..

gotta love GM stuff, GENERAL MOTORS.

think where Jag would have been WITHOUT GM PARTS, and Ford.

 

I do love GM's engineers. Amazing that they followed up he most hot rodded engine ever, the SBC with the next most hot rodded engine ever the LS. Back to back grand slams.

However in this case the ABS system is actually Bosch. Jaguar, Porsche, Mercedes Benz and others all used the exact same system in the mid 80's. The controller did offer a few configurable features, for example the Corvette had a g-force detector for some reason and the Mercedes diesel system has a hall effect sensor for engine RPM for some reason. The GM benefit expresses itself as price and availability. Corvette parts are much easier to come by than Porsche parts.

 

Epic thread. I didn't know it was possible to retrofit ABS. Incredible work. Thanks for linking from the rest-mod thread.

 

I'm confused about the ABS because the original complaint was "I can no longer lock up the wheels."

Lets say it just stopped locking up the wheels when you threw the 235s on it, so it just has enough grip to not skid. If it just barely no longer skids, and you put bigger brakes with ABS that also holds it around the same point of not skidding, aren't those both the same amount of braking?

I mean props on getting it setup, I'm sure its not common/popular to retrofit ABS, so thats going to be a bunch of troubleshooting you can't use someone else as a reference for.

 

Road conditions vary greatly, tire co-efficient of friction and driver inputs vary greatly too. ABS compensates for those variables to some degree by allowing the wheel to keep spinning in low cf conditions.

When you add larger brakes the wheels become easier to lockup especially in slippery conditions, that's the issue.

No matter how small or big your brakes and tires are any car can benefit from ABS in slippery conditions or aggressive cornering. The prevention of locking of rear wheels can prevent a spin, this is why drifters use a hand brake.

ABS was only, one aspect of this project. It included larger front calipers and rotors, and much larger rear caliper and rotors. The larger rear calipers greatly improved rear and thus over all stopping performance but also increased the tendency for the rear wheels to lock first. The ABS mitigates that.

Sadly this car no longer exists. I sold it and removed the ABS system and transferred the brakes assemblies to my 2015 Coupe project. On that project a newer ABS system was used from a 1995 XJS. Same principles, just with a newer 1 piece ABS / Controller package which drastically reduced the wiring. Also the 2015 Coupe Project runs ultra high performance 255 series tires out back so it's more balanced and the rears are less likely to lock before the fronts.

The 12 inch rotors are small-ish by todays standards, most high performance sports cars run 13.5" or larger rotors now. The 2015 coupe will be getting another major brake upgrade soon.

 

I guess what I meant was, the idea was to put bigger brakes on it because the brakes were not strong enough to cause lock up, but then ABS was added to prevent lock up. So unless the brake system was actually faulting, wouldn't you just be back to square one? (in good conditions)

You should be able to regulate the difference between the front and rear mechanically with a proportioning valve, no ABS needed.

Honestly I find the stock brakes pretty good, just yesterday a guy decided to run across the crosswalk once the light turned yellow, banking on everyone stopping. Well I was too close to stop for the light at 60 mph, so I locked it up and turned to the side to avoid him (he would've been right in front of me as I got to the crosswalk). I been in a few situations where the brakes really held up for me. The rears are just a pain in the *** with being so inaccessible.

 

well in a word... no.
Conditions are not always ideal. ABS compensates for that.

Stock brakes are great with stock tires and stock HP. When you have 450+ HP and your 1976 Jag is faster than a new V8 F type, bigger tires and brakes become very necessary to balance the car. I can tell you 1st hand... stopping hard from 125 MPH at the end of a straight with stock brakes is not safe or repeatable more than once with out a lengthy cool down.

Using larger rear brakes moves the bias rearward allow all 4 wheel to slow the vehicle, this more evenly distributes the work and is great for breaking performance but may cause the rears to lock sooner than the fronts in some conditions, ABS prevents this.

As for your brakes...they are supposed to hold up. That's what they are designed to do... dont be so surprised. As for "locking it, and turning to the side" Those are movie tricks... Unless your drifting...I'd prefer to say in direct view and control, ABS allows for that.

I really dont know what point you're trying to make. If it's that smaller brakes, no ABS, and movie star driving moves are somehow superior to larger brakes, ABS and maintaining a direct view and control then... thats gonna be a tough sell for me.

 

Hi there, I know it has been quite some time since you started this post but just stumbled across it now and was inspired! So I went out and bought a C4 ABS system complete with the modulator valve and control module to install on my Mk2. I tried to find some schematics online but wasn't too successful or I don't know what exactly to look for. Would you happen to have a wiring diagram as to how you did it? It would help me tremendously. Thanks a lot for any help you can provide. Cheers

 

I used Alldata DIY.