When I assembled the brake caliper, I had thought that the piston was a little cocked in the bore.
Naively, I thought that if I assembled the caliper onto the bike, a bit of hydraulic pressure would just pop it straight.
Well… suffice it to say that over the past day I have learned a number of lessons, (3), starting with… it won’t just pop back into place.
In the interest of “keeping it as original as possible”, I built the front brake system onto the bike using an OEM Yamaha rubber brake hose.
After bleeding the system for half an hour and removing all the bubbles therein, the brake action was still a spongy as Spongebob Squarepants’ sponge purchased from sponge city on spongeday.
This leads to the second lesson. 40 year old rubber hoses are not the answer.
Anyway, lots of pumping and pressure led to no improvement in the cocked piston, so it had to come off again for investigation.
…and the outer seal had broken. New seals on order along with a length of braided steel brake hose.
And the third lesson?
I had painted the caliper using VHT paint, (as recommended pretty much everywhere). A bit of brake fluid had the paint washing off as iff I hadn’t let it dry… which effectively is true.
It seems that VHT paint needs a relatively high temperature to cure properly. This brake caliper has had no chance to get warm, let alone hot.
So the third lesson? Read the instruction on the tin.
Caliper painting can await the cosmetic build now.
The new seals arrived the next day, and were seated in the grooves with copious amounts of brake fluid as a lubricant.
This time, the piston slid straight in with light finger pressure only. I’m not sure if this is a good thing yet, but clearly, use of a G-Clamp as before is not recommended.
I can only think that the dust ring, (the narrow one) was not seated properly in it’s groove when I tried the first time.
Now we await delivery of the new brake hose before assembling it all and trying again.
The brake hose, (from Wezmoto), arrived two days later. It is the correct length, and came with a rubber ring around the hose to facilitate fitting into the clamp on the bottom yoke.
The guide which bolts to the fork leg has its own split rubber.
It also shipped with included banjo bolts and copper washers of the correct fitment for the bike… Attention to detail from recommended seller.
All fitted and bled through with a decent “feel” at the lever, I can consider the brake done, and ensure all the bolts are tightened and torqued down correctly.