I run silicone brake fluid (Dot 5) in my 67 chevelle and I have gone through 3 master cylinders in 3 years. Any reason that the brake fluid could be causing the seals to go out in my master cylinder?

Go to wilwood's web site.I read something about this today on there.BILL

My understanding is that silicone fluid is extemely "slippery" compared to ordinary dot 3 fluid. I put silicone fluid in my family car a couple years ago and went thru 2 master cylinders before I removed it. Never had a problem after that. Having said that, I use silicone fluid in my vette and have done so for over 10 years without a problem.
I think rebuilt masters maybe don't fit as tight so the silicone gets by the seals. I have heard others say that it can get past seals whereas dot 3 won't.

Wilwood doesn't seem to reccomend it and neither does stainless steel brakes however none mention it causing a master cylinder to go out. Bhawk judging by your experience I feel what I fear is true. However, I am confident that I should be able to find a master cylinder that bolts in and can handle the silicone brake fluid.

so I am also using dot 5 brake fluid, and my master from Baer is done... from yet undetermined causes...

so maybe dot 5 is not a good choice

Dot 5 causing the problem?
Sounds like a lame excuse for poor manufacturing to me, or poor quallity controll when rebuilding?
T.C.

Might be poorly rebuilt tough call. This next one I have ready to install is supposed to be brand new so who knows.

I had the same problem on my modified, went threw several masters, unitl I switched back to DOT3. US brake and Willwood both suggest not using DOT5 in there masters that I was running (independant masters). I also bought a master rebuild, and that went out also. Not sure if the material that they use on the seals can deal with the fluid, not sure why.

Interesting thread. I just filled up with DOT5, so we'll see what happens...

I put in my 55 about a year ago. I don't drive it much but so far so good!

so this is a question to all who are using dot 5
who's/ what brand master cylinder are you using?

so this is a question to all who are using dot 5
who's/ what brand master cylinder are you using?

A cheap Chinese replica. If anything will crap out, it will be this one :) I think it has been about a year since I installed it now, but so far, so good.

Dot 5 has been discussed a few times before; the biggest problem is its lack of ability to deal with the inevitable introduction of moisture to the system. The water then settles to the bottom and begins the rust process of the metal components like pistons and bores.

It amazes me that no matter how many times it is discussed and how many vendors recommend against its use, folks still use it and blame the parts for when things go bad. There is a reason that no automobile manufacturer uses it. Good for trailer queens and that’s about it, although a towel over the fender would work just as well. In over 15 years of filling master cylinders everyday I’ve never spilled on a fender by simply being careful.

so this is a question to all who are using dot 5
who's/ what brand master cylinder are you using?

Not entirely sure... Its most likely a rebuild from A-1 Cardone... But it could have been a "new" raybestos (I was working at an autoparts store at the time, and thats what they sold)...

BUT, its been on the car for 11+ years (with DOT5 ALL that time!!!)... NEVER had a problem... Car is driven infrequently (maybe 7000 miles total in those 11 years) and often sits for 6+ months at a time... I have bled the sytem several times (when changing the rearend, added an adjustable prop valve, etc), but otherwise, the master and front calipers haven't been off the car at all, not even for a pad change, etc...

When it comes out of "storage" for a drive, I always check the fluid level, and always full...

"Inevitable introduction of moisure into the system"... How does this happen? I am in California, but very close to the Delta (higher humidity, lots of fog, etc) where the car has been for 6 years in a standard attached garage (non heated, not totally sealed), car spent two years in the Bay Area/peninsula in a car port and another year in San Luis Obispo (also near the ocean, and in a regular detached garage), so not exactly a "dry" climate... I guess maybe if I pulled the calipers apart, maybe I'd see signs of water/rust, but as of now, no leakage...



I did have a brake problem the last time I drove it. The left rear locked up very easily, but only while braking (no noticable drag)... The front discs were still stopping fine... Maybe that "lockup was cause by the fluid, or maybe something with the drums or adjustment, haven't checked it out yet...

Apparently I have gotten some bad information in the past. I was told that Dot 5 was the one that wouldn't absorb moisture and was the best. Apparently you can't always trust people who say they know cars. I will more than likely be switching to Dot 3 or 4

Apparently I have gotten some bad information in the past. I was told that Dot 5 was the one that wouldn't absorb moisture and was the best.

It doesn't, and as Dennis said, that could be the very problem. I believe this is why some racers use it, as you won't risk vaporlock if there's moisture in the fluid and the brakes run hot. On the other hand, if you're that serious about your brakes, you'll probably change fluid more often than you do in a driver so I can't really see a point in this.

But I'm also wondering how moisture could enter the system and if there's any way to prevent this. The only way I can see for moisure to get in there is when you open the reservoir.

Ahh I see since it doesn't absorb the water it just settles ok I see what Dennis was saying now.

I have been using it since 99 and have never had a problem.

Just my .02 and experience with DOT5: Years ago I was having problems with one or the other of my Chevelle calipers freezing-up every spring after hibernating for the winter. I finally converted to DOT 5. I cleaned the entire system, including disassembly of the master cylinder, thorough cleaning with brake parts cleaner, and a light honing with silicone fluid on the honing stones. I also soaked the seals with silicone and reassembled. I used the same procedure on the calipers and rear wheel cylinders. That was 1989, and I've had zero brake problems since then. When I picked-up my other Chevelle in 1995, I also converted it to silicone fluid and have not had any problems at all.

I built my 67 last year and installed a new master cylinder from Master Power along with the booster. Every thing was new with disk up front. Use DOT 5 silicone and have driven 17,000 miles since last Aug. 05. including the trip to Seattle on the Chevelles Across America cruiz. No problems.

To all of you "never had a problem" guys, have any of you opened the system for any reason since converting and how many are daily drivers being exposed to the cruel elements?

I never even opened my system and I still had problems. I called the tech support for the master cylinder and they said it was compatible. However, I completely understand what you are saying Dennis about the water settling in the system it makes perfect sense. I plan on changing over.

supposedly along wtih the things dennis said, Dot5 also won't bleed alll the way, no matter what you do there will always be some amount of air in it. THis causes a mushy pedal that is known for dot5 use. The one thing that 3/4 will do is take paint off of your booster, and frame if it is painted.

Another thing, that I might be wrong on, but I believe dot5 doesn't have as high of a boiling point as GOOD Dot4 like motul or superblue.

I think most people think, well hey its syntethic(all brake fluid is) and that if dot 4 is good, then dot5 must be even better

To all of you "never had a problem" guys, have any of you opened the system for any reason since converting and how many are daily drivers being exposed to the cruel elements?

I haven't really "opened" much of the system, but I have bled the rear brakes several times (I have removed the rearend from the car several times, and found it easier to disconnectthe brake lines/rebleed than pull the axles and backing plates). I pull the lid off the master cylinder several times a year, just to be sure the fluid is full. While not a daily driver, its just stored in a typical garage... Has not lost any fluid from leaks, and pedal always feels fine...

I also will ONLY use fluid from a freshly opened bottle. I buy a new bottle when I know I am going to bleed the brakes. While that previously opened bottle does sit on the shelf in my garage "in case" I need to top it off someday, I haven't had to use the "old" DOT5... Once I buy a new bottle, the old one gets tossed, no matter how much is left.

It doesn't, and as Dennis said, that could be the very problem.
But I'm also wondering how moisture could enter the system and if there's any way to prevent this. The only way I can see for moisure to get in there is when you open the reservoir.

I wonder if the "moisture" in the fluid is more of an extreme case, or maybe "theoretical" postulating (like Aluminum versus iron cylinder heads, etc)... Does DOT5 cause problems in "most" cars/situations, or is it just the random case that can't be entirely attributed to DOT5 (maybe some other contamination issue)? Maybe those that have had problems with DOT5, the problems could have been caused partially due to some other source? Maybe those "problems" could be attributed to contamination from other fluids/sources.

I also would question how alot of moisture gets into the system. Granted, I don't live in an ultra-high humidity location, but even so, I rarely have the master cylinder cap off for more than a minute or two... Can't see too much moisture getting in...



Dennis, since you work mostly with OEMs (assumption, you do/did work for a dealership, correct?), and OEMs don't use DOT5, how many vehicles have you seen with DOT5-related problems. You might see a higher rate of problems, because if there wasn't a problem, people might not be bringing the car in... And how many problems that you are sure are due to DOT5 directly, and not some other problem (maybe cross-contamination from incompatible fluids, etc)?

Why does the "water" go to the cylinders/calipers? Wouldn't the water settle in the brake lines? For example, in a Chevelle, the rear brake line on the frame is often lower than the rear cylinders, plus the water would have to rise up several inches to reach the frame mount flex hose above the rear axle... same goes for the passenger-front wheel, any fluid that settles to the lowest spot would settle in the brake line under the engine... I can't see where the volume of fluid being pushed through the line would cause the moisture to travel to the wheel cylinders if separated from the fluid...

Honestly, just looking for a little education because I tend to sometimes think too theoretical, and I know this is alot closer to your field than it is for me...

I thought I had heard (in the past, its been years) master/wheel cylinder bores rusting with DOT3/4 fluid (maybe when the car sits and isn't used much)...

I thought I had heard (in the past, its been years) master/wheel cylinder bores rusting with DOT3/4 fluid (maybe when the car sits and isn't used much)...

I had a problem with the calipers on my -71 Camaro. This was pretty much a daily driver during the summer, and sat in a heated garage during the winter. It was sitting outside and driven on a daily basis in the summer, exposed to the elements. I had the car for maybe 6-7 years, and had to rebuild the calipers three times due to the pistons sticking in (rusted) bores. Each time I rebuilt them, I cleaned the bores thoroughly, replaced pistons and seals and changed the fluid (Black Arrow DOT3). After a couple of years, the calipers would stick again and I would find rusty sludge inside when I took them apart.

I really don't know how I could get enough water in the fluid to cause such a problem, especially since the fluid doesn't really circulate in the system, it just moves back and forth a bit. However, I would think that moisture can migrate in a hygroscopic fluid like DOT3. Funny thing is that I never had a problem with the master cylinder.

When I installed disc brakes on my -69 Chevelle though, I didn't find much damage. There was some rust accumulated in the rear brake cylinders, right where the lines connect. There was also a lot of sludge in the reservoir. Not bad at all, considering that it's a 35 years old car, and that it had never been parked in a garage. The climate here is quite humid too.

Responding to Dennis68 comment: My hardtop is not driven much at all ONLY when it's really nice out. However I take the convertible out frequently in the good weather, but have an uncanny ability to get caught in the rain a bunch of times with it.

We tried it in all of our ground equipment when I was at Delta. It caused nothing but problems, even when all the components were new and all the lines had been flushed and blown dry. We had a lot of brake problems. Switching back to Dot 3 cured 99% of the problems.

How many? I have actually seen maybe 4 or 5, all exactly the same problem and caused by exactly the same thing, water. Harley Davidson experimented with DOT5 and pulled it for that reason as well. The water will always settle to the lowest points in the system; caliper bores, wheel cylinder bores, and the bottom of the master cylinder. Do a search for DOT5, you will find lots of reading regarding problems with DOT5. Like everything else, the few that get lucky will assume everyone else is doing something wrong. It's not a few isolated examples of problems but a few isolated examples of success. You would be suprised how much moisture a "sealed" enviornment is exposed to.

I didn't even touch on the problems of running it in a performance enviornment as Cody did; that has been a huge topic of discussion among the regualr O/T crowd over the years.

This is my experience with silicone brake fluid in the 73 vette I used to own which i sold two years ago:

I was experiencing some strange braking situations where the brakes would pull to the right, and then to the left all in the same instance. I then noticed some fluid on the inner sidewalls of the front tires from the calipers leaking. Then I was told by a co-worker that he read an article in a car magazine that stated that silicone brake fluid is good for cars that are stored long periods of time w/out being driven much because the silicone keeps moisture out of the lines, but that the silicone fluid is bad for cars that get driven routinely, because it's so slippery that it squeezes by seals and finds leaks.

I was very skeptical about that theory, but I then bought a gallon of dot 3 fluid, and evacuated all the silicone fluid out of the master cylinder with a wet vac, filled it with the DOT 3 stuff, and proceeded to bleed the snot out of the lines until I was assured that there wouldn't be any residue of the silicone left anywhere (it took alot of bleeding since they don't mix very well).

Well, in the following weeks after that, I learned that not only did all the leaks stop, but I no longer felt the brakes pulling to one side and then to the other like they were with that silicone garbage. The fact is that the silicone fluid was actually getting on the rotors, and that made for a dangerous situation when I hit the brake pedal!! So as for me, I'll never use silicone brake fluid again. I think that it's only good for cars that get stored for years w/out being driven, and personally I drive all of my cars. I don't rope them off to be museum pieces.

To all of you "never had a problem" guys, have any of you opened the system for any reason since converting and how many are daily drivers being exposed to the cruel elements?

Thats probably it. I dont drive this car every day. It doesnt get in the cold weather. But I have been through several rain showers with it. After all is said and done. I really didnt need to go with DOT5 in the first place. DOT 3 or 4 would have probably done just fine for me too. My case is quite similair to 66L78.

As for having a low brake pedal, my pedal has been solid since the day I bled the system when I put everything together with all new parts. I found out the DOT 5 problems a few years after I switched. Many folks here on TC were running it and not having any problems when I was doing my entire system so I switched. If it becomes any sort of a problem I will switch back to 3 or 4.