From: "Scott F. Williams" <sfwilliams at comcast.net>
> To: diy_efi at diy-efi.org
> Subject: [Diy_efi] OT: ABS retrofit into older car...
> Reply-To: diy_efi at diy-efi.org
>
> Hey, I realize that this is off topic, but... Is anyone out there
> knowledgeable about anti-lock braking systems? I'm going to attempt a
> retrofit to an old car of mine and need to figure out some of the logistics
> before hand. Would somebody be so kind as to email me off list?
>
> Thanks,
>
> P.S. If there's a listserv or forum out there dedicated to brake
> development, I'd love to know about it...
> --
> Scott F. Williams
> NJ Scirocco nut
> '99 Subaru Impreza 2.5 RS
> Mazda 323 GTX turbo "assaulted" vehicle
> Golf GTI 16v "rollycar"
> ClubVAC: "Roads found. Drivers wanted."
>
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
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