348 ABS Computer Clarification

My concern would be not knowing enough about ABS algorithims. I could see how normal driving nothing seems different. I could see at limit ABS function totally different and maybe dangerous. It is rare that people drive limits but fairly often that people suddenly exceed them...i.e. crashes. I would be at the race track testing and even at that driver skill varies greatly.

 

Does anyone know if the original can be repaired by any shop ?

 

... and you wouldn't want your insurance company to find out, after an accident, what type of computer was fitted.

 

I think the Vette guys are using ABSfixer.com? Maybe check there?

 

I don't have a circuit diagram for the Lincoln Mark 7 ABS but it appears that, in addition to different circuitry, its pinout may not be the same as the 348's. I plugs in but, as shown on the sticker, it has different "not used" pins as compared with the 348 ABS sticker (see post #36 in "348-brake warning lights on"). The ABS computer that appears identical to the 348's is that of the Jaguar XJS 89-93 (used ones are fairly cheap). It has the same "not used" pins as the 348's. The Jag also has similar MC and the ABS pump. Below are the ABS computer picture and the ABS diagrams of the '89 and '93 Jag XJS (diagrams also attached as pdf) for comparison with the 348 ABS diagram.

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There seems to be the idea here that all ABS systems are the same, regardless of different manufacturers and models, and that, providing the plugs fit, any ABS controller will work with any car.

I would say that they may well operate, but that doesn't mean that they are working correctly.

Different cars have different weight distributions, different brake biases, different braking characteristics, different suspension characteristics, different handling characteristic etc., etc., and each ABS controller is designed to take those factors into account, in order to operate the ABS system correctly.

Think about it - The weight distribution, braking characteristics and handling characteristics of a Lincoln, or a Jaguar sports saloon, are going to be completely different to those of a Ferrari.

Fitting an ABS controller from another model, or from a completely different make, might put your ABS light out for you, but it could also result in your ABS either operating far too soon, or worse, not operating at all when you most need it!

Why else would ATS go to the trouble of designing and manufacturing hundreds, if not thousands, of different models of ABS controllers, if all they really needed to do was design one?

 

The question is... did they design and manufacture hundreds, if not thousands, of different ABS controllers? Or are there a few different models (with lots of different stickers) and a case of "near enough is good enough". In the '80's, did they just stop the wheels locking up and leave the rest to the mechanical ability of the car?

 

I don't think the ABS system "cares" about the weight distribution, suspension, handling, braking characteristics etc. All it does is monitor the rotation of four wheels and prevent from locking those that look they are about to, compared with the rotation of the other "good" wheels. Four simple inputs and a number of outputs to the solenoid valves. The key is the information processing speed (the Intel chips) and the response speed which, again, is only dealing with the rotation of the wheel(s) and rapidly releasing and re-applying the braking pressure and not with any other parameters of the car.

Regarding the Lincoln ABS computer, I could only find part of the ABS diagram from the Mark 7 (attached). Unfortunately, the lines going to the ABS computer (from the solenoids shown) do not show to which pin numbers they go but, instead, show some three digit numbers that appear to correspond to the three digit numbers at the pins of the ABS computer shown on its label (see attached pic). If this is correct, then the Lincoln ABS computer has different pin assignments compared to the 348's, even though the plug is the same. And the unused pins are certainly different. So, it looks like the Lincoln ABS computer cannot be used on the 348. Why it appears to "work"? Possibly because of the different pin assignments it does not light-up the ABS warning light and, by chance, does not cause any shorts and otherwise does not work at all (some of its electronic components might silently be blown the moment it is powered up in the 348). In any case, it would be good to know if anyone who has installed the Lincoln computer in the 348 has actually tested the operation of the ABS and felt pulsing on the brake pedal.

The Jag XJS ABS computer looks promising. I have bought a used one (the new ones are about $1,100) and will look at its internals when I receive it.

Lincoln:

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The case swap is only possible between the 348 and Jag XJS computers as they are identical in all respects (except for the internal circuitry which I am going to assess soon). Swapping the 348 computer casing onto the Lincoln chassis/PC board would be obvious as the holes through the bottom of the casing are different - four on 348, two on Lincoln and there would be no protruding threaded bush-like parts of the internal chassis (see attached pic of a 348 unit, Lincoln does not have them). Also, the Lincoln casing has a rivet-seal to the internal chassis (has to be drilled out to remove the casing) and the 348 unit has an "Ate" seal over one of the screws attaching the casing. So, don't buy a used 348 ABS computer if the seal is missing or broken. I can see only one 348 ABS unit on Ebay at the moment showing the seal and 3-4 other for which the sellers "forgot" to take the picture of the bottom.

348
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Other differences:

348 (note the 5 holes below the bar sticker)
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Lincoln (no 5 holes)
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Jaguar XJS (all holes are the same as on the 348)
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They are calibrated to tire circumference front vs rear, weight distribution, bias and a few other thingy's
***WARNING*** Other units may fit and work but I would never take it on the track or do high performance driving with it.

 

Alfa Romeo Milano has the same ABS system including accumulator and similar “Centralina Antiskid” ECU.

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Not to hijack thread but I have a 348 ABS ECU I found when cleaning out the garage. Too many parts left over from the various Ferraris owned over the years!

 

I am really curious about these systems. It would make sense to me that an ABS system specific to a track or race car is calibrated to that car's setup.
Now, this may sound like dumb question, but on a road car with the out-of-the-box ABS computer, what if you swap out wheels and tires to different sizes or go with a different brake kit? Different size tires and wheels could obviously be different input params for circumference, weight,etc. so I am wondering what happens to the logic built into the ABS computer. Do we assume that the computer is programmed to operate within a range of calibrated values? In other words, wheels and tires can't change the overall ranges enough to change with way the ABS ECU processes its input. I'm not trying to challenge the information, because I really don't know but I'd like to understand. In my simple view, which could be completely wrong, the ABS computer has inputs from sensors on the wheels. if it gets input that a wheel is locked/locking, the computer does it's thing and pulses the caliper to stop the locking. If we have changed the values of wheels,tires, weight, whatever that the computer assumes to be true, could that impact functionality of the computer?

 

Your view is not wrong. The ABS ECU monitors the rotational speed of all four wheels and, during breaking, looks for any wheel rotating slower or decelerating faster than the other wheels. When that relative difference exceeds certain threshold, i.e. when the rotational speed of some wheel(s) approaches zero, the ECU starts pulsing that wheel or those wheels. The ECU ignores smaller differences (up to a certain threshold) in wheel rotational speeds like those caused by going through turns. So the ECU is looking at the relative difference in rotational speed of the wheels, thus tyre size or loading on any particular wheel will not affect its proper operation. The loading on the wheels is changing significantly during driving; for example, when going through turns, almost all of the car's weight can go to the outer wheels; or during breaking when much of the car's weight is pushed onto the front wheels. Still, the ABS operates properly.

On many cars (including the 348), the rear wheels are both pulsed simultaneously even when the signal comes from only one rear wheel. This is because the rear brakes are on the same hydraulic circuit.

 

Very good finding. I can see that the Alfa ABS computer has the same, marked on the label as "not used", pins as the Lincoln's computer. I managed to find the Alfa ABS circuit diagram and it shows that its pin allocations are the same as on the 348's computer, i.e. the sensor, solenoid and other connections are the same as shown on the 348 ABS diagram. This means that the Lincoln computer (for which I do not have a diagram), since it has the same pin "non-functionality" shown on its label as Alfa's, also has the same pin allocation as the 348's. Also, as confirmed by Paul, the Lincoln computer actually works on the 348.

About the "not used" pins shown on the label - in the case of Alfa, Pin 12 which is shown "not used" on the label is actually used. So the meaning of the lines (which I understand to indicate "not used") at some pins on the labels of the ABS computers are not clear. I have attached the Alfa ABS manual (strikingly similar drawings as those in the 348's workshop manual) with the ABS diagram shown on the last page (and also separately attached). You will see that I have added info on which "not used" pins, according to the label, are actually used in the 348's ABS system. It is quite possible that these "|" pins actually have functionality which is just not required in the case of some cars.

 

Yeah, I have a Milano also and these systems are pretty well understood in that world. Always knew the 348 had the same system. I just replaced the accumulator and put new rear calipers on my Milano.

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Here's another version (and a clearer copy, attached as pdf) of the Alfa ABS diagram. The computer pin usage on this diagram exactly corresponds to the pin usage (non-usage) shown on the Alfa computer sticker. So, it is not clear why the Alfa ABS diagram I posted earlier shows that the "not-used" pin 12 (as per the sticker) is actually used. Its connection is shown as a dashed line to a dashed lined fuses and a control module which are probably something optional and not important for the ABS operation.