Master Cylinder Reservoir Cap Gasket? (GT550L 1974)

[Ebayru]

Is there a neoprene type gasket for the master cylinder reservoir cap? I can't find one on any parts fiche. I only see the cap, plastic plate and "diaphragm" which looks like it could be a gasket, but I'm not sure.

I resurrected my bike from a junkyard and there appeared to be a broken down rubber gasket around the plastic plate. I added some silicone gasket material to it and it worked for a while but now it's starting to leak around the cap. The silicone seems to be breaking down and I don't want to gum up the system.

Thanks.

[oldjapanesebikes]

It is the diaphragm that you need, part number 59667-18440 (now 59667-18441) and still available. The plate, part number 59668-18441, fits in the cap and into the top of the diaphragm.

[Ebayru]

Oldjapanesebikes:

Thanks! The diaphragm bulb part was gone when I got the bike. That's why it looked like a gasket only.

It's strange that the brakes worked very well without the diaphragm. In fact, the front brake is better than I expected it would be based on everything I had read about the single disk GT550 front brakes.

Does anyone have any idea why it worked so well without the diaphragm?

Thanks, again.

[oldjapanesebikes]

Does anyone have any idea why it worked so well without the diaphragm?

I'm not completely sure what you mean - the reason its there is just to try and keep air (and the moisture in the air) from directly contacting the brake fluid. Otherwise the brake fluid absorbs the moisture and bad things start to happen with your brakes !

[Ebayru]

Thanks for the explanation. I was thinking in terms of operational function rather functioning to preserve the integrity of the brake fluid.

I'll bleed the system to replace the brake fluid after I install a new diaphragm.

Thanks for your help.