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!

[pierre1409]

Hi everyone I am presently in rear brake calliper hell. My last MOT had an advisory on the rear discs due to corrosion. Ok not urgent but as the next mot is getting closer I decided to replace the discs. Didn't research the job, How difficult could it be? got the thing jacked up, wheels off, and attacked the bolts. Whoa!! big breaker bar cracked them half a turn and no more and where is this bloody brake fluid coming from and dripping on the floor? Now I know!! Anyway, My question is; Can the old discs be removed and new discs fitted without removing the callipers? Please only reply if you have actually done this on a 2004/2008 Citroen C5 . Please don't think I am being abrupt or rude and I really do appreciate reading all the comments on the forum but I would rather not get the thing in the air with wheels off again until I know that it can for sure be done. Cheers Duncan

[wurlycorner]

Rear brakes are the same on a Mk1 (2000-2004) and Mk2 (2004-2008) C5, so the info you see in this thread applies.

You cannot replace the rear discs without unbolting and removing the rear calipers from the trailing arm.
You can normally leave the hydraulic pipe fitting attached to the caliper - just unclip the pipe from the arm and gently swing the caliper up and out of the way, temporarily.
Part number for the mounting bolts may now be 1677082980 by the looks?

[pierre1409]

Cheers Iain, I thought that may be the case but one or two have said it could be done. Having checked the discs I can't see why they should be an advisory anyway so I'm going to leave them as is and just put new pads in there. The callipers are actually in good condition, no corrosion. The car has only done 64k so rather than destroying the callipers and quite possibly breaking the bolts I will see how I go at the next MOT

[PaulC5]

Corrosion on the caliper is at the back of it where it joins the suspension arm. Being different metals it gives galvanic corrosion which builds up and pushes the caliper out. When really bad the caliper can touch the wheel. To check with the wheel off, look at the top of the caliper and see if its seam is in the middle of the brake disc edge, if in the middle it is ok, if further out then the corrosion needs to be removed with the caliper unbolted (leave the brake pipe connected but just unclip it).

You might find the back of the disc is in worse condition than the front so needs checking.

[pierre1409]

Thanks Paul, You have jogged my memory and you are right. Thinking back at when I had given up on the idea of removing the callipers I had to clean off the brake fluid that had leaked onto both sides of the disc and the back of the disc was corroded far worse than the front. I may have to revise leaving those discs on until the mot. My best plan I think is to order 2 new callipers and bolts before tackling this again. I may not need them but it's a price worth paying to have them to hand before I start the job.

[PaulC5]

If you do disconnect the calipers when you come to bleed the brakes you will likely need a diagnostic to get all the air out of the abs system. I found this when I replaced a front caliper.

Since it took me a long time to get the bolts out and drill out the loctite when I first did the job, I did the bolts on a day before I wanted to replace pads, etc.

[pierre1409]

Good tip. I have lexia/diagbox V7.37 on my laptop so should be able to sort it if needed from that.

[wurlycorner]

My best plan I think is to order 2 new callipers and bolts before tackling this again. I may not need them but it's a price worth paying to have them to hand before I start the job.

Yes, this is the route I've gone. For the relatively low cost, it's worth being sure you can get the job done from start to finish without worrying if something breaks or is too corroded to refit.

[PaulC5]

I was thinking on such an old car rear calipers may not be available but they are. As an example https://www.ebay.co.uk/itm/302897445743 ... gJcYvD_BwE

Note that the 2 halves are held together by bolts, when these are removed so they can be put on the car, first fit the pad retaining bolt to stop them coming apart and then remove the bolts. These holding bolts might not be suitable to fasten the caliper to the car which should be 10.9 strength stamped on the bolt head.

[wurlycorner]

The calipers are readily available because they're the same design as fitted to loads of LHM cars.
The through bolts that come with them likely won't be suitable even regardless of grade, because in my experience they're always standard metric pitch bolts, rather than fine (which the actual fixing bolts use).

[aspire_helen]

Note, the 2 halves of each caliper are kept together by the 2 main bolts with na oring between them to seal the hydraulic fluid channel. I always advise clamping the 2 halves together before unscrewing the bolts. If not, the 2 halves may split apart and leak fluid, as appears the case here, and may necessitate a new oring.
When changing either the front (necessary) or rear calipers (just in case) I always clamp the flexible brake hose to minimise fluid loss and air ingestion.