DOT 5 does not retain moisture suspended in it's molecular construction like DOT 3. So the moisture goes directly to the low spots and corrodes things quickly.
DOT 5 traps air molecules and prevents a real quality bleeding.
DOT 5 doesn't tolerate heat well. I think your Exhaust is about 8" away.
I like new stuff just as much as the next guy but I read up on it too. I feel like if you bleed the brakes and replace the fluid every 2 years you are better off than with silicon.
I read where the dirt bike crowd do not like it and they usually go for anything that gives them an edge.
Corvette tried it in the late 70's early 80's for a year or two and got smart.
The dirt bikers (I used to be one) have two problems, a lot of water exposure and for the disc brake models a lot of heat buildup in the caliper. Both excellant reasons to leave the novelty DOT 5 to the crazies.
After rebuilding the whole brakesystem, i filled it with DOT4.
There is told to me to drive the jeep regulary to keep the brakesystem in order, change the fluid every year ot two years.
Dot 5 is absorbs no water, and you need not much water to get corrosion at all the iron brake cylinders !
1942 GPW 71336 my son's jeep restored now
1951 M38 MC11891
1953 VW beetle (genuine german Käfer )
1957 fantastic wife
This is exactly why DOT 5 is a problem. Since it doesn't absorb water the water drains to all the low points and immediately starts a corrosion problem. DOT 3 has a tendency to absorb the moisture and this delays the deposit of plain water at the low points.
DOT 4 offers the best compromise of both DOT 3 and 5.
I am the enemy. I use Silicone fluid.
My practical experience: After rebuilding my GPW brakes back in the early 80's and filling with Castrol LMA I thought I was all set. Within a few years there were problems due to moisture. The jeep was stored in a damp but not wet garage. The fluid had sucked up tremendous amounts of water from the air. When I tore the brake system apart 10 years after rebuild all wheel cylinders were rusted and the MC was junk. Another total rebuild followed, lines, hoses, WC's and MC's. In 1998 I filled it with Silicone. This past spring I put a light down into the MC and it is as clean as it was new.
The right thing to do is change the fluid. I will admit it has not been done regularly. Next spring. I keep the jeep in a much dryer place than it had been back in the 80's now too. So far its all looking good.
I also run silicone in a plastic Chevy for the past 10 years. The disc brake systems in those were horrors for moisture intrusion for a number of reasons. The calipers have now been converted to stainless sleeves with o-rings on the pistons. I did take them apart 2 winters ago to inspect them and drained as much fluid from the system as I blast out. There wasn' any evidence of water in the system either due to damage or drops in the fluid that I could detect. I suspect because silicone doesn't accept water vapor as readily as DOT3 that much of the future water problems would come from rain driving, washing etc. Whereas, it seems that even the LMA DOT3 sucks up quite a bit of water via vapor. Later cars with ABS cannot run silicone.
The following qualifiers apply. Neither vehicle sees rain or winter duty - almost never. They don't get washed much either. Moisture problems would be from air/water vapor. I'm only guessing but thats probably the source for most brake system moisture issues anyway.
If you are going to a high altitude from low you will need to pay additional attention to bleeding your silicone equipped brake system. It is a bit of a job to bleed these.
I have had excellent service from silicone in these cars that don't get a whole lot of road use and would do it again.
Similarly my 89 blazer has DOT 3 fluid and I have never had to change a line. I have changed the rubber hoses, wheel cylinders and calipers a couple times in the past 250k miles. The MC is original.
Sorry Ryan, no answer to this one. Its your decision and certainly there is a lot of experience pro and con out ther. But I have used the dreaded, evil silicone and it has served me well. There is a reasonably good chance that I will use it in my M38 when I get to putting the brake system back in.
fire away...this one always leads to a lively debate.
Maybe we can change the topic to paint colors......
Hello Tom,
No firing today. To each his own. Obviously your 10 year layover on the DOT 3 was at fault since it should have been flushed and serviced every two years.
I won't waste my dime on silicon. That's my choice. I definately wouln't use it where it was exposed to high temps like big disc brakes.
The military fairs well with it because they are a religeous fleet operator. That is to say they over maintain their fleet with all the extra manpower and stateside spare time.
I've owned various oldies for longer than 20 years and the only rusty master cylinders I get are on the new ones to the roost right when I purchase them and bring them home.
No doubt on my fault. That Jeep sat 10 years as life caught up with me and it suffered a bit.
Here's another way to look at this because whenever ithis topic comes up it gets me to thinking.
If this were a daily driver in all weather or a jeep that I were trail riding and fording rivers I would tend to go the traditional way - stay away from silicone and change your DOT 3 frequently.
But, I cant help thinking a vehicle that sits for a long time might do well with silicone. The tendency of the fluid to act as a spoge, like DOT 3 does, is the only means for moisture to get into the system. The moisture content or puddling in low spots might be minimized or zero for these Sunday drivers.
Disc brakes - Dot 5 has a boiling point at 550 deg F. DOT3 has a boiling point around 300 deg F. so heat tolerance is reasonable except heavy braking like racing. Is it the air pumping from disc brakes that would make someone shy away from using it with Discs?
The heat problem is related to the difficulty expunging all air from the silicon when bleeding. The trapped molecules of air expand rapidly with the heat and the pedal will suddenly become a bit more spongy then it usually is. I also believe DOT 5 expands quicker and a little more than DOT 3 when heated.
I'm a dollar and sense guy. Both fluids come with a routine periodic flush recommendation from their manufacturers. The DOT 5 is 3 to 5 times more expensive then the DOT 3.
The only trait of DOT 5 that I like is it's friendly to paint. But with an older vehicle with the master cylinder under the floor who cares!
