I have an old audi 80 quattro that I've had for a few years now and it's been off the road for over a year now and I'm thinking of puting it back on the road.
I know the exhaust is burst and the hand brake cable to one side is broken which is easy enough to get fixed (I hope) but the ABS is also stoped working, I think it's the sensors in the hubs have stopped picking up the wheel speeds so when i press the pedal it thinks it's locked up and doesn't let me brake(scary the first few times) . after about 50meters driving along the road the abs light comes on and the abs is switched off and the brakes all works as normal an the car goes fine. so the question is if I can disable the abs altogether so the brakes work would it pass an MOT even though it was fitted with abs as standard but now it doesn't work?

Mike

i hate to guess, but i think a dash warning light would be a fail, but in my understanding they dont test antilock function as it isnt a legal requirement, hence they would never know it was bust. Im sure one of the members who does MOTs can correct me on that

ie make sure the bulb doesnt come on

[Edited on 2/1/06 by JoelP]

Sure it's only tha ABS warning light operation thats tested. BUT if the brake are not working when tested it will fail anyway . Best to get it sorted properly.My brothers BMW had an ABS fault that I managed to sort out that was a wheel sensor fault . Disconnect ECU and using multmeter and wiring diagram tested each wheel speed sensor and wiring until faulty sensor found , repeated at suspect wheel speed sensor to eliminate wiring . Easy job on that to change . HTH

my overcomplicated locost derivative has ABS.

The SVA states that there must be a test of the warning light on power up, and that the abs light must indicate a fail. And the ABS function must work.

Im guessing that if the SVA needs it to work, so might mot? Also, the 'lamp test' feature might get noticed by a keen eyed tester if he doesnt see the lamp come on cos you took it out..... worth a try perhaps?

could be a wheel sensor at fault?

atb

steve

[Edited on 2/1/06 by steve_gus]

The ABS system on these cars is not very complicated... I would suggest crap in the hub toothed part or loose connector to a wheel sensor. As you probably know the ABS computer is likely to be under the rear seat. Some fiddling should see it right again. Most of these cars had push in sensors so you could pull them, clean and refit.

I have a 90 Quattro 20 valve budget blaster that I run as daily transport. Most faults are easy to find.

Cheers

Instant fail --- testers are well wise to this


You will need to check each sensor in turn and also the condition of the reluctor rings and the connections, however from you description it sounds a deeper rooted fault. As normally a senors fault allows more or less normal braking but without the ABS function.

One other thing are you sure one of the handrake cables isn't stuck in the on position because this can really flummux the abs system and trigger a warning light.



[Edited on 2/1/06 by britishtrident]

quote:

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Originally posted by CaLviNx

But if you were to remove the motor/valves and electric components, and re-plumb the system to be a fully functioning non-ABS system then the braking system would be tested as normal.

Regards

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here's the beast in question:
Rescued attachment old&new.jpg

Find a non-ABS model in a scrappy (if such a model exists) and swap over the master cylinder and duplicate the pipewrok on the non-abs system. If you disconnect it, there has to be no half-measures for the mot, you need to remove the abs pump etc, hence the re-plumbing.

A person of low moral standards might wire the abs light up to a timer relay so it comes on with the ignition switch and goes out after 5 seconds, or even just wire it in parallel with a similar warning light, ie airbag light. Enough to get the MOT, but a car should never be sold in that condition.

Ive found with my honda that if the light goes out several seconds after starting & then comes on when you move off, then its a sensor, if it does not go off at all, then its more serious,
Ive found that if I disconnect all the sensors, the light goes off after Ive started & because the computer never sees a wheel speed, the light stays off, but even then I still fixed it & spent £105 just for the part

Hopefully most Abs systems work on the same principle,so here's my tuppence worth from semi trailer abs systems.

Firstly before you rejoin the sensor cable you cut put a meter on the wires and check that you are getting an ac voltage ( can't remember how high off hand and all my notes are at work) when the wheel is turning, then rejoin the wires
Check the rest of the sensors in the same way. If you can get a pin out of the Ecu plug Its best to check them there as it shows up any broken wires as well. All the voltages should be pretty similar at similar wheel speeds. If there is no voltage then either
1 the sensors fcuked
2 the exciter ring is gummed up ( previous post)
3 the air gap between the sensor and exciter ring is to big.
Other than that your probably speaking huge sums of money for ecu replacement or modulator valve/pump unit. Unless you can get from a scrappy.
And yes it will fail the MOT
I had a prob like this on my old Carlton and all it was was a flake of rust from the brake backplate had fallen between the sensor and the exciter ring.
Hope this helps mate and good luck.

Converting to no-abs is not as simple as just removing the ABS unit and plumbing in a standard master cylinder -- you also have to consider the rear brake hydraulics and may have to fit a pressure limmiting valve.

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Originally posted by planetester
Ive found with my honda that if the light goes out several seconds after starting & then comes on when you move off, then its a sensor, if it does not go off at all, then its more serious,
Ive found that if I disconnect all the sensors, the light goes off after Ive started & because the computer never sees a wheel speed, the light stays off, but even then I still fixed it & spent £105 just for the part

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quote:

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tell me it has switched of the abs and all is well

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Ok so now I'm thinking more along the lines of repairing it , but I remember trying to pull a sensor out before and not being able to get it out, even when I had the bearing out I tried knocking it out from the inside but it didn't budge.
so the new problem being how do I get the sensors out and where/how much for new ones?

Mike

Ok I think it's going to be easy enough to pick up some second hand wheel speed sensors on ebay now I just need to find the best way to get them out

I think I'll go buy meself some wd40 put some on now and again in a few days then if i do get some other sensors to try hope fully it'll have worked and they'll just pull straight out with little persuasion

Mike

Once had to change a wheel speed sensor on a Calibra that was siezed solid in it's hole. In the end I carefully drilled out bulk of sensor and then just removed outer casing. IIRC the internals are just like tinfoil coiled up tight. The cable is normally fitted with a multiplug , probably tucked away from road dirt etc.

I've found out the sensor plug connector is in under the rear seat so that'll explain why I couldn't find it.

Mike