Abs Causing Caliper To Shut Off?

[94xm]

Hi,

Well when driving my car last night and with no previous problem, i braked suddenly and the whole car shot off to the right, Odd i thought, did it again and off to the right and im thinking the front left caliper is not doing anything.
On braking again i could feel those little bumps in the brake pedal you get when the abs cuts in, then brake fine. No more bother.

Got in it cold this morning, torrential rain again and the same thing, no left front brake, same abs brake pedal feel then fine.

Lunch time today go out from work doing no more than 5mph in the car park, i brake and no left front brake and the abs brake judder then fine all. Nothing since.

The abs brake pedal thing happens about 3/4 times each time.
No odd noises no other problems, computer is disconnected as i got sick of abs out of use. Have previously changed the wire (well grafted in) to that abs sensor as the last one had worn through after a spell against the disk by previous owner. The abs out of use became intermittent, then i got bored of it and disconnected the screen. That was months ago.

Seems to me that the abs unit or computer is releasing the pressure to that wheel as if the brake is locked. Is this possible?

When not working i tried the handbrake and it pulled fine in a straight line.

any suggestions

Many thanks

Mark

This post has been edited by 94xm on May 15, 2007 06:11 pm

[94xm]

Well on way back from shop it seems to be doing it every time, so at about 4/5 mph- low speed, you can feel only right piston gripping. Pedal does the tiny little abs thing 3 or 4 times (and you can sort of hear it, if you know what i mean) and then the left piston comes in and car stops. Tried it about 10 times and it was the same every time, bit easier to tell whats going on at low speed.

any ideas greatfully recieved

thanks

Mark

[techmanagain]

I would suggest that your LH brake pads are not sliding across towards the disc as fast as the RH , and I bet you'll find that the little tin hook at the bottom of the caliper (for the brake warning wire) is causing it. Take it off and throw it away.
The "ABS feel" may be caused by a slightly distorted disc on the RH. You'll also hear the RH pads scraping on the disc soon, as they are doing all the work.

[onthecut]

Hi Mark.

Don't know if it's related, but on a couple of the 2.5s I've had, I've had the symptom of having almost come to a halt --- say at a junction --- and the brakes momentarily releasing, pedal going further down and then reapplying. (Perfectly dry road, no other issues) It's no help to you in so far as I never resolved it, but it does mark up to me that this ABS isn't quite as failsafe as 'they' would have you believe.
I do know of one friend who started getting odd ABS symptoms and that was down to having oddly worn or oddly sized tyres, the ABS apparently not being able to make sense of the incoming data.

Mike.

[xmexclusive]

Hi Mark

Check the brake pads. One of each pair of pads should have a small metal pip near the centre of the back. This is to locate in one of the slots in the caliper ram and operate the handbrake auto adjust. If the flush pads and nibbed pads are put the wrong way round the hand brake only adjusts on one side and gives uneven braking from the brake pedal but the cable fulcrum will still give handbrake applied to both sides until the wear is so unequal that one of the cable nipples drops out of its slot and you lose the handbrake. If pad nibs are the cause of the problem and it is allowed to persist the caliper one side can lock up completely causing sudden brake fade/brake loss. A nibbed pad on the outside can also foul the caliper frame and cause extreme wear to that pad only. An easy check is to take the wheels off and look at the back of the pads on the non caliper side. The visible pad rear surface should be flush with no nib. If a nib can be seen, particularly one side only, then check the inside pads have nibs. This is a common problem as it is easy not to notice the nibs and fit the nibs the wrong way round or a nibbed pair one side and a flush pair the other. The instructions with new pads never cover this but surprisingly Haynes does rather well.
These comments are specific to the BENDIX front calipers fitted to XM's from 1991 until 1997.

Regards

XMexc

This post has been edited by xmexclusive on May 16, 2007 10:47 am

[94xm]

THanks Gents,

The brake pads were changed a few months back, and im sure i put them in the right way round with the small lip on the caliper side as i remeber doint it wrong once before. The tyres are as new so hopefully no probs there.
Funnily enough i have had problems with that disk having some run out on it a few months back that i could see with the wheel off and it running on a jack, bumpy pedal etc when braking from high speed but it has gone straight again over time. (i know not the best method for getting round the problem), it was never a prob at 30mph say or less.

I am almost 95% on the fact it was the abs playing some part in the problem, however after my last post it has not done it again. The pedal was doing the same 3 small abs pumps then the caliper applies every time, then suddenly back to normal.

Just to give me some more grief the wheel bearing is now starting to grumple that side, so i think new bearing, new disks and new pads, check all the elec connections and may be remove the low pad warnings and see if it does it again. It may certainly be a collective lack of maintenance around that wheel. Its now averaging 1200 miles a week and im not having time to service it has gone very overdue .

Anyway thanks for the help , i will do the work and then post if it does it again

Many Thanks

Mark

[lez]

is this early style abs with the computer on the innner wing, or the later type all in one abs under left headlight?

just you said at the beginning you unplugged it, if its early type, and you unplug the abs box, then you have no abs working at all so it cant be the abs...