Why do I need DOT 5 brake fluid in my Deuce 1/2 ?

[Valley Rock]

Why ?

I'm sure this has been covered, abstractly, several times over the last 20 years, so if you know why, can you break it down for me, please ?

Because I'm not convinced .

 

[87cr250r]

If you can get all of the old fluid out you can convert to standard fluids.

 

[WillWagner]

^^ What he says. I needed to do a MC when I first got my truck and just converted it to DOT3. Never looked back, no brake isues ever, well except an air pak! But it left me with 3 in it and as far as I know, still going.

If I remember, it was used because DOT5 is silicone and will not absorb water, think fording , and doesn't bother paint. Like it matters, nothing hurts CARC! Dot 3 and 4 absorb water, 4 more than 3, so that can cause corrosion issues on the internals of the system. The rubber pieces parts are the same in any of the systems. One flavor or another won't hurt the rubber parts.....unless they are Chi-Com!

3 and 4 are WAY cheaper and can be found everywhere, 5, not so much.

 

[WillWagner]

Here is a link to a post that explains the differences between the different fluids,

DOT3/4 vs DOT5 - Solicone vs. Glykol based brake fluid

Moin together Short history. My M1123 is from Barstow and was overhauled in 2009. After that it was in the desert and I got it with 2'000mi. For the TÜV a brake force regulator had to go in. The rear axle had over braked too much. Now the good man, who mechanically delivered a clean...

www.steelsoldiers.com

 

[NDT]

If you drive your truck daily/weekly and do fluid flushes every few years, DOT 3 will serve you fine. If you don’t drive often and don’t flush, the brake hydraulic components will turn into a rusted mess. Silicone DOT 5 eliminates this problem. I redid my M38A1 Jeep with silicone fluid in 1981 and haven’t had any issues at all. Try that with DOT 3.

 

[Mullaney]

Why ?

I'm sure this has been covered, abstractly, several times over the last 20 years, so if you know why, can you break it down for me, please ?

Because I'm not convinced .

.
Like @87cr250r said (just above) you can use any DOT brake fluid that you want to use. Naturally, DOT 3 is a lot less expensive. DOT 5 is "better" if you run through water. DOT 3 worked for YEARS

Just Don't mix them (DOT 3 and DOT 5)

 

[oddshot]

DOT 5 is expensive and getting hard to find, at least in north Georgia. The last time I bought any I had to order it from one of the outfits who sell military vehicle parts.

 

[cwc]

NAPA stores usually have DOT 5 on the shelf

Sent from my motorola one 5G UW ace using Tapatalk

 

[VPed]

To be crystal clear, either type will work but 5 is incompatible with 3 or 4. This means your system needs to be cleaned of all old fluid before introducing different fluid.

 

[marchplumber]

DOT 5 is also available online.................like just about everything else.............

 

[Tow4]

DOT 5 is what causes the rust problems. Since it does not absorb water, the water that gets into the system, settles to the bottom of wheel cylinders, master cylinder, etc. No amount of bleeding will remove it because the bleed screw is at the top of the wheel cylinder and water is heavier than brake fluid.

I bought my M35A2 from GL and picked it up at Ft. Jackson. It had DOT 5 in it. When I got home and went through the brakes, every wheel cylinder was corroded beyond repair and several were leaking. The metal lines were rusted out too so I replaced them also. I switch it over to DOT 3 after replacing the entire brake system.

The simple fact is, with DOT 3, the water is suspended in the fluid. When you flush the system and change the fluid periodically as you should, the contaminates (water) go out with the fluid. With DOT 5, the contaminates stay where they are, because they are not suspended in the fluid, they are sitting at the bottom.

 

[oddshot]

To be crystal clear, either type will work but 5 is incompatible with 3 or 4. This means your system needs to be cleaned of all old fluid before introducing different fluid.

During my time as a mechanic, I have never done this. What liquid would be used to flush the DOT 5 out the system? Eeazy Peazy with a power bleeder.

 

[Adrok]

I've flushed the system prior to disassembly and work.

Tapped and installed a bleeder in the bottom of the master cylinder. No problems yet. But once water is in the lines and down stream.....your going to have a challenge.

Post #5, 87cr250r suggests the addition of silicone based vacuum pump oil ( density HEAVIER than water ) as a method to purge water from the system.
I have not tried it (YET) but I like it.

DOT 5 water contamination

I recently had my M116A3 trailer inspected (PA requires this every year), and it passed. I then took the trailer on a 600 mile trip the next day, half of which was in a severe rain storm. Today while walking by the trailer, I noticed the master cylinder appeared “wet” with silicone based DOT 5...

www.steelsoldiers.com

The solvent flush I used on the system before work and repair.

Amazon.com

 

[m1010plowboy]

We found a split, lower brake line on a deuce the PO converted from Dot 3 to Dot 5. Being in Canada with freeze thaw cycles, we likely create more internal condensation.....like the inside of a buried sea can...... and need to flush more. The Mattech figures the water can gather at a low spot and with enough....lack of PMS..... hang out at a low line. Ignoring PMS is the worst thing we can do to internal parts. Regular flushing is part of PMS Preventative Maintenance System

It's interesting because the fluid isn't 'traveling' through the system but somehow water appears to eventually gather at a party spot. Goose the deuce was juiced with Dot 3 in 2012 and here we are, April, 2024, still freezing.

 

[87cr250r]

I just rebuilt the front calipers on my M1008. They had a waterline just below the midpoint, they were nearly half full of water. Luckily the bores are hard chromed and the pistons are stainless steel so corrosion was minimal. I put DOT 5 back in because I didn't really want to get into the rear brakes. There are certainly disadvantages to DOT 5.

 

[marchplumber]

I just rebuilt the front calipers on my M1008. They had a waterline just below the midpoint, they were nearly half full of water. Luckily the bores are hard chromed and the pistons are stainless steel so corrosion was minimal. I put DOT 5 back in because I didn't really want to get into the rear brakes. There are certainly disadvantages to DOT 5.

Thats good info.....thanks for sharing! Definitely a cause for possible concern.....i wonder where it "drew" that amount of water from? Any ideas?

 

[msgjd]

while we're on this topic, how does one determine which DOT number is already in a truck? I don't notice any difference in color, smell, or texture , but that could be just my age .. No I'm not gonna taste it or put my ear to it !

On one of my gov't-direct trucks without "silicone only" decal ,, I added DOT3 and it instantly separated. . It apparently was DOT5

 

[ODAddict]

Great info here, especially regards DOT 5.

As referenced above, the DOT 3 and 4 brake fluids are hygroscopic, i.e. they absorb moisture from the atmosphere. So, over time, water may intrude the brake system simply by removing the master cylinder cap to check the level. Or slightly worn boots or seals also may provide a path for moisture. either from the atmosphere or water splashing around on a rainy day. Or condensation formed in lines or areas that may have small voids.

As to DOT 5 (there apparently also is a DOT 5.1 available with which I am unfamiliar), the silicone-based fluid will not absorb moisture. But the problems of moisture intrusion over time remain. Difference now is where it ends up.

Now, where did I put my free lunch?

 

[HDN]

while we're on this topic, how does one determine which DOT number is already in a truck? I don't notice any difference in color, smell, or texture , but that could be just my age .. No I'm not gonna taste it or put my ear to it !

On one of my gov't-direct trucks without "silicone only" decal ,, I added DOT3 and it instantly separated. . It apparently was DOT5

Take some fluid out of the truck and put it in a jar of water and mix it around. If stuff isn't mixing, it's DOT5 because silicone doesn't mix with water.

 

[msgjd]

Take some fluid out of the truck and put it in a jar of water and mix it around. If stuff isn't mixing, it's DOT5 because silicone doesn't mix with water.

I was hoping I wouldn't have to do something that simple .. It would make me invest in an eyedropper and ruin my reputation as a tightwad !