C5 REAR BRAKE CALIPER PROBLEM

[PaulC5]

What makes you think the caliper bolts will need replacing ? Chances are with the car being so old the bolts will have been removed quite a few times and hopefully nobody put loctite (or other stuff) in the caliper holes again, just copper grease or similar. The bolts are high tensile and have the strength marked on the heads but will likely be 8.8 or 10.9 . With the car still on the ground you could use a socket through the wheel and see if the bolts can be easily undone. Once the bolts are removed you do not need to disconnect the brake pipe, just unclip it from the clips and there is enough give to move the caliper out of the way, rest it on a large paint tin and then clean off the corrosion on the caliper and suspension arm. I have always used copper grease on the back of the caliper and suspension arm and in the bolt holes (coated on the bolts).

Before you remove these bolts, after removing the pads make sure you refit the thin bolt that holds the pad cover and pads in place - if you do not when the caliper bolts are undone the caliper will come apart into its 2 halves and leak fluid out. When fitting this thin bolt back use copper grease on its caliper part/holes so it prevents it corroding and breaking and do not tighten it much.

[wurlycorner]

I believe they're the same as Mk1 C5 and the part number is C440550.
Should be available from Citroen dealer?
Last time I bought them, they were inexpensive: £2.59 each (plus VAT), though that was a number of years ago.

What makes you think the caliper bolts will need replacing ?

They quite often are slighty bent, unfortunately - most garages not putting anti-corrosion between the caliper and rear arm (like you rightly describe to do) meaning you get corrosion 'jacking' between the arm and caliper, causing the caliper to deflect and bend the bolts.
I've bought replacements just in case, whenever I've attacked a 'new to me' C5 Mk1 - useful insurance policy, given they're so inexpensive and you don't really want to be stuck half-way through that job!

[PaulC5]

I checked and they are 10.9 tensile strength. If loctite (etc) is still in the caliper holes then I found to remove the old bolts (one at a time with the other still in place/put back) gradually turn the bolt using a 6 point socket with a crow bar under the bolt/washer head to lever it out. It takes forever but works. Then once out drill the loctite out, refit and then do the other one.

When fitting the caliper back one of the bolts will go into the arm threads easily, the other will not and can end up stripping the arm threads if cross threaded. So if the bolt being put back first does not line up, try the other one. On our first C5 I found this out the hard way and the loctite might have still been in place, ended up snapping a bolt and had to drill it out of the arm. Being very hard steel it needed decent drills borrowed from work but the arm threads were damaged so I ended up getting a longer bolt and putting a nut on it at the back of the arm.

[aspire_helen]

The reason the bolts are a tight fit in the callipers is NOT thread-lock, nor corrosion prevention. The sealant is injected into the bolt holes to harden and create a solid, homogenous assembly. The reason for this is that the bolts are unusually long and are hence subject to huge, almost pure, shear stress on braking. By bonding the bolt inside the calliper the stress is distributed better. The bolts are also Grade 10 steel, stronger than the standard Grade 8 high tensile steel. Hence, never retro fit with normal steel or stainless bolts. Also, Grade 10 is more likely to snap than bend. The more the calliper twists the more static stress is put on the bolts. So, if the calliper is already twisted, the bolts are already under very high static stress and may be approaching failure just sitting there, waiting to snap on hard braking. I know, it happened on my C5 Mk1. So, if a calliper is twisted remove it ASAP. If the bolt does snap off, it will fracture at the calliper/suspension arm junction and likely leave the bolt thread in the suspension arm....another problem!