Caliper rebuild advice

[kcbart]

I am rebuilding the front calipers and wondered what, if any, grease should be used on the metal rails where the floating part slides. I have looked online but have just got confused - many say copperslip, but many others say don't use it! Others recommend synthetic silicone grease. Your help, as usual, will be much appreciated.

 

[colin944]

I have always used copper grease on brake calipers. Never had a problem with it.

 

[Indi9xx]

Controversial.

Coppergrease is not really a lubricant, but an anti seize compound, just like aluminium greases. Which is an important thing to keep in mind.

If two parts come together, and rearely are seperated, then coppergrease or alumiunium grease will stop them seizing up.

If two parts move against one another, ideally, you want a lubricating grease... But then brakes are a little different, because the movement is very slight and low load..

Wherever possible, you are also supposed to keep dissimilar metals apart, such as not having a steel screw going into an aluminium part.. But that is unavoidable, otherwise Porsche would have used aluminium bolts to hold the aluminium head onto the aluminium block.

So there is a lot of talk about not using copper grease on Porsche cars, and one of the reasons for this is that it is thought that using a copper grease on the aluminium wheel nuts of cars like the 944, will promote the degredation of the aluminium bolt.. So, you are supposed to use an aluminium grease, as an anti seize, in those situations.

There is also talk that you should not use any grease or petrolium based product on brakes, mainly because petrolium based products attack the rubber in seals, such as brake caliper dust boots and seals.. In which case, people like Brembo, who make the S2 and turbo calipers, would like you to use their special grease everywhere... which is just Silicone grease, as you can get from a plumbers merchants, which is a lubricant, not an anti seize.

There is also the argument that greases on brakes, could melt with heat, and migrate to friction linings, like brake pads..

So what can you draw from all this????

1. Use some common sense and do not use too much of whatever you use, wipe away excess and keep it off the rubber bits.
2. Use copper grease on single piston calipers where they slide (the caliper has 3 main parts), wipe away the excess.
3. Use aluminium grease on the wheel nuts
4. You should not need to use it on the backs of pads, but you can, just use the minimum you need


I have never seen a rubber boot that has degraded by any copper grease on it, or anyone use enough copper grease for it to end up on a friction lining.. I have seen a lot of wheel nuts that have oxidised so much they crumble, but would not know if copper grease had caused the oxidisation. However, common sense and a little precaution are free... New parts cost money... You pays your money and makes your choices

 

[tref]

I agree with Jon on all except the grease for wheel nuts. Not so much of a problem on the 944, because of the conventional studs and wheel nuts... but if you have a VW or Audi which uses wheel bolts, I felt that brake dust seemed to collect on the exposed ends of the copperslipped-up wheel bolts, and made them bind when you come to take them off after a prolonged time (of the timescales for which those vehicles go on without maintenance). I changed back to HMP Grease, and the problem disappeared... since then I have used HMP Grease on 944 wheel bolts without problem too. This includes a barely perceptible "wipe" over the domed face that pulls up on the wheel... its a subtle thing, but it just feels "right" when they tighten up and the wheel centres home. I clean off the threads on the studs carefully too, as the insides of the nuts are really difficult to clean.

Back on the subject of the calipers... I can't remember if the fronts have the little spacers between the mounting bracket and the calipers? It always amazed me that these were from steel, given the electrolytic action that could occur between them and the calipers, as well as the additional unsprung weight. One day I will make some up out of aluminium, but in the meantime I coat those with copperslip in an attempt to protect the caliper.

 

[robdimond]

I looked for ages to find the grease that porsche specify for wheel nuts and other aluminium/steel interfaces (Optomoly-TA) and I eventually found it here:

http://www.motobins.co.uk/displayfinal.php?function=show&subs=098e&title=EXHAUST+NUTS

I also used it on my water pump bolts. Porsche specify red loctite but I didn't want to be fighting it in 8 years time! Don't laugh at me when the bolts wind out and my water pump falls off.

 

[edh]

I bought Moly Grease from Bert years ago, My tube is still going strong & I use it instead of copper grease. It seems to stuck around better in high temp areas like brake calipers.

 

[ChasR]

Maybe I have been unlucky, but copper grease on certain parts of the brakes (sliders for example) would congeal (I had this happen on a car where I used copper grease on the sliders as part of maintenance) in addition to my 205 (that had an advisory for a sticking front left calliper. You can guess what the sliders had on them from the PO who rebuilt the brakes only 8000 miles (well, a year) before I looked at them.).

Since then I have been using high temperature ceramic brake grease which seems to be long lasting, and seems to lubricate better than what copper grease does. Certainly, I have not had sliding calipers seize again driven under the same conditions etc.

Even around the brake pads I have seem copper grease almost congeal in a strange hard goo, where ceramic grease seems a little more resistant (maybe that was dirt which was attracted to the grease, but who knows?).