Plating Calipers

[jono]

I've stripped my calipers down for rebuild, new stainless pistons and seals, bushing the rear handbrake mech etc.

I intend to have them blasted then zinc plated.

Is it necessary to protect the piston bores and machined faced of the two halves before plating and if so how is this best achieved (for the faces I could simply re join them - will be fitting new bolts anyway).

Cheers

Jon

[Andy8421]

Jon,

I am about to go down a similar route. There are websites that suggest you should plate the bores as well. Their argument is the plating is only a thin layer, won't effect the piston fit, and why wouldn't you want to rust protect the bores?

I am not sure, so I will be interested in replies.

I have a lot of things to plate, so I am thinking of trying the Frost plating kit.

Andy.

Edit: having just posted about the virtues of searching this site, it turns out this topic has been discussed before:

https://lotuselan.net/forums/viewtopic.php?f=42&t=43477&start=

[Emma-Knight]

These guys seem to do very nice Porsche brake restorations.
In their video they show the bores plated, as I remember.


https://m.pmbperformance.com/brake-calipers.html

Cheers
Anna

[miked]

When I have blasted these I have carried out extra cleaning of the bores. However it is pretty hard by blasting alone to clean the seal slots. I have spent ages with a dentist's pick type instrument followed by a small thin rotary wire wheel brush. You will be surprised how much muck and corrosion comes out of these slots. I actually had a problem with some rear calipers that had been overhauled by an unknown company. The retained dirt was holding the seal out of the seat and allowing brake fluid to pass behind and leak out and onto the disc. The bores and these slots need plating in my humble opinion as without it they will rust. Whilst the plater will pickle clean to some degree I would be inclined to do a bit of phosphoric solution cleaning within the bore with focus on the seal slot.

[JJ66]

Hi Jon,

Sorry for the late reply to this post, I had intended to do so a few weeks back but I got into a potential house move and have a lot of clearing out to do! Splitting the calipers is often seen as a brave move, the bolts that join the two halves together were not intended to be re-used as they were torqued to just below yield. Also getting good quality replacements might not be easy - If you have sourced some I would be interested to know their origins. If a thin Zinc plate and yellow passivate is used then protecting the surfaces shouldn't be necessary, as it will only be approx 20 microns think: Note, its worth asking the plater how thick it will be. For example, if you were to paint between the caliper halves this would be a big 'no' as paint is compressible and the bolts will loosen, but I'm sure you now that already.

One of the most critical parts that is often not understood is the point Mike raised about the seal grooves, these need to be pristine and damage free, and the damage free bit is arguably the most important. I have seen copy calipers for certain cars/bikes that have missed the subtlety of this groove - It is a very particular shape and is designed to promote seal roll-back. When a piston is pushed against the pad, you want there to be a running clearance between pad and disc when the pressure is released, and the shape of the groove and the seal promote this. The disc will 'knock' the piston back a little but you don't want to be relying on that otherwise dragging and hot running may occur. The seal needs to physically pull the piston back and generate a small amount of running clearance, and it can only do that if it is a) the right shape, and b) perfectly clean.

Back to the subject of clamping the two halves back together, you need to make sure you have a proper veg fluid compatible O-ring (square section seal may work also) to go between the transfer ports between the two halves (Girling part number for the seal = 64325808) and then the actual bolts that hold them together. The outer pair of bolts are 64110029, and torqued to 54-68Nm (40-50lbft), and the inner pair are 64110032 and have the torque value of 75-95Nm (55-70lbft).

Hope this info is useful, let us see the finished job, I'm sure it will look great!!

Best Regards, Jonathan