On 25/10/2020 22:07, T i m wrote:
I'm working on daughters new (to her, 21 year old) Honda motorbike.
She would normally do it (under my supervision) but Covid etc etc.

I've done the chain and sprockets (un-seizing the rear brake in the
process) and today replaced the fork seals and dust covers and in the
process, found the front brake caliper to be pretty stiff (single
sided floating caliper with dual pistons) so currently have it on the
bench with some Plus Gas round the pistons.

Now in the past I have forced the pistons out with compressed air
(restricting their travel with suitable blocks of wood / rag / clamps
etc) but feel it would be better to do hydraulically because it would
be more predictable and possibly safer.

So I might hook it back up to the bikes front brake system this time
but I was wondering about rigging up a general purpose hydraulic hand
pump for when I need to do such things.

It seems they do them fairly cheap on eBay and I'm assuming I could
use basic hydraulic fluid (less likely to take the paint off?) but I'd
need to make up some fairly high pressure adaptor hoses (25 bar)?

Is this something one can do diy and if so, do you need any special
tools for the joints etc?

I think the pumps come with a 1/2" male (looks tapered) outlet and so
I'd need a mating female to whatever I was working on, in the case of
most motorbikes, a 'banjo' connection of some sort.

Cheers, T i m

Given that you already have a hydraulic pump with all the right fittings
and fluid to hand this seems like a lot of work.

If you are going to make a general purpose system you have a choice
between using mineral oil and "brake fluid". (When you say "hydraulic
fluid" earlier it is not quite clear what you mean). I would generally
use mineral oil (absorbs less water, gives better lubrication for a
stuck or rusted system, and less likely to strip paint). But, you might
then worry about compatibility with seals specified for brake fluid. No
problem if you are going to replace them once you get the thing apart.
In fact in general people worry more than is necessary about
compatibility of mineral oil with rubbers other than nitrile and viton.
Provided the exposure is short and it is cleaned off well with suitable
solvents there should not be a problem. Although mineral oil will cause
natural and many other rubbers to swell and become soft the effect is
generally reversible.