Rear wheel cylinder

[Excalibur]

I have a leaking wheel cylinder as per pic but it gets worse because this is the 2nd time this has happened. About a year ago I'd renewed the cups.

whcyl.jpg (163.59 KiB) Viewed 871 times

'61 FLH
The shoes are dry.
Brake fluid= DOT4
Flushed with fresh DOT4 about 5 months ago.
My rubber assembly grease is very old. Google tells it has only a 3year shelf life.
I'd made a little cover for my master cylinder, thinking maybe water was getting in with hygroscopic however it doesn't explain why the master-cylinder itself isn't suffering the same fate. (It could be brass sleeved I suppose, it's never been apart.)

I'm missing something here...
Thoughts...
Renewing my rubber assembly grease.
Renew or re-sleeve the cylinder (do these sleeve OK with say brass?)
Replace the cups, by the way are these 1"?
Upgrade to DOT5? Is it worth it? It seems there' pros and cons?
What else??

Thanks for any answers, tips, thoughts, experience..

[Mongrel505558]

I would switch to DOT 5, if for no other reason that it doesn't eat paint. It's also silicone based rather than glycol based. When you rebuilt your wheel cylinder did you hone it? I would give it a few spins with a brake cylinder hone to clean it up if it's pitted or scarred. I rebuilt mine and it works well and as far as I know it's containing everything, although I won't really know that until the next time the wheel comes off.

[Andygears]

I would replace the wheel cylinder, rebuild the master, blow the lines clean with compressed air and fill with Dot 5. That wheel cylinder has been rebuilt so many times since 1961 that parts may just be too loose to retain a good seal. And Dot 5 doesn’t absorb moisture.

Andygears

[RooDog]

I have been using DOT 5 since the early 1980s with no issues, ever since I saw how DOT 3 turns to gel in those early aluminum master cylinders. Iron cylinders also benefit the the fact that D-5 does not absorb moisture.....
....RooDog....

[Lowbikemike]

I'd stay away from "rubber assembly grease" whatever that is. Lube the cups with brake fluid when installing. Cups are generally marked with size. I'd take Master Cylinder apart also because that crap is most likely in it too.

[Chief3Kicks]

I too am a proponent of DOT5 but having a failure in 1 year indicates another root cause other than DOT 3/4. As mentioned I'd replace (not rebuild) the wheel cylinder, replace or rebuild the master cylinder as needed and blow the line out with Brake Clean or similar following up with compressed air. Once you do all that it makes sense to go with DOT 5. Its nearly 3 times the cost of DOT 3 but worth it if you plan to keep the bike.
Disassemble the master cylinder before placing parts order as you will need to access the condition of it before deciding on honing the bore and installing a kit, or full replacement.

[RooDog]

I'd stay away from "rubber assembly grease" whatever that is. Lube the cups with brake fluid when installing. Cups are generally marked with size. I'd take Master Cylinder apart also because that crap is most likely in it too.

Agreeing....
I have never used any sort of assembly lube on any hydraulic system other than the fluid as used by that system, including DOT-5, for MC brakes.....
....RooDog....

[awander]

Just to give a contrarian viewpoint:

-DOT3 brake fluid does absorb the moisture that inevitably gets into the brake system.

-The absorbed moisture is much less likely to cause localized rusting in components of the brake system.

-DOT5 fluid will allow the moisture to pool up and cause internal rusting.

If you plan to change the fluid regularly and often, then I'd say DOT5 is a good idea.

But if you plan to change the fluid seldom or only when the brake gets spongey, then I'd stick with DOT3.

If DOT5 was really that great, we'd see it as standard in all vehicles.

[RooDog]

BS:
If we relied on what is standard with all vehicles, there would be no hot rodders....
I made up my brake system on my home made Evo Bagger about 20 years with DOT-5, and have never changed the fluid.
The bean counters keep it out of the OEMs, but as a very low volume custom builder, I don't mind the cost.
Do what you will, and believe what you like, but make your own choices, I know I do....
That's why Ben & Jerry currently offer 54 flavors.....
....RooDog....

[Andygears]

Just to give a contrarian viewpoint:

-DOT3 brake fluid does absorb the moisture that inevitably gets into the brake system.

-The absorbed moisture is much less likely to cause localized rusting in components of the brake system.

-DOT5 fluid will allow the moisture to pool up and cause internal rusting.

If you plan to change the fluid regularly and often, then I'd say DOT5 is a good idea.

But if you plan to change the fluid seldom or only when the brake gets spongey, then I'd stick with DOT3.

If DOT5 was really that great, we'd see it as standard in all vehicles.

I disagree on this. An empty clean system filled with fresh Dot 5 should not corrode anything. Hydraulic brakes are a closed system. Any moisture must enter thru the master cylinder vent from humidity and if it does not mix will perhaps “float” on top in the MC. Whereas dot 3 mixes and works it way throughout.

A small amount of dot 3 added on the road to my fxr dot 5 system swelled the seals and locked the brake 3 days later. This happened to me 25 years ago. Another case when I got my “barnfind” panhead with ‘63-‘66 rear brakes. I rebuilt the master cylinder and replaced the wheel cylinder, filled existing system with dot3. Got it going and evaluated what was wrong with bike. Tore it down for 3 years, and when I reassembled with new brake lines, different master and that recently replaced wheel cyl. It was rusted up. I cleaned it out, 2 new cups and filled with dot5, works great, and never looked back. Even my ‘78 Dodge motor home had all four pistons rusted solid and therefore no rear brakes when I bought it from using dot3.

I feel dot5 is a superior fluid that will do a better job nearly always if the system is clean and free of contamination.

Andygears

[RooDog]

Modern Harley master cylinders are not even open to the atmosphere, they feature a flexible rubber diaphragm that moves with the fluid, fluid on one side sealed away from the ambient air on the other side. Hence we get no contamination of the hydraulic system. The old cast iron Wagner/Lockheed MC is open to the atmosphere and has the potential for contamination. There is always a choice.....
Even my 1973 Ranchero has the diaphragm system, must be why its brakes have been working well for so long (with DOT-3)....
....RooDog....

[awander]

Just giving another argument that I have heard, guys.

And if the modern systems are sealed so moisture can't get in, then DOT3 should work just as well, right?

[RooDog]

Just giving another argument that I have heard, guys.

And if the modern systems are sealed so moisture can't get in, then DOT3 should work just as well, right?

Sounds reasonable...
But Johnnie Cochran got OJ off by sounding reasonable....

[59Panman]

I switched to DOT 5 on my 59 with no issues so far.

[Excalibur]

Thanks for the super stimulating discussion. It creates perfect opportunity to consider aspects I may not have thought about.

I went to get DOT5 but my plan was thwarted. The first place only had 3, 4 or 5.1. The 2nd of my go to retailers listed it on their website but no nearby branch stocked any. I have fresh DOT4 on the shelf so will go with it. The old rubber grease is binned.

Picked up a pair of cups today so the cylinder gets refitted regardless. If it looks bad I'll order a replacement. That will take about 4 weeks one would like to think. In any case I'll be mobile.

And yes, I did hone the cylinder