Rear brake caliper woes….

[Nessy]

The other night, I went to fill up with diesel and could immediately detect the unmistakeable stench of cooking brake pads coming from the offside rear wheel, the disc was too hot to touch.
Having limped home I immediately thought that the caliper was goosed (have been through all this before on my old 8P) and so ordered a new replacement, as well as rear pads and a rear flexy brake hose (just in case it was needed)…
So today I set about changing everything and it went OK, with the caliper off the car it was certainly seized , though the dust boot and piston looked in very good condition….
The pads were certainly ****** on the seized caliper so I had to change the entire rear set.
I have VCDS so calipers were put into lining change mode etc as far as I am concerned everything was done correctly.
With new caliper and pads fitted the system was bled and a 2 mile round trip was undertaken…
On arriving home, I went to check both rear discs (expecting them both to be nice and cool) but no, the O/S/R disc was red hot again .
Something is causing that caliper to stick on, could an otherwise perfect-looking brake flexy hose be causing this?
The new caliper is a Febi Bilstein German-made unit so don’t think that it is a faulty item…..have heard that an internally collapsing flexy hose can act like a one-way valve and cause brakes to stick on, but how common is this?
I plan tomorrow to change the brake hose and see what difference it makes……have really no idea what I will do if this doesn’t cure it…..

 

[Nessy]

I have no idea why the word c*o*o*k*e*d has been substituted by the forum software in my post above ……

 

[Nessy]

I couldn’t wait until tomorrow so went back out to the car and tried a few things …
Jacked up again and with wheel off I undid the caliper banjo bolt to release hydraulic pressure (don't ask me why I didn't just undo the bleed nipple!) and there is no change.
So I do not think residual pressure in the circuit is keeping the brakes on.
Next, I went to the garage and had a good look at the original caliper that came off, try as I might, the piston would not go in despite my best efforts.
I then tore off the piston dust boot and what a sorry sight it was , rust everywhere!
So that caliper was well and truly dead!
I have now come to the conclusion that there must be a mechanical fault with this Febi caliper…..so its coming off and I will have to find another replacement.

 

[Darren92]

do your pads move freely in the carriers, i assume you cleaned the carriers down too?

 

[Nessy]

do your pads move freely in the carriers, i assume you cleaned the carriers down too?

Thanks , yes all as clean as a whistle.
Guide pins cleaned and silicone greased too.
As I was finalising the brake lining change with VCDS there was a single ‘clonk’ noise from the caliper.
I know think that it may have been then that it malfunctioned…..
I really do believe that the new caliper is now the issue ….…

 

[spartacus68]

Febi Bilstein parts are usually excellent. Calipers usually fail with build up of aluminium oxide corrosion under the dust sleeve which swells and causes the piston to stick.

I take it car has electronic parking brake if you’re using VCDS to set? That clonk noise might have been pads sticking on the brake carrier as VCDS reset the handbrake. Take another look. The brake carrier needs to be spotless. It rusts and the pad shims get pushed out. If you have a metal file, then clean the mating surfaces on the brake carrier where the pad shoulders will sit. Wire wheel on a drill helps to a point.

A smear of ceramic grease on the backs of the pads and shoulders.. Did you use the new shim kit too?

 

[Nessy]

Febi Bilstein parts are usually excellent. Calipers usually fail with build up of aluminium oxide corrosion under the dust sleeve which swells and causes the piston to stick.

I take it car has electronic parking brake if you’re using VCDS to set? That clonk noise might have been pads sticking on the brake carrier as VCDS reset the handbrake. Take another look. The brake carrier needs to be spotless. It rusts and the pad shims get pushed out. If you have a metal file, then clean the mating surfaces on the brake carrier where the pad shoulders will sit. Wire wheel on a drill helps to a point.

A smear of ceramic grease on the backs of the pads and shoulders.. Did you use the new shim kit too?

Thanks , yes carriers are spotless and yes the calipers have the electronic parking brake (EPB) motors on them.
There are no separate shims on the 8V set up, they appear to be incorporated into the back of the brake pads….
One factor that I haven’t mentioned was that as I was finishing the VCDS procedure “end brake lining change” where the motors are meant to operate and apply the handbrake fully an error came up “motor out of range” for the offside, and nothing would make it work.
As the motors are only held on by 2 screws I simply swapped the motor over from the old Genuine caliper to the new and everything then worked fine.
Thus, as far as I was concerned the Febi EPB motor was faulty out of the box……
Whilst I have lots of experience with Febi over the years with things like drop links and track rod ends etc I have found some items of theirs to be less than good.
Having once fitted a hard Febi coolant pipe to a BMW Mini which had the rigidity of chocolate (it leaked badly) it was only resolved after I‘d fitted a Genuine Mini item…..
I really do think that this new caliper is the issue now……

 

[NHN]

I'm leaning towards the epb part being faulty or something is making that side stay on, does the wheel move freely on both sides when you release the epb, lift up, block fronts, neutral, etc.

 

[Nessy]

I'm leaning towards the epb part being faulty or something is making that side stay on, does the wheel move freely on both sides when you release the epb, lift up, block fronts, neutral, etc.

Thanks, and yes that is the conclusion that I had come to.
Yesterday I managed to dismantle the old caliper and the old piston was well and truly rusted around the point where the caliper seal is, so to me that is the smoking gun as to why that wheel was seizing/overheating, nothing to do with dodgy flexy hoses etc.
Having sanded off the rust with wet & dry and with some silicone grease applied the piston slid smoothly when re-inserted.
So I’m now going to re-build this caliper having bought a pair of 38mm caliper piston & seal kits.
Going back to the subject of the Febi caliper on the car now, the act of moving the car 50 yards (i.e off and on my driveway to move cars around) is making that wheel noticeably warmer than the nearside rear wheel, so I believe that the EPB side of things is indeed somehow sticking on….
Things felt OK (ie without excessive drag) once I had bled the brakes and cycled the EPB after I had changed the caliper but remember my comment about hearing a clonking noise from the Febi caliper as I was ending the lining change with VCDS?
I do think that was the point when this new caliper malfunctioned.
So now I have a waiting game until the rebuild kit arrives.
Cheers

 

[NHN]

Test it on stands with the help of another, for completeness, not sure if the epb is sided, I'd have to check, if not swap them across from caliper to caliper, see what happens.

 

[Nessy]

Test it on stands with the help of another, for completeness, not sure if the epb is sided, I'd have to check, if not swap them across from caliper to caliper, see what happens.

Cheers , have just been out to car now and defo the mechanical screw part of the parking brake (behind the caliper piston) is naffed on this Febi caliper.
With car jacked up and parking brake released the wheel was really difficult to turn .
Having removed the EPB motor and winding back the piston manually with a Torx E11 socket to what is effectively the brake pad change position (which of course is what VCDS does when the motor is installed etc) there is just the normal drag.
So 100% something wrong with the screw mechanism within the Febi caliper.
Even though I have both another caliper on order (ordered Thursday before I really knew what the issue was, other than this caliper was probably junk ) and also a rebuild kit think that with this experience I’d rather overhaul the original ATE caliper….with a new piston and seals it should be as good as new, hopefully!

 

[NHN]

Voila

 

[Nessy]

Indeed!

 

[Nessy]

Am still waiting on the caliper rebuild kit to arrive ( hopefully tomorrow) but have a question.
The car is on axle stands, wheels chocked and with parking brake in “off” position.
I was not able to use VCDS to put it into brake lining change mode as this dodgy offside rear caliper kept coming up with an error “ motor out of range”.
With EPB motor removed it’s easy to wind back the piston and this has now been done to enable the caliper and pads etc to be removed.
My question surrounds what I need to do once the overhauled original caliper is back on the car.
Can I just operate the parking brake button to close the caliper?
Or does it definitely have to go through a brake lining change open & then close cycle?
I’m not sure whether the motor has to calibrate itself etc when putting the parking brake on fully, hence the need for the brake lining change mode, or is it just something to make the mechanics lives easier?
Must admit that I hate this EPB nonsense, give me a cable -operated system anyday…

 

[Nessy]

View: https://m.youtube.com/watch?v=5kWHFDzoWyk&pp=ygUWRXBiIHJlc2V0IHdpdGhvdXQgdmNkcw%3D%3D

Seems I have found the answer and was somewhat over-thinking things!
Apparently once the piston is retracted and EPB motor re-installed then once whatever work is being done , be that pad or disc or caliper change has been completed then all that needs to be done is close the parking brake via the button inside the car.

 

[AJB]

Cheers , have just been out to car now and defo the mechanical screw part of the parking brake (behind the caliper piston) is naffed on this Febi caliper.
With car jacked up and parking brake released the wheel was really difficult to turn .
Having removed the EPB motor and winding back the piston manually with a Torx E11 socket to what is effectively the brake pad change position (which of course is what VCDS does when the motor is installed etc) there is just the normal drag.
So 100% something wrong with the screw mechanism within the Febi caliper.
Even though I have both another caliper on order (ordered Thursday before I really knew what the issue was, other than this caliper was probably junk ) and also a rebuild kit think that with this experience I’d rather overhaul the original ATE caliper….with a new piston and seals it should be as good as new, hopefully!

Couldn't that still point to an issue with the motor? If the brake was binding with the handbrake released (ie motor should have wound the screw off a bit), but then went free when you manually released it by turning it with the torx socket, wouldn't that be the symptoms you'd get if the motor was sticking/not turning/not turning enough? Or perhaps if it was somehow mis-calibrated? Equally it could be that the screw mechanism is somehow slipping, so needs more turning that normal to get it to release.

 

[Nessy]

Couldn't that still point to an issue with the motor? If the brake was binding with the handbrake released (ie motor should have wound the screw off a bit), but then went free when you manually released it by turning it with the torx socket, wouldn't that be the symptoms you'd get if the motor was sticking/not turning/not turning enough? Or perhaps if it was somehow mis-calibrated? Equally it could be that the screw mechanism is somehow slipping, so needs more turning that normal to get it to release.

Thanks, I have found the smoking gun though!
The rebuild kits arrived this morning and it didn’t take me long to re-build the factory ATE caliper with a new piston & seals.
This was fitted to the car and brakes bled.
Once the hydraulics were found to be OK I then operated the EPB and again all went as it should: rock solid wheel with EPB applied and minimal drag with it off.
After a 3 mile spin can confirm it is now fixed .
It was when I went to examine the now -removed faulty Febi caliper that I made the discovery.
With EPB motor off the caliper , I wound the screw back (using the E11 socket) so that the piston could be fully retracted.
As I happened to be holding the caliper at a slight angle, I wasn’t ready for quite a few ball bearings to then pour out of the banjo bolt hole!
These ball bearings are captive within the thread of the screw that acts on the piston.
Something had gone very, very wrong within the screw for these bearings to be liberated and I am very relieved that it is off my car.
As soon as we get better weather I plan to overhaul the nearside rear caliper , on the basis of preventative maintenance.

 

[AJB]

Thanks for the update.

Yeah - that sounds quite broken... It's always good to find something very obviously wrong though! Glad you've got it sorted. Was it a genuine ATE rebuild kit you bought? It's good to know you can get rebuild kits for them.

Are those balls the thrust bearing you can just see in your first picture? Also how does it actually work - that thread at the top of the part on the left in the first picture - what does it engage with? Presumably not the piston itself, as for a pad change you still have to manually push the piston back after releasing the EPB, as I understand it.

 

[Nessy]

Thanks for the update.

Yeah - that sounds quite broken... It's always good to find something very obviously wrong though! Glad you've got it sorted. Was it a genuine ATE rebuild kit you bought? It's good to know you can get rebuild kits for them.

Are those balls the thrust bearing you can just see in your first picture? Also how does it actually work - that thread at the top of the part on the left in the first picture - what does it engage with? Presumably not the piston itself, as for a pad change you still have to manually push the piston back after releasing the EPB, as I understand it.

It’s hard to explain what those ball bearings do, they are inside the thread of that screw that is turned by the EPB motor to move the piston against the disc.
It’s mentioned at around the 4:40 min
mark on the following video


View: https://m.youtube.com/watch?v=GSec0xHasEc&pp=ygUcYTMgOHYgYnJha2UgY2FsaXBlciByZWJ1aWxkIA%3D%3D

As well as ball bearings there are some springs in there, radially wound around the screw threads , I guess the springs are just acting as a retainer for the ball bearings…
The warning in that video ( about the ball bearings falling out ) only applies with piston removed : if the piston is in-situ you can wind the shaft clockwise or anticlockwise as much as you want.
After all , that is what happens when the EPB motor is operated….
I still don’t know how the ball-bearings became liberated in the Febi caliper?
It has put me right off buying Febi products again.
I just bought a 38mm piston rebuild kit off eBay for 1KE rear brakes (272mm , 10mm solid discs) and rebuilding it was surprisingly easy.
You can see how pitted the original caliper piston was due to rust, I bet the nearside rear caliper isn’t too clever either.
As soon as we get a decent bit of weather again that one will be rebuilt before it has a chance to play up….

 

[AJB]

Thanks - that's a helpful video! Yes, I was guessing there were balls in the thread at the top too - the thread has a very curved base in your photo. I guess it's a way of getting a slow friction, high force, screw action. The threads don't have to slide under load, as there are balls rolling in them.
And your video explains my other question too, which was why you have to push the piston back manually still. It looks like the collar around that thread with the balls isn't the piston, but is a kind of sleeve inside the piston? So it can retract, but the piston will stay out when it does?
Thanks again - mine is 11 years old now, and so far I've not had to do anything to the brakes at all, but it's only a matter of time I'm sure! Good to know what the options will be when I need to get in there.

 

[AJB]

As to the warning about the balls falling out, if you used the torx drive to use the screw thread to push the piston all the way out to remove it, I was assuming that that would be what got the balls falling out as the collar just fell off the end of its thread. That wouldn't happen in normal life as the pads would hit the disc, and stop it before it got that far.

From what I gather, Febi is very mixed quality. Some of their things are great, some are awful. But I guess yours could have been a return? Someone plugged it in, activated it before fitting it to the car to test it and the piston fell out along with the balls, then they put the piston back in, put it back in the box and asked for a refund?

 

[Boydie]

Maybe late to the party but this happened to me relatively recently with over heating rear wheel, therefore seized caliper. Thankfully, stripping the pin, cleaning it and greasing has resolved the issue for now but getting my hands on a spare set of rear calipers to refurb to have handy for when/if they go again

Pin with 100k's worth of dirt/grime on it

Cleaned up

Greased and put back into the caliper with no issues since

 

[Nessy]

Hello again all,
Apologies for not replying for so long, to be honest got so cheesed off with the damn car felt like I needed a break .
The Febi caliper was definitely new/sealed when I received it so think that it must have been lousy quality, yes I think some Febi stuff is junk, though other stuff of theirs is great eg recently bought a new steering damper for a Mk1 SLK and in the Febi box was a Stabilus item , OE maker for both Mercedes and Audi, and identical to the 2002 damper that I took off the car….
I did in fact end up re-building both original rear calipers, and whilst the nearside caliper was in quite a good state, with the piston showing hardly any corrosion, I did have an issue with it.
After being re-built it continually ran hot, almost as if the piston seals were too large?
I noticed this when putting the caliper back together, the piston (new of course) was harder than I would have liked to push back in…
To cut a long story short, not totally happy with both the DIY refurbed calipers I ended up fitting a replacement set of calipers.
No more trouble since.

 

[AJB]

Hello again all,
Apologies for not replying for so long, to be honest got so cheesed off with the damn car felt like I needed a break .
The Febi caliper was definitely new/sealed when I received it so think that it must have been lousy quality, yes I think some Febi stuff is junk, though other stuff of theirs is great eg recently bought a new steering damper for a Mk1 SLK and in the Febi box was a Stabilus item , OE maker for both Mercedes and Audi, and identical to the 2002 damper that I took off the car….
I did in fact end up re-building both original rear calipers, and whilst the nearside caliper was in quite a good state, with the piston showing hardly any corrosion, I did have an issue with it.
After being re-built it continually ran hot, almost as if the piston seals were too large?
I noticed this when putting the caliper back together, the piston (new of course) was harder than I would have liked to push back in…
To cut a long story short, not totally happy with both the DIY refurbed calipers I ended up fitting a replacement set of calipers.
No more trouble since.

Thanks for the update. What make did you go for for the replacement callipers that have worked well? So far mine is showing no sign of dragging brakes, but it's good to know what I need to do or buy if and when it starts causing trouble!