Rust in Master Cylinder

[Tumbleweed]

Pulled the cap off my master cylinder last night. I did this because my brake lights were not working, and I thought it might be the pressure switch. To my surprise the brake fluid was rusty! Where did this come from I thought. I then looked at the cap and the spring insdie the cap (looks like it is under a pressed in cover) was rusty. There is also a small hole in the top of the cap. I have not run through high water so I don't know why it would be rusty inside. My question is should I just flush the entire system out and refill or get another master cylinder cap? The brakes are stock so I wonder if this a good time to get a duel master cylinder?

Thanks,

Tumbleweed

[Carls_jeep]

Brake fluid attracts water out of the air. I think there is a synthetic fluid that would work better in our Jeeps and I am going to look into that when I redo my brakes.

I think it may be a good idea to flush your system with new fluid and replace or clean the cap. Is the reservoir rusted inside?

[Gunslinger]

I'm with Carl on the drain and flush.  The brake re-do is your call, heck its winter...  I'm not sold on the idea of synthetic brake fluid yet; I've read in other posts that the synthetic stuff will compress a bit, giving you the spongy brake pedal problem.  i can't say I've had the problem but If someone has more info on that it would be a good topic to share.

[Tumbleweed]

The reservoir had rust in it but it comes off easy just by rubbing my finger on it. I think I'll give it a good flush, bleed the brakes (they were working just fine), and try and clean the cap as good as possible. I have some synthetic fluid so I will give it a try. I wonder if there is a cleaner to purge through the brake lines, etc.?

[Gunslinger]

I've used those brake cleaners that come in a spray can, they work well.  Put the small tube into your brake line and give it a blast and it will push everything out the other end.  You could use an air compressor and just blow clean air through the lines, then follow up with cleaner as well.

[Tumbleweed]

Thanks, I have so many cleaners in the garage that I forgot all about the brake cleaner!

Tumbleweed........

[dtgolder]

I'd avoid adding silicone as a flush to an existing system. If you don't start with a new system you won't be able to flush out all traces of the old fluid. That will eventually "puddle" and that local concentration of conventional fluid will concentrate any remaining water in the system, and you will end up with localized rust spots.

So...flush with conventional fluid (beat choice) or replace with all new parts (lines, cylinders, etc...the WHOLE system) and use silicone (good choice for those doing a full restoration).

Don't ask me how I know...

[rocketeer]

Brake fluid attracts water out of the air. I think there is a synthetic fluid that would work better in our Jeeps and I am going to look into that when I redo my brakes.

I think it may be a good idea to flush your system with new fluid and replace or clean the cap. Is the reservoir rusted inside?

Carl, as someone who went that route I would recommend against it. When I replaced the entire brake system on my jeep 5 years ago I opted for DOT5 figuring that since it sat in the cool garage for 6 months out of the year, that was the way to go. After 5 years, if I had to do it over again I'd go with DOT4.

For starters, try pouring DOT5 into that MC without making any bubbles, what a PITA! I finally ended up using a small baster like an eye dropper. Second, the brakes do have a spongier feel to them and three, there's the possibility of moisture settling somewhere in the system and causing a rust pocket. I just may flush the system in the Spring and convert back to DOT4. �Just my $.02.

Larry

[Carls_jeep]

Yes, I totally agree with you rocketeer. After I posted that I did a search and some checking and found out that DOT3 or DOT4 is the best to use in our Jeeps. I made a post correction in another thread and forgot about this thread or I would have made a correction here.

One problem I see is when you go to buy the brake fluid you could accidentally get the wrong stuff. I checked my stock and I have DOT3.

I need to check what my pickup and car are supposed to use.

[rocketeer]

It would not surprise me to see DOT5 disappear from the marketplace. It can not be used in ABS brake systems and that's the direction all mfgs are going so I think it's future, outside of military applications, is dim.

Larry

[Tumbleweed]

Larry, are you going to flush your DOT5 system with brake cleaner or just purge with DOT4 until you get good clear fluid and hard brakes?

Thanks,

George

[rocketeer]

George I haven't given too much thought to it yet. I'm in the middle of restoring a 1938 Zenith radio chassis right now and I want to swap out the ring and pinion in the front differential of the jeep before Spring so changing brake fluids is on the back burner. I'm pretty sure I'll just flush with DOT4 though. I don't like the idea of pushing brake cleaner through the system.

Larry

[aboyandhisdog]

This has been an interesting topic.  What is the best way to flush the brake system?  Do I just start the bleeding process and keep adding new fluid until I've put in the systems capacity?  It sounds like it is important to get all of the Dot 5 out before putting in Dot 3, so how do I know when I have gotten all of the old fluid out?  Is there a way to blow the old fluid out first with compressed air?
Thanks for your help.

[rocketeer]

You can blow out the system using compressed air but you would need to take precautions or you will end up with silicone all over the floor. I use Speed-Bleeders on my jeep and when I bought them I also bought the kit. The kit consists of a vinyl bag that has a plastic hose leading into it. The other end of the hose is the right size to form a fairly tight fit over the nipple on the bleeder. Any expelled fuid goes straight into the bag.

Now you don't want to buy 4 kits but what you could do, and I have not tried this, is to buy clear plastic tubing at your local auto supply house, cut 4 sections, slip each over the nipple and run the other end into a can of some sort. I would also twist a piece of wire around the tube and nipple just so the air pressure doesn't blow it off.

Now you could crack open each bleeder and gently apply air pressure, perhaps through the vent in the cap?


OR, it might be easier to install a set of Speed-Bleeders, connect the drain tubes, and just keeping pumping and refilling until only the new stuff is coming out. If I remember correctly, the DOT5 is purple in color to differentiate it so once all the purple is expelled you should be good to go, or stop, as the case may be. �:)

Larry

[aboyandhisdog]

Thanks, Larry.  What a coincidence...I ordered Speedy Bleeders a few days ago.  I just looked at my MC cap and I don't have any kind of a hole in it, so still not sure the best way to introduce air into the system.  Maybe through one of the wheel cylinders?  Then as air and fluid come up into the MC I could just suction and sponge it up and out.  If anybody else has done this, would love to hear exactly how you did it.  

It's strange though...I have a VW that calls for draining the brake system every two years and putting in new fluid.  I have been having it done on schedule every two years by my mechanic, but now am wondering how, exactly, they are getting the job done.  Hmmm.