Rear Brakes, To Use Loctite Or Not

[aspire_helen]

Hi, having reread some of the threads regarding rear brake caliper removal.  Many people seem to think the loctite down the bolt shafts is for corrosion resistance or mere threadlocking. No, its not. It is to enable the very long bolt to cope with the extreme shear stresses which would otherwise be generated due to the relatively short length of thread used to secure it. Without the loctite the bolt is a very slack fit. The loctite replicates the nearest thing to an interference fit to maximise the assemblies rigidity and strength. Also, the loctite prevents the two parts of the calipers shearing even slightly and potentially rupturing the flimsy brake fluid seal.  Using copper grease on the shafts, to prevent galvanic corrosion, instead of loctite will only make the assembly weaker.  Personally, i think citroens loctite solution is a bodge job to correct a design flaw. They have to use one of loctites high strength, high temperature threadlocks using an activator to ensure assist the loctite cures across the relatively wide gap between caliper and bolt  shaft.

 

Ive also read that someone has had stainless steel caliper bolts made. Mad! The citroen bolts are class10 steel, very strong (stronger than normal "high tensile steel") and manufactured and heat-treated through verified processes.  Stainless may be hard but does not have the same tensile properties as class10 steel.   Also, cold machining raises stresses especially where the threads are cut.  Also the galvanic potential between high nickel stainless steel and aluminium alloys is greater than carbon steel zinc plated, so the corrosion will be worse.  If corrosion has taken full hold between the stainless bolt and alloy caliper it is likely to be impossible to turn the bolt at all.  Maybe such non approved repairs have stood the test of time, but they might just fail on emergency braking after a few years of brake cycle fatigue and corrosive winters.......after all, citroen oe bolts are only £13 for all 4.

[paul.h]

Interesting, so what will you be doing when you fit your new calipers and what has been done to the old ones since they will have been removed/cleaned several times previously ? I believe when the C5 first came out the calipers did not have the loctite, so your old calipers may not be the ones with the small holes for the activator addition and the bolts will be easy to remove. I do not think Citroen did a recall on the old calipers either, so they must think they are still ok to use after 13 years.

 

I have found I need to remove/clean up the back of the calipers every 1 or 2 years and to have to remove the loctite each time adds a lot of effort/time and the risk of bolt failure. Or if you just back out the bolts from the suspension arm enough to release the caliper, the loctite remains in place but the bolts are difficult to turn so any torque values are meaningless and doing this I snapped one bolt.

 

Edit.

I have seen from your other post that you have used loctite on the new calipers and had loctite on the old ones. Interestingly though, you have used stainless steel bolts for the disc holding screws and for the caliper cover bolts.

[grin factor]

I like this forum. 

You learn a lot from it. 

[aspire_helen]

Paul

re your observation on stainless steel fastners. I often refit stainless in place of common sized, non-load bearing mild steel, but i always use copperease. The galvanic potential between stainless and mild steel is not that bad, but with alloys a buffer such as copperease or threadlock is essential. Stainless heads do not rust, so bits will always fit. Stainless is harder so heads are more resistant to deformation eg by an impact wrench. I have used hex drives, to replace the torx, as i have a set of impact hex drive bits.

Also, when bolt threads protrude out the other side, the protruding threads expand on rusting preventing the bolt from withdrawing. Its ok if you can get to the reverse side and derust the threads, but if not, stainless never have that problem.

helen

[paul.h]

Thinking about the rear pads cover retaining bolt which contacts the alloy caliper, there have been cases where the alloy on the caliper has gone/corroded away or maybe been broken off due to overtightening. I use copper grease here on the bolt/caliper holes to help prevent corrosion and I guess you will have done something similar.

 

If you find the rear pads now knock when first applying the brakes since they are now free to move, a shim is now listed on the parts diagrams that clips in to the pad spring. I tried this on our last C5 and it worked. The part no. and cost is on the Common Problems pinned topic.

[aspire_helen]

Thanks paul. Yep, coppereased the pad retaining bolt and used a stainless nyloc nut so that the bolt is not overtightened. However, i suspect it may be washed off in time, so worth checking periodically.

My old rear pads had the (yes, stainless) shims. However, the new brembo pads came with the exact same shims already adhered to them so i have not refitted the shims. The brakes are now complete, bedding in and passed mot yesterday. New Brembo discs and pads on rear, new Fujitoyo pads added to existing Apec disk on front. All working very well, no squeal for instance. But then again, the odd brake squeal i have had in the past has only occured during dry summers.

[paul.h]

The extra shim to stop the knocking of the pads goes across the top of the pads and clips to the spring and is quite thick, it is not the ones that go between the pads and pistons.

[madmadmax]

so whats been side is that the caliper fixing holes need a bronze bushing fitting to reduce the size of the hole and if a thred is taped and a coller put on the bush it will holed itself together, that sounds like a nice simple alterntive to lock tight.

[aspire_helen]

Paul, ah ah so thats what partno 440721 (Set 2 shim) is.

 

Madmadmax, bushing seems like a suitable engineer's corrective solution, though someone would have to do the thermal stress calcs to ensure that the different coeffs of expansion with close tolerances did not crack the caliper under heat.  Although, as the alloy caliper is likely to expand the most it should not be a problem.  

 

On another thought, if the dissimilar metal corrosion between the caliper and suspension can be prohibited, there would be less cause to remove the calipers, perhaps only for disc replacement?  From my experience, a new 14mm disc cannot be fitted after the caliper is bolted down, but can a disc be removed and refitted with the caliper partially screwed out, say 10mm?  That would negate removing the bolts and maintain the integrity of the loctite in the bore.  Only one problem, Haynes (eg Citroen) say the bolts must be replaced ie the bolts must be removed from the caliper, or in my case fit new calipers.  On the other hand, cylinder head bolts can be reused as long as they have not been stretched beyond limits.  II can only suppose the difference is that the cylinder head bolts, whilst under significantly more stress than the caliper bolts, are in almost pure tension, whereas the caliper bolts will mainly be under shear (and even more so if not tightly fitting into the caliper bore!!).

 

Yet another thought.  One reason I defaulted to fit new calipers before I had even tried to remove them, was that the corrosion and pitting of the resulting alloy face mating to the steel suspension arm would not provide the smooth and stable face also essential to the assembly's strength.  Ah ah, I thought, as the calipers are not handed, and if the bolts can be removed, all you need to do is to swap the left and right calipers (and swap the brake pipe and bleed valve accordingly).  This means that the non-corroded outer face of one caliper becomes the inner face of the caliper on the opposite wheel.  Further,if one half of one caliper is damaged, you can always make up one caliper by mixing the caliper halves from both wheels.  You might need to renew the twopenny (ok, more like 60p) brake fluid seal (citroen part no 44205).

 

Anyway, for me, job done (hoperfully for a few years).  Now turning my mind to FAP/DPF and dpx42 as I am now using my car much less and for shorter journeys.

[paul.h]

In Citroen's (and Haynes) procedures, they say to renew the caliper bolts only on those with loctite. On the cars before RPO 8879 that did not use loctite the old bolts are re-used. The bolt part nos. are the same. So they must expect some damage to them whilst removing since in use any stresses ought to be the same.

 

On the 2009 on C3, they also say to replace the front caliper bolts which need removing to replace the discs - but when trying to order them, the dealer said they do not replace them unless damaged and the parts dept checked the records and found they had not used any. These bolts have a dab of loctite on them - so maybe it is said to replace bolts to make sure loctite is used since as supplied it is already on them.

 

On the C5, the idea of swapping over the rear calipers if the corrosion is too bad is a good one. It would be worth checking the seating for the bleed screw and brake pipe is in good condition first.

[ESL57]

Just to add to this, I have renewed the rear calipers, bolts discs and pads on my 02 plate C5.

   I etch primed the alloy caliper face and then 2 coats of heat proof engine enamel. The metal face was copa slipped.

     I painted the new bolts prior to fitting, so they should not corrode in caliper. I only put loctite on the threaded bolt section.

 

   I do get a light tap as brakes are applied, so may order extra shim. There was no loctite on previous Citroen designs( Xantia) on those bolts but the disc diameters may have been smaller. Has anyone done away with the loctite in the caliper and had issues on a C5?

[paul.h]

You will probably find most C5s no longer have the loctite on the rear caliper bolts. I removed it from our 2004 C5 about 2006 and used copper grease, changed the car in 2012 for a 2007 C5 and did the same on its brakes in 2012. No problems on either of them. I still have to remove the corrosion on the back of the calipers every couple of years though but do not have to spend a day each time removing the bolt loctite.

[ESL57]

Thanks Paul, that is encouraging. Citroen may have put Loctite in there as an OTT belt and braces approach.

  Rather than having the minutest chance of the caliper splitting, they just eliminated it altogether and gave maintenance scant regard.

[YOG]

Bought our 2002 2.2l Auto SLX in 2007 at 20,000 miles, with 1 year warranty, from a Citroen dealer. No work had been done to the brakes. A couple of months before warranty end (around 10,000 miles later), rear brakes started squealing. Predictably, "It's not bad enough to fix under warranty, sir"!

 

Around 43,000 miles, I decided to overhaul them myself. As expected, rear pads had the usual "tilted" wear. When I spoke to the garage, they said I would have a difficult time removiing the bolts, and may snap them. In fact, they were fairly easy to remove. I cleaned Loctite from the bolts, "drilling" it from calipers holes, and cleaned up caliper and hub faces, Each face was "copper" greased and refitted, with correctly torqued bolts, using gaskets made from thick polyurethane sheet. Each bolt had the shaft copper greased and thread lock applied to the end thread. New pads and discs were fitted all round.

These remained until 88,000 miles, when both front and rear pads were replaced. The wear was completely even on all the rear pads.

99,000 miles arrived, where I changed front discs and obviously fitted new pads. On inspection, rear pads were hardly worn and still wearing evenly.

The mileage is now 123,000, and has recently passed it's MOT.

 

If you spend a little time making the "Gaskets", you can save a lot of trouble in the long run. I did the same with the gaskets/copper grease/thread lock on our V6 and Activa Xantia's. I don't know why Citroen didn't do it.

Edited December 5, 2015 by YOG