Right. I telephoned Motorworks this morning and discovered that the caliper pistons for the K1100 caliper originally came with the back of the pistons covered by a ceramic disc, and that as this disc is fragile, it can often break then the piston is removed. Hence all of my pistons I took out of the Brembo caliper were bucket-shaped yet the new ones are drum shaped.
I have no idea what purpose these little discs have as the front brake worked well enough (but not brilliantly) like that.
I must take an image of the two as clearly not many people understand what I am talking about.
Well what a strange day. I received a couple of small parcels from Motorworks who have (in error) sent me TWO gearbox gaiters plus the overhaul kit for the master cylinder. I am going to have a good front brake even if it kills me.
Motorworks now supply a slightly oversize gearbox gaiter which is easier to fit. In fact I think the rubber is a little thinner which makes it very difficult to fit rather than impossible. 1 1/2hrs later (Jeez!) it was in place.
Next the Bevel drive. Well that was impossible. I even had the central heating man around who was once a motorbike mechanic and try as we might, we just couldn't get the male and female splines to engage. After two frustrating hours I put everything away and went to phone Jim Cray. Jim tells me that this is one of the most frequent problems from Airhead owners. Half the problem is at the Bevel Drive is heavy and one needs two pairs of hands. He tells me that the technique is to fit a couple of wheel bolts in the bevel drive to help turn the male splines (already done that) and to fit the torque arm bolt. This then will allow me to pivot the bevel drive around the torque arm bolt and line the male and female splines.. Then it's a matter, he says, of gently jiggling the female splined UJ with a screw driver and turning the wheel nuts. It should take between zero and five minutes (he said). I will go back to it tomorrow.
I also, using the repair kit, fitted new seals and ceramic pistons in my K1100 4-pot caliper. The seals are a bit fiddly so I needed good light and the internals of the bores were immaculately clean and lubricated with the sachet of Brembo lubricant provided in the Motorworks kit. I was amazed at how difficult the pistons were to replace as I've refurbished car disc brake calipers in the past when just thumb pressure get's them back. Not this time. The pistons are also dead easy to to get cocked so needed checking regularly as I squeezed them in in the vice with lots of rag to protect them. Quite a bit of pressure was needed to get them home.
Incidentally Motorworks DON'T recomend seperating the halves of the caliper, as it seems they are difficult to properly seal again afterwards. This is contrary to what the Haynes manual states. That's why the tiny O-ring where the brake fluid passes from one caliper half to it's neighbour is not provided so the old one has to be re-used. I also applied a very thin film of Hylomar sealant between the halves and tightened the socket hd cap screws down with a torque wrench, something I rarely bother with. The screws and caliper pin I bought from Chris Shaw Engineering (
www.shawstainless.co.uk). The head are all turned down to remove the lettering and are immaculate. First class service too.