Thread: Abs locking up

Sounds like an ABS sensor not making correct air gap contact with the exciter ring. There is a set on each wheel. The most likely problem is worn wheel bearings on one or more wheels. As I understand it, the computer thinks one wheel is stopped, therefore you must be trying to brake. To help you it stops all the other wheels.
Simply jack up each wheel, hold the top and bottom of the wheel and try to move it inwards and outwards. There should be absolutely no play at all. The abs will tolerate a little movement (but you shouldn't) so it would need to be excessive to cause your problem.
If it is the front axle, then you should also check the swivel pin housing for play.
If all the wheels are good, then you are in luck. It could just be that one of the sensors has lifted too far off the exciter ring. Simply check each sensor in turn by gently tapping it inwards until it hits the exciter ring. It will bounce back as soon as the car is driven and find it's own air gap setting. It should be an interference fit, that is, it should be easy to tap in with little force. If it is too loose, try sealing it at the oil seal with a bit of silastic.
See attached pdf

Thanks mate I will test this week

Re: swivel pin bearings........ If you hold your hands on the wheel at 12 and 6 o'clock and rock it, any movement could be swivel pin bearings or wheel bearings.

If you hold your hands at 9 and 3 and do the same, the problem will be wheel bearings or tie rod ends. If it is tie rod ends any movement in those (however small) would be pretty obvious to an assistant observer.

If no TRE movement, but the wheel has movement when held horizontally, then it will be wheel bearings. Usually solved by adjustment.

If wheel bearings have been adjusted and there is no movement with hands at 9 & 3, but movement at 12 & 6 then swivel pin bearings need attention too.

Might save you some time.

Cheers, DL

Ok thanks

So shaking the wheel at 9-3 it's pretty solid as for 12-6 there is a slight bit of movement you can feel and hear. It seems the seals are leaking also. As for the exciters I will have to check them more thoroughly tomorrow

Originally Posted by DieselLSE

Sounds like an ABS sensor not making correct air gap contact with the exciter ring. There is a set on each wheel. The most likely problem is worn wheel bearings on one or more wheels. As I understand it, the computer thinks one wheel is stopped, therefore you must be trying to brake. To help you it stops all the other wheels.
Simply jack up each wheel, hold the top and bottom of the wheel and try to move it inwards and outwards. There should be absolutely no play at all. The abs will tolerate a little movement (but you shouldn't) so it would need to be excessive to cause your problem.
If it is the front axle, then you should also check the swivel pin housing for play.
If all the wheels are good, then you are in luck. It could just be that one of the sensors has lifted too far off the exciter ring. Simply check each sensor in turn by gently tapping it inwards until it hits the exciter ring. It will bounce back as soon as the car is driven and find it's own air gap setting. It should be an interference fit, that is, it should be easy to tap in with little force. If it is too loose, try sealing it at the oil seal with a bit of silastic.
See attached pdf

Originally Posted by 350RRC

Re: swivel pin bearings........ If you hold your hands on the wheel at 12 and 6 o'clock and rock it, any movement could be swivel pin bearings or wheel bearings.

If you hold your hands at 9 and 3 and do the same, the problem will be wheel bearings or tie rod ends. If it is tie rod ends any movement in those (however small) would be pretty obvious to an assistant observer.

If no TRE movement, but the wheel has movement when held horizontally, then it will be wheel bearings. Usually solved by adjustment.

If wheel bearings have been adjusted and there is no movement with hands at 9 & 3, but movement at 12 & 6 then swivel pin bearings need attention too.

Might save you some time.

Cheers, DL

so i have checked wheel movment and there is very minimal movement at 12 and 6. i couldnt get to the sensors to properly diagnose. as for movement it feels like a mm or so but have noticed the seals are leaking so could be time for an overhaul. another point i have noticed is the pump runs and will turn off but there is a whistle noise coming from the area if thats any concern. also could it be a bleeding issue as have been told it was bleed but bled like a normal braking system

thanks for the help in advance

>the seals are leaking
Probably best to look at checking the hubs before the bearings wear the stub axles too much (if it hasn't already happened). I've just been through this as I replaced all the disk rotors. Started out expecting to simply replace the bearings and seals and finished up renewing the stub axles and overhauling the swivel pin housings as well. I started out with aftermarket parts, but was unimpressed with the quality and finished up buying genuine for everything. Not cheap, but I expect to keep the car for another 20 years.
>a whistle noise coming from the area
The pump pressurizes the ABS to about 2700psi. If there's an external leak in the high pressure system, the fluid will escape as a fine spray, but should be visible as well as audible. You'll have to track this down, otherwise you'll overwork the pump and it could burn out. The pump should never run for more than 45 seconds at a time, and then usually only at startup and thereafter for about 15 seconds at a time. The leak could be at a union, or a fine puncture in a pipe. I suppose it could be the check valve in the pump allowing pressurized fluid back into the low pressure reservoir or a leak in the accumulator, but I don't have enough experience to know if either of these faults are audible.
Another alternative is an air leak in the front right airbag or connector. Sounds can be tricky to trace without a stethoscope.