Rear ABS Sensor

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Chris

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Sorry Jon, my point was that I have never had a test of my ABS as far as I know. They roll it onto the rollers, press the brake pedal and it passes or fails. I have been using the same place for years and I cannot recall there ever having been any specific discussion on ABS. I can't recall the ABS even cutting in during the test. They certainly don't switch the engine off then on and watch the dash. I drive it in, they do the test and then they drive it out. They ARE thorough and I trust them to check properly. Yes they have failed stuff.

Is ABS really part of the MOT? It does not improve braking force, it just retains steering under the heaviest of braking. A locked wheel is an inefficient wheel I know - so don't need the science behind this. Just the legal aspect. I might ring them in a bit. I asked them about the tow bar last year. Not interested.

Chris
 

Gav Peter

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Would you 'adam & eve' it, he's only gone & fixed the fnckin sensor!!! MOT in the bag - going home in style tonight!!!

I AM A VERY VERY HAPPY BUNNY!!! :happy-smileygiantred: :happy-smileygiantred:
 

Jon Wildsmith

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The ABS being fault free is part of the test Chris but the system is self testing. They don't test that the ABS operates but they should check the light that tells them self testing is happy. They have access to details of when the light should come on and how long it should stay on for etc for each vehicle. If the vehicle has ABS it must be fully functional i.e. present and pass self testing. Some testers are more observant of this than others. Your 80 shouldn't have its brakes tested on the rollers, it is a full time 4WD and they should use a decelerometer ;)
 

Chris

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Why Jon? They drive it onto driven rollers, out of gear and then press the brakes. They measure the force against the roller. They don't drive the rollers with the road wheels. They check each wheel independently and the handbrake too side to side. Always looked like a good test to me. We have a massive central workshop for our fleet and this is how we do our goods vehicles. Brand new too. Good enough for me.

Appreciate it's FT 4x4 but each wheel takes about 3 seconds. Get what you mean about being fault free, but is disabled a fault? Only working on one side for example could be dangerous. But to not having it work on any wheel just means you have no ABS. OK I fully appreciate that if you say it's part of the test then no point arguing - but for the sake of sense, does it need to be?

Chris
 

Jon Wildsmith

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Chris said:
Why Jon? They drive it onto driven rollers, out of gear and then press the brakes.
Because the braking effort is shared by the other axle if the brakes are any good or if they're not it may jump out of the rollers. Putting the transfer box in neutral would fix that but AFAIK there's no provision for that and what they're actually supposed to do when only 2 rollers are available is use a decelerometer. I'm only repeating what MOT testers have told me over the years BTW.

Chris said:
but for the sake of sense, does it need to be?
The effectiveness of the brakes and controlability of the vehicle in a low traction braking situation has been compromised if ABS is disabled?
 

Chris

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But it's not LAW to have ABS is it. All you get is standard brakes if you disable it. They aren't actually deficient without the ABS that's my (pointless) point. There are 80s without ABS and they pass the brake test. It's an enhancement. I believe you Jon, it's just that I have never heard of the ABS being present as part of the test. OK not working on one side, sure, but actually being switched on if you like, if fitted, no. That is a new one for me.

I have been taking my vehicles to this place for 28 years. There is no way they are going to jump out of the rollers. The rollers rotate anticlockwise to the roadwheels. ie they are pushing it backwards when you brake, the car climbs up, but that doesn't matter. Either release the pedal or let it pull you up and out, that's where you are headed anyway.

All getting a bit circular this argument. I know. There are two rollers and they can test left to right or both together. With handbrake applied, or simply natural drag, when they turn the front wheels, the back ones don't turn. The middle diff takes up the difference yes - only the fronts turn. When the back wheels turn on the roller you get the same thing. When they stop one front wheel momentarily, the opposite wheel gets all the movement - not drive, it's not being driven. Other than the bit of coasting you get on an auto on tick over whilst the engine is running for the servo

I just can't see a problem here. Sorry if I am being dense again. All this does is replicate (in reverse if you like) being cross axled with three wheels with no grip. I wouldn't want to try it with the centre diff locked! My 80 is outside on stands with no wheels on. I have just tried this on tick-over. When I pull on the handbrake, the back two stop dead and the front two whizz round like billy-o. Same as in the test which takes 30 second start to finish. These blokes are red hot on MOTs and do nothing else. Absolutely nothing. Just MOTs all day. They have no hesitation to fail or in one case on my old 95, refer to the authorities on the limits of steering rack movement. They're not back street. Not liek the person that passed my 80 just before I bought it. Blind Pugh's auto testing ltd.

Chris
 

Paul_Humphreys

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Chris, I agree with Jon. If ABS if fitted it must work, also the ony way to test a FT4x4 on a break rollers is to remove one of the props. Anyother way you could damage the gear boxes.

One way around the dash light is to rewire the bulb to the oil light, well someone told me that!!

Paul
 

Chris

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OK last go from me. Forget the ABS thing being MOT or not. I still think that if declared disabled then it would pass a test. But, on the only way to test, let me see if this is right.

If I have an 80, with no abs fitted - and they do exist, if I brake on a mixed surface and some wheels lock up and others don't then I will damage the gearbox? Pushing a point here to prove it, but you just said that locking the two back wheels but having the front ones moving would (or could?) cause damage. Off road or at least on soft ground there are plenty of opportunities for only two wheels to be turning under braking as grip changes. And furthermore, in low box, the ABS is totally disabled

C
 

Jon Wildsmith

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The legalities and functioning of ABS are not connected to the brakes of full time 4x4's having to be tested either on a 4 wheel roller or with a decelerometer.

If ABS was fitted to your vehicle during manufacture then as far as MOT is concerned it must work. The system should tell them if a vehicle has ABS or not. If you remove or disable the ABS you will have to go talk to VOSA or someone like them about it to get it accepted and your vehicle details changed. Don't forget to tell your insurance company who will probably cancel your policy! This is just my understanding but it's a bit like seat belts - there are cars without them but it doesn't mean they're safe :) A common trick is to wire the ABS light to another that comes on with the ignition and goes off after a bit ... but we're back to thinking about serious accidents and fine tooth combs again on that one.

The issue with full time all wheel drive and single axle rollers is they don't have sufficient information on their database to tell which ones have e.g. a viscous coupling or some other limited slip traction aid linking the axles and which ones run an open diff. On your 80, when the rollers are turning the front wheels some of the torque is applied to the rear wheels via the VC and held by the rear brakes. If you have a failing VC then a significant amount of the work may be being done by the brakes on the other axle. There are all wheel drive vehicles where the link between the axles is much more direct. There are vehicles where there is a risk of damage. So there are a combination of reasons why MOT's on all wheel drive vehicles are supposed to be carried out either on a 4 wheel brake roller or using a decelerometer.
 

Chris

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OK, I have to bow out at this point. I fail to see how there is any drive when it's in neutral. I don't get it. Back wheels on concrete, front wheels on driven rollers for 5 seconds, transmission in neutral, press brake pedal, nothing actually happens at the back as the wheels aren't moving, resistance measured on a roller under each wheel, one at a time, at the front. MOT station certified by the Min of Transport. Sorry, but it's good enough for me. I wouldn't want to test cars that I didn't know by driving on the public highway with a decelerometer.

Honest guys, not being funny, I just don't get your argument. I cannot see the 'engineering' in this one. The front wheels can turn without the back ones. There is no shared braking force. Nothing is driving the back wheels. Is it? I know it's full time 4x4, but the engine isn't doing the driving through the CD. The front wheels are being turned externally. I know it's a bit like towing, which you shouldn't do because of lack of cooling to the AT. But why this isn't a valid test of if your brake is simply beyond me.


Jon, you know some serious stuff but this time you've lost me really. I admit defeat.

Chris
 

Jon Wildsmith

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These links are from http://www.transportoffice.gov.uk/crt/d ... guides.htm :

ABS:
http://www.motinfo.gov.uk/htdocs/m4s03000401.htm

LSPV: (just for anyone thinking of removing this rusty clump of metal ;) )
http://www.motinfo.gov.uk/htdocs/m4s03000604.htm

Roller testing:
http://www.motinfo.gov.uk/htdocs/m4s03000701.htm

While your truck is in the air Chris, with the main box in N, hand brake on, transfer in H, turn the front prop, should be resistance but it turns? Release the hand brake, turn front prop, should be less resistance and rear prop should turn? The resistance is the VC transmitting torque across the open centre diff.

I'm not trying to suggest your MOT is invalid or dodgy Chris, just how they're supposed to be done on a permanent 4x4 according to VOSA ;) The MOT place I use does the decelerometer testing on the premises not the public highway and they only do MOT's and have done for ages, well, I thought he was an old bloke who'd been doing MOT's since time began when I left school and that was a few years ago but don't tell him that!
 
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