Brake Master Cylinder help

craig_uk · Post by **craig_uk** » 21 Jul 2007 18:10

The front brake is poor on my '76 3 1/2 disc braked Strada.

There appears to be a jet of fluid coming back through the small port, back into the brake fluid master cyclinder reservoir. This occurs all the way through the brake level travel.

I suspect the master cylinder seal has gone.

a) Any advice or diagnosis welcomed.

b) Has anyone any experience of repairing master cylinders? I will ask NLM is theye have a seal kit.

(I've replaced seals on car master cylinders but I've never done a bike one.

Thanks, Craig

3potjohn · Post by **3potjohn** » 22 Jul 2007 05:41

Well not much use to report I did a K75 one a few months ago by fitting a new seal kit. My Morini will not be needing it's brakes for a while.I have the engine to pieces now. Something unpleasant has happened to various surfaces where oil should have kept them apart.
Actually the brakes were one of the few bits that worked well.However after removing the bleed nipples (hey they didn't round off it must have been a good day) One had slight corrosion and would not seal again properly until I cleaned it up carefully. I expect there was some muck in the calliper too.

EVguru · Post by **EVguru** » 23 Jul 2007 14:11

NLM do a complete piston assemby for less than a tenner which takes all the stress out of the job.

If you're only running one front disc, then consider spending Â£50 on a new 250 mastercyclinder, it does wonders for the feel. The original 350 cylinder is perfect for twin front discs.

boris tarpit · Post by **boris tarpit** » 23 Jul 2007 14:47

I've got a 250 master cyl+350 caliper on my bike - its much better than the standard 3 1/2 set up.

craig_uk · Post by **craig_uk** » 23 Jul 2007 17:56

Guys,

Thanks for that advice.

I aim to take the master cylinder apart tonight to see if it is serviceable.

If not then that make the decision to go to a 250 cylider even more of a no-brainer.

Craig

craig_uk · Post by **craig_uk** » 23 Jul 2007 20:46

Well, the master cylinder bore looks ok.

I will talk to NLM tomorrow re: either a new piston assembly or a new master cylinder.

The piston diameter is 16mm. If anyone has details on brake components can you let me know. It would be useful to know if this is a standard master cylinder off a 350. I assume that the 250 and the 350 have different diameter pistons and that gives different braking effects.

Detailed question, I know....!

My bike was a 76 single disc/spoke wheel Strada but made to look like a Sport so could be built out of all sorts of bits....

Craig,
UK

EVguru · Post by **EVguru** » 23 Jul 2007 22:06

16mm is standard 350.

I think 250 is 14mm. The 250 runs the same wheel, disc and caliper as a 350.

craig_uk · Post by **craig_uk** » 24 Jul 2007 08:34

Thanks for this info Paul. Very helpful.

I've just ordered a piston assembly (350 type) from NLM and I'll see how that goes.

Craig UK

p.s. I once bought a Ducati 250 from a Paul Compton, not you by any chance?

EVguru · Post by **EVguru** » 24 Jul 2007 08:57

No, couldn't possibly be me, I've never really got the hang of selling bikes.

That would proably be why I've got two 250's, three Sports (well, two and most of one in bits), two Darts, a '66 Corsaro, a 501 engined Valentini replica, a Motobi Tornado, a couple of Freccias, and shortly to come a WD BSA B40.

I seem to have run out of space.

craig_uk · Post by **craig_uk** » 24 Jul 2007 09:03

I know the feeling.

'76 Morini 3 1/2
'54 Norton Domi 88
'74 Ducati 250

ZZR1100 powered hillclimb / sprint car
+ spare engines.

Bridgeport Milling machine
Colchester Student Lathe
Sheet folder
4 welding sets
etc...etc

Tripping over stuff here....

3narf · Post by **3narf** » 02 Aug 2007 21:43

The Guzzi V50 one (Brembo) is also 14mm. I use one of those on mine...

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Brake Master Cylinder help

Brake Master Cylinder help

...moving to a 250 master cylinder