[GliderRider]

Hi, I've just bought a Fantic 243 with Grimeca disc brakes front & rear. Its the type with a cable going from the handlebars to the front master cylinder behind the competition number position on the front forks.

I bought the bike knowing it needed work and both brakes have problems at the moment. The rear one appears to have the master cylinder stuck at the top of its stroke, and the front one just doesn't work, possibly due to a lack of fluid.

My question is, what type of fluid should these Grimeca brakes use? I found a scan of the original manual for the bike which only says use 'Castrol Disc Brake Fluid'. Presumably this is a DOT 4 type?

Has any one else had problems with these Grimeca brakes and/or got tips on servicing/overhauling them? Any advice is much appreciated.

Thanks, Robin

[axulsuv]

Dot 3 or 4 won't matter they are compatable in a pinch , Only major difference is the boiling point of the fluid , But flush and bleed system and use one or the other . Age of bike would lead me to believe it came with dot 3 standard ... If you have to rebuild everything you can run dot 5 (silicone fluid) BUT do not mix dot 5 with 3 or 4 in anyway ! But a synthetic dot 3 will probably work just fine for you .
Just a W.A.G. But I think it is correct ...
Glenn
And PS., it should say on one of the mastercylinder lids what type of fluid is used ....

This post has been edited by axulsuv: 29 June 2010 - 11:31 AM

[GliderRider]

Thanks for the reply Glenn. I've added some DOT4 fluid, and tried to bleed the brakes. The front one is ok from the second pull onwards, but the back one is non-existent. I took the rear caliper off and checked that both pistons move.

What baffles me is that the rear master cylinder takes the fluid upwards and then down into the pipe to the rear brake. I can't see how it is possible to get all the air out of this, as one would expect the air to collect at the highest point. Short of laying the bike on its right hand side and bleeding with the caliper nipple as the highest point, I find it hard to believe all the air would come out.

I did try slackening the 13mm union nut at the top of the rear master cylinder to bleed air out of it as I pressed the brake pedal, but this didn't seem to help.

Any other thoughts?

Thanks, Robin

This post has been edited by GliderRider: 29 June 2010 - 10:36 PM

[axulsuv]

You may have to invest in a Motion pro brake bleeder or a mightyvac bleeder set , I find my mightyvac indispensable at times ... And some times it just takes two people to get it done . You may also be able to hang the bike by the rear wheel and let nature help ...
They can be frustrating but patience and some common sense will prevail !
Have fun , And where are you located ?
Glenn

[GliderRider]

Hi Glenn, I like the 'hang it from a tree' idea; a nice bit of lateral thinking! Its just a shame I cut down what would have been the perfect tree for this a few months ago...

I did have a pressuried brake bleeder, but ebayed it, thinking I would never have a need for it, so hanging the bike from a tree looks like my next move.

I'm in Farnham, Surrey in England. Farnham is about 35 miles South West of London.

Thanks for the info.

Robin

[Lee Harris]

2 options gents.

Worth a try is to buy a 250ml syringe from a doctors and fill it with brake fluid of your choice. Attach using a suitable tube to the bleed nipple and open the master clyinder with the brake pedal open, i e. In its resting position. You can bleed brakes and clutches this way in seconds. 2nd option is to look at the reservoir for the MC. I drilled and fitted an old schrader valve from a innertube. I then fill the MC., pump up to say 2 bar and then try std bleeding. Works only for max three stokes. The de-pressurise, refill and start again


I guess the the MC seals are AWOL if these two methods dont work

This post has been edited by Lee Harris: 03 July 2010 - 10:08 AM

[Baldilocks]

You may be able to do this which I did with a Beta Rev 3 which has the master cylinder on the right and the caliper on the left.

remove the whole system from the bike and use some screws to attach it to a plank of wood. You should be able to line the whole system up so the little resevoir is at the top of the system and the caliper is at the bottom. you need to get the angle of the master cylinder correct so that fliud is flowing up to the little resevoir.

you can then back bleed it by forcing the pistons into the caliper and this should force air to the top., use a ball ended alan spanner to work the master cylinder to push the pistons back out. should work in a couple of goes, if not the seals are gone somewhere. The 303 I had years ago did two sets of master cylinder seals in 6 months.