Dot 3 or Dot 5

[2deuce]

I had to replace the brake booster on my new to me truck and I caught the fluid in a plastic bottle when I disconnected the lines. The color was an amber yellow. The truck does not have any notices saying to use dot 5. I poured some dot 5 into the amber fluid I salvaged in the bottle but it didn't appear to mix by shaking it. It became cloudy and the purple dot 5 seemed to somewhat separate after an hour or so. Is this what happens when dot 3 and 5 are mixed? I haven't poured anything into the MC yet. I'm thinking I should use dot 3. I wish I saved some of the salvaged brake fluid, to test how dot 3 mixes, but I expected I had dot 5. I have seen dot 5 loose it's purple color over time. Anyone have any recommendations?

Thanks

 

[MT4222]

Yes that is dot 3 and 5 mixed together. Just use dot 3 in your truck. Just to be shure i would siphon some of your existing fluid and mix it with some new dot 3 and look to see if they seperate.

 

[porkysplace]

Brake fluid -how to tell which kind you have DOT3 or DOT5

If you mix DOT 5 and DOT 3 it will gel up and cause you all kinds of problems

Mixing Brake Fluids
Changing from DOT 3 to DOT 5
DOT 3 vs. DOT 5
Dot3,4,5, why
switching from DOT 5 to DOT 4 brake fluid​

 

[welldigger]

Dot 5 turns amber very soon after being added to the system. DO NOT add dot 3 until you are sure what is in your truck. Dot 3 and dot 5 combined will gel and possibly cause brake failure. More than likely you have dot 5. But siphon some out and add some dot 3 and see what happens.

 

[2deuce]

I wish I could siphon some out, but the MC is dry after changing the booster. If the salvaged fluid that I added dot 5 to gels, should I then be confident that what is in the truck is dot 3? How long does it take to gel when 3 and 5 are mixed? I did not add much dot 5 to the salvaged bottle of fluid. I certainly fouled up by not saving some of the fluid so I could test it with dot 3. I was certain that dot 5 was in there. Now I think not. Thanks Porkysplace for the links.

Greg

 

[welldigger]

If you haven't already build a pressure bleeder. There's a thread about it in the stickies. Well worth the 40 or so dollars to have one. Then once you have your pressure bleeder hook it up empty to the master cylinder. Pressurize the brake system and salvage some fluid from a wheel cylinder. Then test fluid.

 

[porkysplace]

If you haven't already build a pressure bleeder. There's a thread about it in the stickies. Well worth the 40 or so dollars to have one. Then once you have your pressure bleeder hook it up empty to the master cylinder. Pressurize the brake system and salvage some fluid from a wheel cylinder. Then test fluid.

Sticky: Deuce Power Bleeder R4x4 Style

 

[welldigger]

O and simple test for brake fluid is pour some brake fluid into an empty water bottle. Then add some water and shake. If you have dot 5 it will separate out and float on top after a while. If you have dot 3 or 4 then they won't separate since dot 3 and 4 absorb water.

 

[doghead]

Where did you buy your truck from? If it was a government purchase, 99% bet it is dot5.

I've seen the dot 5 label on the door,dash,under the hood, under the floor door, on the trans tunnel...

 

[bigmike]

Some may not like this suggestion but here goes.

I just replaced my M.C. on the M543A2 the fluid was questionable about whether it was DOT 3 or DOT 5. After replacing the M.C., I hooked up my power bleeder and bled the system thru all the wheels and lines and flushed the system with a gallon of DOT 5 fluid to insure it bled purple for many minutes. Now I know what I have and have fully bled my system. My theory is "if you don't know what it is, flush the entire system with fresh fluid to eliminate any questions". I've done this with other M35s with no issues at all. DOT 5 is not cheap but I concider it good insurance.

 

[glcaines]

Some may not like this suggestion but here goes.

I just replaced my M.C. on the M543A2 the fluid was questionable about whether it was DOT 3 or DOT 5. After replacing the M.C., I hooked up my power bleeder and bled the system thru all the wheels and lines and flushed the system with a gallon of DOT 5 fluid to insure it bled purple for many minutes. Now I know what I have and have fully bled my system. My theory is "if you don't know what it is, flush the entire system with fresh fluid to eliminate any questions". I've done this with other M35s with no issues at all. DOT 5 is not cheap but I concider it good insurance.

Your suggestion has a lot of merit. DOT 5 is expensive in parts stores, but if one looks around, NOS DOT 5 can be found for a reasonble price. DOT 5 is far superior to DOT 3.

 

[2deuce]

The truck was in civilian hands for a long time. He said it was used in hollywood, who knows maybe it was, but it is looking very rough right now.

What is a reasonable price for dot 5?

There might be a small amount of fluid left in the old booster. I'll check.

I was hoping that if I bled the booster I might not need to bleed each wheel cylinder, but I have no experience with this.

 

[welldigger]

Dot 5 can be found at Napa for around 35 bucks for 32oz. If you had to bleed the air pak then yes you must bleed each wheel also. This way you get fresh clean fluid to each wheel and get the air out. Start at the furthest away wheel from the Mc. This would be the rear passenger side wheel. Then go to driver side rear wheel. Then passenger side middle wheel. Continue pattern all the way to the front.

 

[VPed]

Carquests around here have DOT5 for about $25/qt.

 

[Rustygears]

There are vendors sponsoring this site that sell mil DOT5 for around $65 a gallon. Others have had it on occasion cheaper. Check the vendors section and patronize the sponsors.

 

[glcaines]

The last I bought was$25.00 per gallon, but he vendor is now out. I should have bought more.

 

[rustystud]

You do NOT want to go to DOT 3 fluid ! DOT 5 is far superior to any alcohol based brake fluids. First , it repels water, meaning it will not absorb it and carry the water through-out your system, rusting your brake lines from the inside out. (Ask me how I know about rusting brake lines ! ). Second, it actually lubricates the seals in your system ! That is way you have 30 year plus old trucks still having working brakes. Have any of you worked on old cars or trucks ? The first thing you almost always have to do is fix the busted up old brake system, usually rusted out. The Europeans have used DOT 5 in there expensive sports cars for years, there is a reason for this. The only reason the modern cars do not have Silicone Brake fluid, beside the price is that the fluid will foam when used in anti-lock brake systems. I have used Silicone brake fluid in all my cars and trucks for over 30 years now, and you can still see to the bottom of the master cylinder in my 1984 Chev 1ton. Nice clear purple fluid. If your going back to use silicone fluid you will have to totally dismantle your brake system. New seals in the master cylinder, new wheel cylinder seals, and all the brake lines cleaned out . Any remaining DOT 3 or 4 fluid will containment your silicone fluid. The third reason to use silicone fluid is you do not have to change it out every 2 years like DOT 3 fluid. In my riggs, once I convert them to silicone I only have to top-off the master cylinder. As long as the fluid remains clear and purple, it's still fine to use.

 

[JasonS]

You do NOT want to go to DOT 3 fluid ! DOT 5 is far superior to any alcohol based brake fluids. First , it repels water, meaning it will not absorb it and carry the water through-out your system, rusting your brake lines from the inside out..

DOT 3 is actually designed to adsorb the water and hold it in suspension. I flush my brakes once a year and have clean brakes. An easy job with a remote reservoir.

I have taken apart brake systems with DOT5, water still gets in there but now you can't get it out.

 

[Tow4]

DOT 3 is actually designed to adsorb the water and hold it in suspension. I flush my brakes once a year and have clean brakes. An easy job with a remote reservoir.

I have taken apart brake systems with DOT5, water still gets in there but now you can't get it out.

Right you are. My M35A2 had Dot5 and all the wheel cylinders were pitted beyond repair. I replaced the wheel cylinders with new ones, pressure flushed the system and used Dot3. Since the bleeder is at the top of the wheel cylinder, the water settles to the bottom with Dot5. Flushing will not remove it. With Dot3, the water is suspended in the fluid and come out when you flush the system.

 

[Rusty nuts]

Best current price I have found for Dot 5 is Amazon, case of 12 - 12oz bottles for $73.58, free 2 day shipping if you are a Prime member. That's over a gallon for fresh new fluid.