Help. Cannot remove dead front ABS sensor.

Ian21401 · Jun 23rd, 2015, 21:29

1992, 940 estate, 2.0 Litre, petrol with ABS.
Problem 1. Dead sensor on front right side. New replacement obtained. Cannot remove the dead one as it is seized solidly in the front hub steering arm.
Problem 2. The FAQs refer to an "O" ring in the sensor location which establishes the correct clearance between the sensor tip and the pulse ring. The replacement Bosch sensor is supplied with an "O" ring fitted to it's outer end near it's plastic moulding. I thought that that was the one referred to in the FAQs, but it isn't. There are the remains of an "O" ring in the steering arm locating hole.
Question: Does anyone know the precise dimensions of that "O" ring? I have a selection box of assorted "O" rings but I'm not sure which size to use.
Re problem 1: The allen bolt removal was quite easy, taking into account that it has probably been in there for 23 years. I tried removing the sensor by twisting but the plastic moulding snapped off. I've tried drifting the sensor body from the steering arm but the thin soft sensor casing has simply collapsed. That was when I found the remains of the other "O" ring.
The steering arm appears to be part of the hub carrier casting which is part of the suspension strut so any bench work would appear to require the removal of the suspension strut.
Does anyone have any experience of this and any suggestions please?

Volvanman · Jun 24th, 2015, 07:57

I'm no expert, but have had the very same problem. I hadn't read the FAQS, & so was unaware of the o ring, but perhaps in my case ignorance was bliss!

Removing the old sensors for me was getting brutal with a drill. I was very careful whilst drilling not to damage the hole, and the more of the old sensor you remove, the easier the rest comes out. It is time consuming, and it's not a perfect job, but it worked for me. The new sensor fitted in ok, and all has been well since.

There will hopefully be others on here with far better plans of attack - but that's what I did - hope you get it sorted...

Forrest · Jun 24th, 2015, 19:44

I had to replace one and experienced exactly the same issues. Since I didn't, and still don't, possess a 10mm hex socket to remove the calliper bracket I was also seriously limited by the amount of space obtainable by just loosening but not removing the front disc.

My extraction method basically involved breaking up the old sensor with a screwdriver and fetching it out in bits. My installation of the new sensor involved applying a smear of grease and then lining it up correctly and hammering it into the hole with a wooden mallet. This all worked and resolved the intermittent ABS fault.

With hindsight, what I would do differently now would be to remove the calliper and disc properly and clean out the hole with a dremel or similar before installing the replacement.

I infer from the success of my original method that the tolerances are not too fine for the successful installation of a new sensor. Either that or I got lucky.

Ian21401 · Jun 24th, 2015, 23:26

It doesn't help the actual problem but it is good to know that I'm not the only one who has butchered the old sensor and retrieved it in small pieces.
I haven't had a chance to do anything today due to family commitments (apart from give it another dose of Plusgas) but I had more or less decided to adopt the drill out method. I have also considered using a drift fractionally less in diameter than the hole in the steering arm in an attempt to break the grip. Then use a nut and bolt, suitably sized washers and a piece of tubing as a form of puller, but that is just an idea at this stage.
Jerry, did you use a small diameter drill bit to attempt to "cut" down one side or a larger diameter to just "grind" it out? I suspect that the drill bit will tend to follow the softer metal of the sensor.
Forrest, I'm very surprised that the new sensor survived the hammering. I agree regarding the "dremel" as I have considered similar when I eventually get the so an so out of the steering arm.

Forrest · Jun 25th, 2015, 21:20

Quote:

Originally Posted by Ian21401

I'm very surprised that the new sensor survived the hammering.

Well said. There's someone on here who has in their footer "if you can't fix it with a hammer then it's an electrical fault" and that just asks to be proved wrong! I reasoned that the sensor and plastic back would be quite strong in compression. It's twisting that yanks that plastic bit off. The sensor itself is a fairly simple magnetic device so not too much to break really. I think the usual failure mode is the connecting wire wearing out under the insulation.

Ian21401 · Jun 27th, 2015, 23:48

Well I've finally managed to remove the old sensor. The idea with a drift from the inboard side to break the grip didn't even move it. Similarly the idea with the makeshift puller so I resorted to the drilling method. Drilled out what I could working from the inboard end. No finesse involved as difficult to line up the drill properly. The drilling eventually broke up the remains of the plastic moulding of the sensor and I pulled the pieces of it out with snipe nose pliers. It seems that it was the main cause of not being able to drift out the main body of the sensor as once it was removed the other remains drifted out quite easily working from the wheel hub side. It was impossible to insert the new sensor into the steering arm hole due to the corrosion so I removed as much as I could with my cheap "Dremel" imitation tool fitted with an appropriate sized emery drum grinder until the new sensor was a gentle push fit. After removing the corrosion I could see that the hole through the steering arm is not a constant diameter. About half the length at the inboard end is the same diameter as the sensor body.(as one would expect.) But then the diameter increases by a few millimeters. Then the final few mls. of the hole (the outer or hub end) reverts back to the same diameter as the inboard half of the hole. This means that there is a "step" in the bore of the hole. It was against that step that I found the remains of an "O" ring when I first started my attempts to remove the old sensor. I had managed to retrieve about 3/4 of that "O" ring so I found the nearest match from my selection box. I tried fitting it in the obvious position (in the larger bore area against the step) but that prevented the sensor body from locating fully into the hole. (The plastic end and it's fitted "O" ring were not fully seated into the hole.) Simply fitting the outer "O" ring into the outer end of the hole would serve no useful purpose at all and it would simply fall out. The only method which seemed to work was to install the sensor almost completely then manouvre the "O" ring around the outer end of the sensor body then push the sensor fully home. But I do not understand why that should be necessary. I haven't finally installed the sensor as I thought I would give this some more thought and post this update to tempt any responses.

Ian21401 · Jul 27th, 2015, 16:30

Sorry for the long delay in finalising this thread but I've had several other issues to deal with.
I installed the new sensor as described above with the outer "O" ring manoeuvred around the outer end of the sensor body. The ABS warning light does not now illuminate to indicate a fault so it would appear that the problem is sorted. I noticed when inspecting the remains of the old sensor and the other debris which I had removed from the steering arm that there appeared to be the remains of three "O" rings. As previously stated, the location of one "O" ring is known but I've no idea where the other two were fitted.

Forrest · Jul 27th, 2015, 21:46

Sounds like you fixed it. It's worth double-checking that your ABS light illuminates with the ignition and then goes out again. I once spent ages chasing an ABS fault that was combined with an intermittent ABS lamp fault.

The best way I found to test the functional operation of the ABS was to deliberately brake hard on a grass surface. You can induce a skid without scrubbing your tyres.

Mark 1 · Jul 30th, 2015, 09:54

Thanks Ian, Volvoman and Forrest for the info - more or less came same conclusion to drill it out, just didn't want to go too far without second/third opions!!
Many thanks Mark

jpliddy · Jul 22nd, 2020, 20:44

hi all
i will hopefully soon be doing this job to fix my ABS problem .
ive done the fault find with the on board fault finder it flashes
1-5-2 which indicates front right abs sensor fault .
i have ordered 1 of ebay less than £20 BRAND lexmark
so just hope i can perform the job ok
i will remove calliper and brake disc . i have various drills but no dremel
wish me luck !

Jun 23rd, 2015, 21:29	#1
Ian21401 Premier Member Last Online: Feb 11th, 2023 20:32 Join Date: May 2010 Location: Blyth, Northumberland	Help. Cannot remove dead front ABS sensor. 1992, 940 estate, 2.0 Litre, petrol with ABS. Problem 1. Dead sensor on front right side. New replacement obtained. Cannot remove the dead one as it is seized solidly in the front hub steering arm. Problem 2. The FAQs refer to an "O" ring in the sensor location which establishes the correct clearance between the sensor tip and the pulse ring. The replacement Bosch sensor is supplied with an "O" ring fitted to it's outer end near it's plastic moulding. I thought that that was the one referred to in the FAQs, but it isn't. There are the remains of an "O" ring in the steering arm locating hole. Question: Does anyone know the precise dimensions of that "O" ring? I have a selection box of assorted "O" rings but I'm not sure which size to use. Re problem 1: The allen bolt removal was quite easy, taking into account that it has probably been in there for 23 years. I tried removing the sensor by twisting but the plastic moulding snapped off. I've tried drifting the sensor body from the steering arm but the thin soft sensor casing has simply collapsed. That was when I found the remains of the other "O" ring. The steering arm appears to be part of the hub carrier casting which is part of the suspension strut so any bench work would appear to require the removal of the suspension strut. Does anyone have any experience of this and any suggestions please?

Jun 24th, 2015, 07:57	#2
Volvanman Slewmeister... Last Online: May 15th, 2019 15:30 Join Date: Dec 2013 Location: Market Rasen	I'm no expert, but have had the very same problem. I hadn't read the FAQS, & so was unaware of the o ring, but perhaps in my case ignorance was bliss! Removing the old sensors for me was getting brutal with a drill. I was very careful whilst drilling not to damage the hole, and the more of the old sensor you remove, the easier the rest comes out. It is time consuming, and it's not a perfect job, but it worked for me. The new sensor fitted in ok, and all has been well since. There will hopefully be others on here with far better plans of attack - but that's what I did - hope you get it sorted... __________________ Regards - Jerry 97 940 HPT, 25mm H&R spacers, Tethys alloys - 225/45 rear & 215/45 front, slotted discs all round & EBC Yellowstuff pads, MBC @ 14psi, 19t, blue injectors, 3" turbo back single silencer system... 96 960 3.0 Auto

Jun 24th, 2015, 23:26	#4
Ian21401 Premier Member Last Online: Feb 11th, 2023 20:32 Join Date: May 2010 Location: Blyth, Northumberland	Thanks Guys. It doesn't help the actual problem but it is good to know that I'm not the only one who has butchered the old sensor and retrieved it in small pieces. I haven't had a chance to do anything today due to family commitments (apart from give it another dose of Plusgas) but I had more or less decided to adopt the drill out method. I have also considered using a drift fractionally less in diameter than the hole in the steering arm in an attempt to break the grip. Then use a nut and bolt, suitably sized washers and a piece of tubing as a form of puller, but that is just an idea at this stage. Jerry, did you use a small diameter drill bit to attempt to "cut" down one side or a larger diameter to just "grind" it out? I suspect that the drill bit will tend to follow the softer metal of the sensor. Forrest, I'm very surprised that the new sensor survived the hammering. I agree regarding the "dremel" as I have considered similar when I eventually get the so an so out of the steering arm.

Jun 27th, 2015, 23:48	#6
Ian21401 Premier Member Last Online: Feb 11th, 2023 20:32 Join Date: May 2010 Location: Blyth, Northumberland	Progress Report and Queries. Well I've finally managed to remove the old sensor. The idea with a drift from the inboard side to break the grip didn't even move it. Similarly the idea with the makeshift puller so I resorted to the drilling method. Drilled out what I could working from the inboard end. No finesse involved as difficult to line up the drill properly. The drilling eventually broke up the remains of the plastic moulding of the sensor and I pulled the pieces of it out with snipe nose pliers. It seems that it was the main cause of not being able to drift out the main body of the sensor as once it was removed the other remains drifted out quite easily working from the wheel hub side. It was impossible to insert the new sensor into the steering arm hole due to the corrosion so I removed as much as I could with my cheap "Dremel" imitation tool fitted with an appropriate sized emery drum grinder until the new sensor was a gentle push fit. After removing the corrosion I could see that the hole through the steering arm is not a constant diameter. About half the length at the inboard end is the same diameter as the sensor body.(as one would expect.) But then the diameter increases by a few millimeters. Then the final few mls. of the hole (the outer or hub end) reverts back to the same diameter as the inboard half of the hole. This means that there is a "step" in the bore of the hole. It was against that step that I found the remains of an "O" ring when I first started my attempts to remove the old sensor. I had managed to retrieve about 3/4 of that "O" ring so I found the nearest match from my selection box. I tried fitting it in the obvious position (in the larger bore area against the step) but that prevented the sensor body from locating fully into the hole. (The plastic end and it's fitted "O" ring were not fully seated into the hole.) Simply fitting the outer "O" ring into the outer end of the hole would serve no useful purpose at all and it would simply fall out. The only method which seemed to work was to install the sensor almost completely then manouvre the "O" ring around the outer end of the sensor body then push the sensor fully home. But I do not understand why that should be necessary. I haven't finally installed the sensor as I thought I would give this some more thought and post this update to tempt any responses. Last edited by Ian21401; Jun 27th, 2015 at 23:50.

Jul 27th, 2015, 16:30	#7
Ian21401 Premier Member Last Online: Feb 11th, 2023 20:32 Join Date: May 2010 Location: Blyth, Northumberland	Final Update Sorry for the long delay in finalising this thread but I've had several other issues to deal with. I installed the new sensor as described above with the outer "O" ring manoeuvred around the outer end of the sensor body. The ABS warning light does not now illuminate to indicate a fault so it would appear that the problem is sorted. I noticed when inspecting the remains of the old sensor and the other debris which I had removed from the steering arm that there appeared to be the remains of three "O" rings. As previously stated, the location of one "O" ring is known but I've no idea where the other two were fitted.

Jun 24th, 2015, 19:44	#3
Forrest VOC Member Last Online: Today 04:12 Join Date: Feb 2008 Location: Gloucester	I had to replace one and experienced exactly the same issues. Since I didn't, and still don't, possess a 10mm hex socket to remove the calliper bracket I was also seriously limited by the amount of space obtainable by just loosening but not removing the front disc. My extraction method basically involved breaking up the old sensor with a screwdriver and fetching it out in bits. My installation of the new sensor involved applying a smear of grease and then lining it up correctly and hammering it into the hole with a wooden mallet. This all worked and resolved the intermittent ABS fault. With hindsight, what I would do differently now would be to remove the calliper and disc properly and clean out the hole with a dremel or similar before installing the replacement. I infer from the success of my original method that the tolerances are not too fine for the successful installation of a new sensor. Either that or I got lucky.

Jul 27th, 2015, 21:46	#8
Forrest VOC Member Last Online: Today 04:12 Join Date: Feb 2008 Location: Gloucester	Sounds like you fixed it. It's worth double-checking that your ABS light illuminates with the ignition and then goes out again. I once spent ages chasing an ABS fault that was combined with an intermittent ABS lamp fault. The best way I found to test the functional operation of the ABS was to deliberately brake hard on a grass surface. You can induce a skid without scrubbing your tyres.

Jul 30th, 2015, 09:54	#9
Mark 1 New Member Last Online: Jan 11th, 2024 16:32 Join Date: Nov 2008 Location: Oxford	Thanks Ian, Volvoman and Forrest for the info - more or less came same conclusion to drill it out, just didn't want to go too far without second/third opions!! Many thanks Mark

Jul 22nd, 2020, 20:44	#10
jpliddy VOC Member Last Online: Feb 15th, 2024 17:04 Join Date: Dec 2006 Location: stoke on trent	ABS light on permanent hi all i will hopefully soon be doing this job to fix my ABS problem . ive done the fault find with the on board fault finder it flashes 1-5-2 which indicates front right abs sensor fault . i have ordered 1 of ebay less than £20 BRAND lexmark so just hope i can perform the job ok i will remove calliper and brake disc . i have various drills but no dremel wish me luck !

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