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

[Amenson Scott (AC/ESC4)]

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
http://www.diy-efi.org/mailman/listinfo/diy_efi