Leaking Master Cylinder

[70 FJ40]

Popped the hood and noticed I've got a leak coming from the brake master cylinder. Paint on the steering box is starting ro bubble. Originally looked like it was leaking around the bottom of the front reservoir but the rear reservoir was the one that was low on fluid. After getting back home, it looks like the rear reservoir is low again, although it's harder to see if it's leaking out of the front or back now. Brakes still seemed good on the fairly long drive home. Can I tighten the nuts on the bottom of the reservoirs or replace the rubber washers to stop the leak or is it better to just get a new master cylinder?

 

[samatulich]

Rebuild kits are available. Pretty straight forward job.

 

[charliemeyer007]

I have never has a leak in the reservoir seal. Rebuild kits I have used don't have those seals. It wouldn't hurt to try and tighten the nuts IMHO. New unit are in the $150 vs kit $50 range. That unit looks more like later year ones than the 1970.

Brake Master Cylinder

 

[middlecalf]

An additional thought: how are the rubber caps? I have replaced a number of them, they don’t like any off-gassing (from carb) in the engine compartment (they get too soft and lose their snug fit), and if the reservoirs are filled then they leak around the rim when the rig is bouncing around (which these rigs like to do). I’d love to find an alternative lid that’s gas-fume proof, so far my attempts at going back to original tin cups have been failures (finding cups that don’t leak for less than $$$ has been a challenge - and I’m cheap ). There’s a float thingy that goes inside the reservoir that supposedly helps with fluid sloshing, but I only have them in one of my four MCs, not sure if they are available alone or why the other MCs didn’t come with them.

 

[70 FJ40]

Cruiser is a '77. They are not a real snug fit and my hands get black whenever I touch them. There was definitely a lot of bouncing around. 3 days with no pavement in sight. First noticed low level halfway through second day. I'll wipe it all up and see if it was just sloshed from the top. Can I get new rubber caps somewhere? I'm generally an OEM parts guy when available. Cruiser Outfitters has OEM for $260ish and after market AISIN for $150ish. Are the aftermarket good enough.

 

[middlecalf]

Caps

Search Results

Search Results -

www.coolcruisers.com

SOR has the caps also.

Don’t know about cruiser outfitters, don’t see anything on their website, a call may be necessary.

 

[middlecalf]

That black on your hands and loose fit points to cap deterioration. So not only the leaking potential, but also air (with moisture) introduction. Brake fluid being hygroscopic that’s a long term issue, at a minimum. Not sure why this isn’t more prevalent in Mud discussions, I see virtually every MC-updated cruiser picture with these plastic MC reservoirs and rubber caps. I know the motorcycle and Jeep worlds have dealt with this issue for a long time. Most modern vehicles have screw on caps. Wish us’n early cruiserheads had a better option. Anyone want to repro a tin cup MC?

 

[Roastchestnuts]

An additional thought: how are the rubber caps? I have replaced a number of them, they don’t like any off-gassing (from carb) in the engine compartment (they get too soft and lose their snug fit), and if the reservoirs are filled then they leak around the rim when the rig is bouncing around (which these rigs like to do). I’d love to find an alternative lid that’s gas-fume proof, so far my attempts at going back to original tin cups have been failures (finding cups that don’t leak for less than $$$ has been a challenge - and I’m cheap ). There’s a float thingy that goes inside the reservoir that supposedly helps with fluid sloshing, but I only have them in one of my four MCs, not sure if they are available alone or why the other MCs didn’t come with them.

Pretty sure mine leaks through the cap like this too. Kinda one of my big annoyances. I would love to have one of the Tin MC

 

[B y r o n]

Leaking caps will not cause a reservoir to go empty. There appears to be wet areas around the fluid level sensors. I would also look at the booster for signs of a leak. Masters are available as well as rebuild kits but you need to disassemble before determining that it is rebuildable.

 

[middlecalf]

His, and mine, aren't empty, just lower than full.