Plate Lift - preventative maintenance?

[stevep2000]

I'm aware that plate lift on the calipers can be a pita, and although mine are ok currently I've wondered whether there is any worthwhile preventative measures to avoid them becoming a problem - or is that likely to be nearly as much work as fixing them when they do go?

 

[morris944s2john]

My annual brake maintenance is now to remove the callipers from the car, undo the plate bolts, remove the plates clean up the part of the calliper in contact with the stainless plates, clean the plates while off, paint the area of the calliper and apply copper grease to protect between plates and calliper. and re-assemble. Once you've done it a few times, its not that hard. I also make sure all the pistons are still moving. Its the only time I would use stainless bolts (the originals are mild steel- better to have two metals there than three).

Do this just before the MOT and the brake performance is great! Also give you a chance to inspect the discs and pads and brake pipes in the area.

So, in summary, yes, the only maintainance is as much work as the stripdown. Once a year is enough to keep your brakes good though!

 

[zcacogp]

It's a good question. I was investigating the idea of using a sacrifical anode in the area to deter corrosion, but looked at the cost of zinc plates from a local yacht chandlers and was deterred at that point. (Four small bits of zinc cost not a whole load less than a caliper ... ) I need to have a look on the internet to see if I can find it cheaper, but never seem to get 'round to it.

Plate lift is not that difficult to rectify, if you have a decent workshop. I did mine with only minor grief. When I reassembled them I did so with some stainless bolts, for the same reason as stated above. I also used bolts with 'normal' heads, as they will be much easier to remove in a few years time. (There is space in there to fit such a bolt, with only very minor filing necessary on one side of the head.)

Liberal use of Copper Grease is key as well.

An ideal solution would be something to electrically insulate the plate from the caliper, but it would need to be very thin (so as not to disturb the alignment of the plate), and fairly heat-proof. A very thin bit of plastic may work, but would probably melt. A thin bit of mica would probably crack too readily.


Oli.

 

[morris944s2john]

A thick layer of calliper paint (or smoothrite) seems to help. Then copper grease on top as said above. You can insulate the plate from caliper but the bolt still makes the electrical contact between the two. And the brake pad metal is made of mild steel, so you still have three metals in that area in close contact. Thats why a refurb on the plate area is now part of my pre- MOT check.

 

[944psi]

ORIGINAL: morris944s2john
Its the only time I would use stainless bolts (the originals are mild steel- better to have two metals there than three).

Do you have a source or specification for the stainless bolts? Or is it just a case of taking the originals to a fastener supplier for a match?

Is there a torque specification too for them?

Thanks, Phil

 

[morris944s2john]

12mm length M6 thread dome head bolts with 4mm allen head, from Namrick http://www.namrick.co.uk/, I think they were under £5 including postage for a pack of 20 (A2 stanless steel).

 

[vitesse]

Excellent article in Porsche Post re' 968 brakes-July edition I think covering all aspects.I have just been doing the rear brakes on our 964 and got new A2 stainless button head bolts-M6 thread 15mm long from our local Engineering Merchant 20 no for £4.They were a wee bit longer than the Plated mild steel ones we extracted(using the weld on nut technology featured in the above article) but still did not "bottom" in the counterbored then tapped holes in the caliper. I reversed the SS wear plates so that the marked areas were nearer the wheel hub,flattened them on an anvil and carefully checked them for a flat fit on the calipers-they can be gently bent by hand to be a good flat fit,and refitted them using copper-ease on the lower thread with Loctite sealant on the upper thread.

Cleaned the seating areas with a fine file,then wirewool and prime painted with a fast drying etch prime paint for aluminium.finish sprayed with several coats satin black paint aerosol.Checked with new pads for a sliding fit and used copperease on just the edges of the pads,on the wearplates,between the plates& caliper & plates & pads.

Porsche suggest optimoly,but it has been discontinued,don't think that dissimilar metals contribute that much as far as copper based greases go,it seems to be more capillary action of water staying between the plates & the seating area.

 

[morris944s2john]

-snip-
Is there a torque specification too for them?
Thanks, Phil

I just carefully hand tighten and use Loctite lock and seal on the threads. No problems with the bolts loosening. You don't want to tighten a steel bolt too much in an aluminium thread! Tap the thread (M6 tap) to remove old Loctite/old corrosion before re-fitting the bolts.

 

[sawood12]

I think you can get away with carrying out preventative maintenance as you get plenty of notice of it before it becomes a real problem. I'm a real preventive maintenance advocate but I think it is unnessesary in this case unless it's a 'while you're in there' type of job (e.g. one of your piston sizes). You might not even come across the problem in your period of ownership. Don't forget that it has taken circa 20yrs for this to become a real issue - most other cars calipers don't last that long period. The problem with the anodic sacrificial material in between the caliper and the plate is that it is corrosion that is causing the problem in the first place, so the act of the sacrifical material corroding will give you the same problem - it will just be the sacrificial material that corrodes rather than the caliper material. If you just repair it in the standard way then you should be good to go for another 20yrs.

 

[morris944s2john]

The callipers on my car lasted 10 years before needing the first lot of plate lift work (at great expense, professionally), This lasted 5 years ane I did the work myself in 2006 and this year. (some corrosion evident even after one year). I would say new callipers will last a long time, but once the factory protection is broken through then you will have to have the job done about every 4-5 years (depending on use)- even if you clean them up as best as you can, etch prime and paint. Failling brakes can creep up on you! In '06 I also changed all the front calliper seals and two of the pistons.

I like to keep an eye on my brakes and keep them tip top! Maybe if you had the callipers media blasted and powder coated they would last longer!

 

[333pg333]

I've mentioned the term 'Plate lift' to my mechanics in the past and it's not one we use down here. Could someone give a brief description of this please.
thx.

 

[Diver944]

Maybe you don't see this issue 'down under' due to the milder climate, I am guessing that your roads are not plastered in rocksalt during the icy winter months? []

Basically the brake pads slide in and out of the soft alloy calliper on two stainless steel plates, one at the top and one at the bottom of each calliper. As the years pass and water, muck, salt etc get in between the plate and the calliper a layer of corrosion builds up in between. This is helped along by the natural chemical process of two different metals in close contact and gradually the layer of corrosion is so thick that it lifts the plate away from the calliper and squeezes the edge of the brake pad. At this point they don't slide in and out properly and you lose braking efficiency.

We are always prewarned of plate lift when it gets increasingly hard to get the pads in and out of the calliper.

 

[333pg333]

Thanks Paul. We figured that it was salt related. We don't suffer this issue down here.

 

[Diver944]

ORIGINAL: 333pg333

Thanks Paul. We figured that it was salt related. We don't suffer this issue down here.

Grrrrr

Maybe you should drive it on the beach more often just to even the score

 

[morris944s2john]

I expect they also don't have problems with sills and bottom of front wings rotting out either!

 

[333pg333]

We do get rust but that's because we live near the coast most of the time and there is a fair bit of salt in the air, however not like pouring it all over the road granted.[]