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+--- Thread: ABS questions (/showthread.php?tid=4898)
ABS questions - EmJay - 09-12-2013
The following question is for Project Redemption.
What all is required to make the factory ABS work? Do I have to wire in a sensor to the brake petal, do I have to connect the ECU for it to work, a separate computer for the brakes?
I do have access to the parts car, it's in my backyard, and I haven't sold anything brake related from it.
RE: ABS questions - EmJay - 09-12-2013
another question to add, would it be better to use the MB brake booster, or would I be alright with using the Mazda booster?
RE: ABS questions - Simpler=Better - 09-13-2013
Any booster is fine they're all the same basically/ probably.
For ABS you need some kind of wheel speed sensor(s), whatever brain the old computer used for ABS (follow the wires-it might be a dedicated brain), the ABS block, and possibly a vehicle speed sensor.
RE: ABS questions - raysorenson - 09-13-2013
You'll need to look at the ABS wiring diagram to see all the required inputs. Yes, it uses a brake on/off switch. You'll need switched (hot in RUN) power to the ABS module, ground and a hot at all times circuit. Speed sensor wiring is a twisted pair- the wires connecting the wheel speed sensors to the ABS module will need to be twisted together. IIRC, the rear sensor tone ring is matched to the ring and pinion ratio. If you change the gear ratio, you'll also need to swap the tone (toothed) ring.
RE: ABS questions - EmJay - 09-13-2013
Good stuff there Ray, thanks!
I did save the sensor in the rear end, and I should have all the appropriate sensors at the brakes as well. I am using the factory speedometer so I should be able to get a signal from that if necessary. I'll see if I can find a wiring diagram for the ABS system, I haven't had much luck finding wiring diagrams for anything other than my 201.
RE: ABS questions - SurfRodder - 12-24-2013
When I gathered all the parts for my future plans in this vein, I was able to pull a complete ABS setup, all sensors and harness and computer/sensor box, unmolested (maybe one wire cut), from a donor 560 ('86 I believe, but if later ones are still modular, I'd grab the latest one you can find...prolly be helpful to know when they made it standard equipment as that would dictate if it would be relatively easy to pull, i.e. less integration to chassis harness). Extra bonus is that wiring the speed sensors to the front wheels requires the w126 spindles and thus bigger brakes are part of the setup as well. Anyway, as far as wiring is concerned, pulling a complete system is really the best way to go and if you do it yourself, you can learn where this are located/take pics, etc.
The really trick piece is the rear diff from an '85 300SD which should have the proper 2.88 ratio and ABS sensor mounted (I believe that ABS was optional back then, but every '85 SD Ive seen has it)... My original plan was to pull the entire ABS setup from that car, but I saw it on a Tues and it was smashed by the time I returned on Sat(complete car too, real shame)... If you plan on using a different ratio diff, any ABS w126 up to '89 or so when they changed to the different subframe should work, large or small diff.
In fact, I think there may be an '85 SD in my local yard now, but its been a while since this has been on my radar (due to other 124 related projects) so Im not 100%...Ill check this weekend when Im back in town...