Oddjob

Anyone installed the factory ABS system on a non-ABS equipped car?

I have been told and can see that this will be a big project. I know what components are needed to include the pump, brain, brake lines, wiring harness, sensors, hubs with pickups, etc. But is the harness absolutely necessary, or can it be custom wired?

Im not too concerned with not being able to figure it out, but if anyone has done it, I would appreciate any insight to save some time.

Thanks

Jfrahm

Oh man, what a chore. I would just do a driver swap.

-Joel

Bret 944

Is ABS that big of a deal? The only way I can lock up my non-ABS '88 is to slam completely on the brakes at about 80 or above. Even then they only lock up for an instant. My g/f has ABS on her Durango, and I hate it. The hop-skip-jump effect really sucks. Just my opinion.

Bret

James86-951

That's a really bad idea. If you want ABS, go to a stand alone aftermarket unit. It will be much easier and above all, safer.

odie

I seem to recall an after market product. Some kinda metering valve or something that installed on the brake line after the MC. No wiring or other hook ups required.

I read some car magazine tech article wite up about it. They gave it a good review. It might have been Kit Car, European Car, VW Trends or something like that. I read the tech oriented car magazines.

Cost was low too. Fits any car. Not true ABS but it did improve braking distance and reduced wheel lockup.

ninefiveone

I can think of a couple reasons for wanting ABS.

- It never hurts to be able to just stomp on the pedal on the street in all conditions. (Rain, snow)

- At the track, it helps a person run consistent lap times. Might be viewed as a crutch but it does work.

Also, keep in mind that the ABS you experience on one car will be different from another. I happen to like the ABS on 944's and have given thought to what it would take to retro fit it to mine.

It looks like a bear but I know people have done it. A short time ago, Scott Gomes of Under Pressure had a complete 968 setup for sale and it wasn't long before someone snatched it.

924RACR

Do not use the "aftermarket" gimmicks. Definitely not safer than a properly designed, engineered, and implemented ABS system.

I am an ABS/TCS/ESP engineer for Bosch. You'd be far better off retrofitting a 944 ABS system to an non-ABS 944 than using that junk. But no, I would not recommend a retrofit. It'd take an absurd amount of work, far beyond the value of the system, not enough to justify not just learning how to drive.

For the record, my daily driver is an '82 931. No ABS, airbags, etc. In the winter (being as how I live in Detroit), I use my '86 Suburban for transportation. Likewise, no ABS, traction or stability control. Not even a locker.

Oh, by the way, and this is just my personal opinion, the Durango is by no means the best ABS system. You should try some others if you really want to compare. Really, try a 944 w/ ABS.

As for not getting into ABS on dry pavement - that should be no problem. If it is a problem, you need to service your brakes or do some leg exercises. Don't take that as an insult; I'd never had an ABS car before I came here, and it took me a while to get to the point where I could hit the brakes hard enough. That said, your brakes should of course be recently bled and the pads/rotors in good shape. If they're glazed or cooked, you'll have trouble getting enough pressure to lock the wheels.

That's the short answer. I would only consider retrofitting the correct 944 system, if any.

Oddjob

I appreciate the input, but I was looking more for the how to tech info, rather than the why or why not.

Car is set up for stock PCA club racing, which limits/restricts my retro fitting to factory OEM standard/optional equipment. So its the 15 year old Bosch system or nothing.

The driver: even a pro will admit that ABS cant be beat by a well trained and disciplined right foot.

Yes, ABS is of limited value on the street (panic stops in the wet…), and depending on the aggressiveness of a driver, is rarely triggered in DE events; but it does come in handy in racing. It doesn’t take much of a chirp to flat spot/cord a hoosier, and ruin your day.

Your choice: trying to out-brake a 2500 lbs 911 going downhill into the brake markers at turn 5 at Road America (more often than not a 5th to 2nd downshift), with or without ABS?

924RACR

I'd feel fine doing it w/out... having out-braked 2100lb CRX's... but we digress.

You'll need the wheel speed sensors, which'll mean hubs, etc. to accomodate. Plan on just replacing the corners. You'll need the HU (hydraulic unit) and ECU, not to mention wiring harness... not sure if it's a subharness or built into the main wiring harness. This is a pretty old system compared to the ones I know, so I can't offer much direct technical direction. Naturally you'll need to re-plumb the hydraulics to incorporate the HU - bend and flare new lines. Power and a good ground for the ABS ECU. Those are the most obvious. Not sure where the ECU would be located in those cars, though I would expect theyd' rather have had it in the passenger compartment. Nowadays it's attached directly to the HU.

Did I mention that the ABS will not be correctly calibrated for a race suspension, brake pads, and tires? And yes, it does matter - that's what I do for a living, and it takes much time to tune. You'll also want to rig in a reset switch in the power feed to the ECU, since hitting the gator's teeth will cause the unit to fault out (bad wheel speed sensor), and you'll probably want to reset it on track before you finish the session.

At least you're not trying to retrofit a PSM system...

Oddjob

I ran a 944S for several years with the stock cray fish claw sized calipers. With fresh track tires, it would take almost an intentional effort to lock up the wheels under braking. Mostly just a chirp was possible in slower corners. Not so with the 4 piston bembos on a turbo/S2, they are capable of locking a wheel even at high speeds.

Racing is competitive, and most driver/owners are trying to get any advantage they can (within and outside of the rules) over their competition; to win even if it is just an amatuer venue. I have found, from some recent on track experiences, that it would be to my advantage to have ABS. Just like guys with S2s run the 928S4 calipers (it was the factory M030 option); because they can, and because it offers an advantage over cars w/o.

Ive got about 75% of the components including the hubs, sensors, pump, control unit (outboard passenger footwell), and most the the brake lines. Just need the wiring harness (it is separate) and a couple of the lines that run along the fire wall. I was hoping someone had done the install recently and could offer a few hints if there are a couple problem areas to encounter.

I am aware of the use/need for the dash mounted reset, but want to ask about the calibration.

Im guessing here and over simplifying: The amount the pump pulses to release the locked wheel is based on an assumed amount of friction between the tire and road surface and the friction between the pad and rotor? So the braking force (fluid pushing against the piston) has to be interupted/reduced enough so that the sliding frictional force between the road surface and tire will over come the clamping force between the pad and rotor, allowing the wheel to start turning again?

So by using a much different tire compound and a pad with a different friction coefficient, the pump pulse may not reduce the braking force enough to release the rotor and allow the wheel to start turning?

So this being an issue to use stock ABS units on street cars converted to track use, who/where do I go to have the control unit (or pump?) recalibrated?

924RACR

The pump only recirculates the fluid. The main control is in the valves; inlet and outlet valves to each wheel. Your basic synopsis is otherwise correct. It is essentially a pressure-based control; ramp up and hold pressure as long as possible until the wheel speed falls off from calculated vehicle speed, then release as little pressure as possible to allow the wheel to reaccelerate back up to vehicle speed. Rinse and repeat.

However to understand the variation from stock, you need to take additional factors into account. The different mu-slip curve (in both lateral and longitudinal directions) of a race tire vs. a street tire vs. the original tire the car was sold with in '87, the different compressibility of the pads you're using now vs. stock OEM parts, the different weight transfer and loading of the car in transient response conditions with a race suspension (springs and shocks, including swaybars in later cars with more advanced control algorithms). A whole lot of stuff.

Now, don't take this as saying you're screwed once you put non-OEM tires or pads on your car. Obviously the system can tolerate those kind of changes. But the extreme degree of modification you're going to (being a race vs. street setup), combined with the degree of performance you're wanting, makes it a losing battle.

Simplest way to give an example - longitudinal force capability of the tire. A street tire will typically give best decel (I should clarify, I'm talking about a new current, say MY04 car and OEM tire) around 7-8% slip (wheel speed vs. vehicle speed, as in wheel speed is 92-93% of vehicle speed. Really aggressive street tires, say a Comp TA, you could go as high as 10%. Race tires, say a Hoosier R3SO3, could be much happier and give much better decel at much higher levels, say 15% or more (I've tested with them, but didn't do any tuning for them, so can't say for sure).

So, what you'd actually likely end up with is underperforming ABS, where it's not letting you use all of the tire. Do you really want that?

I still think you ought to consider a pad change. I trust you have the same braking system as the original '83-84 944, or close enough? I have no problem locking the wheels, if I so desire, with this braking system on my 924 using Hoosier R3SO3's. Likewise, you should always be able to lock a wheel. What pads are you using, and do you have cooling ducts? Or is it the 951 you're racing now, and it's not a problem? I'm a little confused now.

As for recalibration - that'd be Bosch, but it's at notgonnahappen.com. This is not like burning an engine chip. It takes years to develop ABS SW, and hundreds of thousands of dollars. Not to mention that what you have is horribly obsolete. I finished working on the MY04 Grand Prix GTP Comp G two years ago, if that gives you any perspective, and am currently working on projects through '07.

Oddjob

I appreciate the insight on ABS, the basic theory in plain terms, thanks. Always trying to learn and understand more....

>"So, what you'd actually likely end up with is underperforming ABS, where it's not letting you use all of the tire. Do you really want that? "

Well, its relative. No, I know it wont function as well as newer race tuned systems that are in use on say a 2003 GT3RS. But in comparison to the cars Im running with, Ill either have the same underperforming ABS setup or none at all. Im inclinded to believe that, even in an uncalibrated state, its better than none at all.

>"I still think you ought to consider a pad change. I trust you have the same braking system as the original '83-84 944, or close enough? I have no problem locking the wheels, if I so desire, with this braking system on my 924 using Hoosier R3SO3's. Likewise, you should always be able to lock a wheel. What pads are you using, and do you have cooling ducts? Or is it the 951 you're racing now, and it's not a problem? I'm a little confused now. "

Didnt mean to be confusing, I was just being vague to keep the discussion from getting too long. Its not a pad or cooling issue. The point I was making with the 944S is that I have driven non-ABS cars for years in drivers ed and club racing w/o feeling any real need or use for ABS. The heavy, lower powered car with small brakes and sticky tires is not prone to easily locking up its wheels.

But Ive been running a turbo for the past couple years, and with the higher speeds and stronger brakes (same weight, same tires), chasing faster cars, Ive got into some racing situations that ABS would have been a "nice to have". Its certainly not necessary to have, but Ive smoked a tire or two either trying to outbrake a car I want to pass, or trying to keep from being passed under braking by another car. My thought is ABS would give me a little more confidence in those situations that I can push my brake point in that extra car length, stand on the pedal and not worry about wrecking a tire ($$$). Im not expecting to improve lap times with this, but just get a little more comfort/control in the braking zones while dicing with traffic.

An opportunity popped up to get the majority of the ABS components off a wrecked car, and I took it. So Im just doing a little fact finding for one of my upcoming winter projects.

James86-951

This might be dumb questions; but I am not familiar with the 944's ABS system.

1) Is it a 3 or 4 channel system? (Curious)

2) Is it the constant-pressure type whereby the pump is on all the time? or does it only come on during ABS situations? The reson I ask is that I worked for Chrysler when they were changing over from the Tevis system to the Bendix system. The older system had a problem of loosing pressure and the brakes would completely fail. (That was my concern on the retro fit.)

3) When you install the ABS system, won't you be in violation of stock class? (as it was not available even as an option.) I don't know what was available. I just want to make sure you wouldn't be in violation.

I would like to see how your work turns out. I have a vibration now after an incident with a Bubba in a Dodge truck. (I slid about 100ft) I hate having to buy new tires for stuff like that!

924RACR

I do believe the 944 has a 3-channel system, since as I recall it's got a front/rear split. The pump will only run when the system is active (modulating brake pressure).

Oddjob, the point is that with a stock ABS system and race tires, you'll be underbraked as compared to a capable driver (same car and tires) who knows how to use his tires. He'll be able to get more out of the race tires, as the calibration of the ABS will keep you from using all of the potential of the race tires (since they have more potential than an old street tire from the 80's). Thus you will be outbraked.

I disagree with your statement that it's not a pad or cooling issue. If you can't readily lock the wheels, then you DO have a pad issue. If you're saying that it's easier to modulate the pedal pressure and prevent lockup, that can be a function of hydraulic system design, or perhaps you'l not pushing the tires hard enough. I know when I switched to Hoosiers that it took a while to get comfortable pushing the tires that hard, since they can brake so much harder.

However, we're mainly focusing on the turbo now, which could've had ABS (this may resolve the legal issue, right? I mean, if it was an option). Yes, having ABS might give you a higher confidence level. So would practice, wouldn't it? Not being a snot, just trying to weigh all the options.

924RACR

Here's another thought... if you hadn't already spent the money, I'd say spend it towards some really fancy high-end shocks. Better wheel control, leading to less likelihood of wheel overslip (since the wheels will be in better contact with the ground).