Hello all!
As I said in my self intro thread, the bike I recently bought at an auction had non-working front brakes. I've had the bike since Tuesday and had another chance today to look in more detail at the front brake situation.
No parts appeared to be missing as I said before. I had cleaned out the front master cylinder the other day and wanted to remove the calipers today to start inspecting and cleaning them up.
I discovered that the ABS sensor had been interfered with at some point. The outermost hex bolt holding the sensor in place was chewed up and I managed to loosen it with some vice grips. It then sheared off and I discovered it had been partly drilled out from the underneath - a small drill hole that had obviously weakened it. I managed to remove the other hex bolt OK. The sensor itself was as if welded in place. I could not budge it. I decided I wouldn't be keeping it and eventually got it out, destroying it in the process. This was perhaps not the right thing to do but I figured the ABS wouldn't be working anyway...
So, I will replace the seals I think and go from there... 
I wondered if the previous owner had tried to work on the brakes and get the sensor out and given up on the idea and as a result the bike ended up off the road - the last MOT expired in 2020. Just a theory...
Those sensors are meant to pop out when the bolts are undone, right? According to my manual it looks so easy but I guess all that grime in there over the years is a pretty strong adhesive...

Question: should I try to get a used sensor? Or used caliper with sensor? Or just remove what's left of the old one altogether and proceed without ABS?

I meant to say the Torx head bolts that hold the front sensor in place. 

That makes sense now and I presume you mean the front sensor.  There is a duplicate set up on the rear.  What a coincidence I have the rear wheel off at the moment.  

The sensor itself is adjusted in height by the use of shims.  As you say all that road grime builds up over the years and in a perfect world it should be able to be removed easily.  

It really depends on if you want to attempt to re-use the ABS system.  

If not then remove the bracket as well and I have fitted smaller depth bolts on another moto.  Just in case, as I don't like the look of exposed threads.  Also the wheel's inner ring with the teeth attached can be removed to save weight (three countersunk bolts I think?).  If you wish to re-use the system then it is worth cleaning up the surface of the teeth by lightly sanding the surface that passes by the sensor which would also need a clean.  Does your right fork still have the small yellow ABS sticker attached?  

If you wish to remove the ABS system completely you will have to have new brakes lines made up and replacing them anyway to stainless ones is a good idea for the age of the bike.  The originals have a habit of swelling internally over the years.  

Finally once the two ABS units at the rear are removed then there is a big gap which is a trap for a passenger's feet.  The non-ABS motos have a piece like an inverted triangle as part of the footplate whilst ABS bikes don't.  

I also clean all my brake parts in white spirit and nothing else as it dries with no greasy film on components including painted items.  

Hope this assists and Happy Easter.

Thanks Tickler!
I am referring to my front brake yes. The sensor is now toast but never mind. I am going to get one second hand and first of all flush out the system and bleed afresh to see if I can get the front brake into an operational state. I will tackle the ABS deletion question later on I think.

There were three shims in place which are in good condition still.

I haven't noticed the sticker. There is a shiny sticker-shaped patch more or less in line with the disk - maybe that was where it was...

In any case, thanks for the tips and I will see how the cleaning up, new caliper seals and bleeding go.

I mean Tackler!!

In my experience, the ABS sensors in the front and rear callipers are a real sod to remove. The sensor is encased in a thin aluminium case…a seldom disturbed aluminium case in a steel calliper exposed to all the dirt, salt & grime of UK roads and heat from the brake pad friction during use. Net result the sensor corrodes tightly in place. Any attempt to punch it through tends to make it act like a rivet - expanding into the hole and getting tighter. With the torx bolts removed, I have tried gently levering up the flange on the sensor but without much success. Heating the calliper would possibly help, but likely to destroy the calliper seals. I really don’t know why BMW designed the calliper with such a tight fit. The sensor needs to be secured firmly and it’s height adjustable with shims - the distance between sensor face and ABS ring on the wheel is critical but I’m sure the calliper hole could be a little larger to prevent seizing.

You can get second hand sensors from the likes of motorworks - cost about £60, even those come with removal marks in the sensor casing. I got a rear one like that recently but at least it works. 

It is worth stripping down and cleaning the calliper to ensure both pistons move freely. I successfully removed one of my stubborn ones by blanking the brake hose inlet with the bleed nipple and putting my tyre air compressor on the remaining port (using that mostly useless conical plastic attachment that comes with most compressors). Top tip, place an old towel or some such over the piston before applying air pressure - it will come out with a pop and you neither want it hitting you in the face nor flying across the garage and damaging the pistons high tolerance surface finish.

Oh…and if you are going to disable the ABS system, then rather than remove all the ABS hardware (sensor rings, modulators, pipe work and ABS brain in the ducktail etc.) just remove the ABS relay from under the fuel tank. That will stop the annoying flashing red light on the instrument cluster. For MoT tests in the UK, they can’t test the ABS function anyway as they are testing the brakes one wheel at a time with the other stationary.

Just further to BAE's comment about using compressed air.  

Use a rag, a towel or a plastic bag to place the brake caliper in and place in a plastic ice cream container or similar.  Don't be afraid to use 100 Psi* in there either.  Place your hand over it and as long as it is safe.  You want to make sure there is no piston or mess escaping.  I've done that many times in the past on aircraft brakes.  Some will pop first time and others take a bit more effort.


*  None of those pesky metric measurements either.  They just don't work the same.

Born Again Eccentric wrote:In my experience, the ABS sensors in the front and rear callipers are a real sod to remove. 

I bought a quality T25 Torx driver for removing those sensor screws. Makes removing them much easier. I replace the Torx bolts with M6x16 Allen cap head screws when reinstalling.

I have had mixed success removing ABS sensors. A good dose of WD40 or something smilar may help a little.

The ABS brain can be repaired, Tosi in Japan is the go to guru for this.

duck wrote:

Born Again Eccentric wrote:In my experience, the ABS sensors in the front and rear callipers are a real sod to remove. 

I bought a quality T25 Torx driver for removing those sensor screws. Makes removing them much easier. I replace the Torx bolts with M6x16 Allen cap head screws when reinstalling.

That looks just the ticket as they used to say.

Closer inspection of front right calliper revealed a chipped piston. Big chunk missing from the brake pad side outer edge. Maybe a stone… The ABS sensor bracket hole had hard deposits on the inner surface. Like limescale in fact. Gave it a clean up with the Dremel. At least one of the sensor retaining thread holes is stripped. Would you re-tap it? Use an insert? Or can that bracket be purchased separately I wonder. Have asked Motorworks…

NealC wrote:Closer inspection of front right calliper revealed a chipped piston. Big chunk missing from the brake pad side outer edge. Maybe a stone… The ABS sensor bracket hole had hard deposits on the inner surface. Like limescale in fact. Gave it a clean up with the Dremel. At least one of the sensor retaining thread holes is stripped. Would you re-tap it? Use an insert? Or can that bracket be purchased separately I wonder. Have asked Motorworks…

You could try an insert but there is probably not enough material in the bracket to do it successfully.  However I would not use one simply because it is part of the braking system.  A new-ish bracket from Motorworks would be the best solution.  Run a tap through the threads to ensure you have removed any excess crud.  

You can clean the piston up as long as the repaired area is not going to interfere with its movement.  It does not sound as if it is an area that is going to interfere with the hydraulic seal of the brake unit.  

If you decide to replace the piston then replace the the left one at the same time.  That way you have two front brake units both rebuilt to the same standard.  Even though you may have one pair of brake pads wearing more than the other always replace both sets at the same time.

NealC wrote:Closer inspection of front right calliper revealed a chipped piston. Big chunk missing from the brake pad side outer edge. Maybe a stone… The ABS sensor bracket hole had hard deposits on the inner surface. Like limescale in fact. Gave it a clean up with the Dremel. At least one of the sensor retaining thread holes is stripped. Would you re-tap it? Use an insert? Or can that bracket be purchased separately I wonder. Have asked Motorworks…

Unlikely that chip to piston face would be caused by a stone…with pads in place, there is very little clearance. I suspect that the damage was probably caused by the previous owner using something hard and metallic to try and force the piston back when replacing the brake pads. 

The hard deposit ‘like limescale’ is probably an aluminium oxide - as per my previous reply, aluminium sensor housing in a steel bracket in a crappy wet/salty environment. Removal with Drexel (as you have) and a light smear of grease on reassembly should make future sensor removals a bit less hassle.

As Tackler says, retap the hole if you can. If it is too badly stripped (i.e. there will still be insufficient thread to secure the bolt) then consider drilling out and tap to the next bolt size (M8?) and fit new M8 bolts. Fitting an insert effectively achieves the same result but allows you use the original size bolts. As Duck says, replacing the torx M6 bolts with an Allen headed bolt is a good idea anyway.

TacKler wrote:

NealC wrote:Closer inspection of front right calliper revealed a chipped piston. Big chunk missing from the brake pad side outer edge. Maybe a stone… The ABS sensor bracket hole had hard deposits on the inner surface. Like limescale in fact. Gave it a clean up with the Dremel. At least one of the sensor retaining thread holes is stripped. Would you re-tap it? Use an insert? Or can that bracket be purchased separately I wonder. Have asked Motorworks…

You could try an insert but there is probably not enough material in the bracket to do it successfully.  However I would not use one simply because it is part of the braking system.  A new-ish bracket from Motorworks would be the best solution.  Run a tap through the threads to ensure you have removed any excess crud.  

You can clean the piston up as long as the repaired area is not going to interfere with its movement.  It does not sound as if it is an area that is going to interfere with the hydraulic seal of the brake unit.  

If you decide to replace the piston then replace the the left one at the same time.  That way you have two front brake units both rebuilt to the same standard.  Even though you may have one pair of brake pads wearing more than the other always replace both sets at the same time.

Thanks Tackler! Sound advice! The puck is knackered I reckon - so two new ones will do the job. Cheers!

Neal - PM me. I'm swimming in caliper pistons extracted from various Guzzi and BMW F- and P- series calipers and won't miss a couple. Just confirm the diameter and overall height please to make sure nothing funny is going on.

Thanks Dai! I have PMed... dunno if it got through to you.

Good news from Motorworks - they are sending me a bracket for my ABS sensor (right caliper). Ten quid! Happy with that!

PS: I hadn't retained your location...