rear caliper bolt sheared off help!!

[admiral51]

Hi all
just got back from a good day out and SWMBO decides to tell me that the 1.9td has been making a squeaking sound every time she turns hard right
Had the n/s/r wheel off to see if i could make the car make the noise and noticed the top caliper bolt looked "loose".Put a socket on it and it was spinning feely came out with half the thread missing

Am going to drive it to work tomorrow and hopefully drill the old thread out any tips as to how to achieve this without causing too much damage and any idea of size for the tap tool if thats what i endup needing

Have got a couple of spare bolts so thats not a worry just unsure of why it snapped in situ as it was only done for mot 3 weeks ago

Colin

[reblack68]

I believe it's an M9 thread, it certainly isn't M8 or M10.

When three of mine broke in the hub they were extracted by MIG welding nuts on. Even the one that broke under the surface was extracted this way by building it up with weld. It took several goes but each try added more heat, which helped things along.

As for driving it- EXTREMELY gentle braking, much anticipation and use of the handbrake is the way to go.

[red_dwarfers]

Tell me about it, those bolts are fragile. I had all three shear off when I was replacing an ABS sensor.

Really, Toby HDI and MikeT are the people to speak to as they had this happen most recently and I know he retapped his threads.

Heres a link to the bit in his blog - http://www.frenchcarforum.co.uk/forum/v ... hp?t=24739

[Toby_HDi]

I believe Colin is referring to the two long bolts that hold the caliper to its mounting bracket, and not the three small bolts holding the ABS shield on.

However, it is a similar issue to what I had.

As for damaging the caliper when drilling, wouldn't know. Am sure if you take it nice and steady you'll be fine. If you are going to remove the pads when doing it be wary of the fact the rear caliper splits into two halves. The pad retaining pin will have to go back in and be tightened to hold it together, I found it didn't really hold it together well though, it was only when the two caliper bolts were tightened that it sat together. It all depends on where it has snapped.

As for a tap, a quick look at Citroen Service shows the bolt to be an M9 diameter with a 1.25mm thread pitch.

[Stempy]

I've actually recently been trying to source a replacement M9 caliper bolt in stainless steel, but as yet have been unable to find even a normal M9 bolt other than from Citroen. I'm sure somewhere could make up specials, but that would probably work out quite expensive for just four.

[admiral51]

Thanks to one and all for the replies

As Toby says it is one of the two main caliper securing bolts that have sheared and i have not really investigated whether or not its left part in the caliper or not
Im hoping its left it all in the securing plate for removals sake but half hoping its left a bit in the caliper to help hold it in place on my drive to work

As i only have a 13 mile trip and its going to be done around 4am im hoping i can be very gentle on the brake pedal

But still not sure if the "sqeak" was from a broken bolt or something else or why the bolt sheared will endeavor to delve deaper tomorrow

Colin

[citroenxm]

Is there a White power behind the caliper???

The bolt WILL have snapped IN the Arm!!!!

Ive had this twice, water gets behind the caliper and the alloys calliper reacts with the steel arm!!

This then pushes the caliper out as it expands

This has caused the snapped bolt!!
Will be interesting to see if this is the case, you'll also find that the rear pads will have worn unevenily, leaving a nice lip in the leading edges...

Paul

[firstrebel]

I had 2mm of the white crud between the caliper and mounting and was lucky to get all 4 bolts off. I had never heard of this until DickieG told me. This has to be a safety issue. I have never seen pads like it. I made a gasket from thin strong plastic to hopefully prevent this happening again.

I suppose removing and cleaning annually would be preventative action.

Bob

[AndersDK]

Its a known issue since the BX, CX, and XM as the rear arm and brake calipers are almost exactly the same setup with the same parts on these models as on the Xantia.
Even the C5 range of models uses this same setup.

The calipers and bolts are the same for the LHM cars, so should not be a big problem finding spares at scrappers.
Using latest technology drill bits in either titanium or cobalt it should not be a problem drilling out the sheared bolt from the rear arm.

AFAIR the calipers will just barely accept an ISO M10 bolt, so the rear arm can be tapped for a M10 bolt.
Otherwise the caliper would only need a slight re-doing with a 10mm drillbit.

That would exactly fit the 9mm drill bit required to clean up the old bolt hole in the rear arm making it ready for a 10mm tap.
Smear the bolts well with aluminium paste (silver paste) which is the cupraslip counterpart used on alu alloy parts.

Keep the caliper halves together using the long 5mm pad bolt.

[CitroJim]

Something that seems to work for me, touch-wood, is to wire brush the ends of the threads poking out of the back of the trailing arm and giving them a good douse in Plus-Gas and then walking away from them for a while. This removed any crud that has built up on the exposed ends of the threads and in my experience, it's this crud that helps shear the bolts as it binds the threads as they are unscrewing. The Plus-Gas will penetrate and help the proceedings.

Then, use a long breaker bar on them and gently apply sustained light pressure on the end of the breaker bar and if you feel the bolts begin to twist (but not undo at this stage) back off slightly whilst still mainting pressure and let the twisting tension in the bolt relieve itself. Then apply more gentle pressure again until the bolts finally start to undo. They snap because they twist beyond their elasticicity. Gentle and easy is the way to go.

It seeems to me that heavy, snatching pressure on a short bar is more likely to snap bolts than gentle pressure applied carefully from a long breaker bar.

A big, long breaker bar is just like a big hammer. When used carefully it is your best friend.

Bob, that's an excellent idea to make up a plastic gasket to avoid a reoccurrance

[admiral51]

Thanks for the replies still not had time to have a real good look at this yet fingers crossed it will last till the weekend work gets in the way of most things these days

Is there a White power behind the caliper???

The bolt WILL have snapped IN the Arm!!!!

Ive had this twice, water gets behind the caliper and the alloys calliper reacts with the steel arm!!

This then pushes the caliper out as it expands

This has caused the snapped bolt!!
Will be interesting to see if this is the case, you'll also find that the rear pads will have worn unevenily, leaving a nice lip in the leading edges...

Paul

Yes Paul this was the case with white powder and wedge shaped pads when i first removed the bolts/pads and discs to replace them for the MOT but the bolt didnt snap then. i put it all back together and it passed the MOT 3 weeks ago cant figure out why it is now sheared unless i didnt tighten it up enough and the movement of the caliper has caused it to shear>
Mind the way SWMBO drives full speed or stop i bet shes anchored up a bit sharpish and highlighted my improper refitting

Colin

[lexi]

Stainless will not usually have the same tensile strength as a rated and stamped steel item.

[cachaciero]

I've actually recently been trying to source a replacement M9 caliper bolt in stainless steel, but as yet have been unable to find even a normal M9 bolt other than from Citroen. I'm sure somewhere could make up specials, but that would probably work out quite expensive for just four.

Stainless into alloy is not the good idea it first appears to be, ask anybody with a sailboat with stainless fittings on an alloy mast. Stainless threads into alloy will corrode together very quickly as will a stainless shank in an alloy casting unless a coated with an appropriate sealer. Grease doesn't work too well at least in a Marine environment boaters use something called Duralac (obtainable from most good chandlers) but "soft" Loctite would probably work o.k. I would not recommend Coppa Slip, in theory copper and alloy do not go well together Graphite grease might be a better bet.

I really do not see much point in going for stainless there are differences in strength stainless generally being weaker, ordinary HT bolts used in conjunction with one of the solutions above and plastic / PTFE / paper gaskets between mating alloy / steel faces to reduce electrical paths should improve the situation markedly.

Cahaciero

[fred1]

Hi,

I have had great success using a polythene gasket between calliper and rear arms on a C5.

Regards

John

[cachaciero]

Hi,

I have had great success using a polythene gasket between calliper and rear arms on a C5.

Regards

John

Hi John

I thought about polythene which I have used in another situation but I was a bit concerned about heat transference.

In reality I know nothing about the amount of heat generated into the caliper except that there must be some and I assumed that some of it must get dissipated from the caliper into the rear arm, if that was the case at higher temperatures polythene might not be the best material as it does not conduct heat too well and has a low melting point. However it is very good insulator which is what is needed to reduce electrolytic corrosion.

It is interesting to hear that you have used it without problems.


Regards Cachaciero