Changing from DOT 3 to DOT 5

A friend of mine used my My M35A3 and put DOT 3 brake fluid in it, and didn't tell me. The fluid in the reservoir is looking strange and I want to change it to DOT 5 as it should be. Do I need to completely blow out (with air) the old fluid, or just push the DOT 3 out with the DOT 5? I don't want to screw this up.

If I don't change it right away am I going to cause any damasge?

A friend of mine did this recently on a WWII CCKW. He flushed the drake lines with alcohol before putting the DOT 5 into the system. I don't know what type of alcohol was used, but he bought it at Home Depot.

Complete flushing with the alcohol would be the *best* way, but very costly once you start filling/bleeding it back with DOT 5, as you have to flush the alcohol out as well.

Good luck with the corrective action! I think a huge warning label should be on all the brake fluid reservoirs saying DOT 5 only.

It needs to be cleaned out. You might get lucky that it is only in the master cylinder but most of the time some has migrated throughout the entire brake system. The best solution is a complete brake job and clean or replace everything including the air pack.

These have related info ; Brake fluid -how to tell which kind you have DOT 3 or DOT 5
DOT 3 vs. DOT 5
switching from DOT 5 to DOT 4 brake fluid

I know originally the gov used DOT 5.Depending on the amount the owner drives it why dosent he just flush it (since he has to anyways) and replace with 100% DOT 3? He HAS to do a flush. He might as well save about $80 and do it with DOT 3 unless anyone can think of a reason to stay with DOT 5.

I know, It was made with DOT 5 for a reason. My question is what for? DOT 5 is for High Heat I have been told. But if it's not going into combat, and it's coming out of our wallets... not the GOV... Why bother?

crazywelder72 said:

I know originally the gov used DOT 5.Depending on the amount the owner drives it why dosent he just flush it (since he has to anyways) and replace with 100% DOT 3? He HAS to do a flush. He might as well save about $80 and do it with DOT 3 unless anyone can think of a reason to stay with DOT 5.

I know, It was made with DOT 5 for a reason. My question is what for? DOT 5 is for High Heat I have been told. But if it's not going into combat, and it's coming out of our wallets... not the GOV... Why bother?

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DOT 5 doesnt attract moisture like DOT 3 and should prevent corrosion in the system.

Rubenk said:

DOT 5 doesnt attract moisture like DOT 3 and should prevent corrosion in the system.

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Oh, I didn't know that.. see good question gets a good answer.
Thanks..

You may, or may not, find this interesting.

That was cool... Simple to read and understand. Basically what i took from it in short is the Dot 5 silicone that repels moisture is mostly due to the storage of the vehicles.

The long and short of it is that DOT3 and DOT5 are incompatible. They clump and gel when in contact with each other. You need to flush the system but good. Thoroughly. With rigor. You get the point.

If there is a smidge of DOT3 left behind, getting pushed further and further downstream, it could cause the sort of problems you do not want to have in a 13,000 pound vehicle with a single circuit system.

Unfortunately, the clotting you can see is probably the tip of the iceberg. I feel for you as even though the flushing process itself is straightforward, in practice doing it properly on a Deuce is a great deal of work.

Would I sound like a jacka** if I said I have yet to crack open my master cylinder since I bought the truck in 2010? Its under the cab right?
























































LOL..Just kidding Its on the firewall next to the clutch resevoir (I am totally kidding by the way)

plym49 said:

The long and short of it is that DOT3 and DOT5 are incompatible. They clump and gel when in contact with each other. You need to flush the system but good. Thoroughly. With rigor. You get the point.

If there is a smidge of DOT3 left behind, getting pushed further and further downstream, it could cause the sort of problems you do not want to have in a 13,000 pound vehicle with a single circuit system.

Unfortunately, the clotting you can see is probably the tip of the iceberg. I feel for you as even though the flushing process itself is straightforward, in practice doing it properly on a Deuce is a great deal of work.

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actually you should have your friend that contaminated your fluid help for punishment... that will teach him.

crazywelder72 said:

actually you should have your friend that contaminated your fluid help for punishment... that will teach him.

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I agree...I hate when people fill fluid levels on things that they really dont know what it is....Someone borrowed my old ford tractor and brought it back puking green milky stuff out the bottom. He put hydraulic oil in the tranny because he had remembered I told him the hydro pump was inside the tranny and leaking a little...he didnt ask where the actual resevoir was so I had about 3 gal of hydro in there...it was gross lol. He is helping me with cleaning it out and refilling it..and paying for new GL3 lol...though not as difficult as bleeding brakes on a Deuce....

Happy used of DOT 3 in my deuce.

I bad side effect with using DOT 5 is silcone based and it repels the water and the water collects in the lowest part of the brake system and that is the wheel cylinders !! My opinion is DOT 3 is a better choice not only for the lower cost but it absorbs the water and does not cause as much corrision inside your wheel cylinders and brake system like DOT 5 does . I do not think I would flush the brake system with alchohl because it will dry out the neopreme / rubber parts and cause them to fail long term . I would justflush with DOT 3 and refill with DOT 3. Good Luck .

Not to hijack this but what is the chances that a '83 M35A2 would of had dot 3 in it when it came from surplus. The guy I purchased it from claimed It hadnt been converted to silicone. Well after a day if owning it the brakes went soft. The tranny tunnel says "HB brake fluid only" after only a few minutes of research i had found "all military vehicles use dot 5" so I poured some in without checking and watched it not mix. So I power bled it all out. Is it more likely someone flushed it with dot 3 than it coming that way?

turbo,

If you had read this thread you would have seen the 5th post in it and the link to the following...Brake fluid -how to tell which kind you have DOT 3 or DOT 5

M813A1 said:

I bad side effect with using DOT 5 is silcone based and it repels the water and the water collects in the lowest part of the brake system and that is the wheel cylinders !! My opinion is DOT 3 is a better choice not only for the lower cost but it absorbs the water and does not cause as much corrision inside your wheel cylinders and brake system like DOT 5 does . I do not think I would flush the brake system with alchohl because it will dry out the neopreme / rubber parts and cause them to fail long term . I would justflush with DOT 3 and refill with DOT 3. Good Luck .

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That can be risky as a clot can get lodged in a nook or cranny and work loose later on. Sometimes the clots also just plug the entrance to a wheel cylinder, negating that cylinder from operating properly.

On motorcycles, sometimes an owner makes the same mistake, and tops off their DOT 5 system with DOT 3. SOP in that situation is an all-new everything: master cylinder, brake lines and calipers. And every component of those systems is staring you right in the face! You would think they are easy to flush. But no. The reason is that no shop wants the liability if the bike does not stop some day and the rider goes down. Brake fluid screw-ups can be expensive, indeed.

Also, never shake DOT 5 because it air entrains microscopic bubbles that can make it difficult or impossible to bleed. This is usually more of a problem with smaller systems, like on motorcycles. The usual way of eliminating the bubbles (if you pour in bubbly fluid) is to let the system sit overnight. You can't see these bubles, but they are there. I have watched bike mechanics running through quarts of DOT5 on a system that holds a half pint, wondering why they cannot bleed the system.

Speddmon said:

turbo,

If you had read this thread you would have seen the 5th post in it and the link to the following...Brake fluid -how to tell which kind you have DOT 3 or DOT 5

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This is true. If I would of read this thread before my brakes went out I could of saved myself like $10 bucks! boy a little can of that Dot 5 is expensive. But when I was googleing "deuce brake fluid site:steelsoldiers.com" it didn't seem to show up. Oh well at least I noticed right away and was able to flush it out of the master before it jellied anything. further downstream... I should have my own thread on how to tell... "Pour some kind of brake fluid in there and look down the hole and see if it looks like you dropped a jelly fish in there, if it does its the wrong fluid"

And I think I have decided to fill her up with DOT 4. Its what Ive always ran in everthing Ive owned and the old fluid was clearly an organic fluid I know MV's are ALWAYS diffrent from everything else but Ive never had a corrosion problem. I think with adding a remote resevoir and getting rid of the vent most corrosion problems will be avoided. That vent pulls moisture I'm sure. I would bet if the military would have eliminated that vent they wouldnt have found much diffrence in dot 3 and dot 5