Brake Caliper Piston Overhaul Kit

[robwright]

I have decided this will be one of my winter jobs this year. So if I am correct for my 88 car I have 3640mm front pistons and 2830 rear pistons. But what does this actually mean? Is the piston diameter 40mm front and 30mm rear and are they the kits that I order I.e. 40mm seal kit for the front and 30mm seal kit for the rear?

 

[robwright]

Hi Rob,
The front caliper has 2 x 40mm pistons and 2 x 36mm pistons, and the rear caliper has 2 x 30mm & 2 x 28mm.
Cheers,

 

[Chrishazle]

Last August Waylander posted this on the 968uk forum :

"Hi All

I have had a chat with mode performance.

http://www.modeperformance.co.uk 01327 855 999

they are Brembo dealers.

and they have all the piston fluid seals and dust covers in stock

seals (does not matter on the size) 44,40,36,30,28mm £4.00 each
Dust seals the same 44,40,36,30,28mm £7.00 each

cheaper if you buy in packs of 8 if you want to do a shared buy

44mm (M030) seals Part number 105.5955.60
40mm Seals 105.5955.58
36mm Seals 105.5955.56
30mm Seals 105.5955.53
28mm Seals 105.5955.52

Dust Covers
20.4872.40 28mm
20.4872.41 30mm
20.4872.42 32mm
20.4872.43 34mm
20.4872.44 36mm
20.4872.45 38mm
20.4872.46 40mm
20.4872.47 42mm
20.4872.48 44mm
20.4872.60 46mm"

Apparently Steve is the automotive guy to talk to. Hope this helps.

 

[bmnelsc]

Hi Rob,
The front caliper has 2 x 40mm pistons and 2 x 36mm pistons, and the rear caliper has 2 x 30mm & 2 x 28mm.
Cheers,

As per Steve - each caliper has 4 pistons - so you need to check the contents of the "kit" you order to ensure you get the right size and number of piston seals - e.g. does the "kit" do one caliper or one axle (both calipers) front or rear. I'd be surprised if the vendor offered a "kit" that only provided one size of seal - e.g. a front "kit" should have 2 x 40mm and 2 x 36mm for one front caliper or 4 x 40mm and 4 x 36mm for the front axle (I know it is odd to refer to the front or rear as an axle when our cars are fully independent suspension and therefore we have 4 axles but this terminology is a carry over from bygone days). Likewise for the rear with 30mm and 28mm seals.

I recommend you study up on the workshop manual before you get stuck in as the consequences of mucking this up could be serious indeed.

 

[robwright]

Well bugger me I have never noticed that each caliper has different sized pistons. I haven't ordered anything yet just doing research. I talk about kit as if I imagined there would be one you could get. The Brembo info above is excellent. Guess you can't do better than the OE stuff?

 

[Chrishazle]

Reason for the different sized pistons in a caliper, courtesy of Stu on 968uk (Mr968 on here) :

"The reason for different sized pistons in the same caliper is because the front of the pad will tend to wear faster(it digs in), so what they do is put a bigger piston on the trailing edge of the pad to apply more force at the back end and so evening out the wear across the pad."

 

[924Srr27l]

I have decided this will be one of my winter jobs this year. So if I am correct for my 88 car I have 3640mm front pistons and 2830 rear pistons. But what does this actually mean? Is the piston diameter 40mm front and 30mm rear and are they the kits that I order I.e. 40mm seal kit for the front and 30mm seal kit for the rear?

Are you replacing the Plates also?, they are common for lifting when the aluminium caliper corrodes and pushes the plate so much it stops
the pads sliding and clamping the disc.

Are the brakes poor, leaking or are you just replacing seals as a matter of servicing?

If they need Paint also? there are a few companies that can do the lot strip, replace the plates, pistons and seals, and reapaint
but this can add up @ £200 a caliper

R

 

[robwright]

I have actually refurbed the callipers myself previously and sorted out the plate lift. They have also been painted in red to match the car. I didn't do anything with the pistons at the time because I had no issue and money was also a factor at that point. Just feeling a little bit of bund at the minute so thought it was probably to sort the pistons out.

 

[robdimond]

Don't the 88 cars have the scraper seals rather than the bellows type seal on the pistons. Harder to get and to change (pistons and seals)
Only available direct from Porsche was my understanding and £££

 

[robwright]

As I understand it yes Rob. They have dust/scraper seal as opposed to the boots. Not sure what type the number listed above are? What are the difficulties in changing the dust seal/scrapers?

 

[robdimond]

I have not tried but the scraper rings look like they are pressed in and hence difficult to remove and reinstall.
The pistons and seals are fairly standard and easy to change with an airline to pop the pistons out.

When I looked into it the scraper rings and pistons were Porsche only and expensive, whereas the later calipers there are standard Brembo and cheap aftermarket parts. I hope the situation has changed.