Has anyone fitted a front brake master cylinder repair kit and is it straight forward.
Just taken the bike for a test run after 12 months of restoration, only for the front brake to nip up
and throw me off as I was trying to get into a quiet side road.
Minimal damage ie 2 indicator lens, a casing scrape and the usual bit of nose fairing by the mirror
Snapped off.
Mad as fuck at the mo, wanna put it straight on ebay but will fix up when I calm down !!!!

Agggh; fooking disaster,you put so much work into that paint and bodywork.

What master cylinder, the original Yamaha .....?


You did not fit an aftermarket/replacement lever by any chance ?

Did it just lock and give no indication of binding prior ?

I have used various kits from different sources on the later intergral reservoir master cylinders (not pictured)
that come from the fazer /whatever ? that the " blue dot/spot" upgrade callipers match , with various degrees of success depending on the quality of the seals.
It is not a complicated job.

Yes it's the original Yamaha item. It was fine during the rebuild.
The brake did lock solid earlier and left me stranded on the road in a 50mph limit with no phone thinking what the f&@k can I do. I couldn't leave it anywhere safe so I waited til it cooled enough to move. When it did, i crawled along the gutter in 1st gear thinking come on come on nearly there, 100yds to the turn off where the bike would be safe to leave. 10 mins walk from home.
It started binding again and when I've turned in (slowly!!!) the wheel locked having less weight on it.
What a shock it was
Anyway, I go on holiday for a couple of weeks so I'll have a think on what I'm going to do, but at the mo I can't be bothered.
Still simmering !!!!
Thanks for the response

Just re read your post will. Original master cylinder but after market lever. What would that do ??

What you could have done is ;go into your toolkit and use the 8mm spanner to release the pressure at
both bleed nipples then about turn/straight home/minimal front brake usage.

This is often a shakedown run scenario after rebuilding an old motorcycle.

I usually will stop 5 mins. into the first test and check everything over in a layby...esp. disc temp and chain tension.

You did not answer my query on lever replacement. ?

Right...I have just been notified you have answered that !

The lever MUST MUST MUST have a clearance at the piston.

If not; a continuous pressure is maintained in the system, the pads rub, the calliper overheats transferring heat to the fluid that expands yet more and because the relief port in the master is left covered by the badly fitting lever the brakes lock.It is compounded by braided lines with no capability of swelling.

This is by far the biggest problem when new non OEM levers are fitted to any bike and extremely common..

I infact doubt very much that you require a master seal kit.

Usually the master has been left for years empty or unused.

When brake bleeding commences, the cylinder bore is corroded and tears seals or the stroke of the piston is longer than than it has been for a long period and the previously good seal travels over a longer distance and deforms or fails.

This results in no pressure at the master cylinder; You are suffering the reverse.

Also inspect the relief port (the very tiny hole in the reservoir nearest the lever) and ensure it is not obstructed
by debris.

Old and hardened seals combined with dirty pistons in the callipers can give the same effect but the pads will drag continuously and you would have noticed this prior.

Bill....I love brakes me !

Edited for punctuation/clarity

Did you clean the calipers ? Yam brakes are quite good but the calipers can catch dirt and give the same result as Will said, the disc and calipers heat up and it will seize. It's a 'stard of a way to find out though.

Anyway forget this and enjoy your holiday

Just been out for a look and found that the adjuster bolt in the lever was already touching whatever it touches with no play whatsoever. I wound the bolt out at least 5 turns to get some play. Presume this was the cause. Didn't check this once brakes were refurbed. I thought that if the wheel spins, then stops with the lever, then thats ok, my bad
The calipers were stripped and cleaned with easy moving pistons.
Anyway, I'd like to thank will and evil for all their invaluble advice over the last 12 months, couldn't have done it without it.
I'll post a photo of the finished article under graphics and style. (Before drop, but tbh I've been really lucky with such minimal damage)

redbandit12 wrote:Just been out for a look and found that the adjuster bolt in the lever was already touching whatever it touches with no play whatsoever. I wound the bolt out at least 5 turns to get some play. Presume this was the cause.

There's the culprit right there.

As you now know; the lever pressing on the piston stopped the relief port from being open and pressure built up and up.

Only consolation is : the road could have been damp with you riding at speed when it locked up and ending up under a bus.

I have numerous experiences of riders altering the clearance at the lever via that adjuster on Yamaha master cylinders in order to get what they think is increased braking performance or a span adjustable lever.

It invariably ends up in tears.