Brake Master cylinder caps (1 Viewer)

[sggoat]

After just replacing my 77 FJ40's MC, I was thinking about how every time I opened the reservoirs(esp the rear-which was leaking and the reason for the replacement), that the little metal baffle in the cap was always rusted badly. I tried lots of fixes to try and keep this little thing clean--no one made a stainless one, so I just tried oil/Nox-Rust/silicone/etc. nothing worked. I had a feeling this thing was just being subjected to moisture from the natural "breathing" of the system--contributing to rust forming in the steel brake lines and messing with the MC.
Here's an idea I came up with to combat this--
Remove the little baffle that's in the cap(s). Poke a 1/8" stainless tube into the cap vent hole. Hook this tube up to some common fuel line(used for weedeaters and chainsaws). Pipe this to a small canister(I used leftover shampoo and body lotion bottles from a Hotel in Cody, Wy.) Fill the little canister with indicator Silicon Desiccant. This will be bright blue when dry, when it gets saturated with moisture, it turns pink.
When the dryer gel gets loaded with moisture, simply replace it with fresh. Put the depleted gel into an old hair curling iron heater and dry it back out. Store in an airtight container til you need it again--note: the gel must not be subjected to temperatures higher than 180 deg F, or it will be rendered unusable.
I do not know if this fix will work perfectly, as the system may need an atmospheric vent(as it was designed)----in that case, it would be an easy thing to poke a small(<1/64th) hole in the gel canister to accommodate.

 

[lostmarbles]

Now that's OCD!

Yes. My little baffles like to rust too but so far I've done nothing about it..

I know brake fluid absorbs moisture from the air and those baffles always seem to have fluid splattered on them so I assume this is what's promoting the rust.

If they start dropping rust into my reservoir then I may do something .. like using your idea of "stainless baffles".

(They shouldn't be too hard to make oneself.)

 

[DougAustinTx]

If you switched to DOT5 silicone (after a thorough cleanout of the brake system), you'd have no more worries about moisture and rust in your brake parts. (I know we've had pointed discussions on this board before, but the fact remains that rust will not occur in the presence of pure silicone brake fluid.)

 

[lostmarbles]

If you switched to DOT5 silicone (after a thorough cleanout of the brake system), you'd have no more worries about moisture and rust in your brake parts. (I know we've had pointed discussions on this board before, but the fact remains that rust will not occur in the presence of pure silicone brake fluid.)

But .... and this is a BIG "but" ....you'd probably need to simultaneously change all the seals throughout the brake system to a silicone-compatible rubber.

Neglecting to do this could see seals swelling and jamming up multiple wheel cylinders etc

(I changed my Triumph Bonneville motorbike to silicone and intensely regret that decision. It now sits awaiting my time to change it back to traditional fluid and change out all the seals.)

 

[edwjmcgrath]

SG, that's what happens when you live in the humidity capital of the US!
I had my HVAC guy cut in one vent in the air handler in my garage. I only open it in the summer but that's enough to take the curse off the humidity.
No more mold and rust. If you park outside, there's not much you can do.

 

[sggoat]

SG, that's what happens when you live in the humidity capital of the US!
I had my HVAC guy cut in one vent in the air handler in my garage. I only open it in the summer but that's enough to take the curse off the humidity.
No more mold and rust. If you park outside, there's not much you can do.

You are right about that!. My garage is full of the Windsor Chair stuff--chisels/planes/drawknives, etc. - all needing low humidity--no room for the cruiser- so, yes-it sits outside, and it suffers. I think I'll hook this gomthrob up and see if it helps-I know about the seal issue with Silicon oil, so I won't be going that route--.
Oh for another garage!!

 

[DougAustinTx]

There is NO seal issue with Silicone DOT 5 on FJ40's. I think it would be apparent after over 4 years in two different trucks. I have been using silicone in all my collectable cars for over 10 years and none have shown any evidence of swelling of the rubber (this is in GM, Honda, Toyota and Mopars).

 

[Honger]

If you switched to DOT5 silicone (after a thorough cleanout of the brake system), you'd have no more worries about moisture and rust in your brake parts. (I know we've had pointed discussions on this board before, but the fact remains that rust will not occur in the presence of pure silicone brake fluid.)

I'm interested in this... How do you do the thorough clean out though? Several bottles of the DOT5 bled through the system?

 

[Honger]

After just replacing my 77 FJ40's MC, I was thinking about how every time I opened the reservoirs(esp the rear-which was leaking and the reason for the replacement), that the little metal baffle in the cap was always rusted badly. I tried lots of fixes to try and keep this little thing clean--no one made a stainless one, so I just tried oil/Nox-Rust/silicone/etc. nothing worked. I had a feeling this thing was just being subjected to moisture from the natural "breathing" of the system--contributing to rust forming in the steel brake lines and messing with the MC.
Here's an idea I came up with to combat this--
Remove the little baffle that's in the cap(s). Poke a 1/8" stainless tube into the cap vent hole. Hook this tube up to some common fuel line(used for weedeaters and chainsaws). Pipe this to a small canister(I used leftover shampoo and body lotion bottles from a Hotel in Cody, Wy.) Fill the little canister with indicator Silicon Desiccant. This will be bright blue when dry, when it gets saturated with moisture, it turns pink.
When the dryer gel gets loaded with moisture, simply replace it with fresh. Put the depleted gel into an old hair curling iron heater and dry it back out. Store in an airtight container til you need it again--note: the gel must not be subjected to temperatures higher than 180 deg F, or it will be rendered unusable.
I do not know if this fix will work perfectly, as the system may need an atmospheric vent(as it was designed)----in that case, it would be an easy thing to poke a small(<1/64th) hole in the gel canister to accommodate.

And this is a slick idea. Are there other items on the 40 where condensation/moisture is a problem? It'd be slick to use this to aid multiple issues. The distributor cap perhaps?

 

[lostmarbles]

There is NO seal issue with Silicone DOT 5 on FJ40's. I think it would be apparent after over 4 years in two different trucks. I have been using silicone in all my collectable cars for over 10 years and none have shown any evidence of swelling of the rubber (this is in GM, Honda, Toyota and Mopars).

My experience (and consequent advice about having to change seals with silicone) relates only to changing to silicone in my 1977 Triumph motorbike (and I admit to having very little confidence in the quality of the parts I was getting for this motorcycle here in New Zealand from a local "classic motorcycle parts supplier" so maybe inferior seals were the culprit).

Soon after changing the fluid, my front caliper seal swelled to the point where it gripped the piston so hard that it stopped my front brake from releasing. So now if I'm heading into a corner and hit the front brake to drop speed, the front brake will lock on and I'll have no choice but to actually take that corner in that state .... which would be extremely dangerous as any motorcyclist would know. (To release that brake I must come to a complete halt and push the bike backwards a little.)

My reason for changing to silicone was a poor one. I noticed the brand new brake hoses I had fitted were sweating brake fluid so the "Silver Jubilee Paint Job" on my front mudguard was getting eaten away where the hose touched it. (For some strange reason I didn't question the quality of these brand new hoses but decided instead to keep them and changed to silicone knowing it wouldn't harm the paint.. (And of course ... these s***ty brake hoses were supplied by that same "Classic Motorcycle Parts Supplier" that I now consider dodgy.)

(I never have enough spare time so this bike sits in my garage unridden and has been in this state for quite a number of years now.)

Looking on the Internet just now, I see plenty of advice supporting your view that modern seals don't mind silicone......

The subject is interesting.

As a side-note, I have a Wurth brake bleeder that some here will have seen me rave about in brake-bleeding posts. This has a big O-ring to seal the cannister to the top cover (that I bought less than 5 years ago from a local Engineering Supplies Company) which swells even when exposed to ordinary brake fluid so heaven only knows what it is made of. (It became way too long due to the swelling so I cut a section out of it and rejoined it using superglue to once again have the correct size of O-ring.)

I personally have never been able to look at a seal (cup O-ring or whatever) and been able to judge what type of rubber it is made of. (Real, artificial or ?.) And manufacturers seldom bother giving you this information. Consequently I'm very wary about getting compatibility issues.

 

[DougAustinTx]

Tom: I was aware of your Triumph story, and I had heard other horror stories in the past about DOT5 silicone, but my experience has been great in everything I have tried it in. I buy DOT5 silicone off Ebay when someone is selling off U.S.Mil Spec bottles. It's purple just like the commercial stuff, and it's usually DOW branded.
Honger: In answer to your question, the system must pretty much be taken apart to be properly cleaned. I pour acetone or lacquer thinner through the lines, then blow the lines out with compressed air. On one system that I did not clean out the slave cylinders manually, I later found small rust spots at the bottom of the cylinders where tiny droplets of the original DOT3 had settled and the moisture in it was enough to rust tiny areas. The good part about bleeding DOT5 silicone is that you can use it over and over because impurities drop to the bottom. Then I run the DOT5 through a fine paint strainer to catch any particles.

 

[sggoat]

This is good info. I have thought I might like to change over to the silicon-based DOT5 fluid for some time, but was worried about the seal issue.
My M101A2 Mil trailer runs this in the surge brake system---however, it still has the rust issue in the top cap, no matter how many times I change the fluid and clean it up--a year after the clean, it's rusty again. Maybe a leak in the system? I'm thinking maybe this dryer mod might help--can't hurt-----
I do love testing, though--I'm going to put seals into DOT 3 and into DOT5 fluid for a while-see if the seals change significantly--I have epdm, Viton, Nitrile, rubber, and several other materials--we'll see if how they perform. Test conditions and data will be reported

 

[DougAustinTx]

EPDM is good where exposed to UV radiation, but not good at all in contact with petroleum based chemicals. Will be interested to see if silicone has any effect on it.

 

[Honger]

Honger: In answer to your question, the system must pretty much be taken apart to be properly cleaned. I pour acetone or lacquer thinner through the lines, then blow the lines out with compressed air. On one system that I did not clean out the slave cylinders manually, I later found small rust spots at the bottom of the cylinders where tiny droplets of the original DOT3 had settled and the moisture in it was enough to rust tiny areas. The good part about bleeding DOT5 silicone is that you can use it over and over because impurities drop to the bottom. Then I run the DOT5 through a fine paint strainer to catch any particles.

Thanks. Good info here. I need to plan for this... Sounds like a job to be done when I overhaul and replace all the soft lines and run new hardlines.

I do love testing, though--I'm going to put seals into DOT 3 and into DOT5 fluid for a while-see if the seals change significantly--I have epdm, Viton, Nitrile, rubber, and several other materials--we'll see if how they perform. Test conditions and data will be reported

I, for one, would be very interested in the results and findings you come up with.

 

[honk]

Dot 5 is good stuff but it does require a thorough removal of all residual D0t 3, 4, or 5.1 fluid before use.
If the system is not well flushed THEN the Dot 3 contaminated Dot 5 might cause seals to swell or fail.

The flushing described by DougAustinTX is likely the reason for success with the purple stuff.