rear caliper failing but almost new

[Oskar]

the rear calipers are just a few years old but they failed MOT (handbrake and brakeforce is excelent). Im pretty sure its the famous alu vs iron that makes the piston stuck...

for how long will the overhaul last? I mean will the aluminumhouse be clamped again? 

[lewisman]

One of the guys at work is ex-army, tank division, and he claims to have used a product to stop the chemical reaction between aluminium and steel parts.  Obviously this would help with the bagheera caliper problem.

I will quiz him again to see if he can remember what it was called.

[roy4matra]

the rear calipers are just a few years old but they failed MOT (handbrake and brakeforce is excelent). Im pretty sure its the famous alu vs iron that makes the piston stuck...

for how long will the overhaul last? I mean will the aluminumhouse be clamped again? 

If the original calipers have not been damaged by previous poor repairs and they are overhauled correctly, there is no reason why they should not last ten years - as on my own car, and others I have done.  There are examples running around like Chris House (Bagheera), John Holt, Anders Dinsen (Murena 2.2) that prove it.  The problem from new is that they were assembled totally dry.

Roy

[lewisman]

Is there a puller availablr to separate the caliper body from the frame?

[roy4matra]

Is there a puller availablr to separate the caliper body from the frame?

No.  I have a special tool made specifically for the job, because you need to use a hydraulic press in most cases where they have not been apart before.  You make sure the locking pin is depressed first and then slowly press them apart.  I have seen many tons on the press gauge before the seal 'breaks'.

Roy

[michaltalbot]

Once in past, when I leaved my crashed Murena (silver 2,2) on the back yard, on the grass, and after few months the calipers were blocked because of the wet was under the car. So, maybe, if Your Murena was standing long time in wet surround... ?

[Oskar]

the sliding function dont have any grease. but the piston seems fine.
could it be that the caliper dont have any grease on it that makes it rattle ?  could some coopergrease help me get rid of the brakeproblem?

[Oetker]

quote
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could some coopergrease help me get rid of the brakeproblem?
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I think there is only one solution, and that is to rebuild the complete rear brakesystem to something completely different.
If it doesn't rattle it sticks.
At the moment my left side has a rattle and my right one is sticking.
It was done just 2 months ago.
3 times driving a week helps.

There are not much options to put on another brand.
I am considering my options on this an maybe I find something else that will do better.
So far no luck.

[roy4matra]

the sliding function dont have any grease. but the piston seems fine.
could it be that the caliper dont have any grease on it that makes it rattle ?  could some coopergrease help me get rid of the brakeproblem?

Unlikely that copper grease will solve your problem.  Rattles are caused by one of three things - the pad anti-rattle springs are missing (which causes more of a knocking sound than a rattle really) or the caliper to frame springs are poor or incorrectly fitted, which allows the caliper to rattle in the frame; or the most likely cause of rattles is that one or both of the units has been overhauled badly and the alloy part is no longer a tight fit in the steel section.

People don't understand these units, and because they corrode at the interface of the alloy and steel and the alloy being softer than the steel, the alloy becomes squeezed into ovality, which then makes the piston stick.  If they are correctly separated and the corrosion cleaned off, the alloy will regain its round shape and the caliper will work correctly again.  Unfortunately people take metal off not just the corrosion crud, and I've even seen a caliper which was machined whilst oval making it even worse!  I have some calipers here at the moment where the clearance between the alloy and steel is 1 mm!  These should be a tight slide fit!!  The calipers have other faults and are effectively scrap all due to poor previous work.

Download a copy of my brake booklet from my FAQ pages which explains it all.  There is nothing much wrong with these calipers if overhauled properly.

Roy

[Oskar]

yeah ive looked at your pdf (its very good and detailed) but im afraid its a short time solution if the corrosion wont stop.
the caliper is very new and in very good condition

and another thought, aluminium expand faster then iron when it gets hot, so the piston will get stuck anyway? or is this just to little to take in hand?

[roy4matra]

yeah ive looked at your pdf (its very good and detailed) but im afraid its a short time solution if the corrosion wont stop.

Short term solution?  Sorry I don't agree and I have the proof.  If an overhauled caliper stays free for ten years without any further overhaul, and the next time it need's to be cleaned it's also very easy since it can be taken apart easily (since the items are not seized tight together) then you only need two overhauls to give you twenty years of problem free braking!  I consider that far from short term and much better than even the new car market achieves.

the caliper is very new and in very good condition

And there in lies the first problem.  New calipers are assembled without any protection and deteriorate quickly.  Any new calipers I have bought I strip first and rebuild them properly before fitting them.  Most people simple fit a new part without thinking.

and another thought, aluminium expand faster then iron when it gets hot, so the piston will get stuck anyway? or is this just to little to take in hand?

No that does not happen.  Heat is also transferred and the individual components cannot be considered in isolation.

I will repeat this again...  Properly overhauled calipers can last ten years without further jamming problems and I know this for a fact since those that I have done on my cars and those of others have proved it.  The original unprotected calipers did not last this long from new (I had my Murena from new) and similar calipers on later Espace and other new cars models corrode and jam just the same, as I have found and have had to change at work. (We had to replace with new at work as overhauling was not allowed, as I have explained before)  Corrosion and things seizing together is common with new parts on vehicles because they will never assemble them with even a little grease which could be helpful - it's all down to cost and accountants!  Let's face it, they don't even fill the brake reservoir in most cases as this saves them money - the dealer ends up topping the reservoir up and standing the cost since you cannot claim warranty on this!  It is a typical 'cheat' factories use to reduce their costs!!

Roy

[RazorbackNOR]

And there in lies the first problem.  New calipers are assembled without any protection and deteriorate quickly.  Any new calipers I have bought I strip first and rebuild them properly before fitting them.  Most people simple fit a new part without thinking.

Roy, how would you protect the alupart without adding any thickness to the openings considering clearence? Elox? Paint?

[Oskar]

let us know 

[Oskar]

yesterday I got the murena through MOT, nut it was just... I told him about the rearbrakes etc how it can oxidate etc.  The brakes where a bit stuck be he was kind.  so im glad

however.. couse it only has 97bhp (id say 80) its a mess when going uphill in 90km/h and not be able to accelrate 

so, how do we protect the aluparts after taking it appart?  PLZ pretty sugar 

[Oetker]

most likely heat resistant grease.
Same stuff you use with wheel bearings.