Brake fluid reservoir glass repair

[Skinner]

So I removed the cracked and cloudy plastic lens from the sight glass opening. The rubber gasket was tough to remove but it eventually came out in pieces. All that’s left is the metal retainer - how do I remove this? I tried heating it but it won’t budge. I don’t want to force it for fear of damaging it.

Cheers!
K

[Steve]

I have never worried about saving that ring.

I just pry it out. Cut a small piece of 1/8" Lexan, round it out so it is just a little bit smaller than the opening. Mix up some epoxy. Put a bead of epoxy around the shoulder in the opening, lay the Lexan lens in place, carefully dribble the rest of the epoxy around the edge. If you use a heat gun (VERY carefully), you can warm up the epoxy a bit. That will thin it out so it removes any "wrinkles". Just don't thin it out so much that it runs into the reservoir. Let it sit flat overnight, then put it on the bike fill it up and bleed the brakes.

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[Skinner]

Thanks Steve,

I bought a replacement sight glass lens off Fleabay. It's 18mm and has an o-ring seal - I'm hoping it will press fit nicely. If not I'll add some epoxy as well. Looks like the metal ring is toast.

Cheers!
K

[bwringer]

A replacement sight glass should have the metal shield and o-ring.

It's a press fit, but be very careful -- it does take a good bit of force, so plan carefully and support the aluminum of the master cylinder.

[Skinner]

As it turns out, the glass and o-ring are too small for this application. The glass unit is 18mm diameter which does not fit well, even with the o-ring in place. It's not designed for my particular installation. I ordered some watch glass crystals yesterday and will install them per Steve's suggestions.

[greg78gs750]

this worked for me....

As it turns out, the glass and o-ring are too small for this application. The glass unit is 18mm diameter which does not fit well, even with the o-ring in place. It's not designed for my particular installation. I ordered some watch glass crystals yesterday and will install them per Steve's suggestions.

[Gorminrider]

I used jbweld and epoxied a cracked + dirty one with good result.
Always excepting a "showbike", frankly, I have never noticed these windows did anything useful ...the one time I lost fluid it was obvious to me (fluid on gloves!) without peering at fluid levels through faded or even (temporarily) clear plastic . Likewise in other circumstances...(brakes will fail, fluid around calipers etc) The round pvc reservoirs are silly too. I always to take the top off to check brakefluid anyways.

[bwringer]

Did you remove the metal "shield"? If the old one is still in there, the new window won't fit.

18mm is pretty much the universal sight glass size on any metric master cylinder, so it's a little surprising it wouldn't fit.

This is similar to the kit I ordered:

https://www.amazon.com/Master-Cylinder-Sight-Lens-Rings/dp/B01N20CXY0/ref=pd_day0_263_5/134-4085062-9263317?_encoding=UTF8&pd_rd_i=B01N20CXY0&pd_rd_r=8C917DZQX7SDSGYAE1TQ&pd_rd_w=gwCF0&pd_rd_wg=HpaRr&psc=1&refRID=8C917DZQX7SDSGYAE1TQ

It's a simple press fit -- no mucking around with epoxy.

[jsandidge]

Did you remove the metal "shield"? If the old one is still in there, the new window won't fit.

18mm is pretty much the universal sight glass size on any metric master cylinder, so it's a little surprising it wouldn't fit.

This is similar to the kit I ordered:

https://www.amazon.com/Master-Cylinder-Sight-Lens-Rings/dp/B01N20CXY0/ref=pd_day0_263_5/134-4085062-9263317?_encoding=UTF8&pd_rd_i=B01N20CXY0&pd_rd_r=8C917DZQX7SDSGYAE1TQ&pd_rd_w=gwCF0&pd_rd_wg=HpaRr&psc=1&refRID=8C917DZQX7SDSGYAE1TQ

It's a simple press fit -- no mucking around with epoxy.

I used one like that for my 850 - pressed it in with my vise. I have another that will be going in the 750, they work great.

[Skinner]

Did you remove the metal "shield"? If the old one is still in there, the new window won't fit.

18mm is pretty much the universal sight glass size on any metric master cylinder, so it's a little surprising it wouldn't fit.

This is similar to the kit I ordered:

https://www.amazon.com/Master-Cylinder-Sight-Lens-Rings/dp/B01N20CXY0/ref=pd_day0_263_5/134-4085062-9263317?_encoding=UTF8&pd_rd_i=B01N20CXY0&pd_rd_r=8C917DZQX7SDSGYAE1TQ&pd_rd_w=gwCF0&pd_rd_wg=HpaRr&psc=1&refRID=8C917DZQX7SDSGYAE1TQ

It's a simple press fit -- no mucking around with epoxy.

My EBay sight glasses are exactly the same - 18mm diameter with an o-ring. Unfortunately the opening on my master cylinder reservoir is 21mm so the sight glass will not work as is. I could epoxy it in place but that would not be a very clean install. Also, the sight glass blocks the opening in reservoir that allow the brake fluid to get into the sight glass. Not going to work, so I'm waiting on my watch crystals.

[bwringer]

Ah. I was not really aware there was a different size sight glass out there. Good to know!

[Chuck78]

Good tips to know. Are these watch glass crystals readily available on eBay in metric sizes? Or do you just use epoxy to make up the slight difference?

Are most of the GS master cylinders 18mm sight glass size? Or are many of them 21 mm?

[Skinner]

Good tips to know. Are these watch glass crystals readily available on eBay in metric sizes? Or do you just use epoxy to make up the slight difference?

Are most of the GS master cylinders 18mm sight glass size? Or are many of them 21 mm?

There were dozens of vendors for watch crystals in various thicknesses and diameters. I ended up going with 20mm diameter, 1.5mm thick. In hindsight I wish I'd gone for the 21mm diamter because I had to build up the RTV (used this instead of epoxy) a bit too much for my liking. But it works.

My rear master cylinder has a 18mm opening and the EBay sight glass/o-ring combo pressed in nicely. The front master cylinder (1982 Katana 750) is an oddball size apparently.

[bwringer]

Uhh, brake fluid dissolves RTV... might want to rethink that.

[Skinner]

Uhh, brake fluid dissolves RTV... might want to rethink that.

Damn, I was not aware of that - I’ll redo with epoxy. Thanks for the heads up.