Big_Will

Hey,

I'm thinking about doing a project car that involves putting a Rotary into an old skool Toyota (Starlet, or AE86). Since the car is so old skool, I'm most likely going to do a rear end swap and swap as much of the suspension, steering, and brakes on the front as I can.

My question is this: Would I be able to take the ABS sensors and ABS computer off the donor car and use them on my project car? The hardware should all bolt right in since I'm taking the complete assemblies from the donor. Will the ABS computer recognize that the car that the brakes are on now weighs like 1/3 or 2/3 as much as the original donor car?

Just a crazy idea that popped into my head. I wonder if it will work. Thanks for your help.

Will

ajmacdon

Don't do it! I am an ABS/TCS/ESP engineer and I can give you a huge list of problems associated with this swap. Some of these involve all the valves closing and giving you a hard pedal with no braking. There are teams of engineers to tune each ABS system to any given vehicle. The tuning involves a complex vehicle model which takes into account things like weight, CG location, tire rolling radius, suspension geometry and tuning, etc. It may work most of the time but you will almost surely find that it will falsly activate under certain conditions such as pulling into a driveway or driving around a parking lot, again, possibly leading to a hard pedal. I have wanted to put ABS/ESP on a personal project car for a long time but the hardware and knowledge (1000+ tuning parameters!) to tune these units is not available outside the companies that manufacture them (it kills me to do this at work all day and not be able to do it for my own car).

Alex

Node

iTrader: (1)

Since you do this for a living, I guess you'd be a good person to ask.
Are there any disadvantages of taking off the ABS system, other than not having the ABS.
And can the ABS like wear out over time?

Big_Will

Well darn,

Not to be disrespecting on your post, but here's a few more specific questions.

I'm going to be using all of the hardware from the donor vehicle down to the wheels, brakes, sensors, and suspension. So the actual hardware recognization wouldn't be a problem. There will just be different weight loads on the suspension.

So my question is this: if getting ABS to work is as complicated as you say it is (and I'm not saying you're lying, mind you, I'm just curious), how does ABS recogize weight shifts in the car such as extra passengers, cargo, or like new light weight parts such as carbon fiber hoods etc. Also, if you use an aftermarket wheel that is a whole lot wider (more rubber to the road), then how does it recognize that? I never knew ABS was so complicated. This intrigues me.

Hey, maybe you could start an aftermarket company that retrofits simple ABS to old skool cars. I'm assuming that full blown ABS is geared towards safe daily driving like stopping when it's slippery or when the wheels are on surfaces with different traction levels. Perhaps you can make a bare bones ABS that detects wheel lock and can be calibrated to "pump" the brakes using a certain amount of force. This racing ABS's sole purpose in life would be to reduce 60 to 0 distances. This was just a random thought in my head, so it's probably stupid.

Thanks for your help. You sound like you have a pretty cool job.

Will

Gene

iTrader: (1)

Don't use the ABS out of a 2nd gen! The hydraulic box will start leaking and turn to ****.

Doing the suspension swap into the back of the AE86 would be quite a challenge, what with the live axle rear and all... maybe if you used a first gen rear? The stock AE86 suspension is reputed to be very good however.

ajmacdon

Good questions, I'm surprised that there's interest (most people just want to pull the fuse

First, any ABS from 1993-95 will slow you down (interms of lap times) on a dry track that you know your way around. If you are going for all out dry speed in a car this old I would disconnect it. However, I did a track day in the pouring rain last fall and used ABS for the entire last half of most of the straights (new track, no traction) Keep in mind that it also allows more relaxed cruising, if something surprises you just pound the pedal and TURN, that's the benefit of ABS.

Second question(s): I looked into this type of ABS because the question got me interested. Current ABS (beyond 1998 or so) chooses a level of slip based on tires (compound and size), weight, cg, surface, etc and then holds the wheel there by knowing weights and inertias of various rotating components and the efficiency of the braking system. These systems are very tightly tuned to a specific car as it came from the factory and really don't deal well with changes. For instance, if you put sticky race rubber on the car and the tires would like more slip to generate max force, the ABS controller won't give it to them. The result is that you will get the same slip as before and will stop in just about the same distance (or longer). On the same note lighter wheels/bigger brakes could cause rough control that the dirver may or may not notice (there's lots of math here, basically the goal is to eliminate costly sensors by knowing/predicting how the tire/wheel/brake combo will behave without having to measure it on each car and each stop).

1993 ABS (in general, I don't work for Denso so I don't know the Mazda system) is quite different, it drives the wheel to almost lock (~25% slip) and then lets it recover by releasing the brakes. By doing this and monitering how much brake pressure it takes to get there it hones in on an optimal level of slip for that tire/surface combination. The reason the industry went away from this is because it was harsh for the driver and the tire spent more time away from it's optimal slip level causing longer stopping distances.

The good news is that I think this type of system *might* retrofit OK. As I said, your stopping distance *will* get worse on the track but your margin of safety will be higher on different surfaces and you wil always be able to steer!

Ok, this is too long, I love this stuff and could go on and on about why the newer systems are better (I know it doesn't sound like it here) and the overall pro's and con's of ABS on performance cars and family sedans. However, I have an ice field to play on this time of year (Yes, it's a cool job

Node

iTrader: (1)

you said you can just pull a fuse, could you setup a switch to turn ABS on and off, like have it off at the track and on when daily driving?

Gene

iTrader: (1)

Yeah you pull the fuse under the hood that says "ABS" on it, and the abs box now no longer has any electricity to operate. Your abs light will come on though. Lots of guys do this for solo2.

Ajamacdon, (wtf?) sounds like you have a really cool job.