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DOT 5 Brake Fluid???


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I'm looking for some opinions-

I have a tired '61 Olds Ninety Eight convertible project. I'm in the midst of going through the entire brake system. It's almost totally shot, so every component will be either new or rebuilt.

Since I'll be starting with a new & empty system, I'm considering using DOT 5 fluid. I used it once before with excellent results, but I'd still like to hear some thoughts & experiences of others.

Thanks!

Chuck

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Guest pfloro

Hello Chuck:

Echoing Joe, DOT 5 has been in our '66 Mustang for 6 years. It's been completely trouble free. <span style="font-weight: bold">ALL</span> the hydraulic brake components were new

before DOT 5 went in so there was no risk of contamination... The Mustang

was driven with DOT 5 in below freezing weather back east & now in 100+

temps in Arizona. I've never had to add a drop either.

I recommend it...

Paul

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I echo the replacement of rubber parts before converting to DOT5, but I will admit that in my young and stupid days, I simply drained the DOT3 out of a 71 Cutlass and filled it with DOT5. The brakes worked fine for about 10 years (though this was not a daily driver) and I never did need to add any fluid.

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Guest Dave Wyatt

I put DOT 5 in my 4-4-2, back in 1984, and the brakes are still working fine. I have added a little fluid over the years, but very little.

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  • 1 year later...

I've used DOT 5 for several years. The only problem was the failure of the brake light switch. I keep a few extra switches on hand. I've only replaced the switch in my Ford once in 10 years. I've never had to add fluid. No leaks have ever occurred.

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The drawback is that at high altitudes, it gets mushy on you. I have noticed this effect when we go over 10-13K feet passes in Colorado. It isn't really bad, but it is noticeable when we drove our 1963 Cutlass Conv to the show in Denver.

As soon as we where down the hill you sould feel it get harder again....

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  • 3 weeks later...

Question,

If I wanted to convert to DOT 5 what would I have to do to purge the system of the old stuff? Will a denatured alcohol or some other chemical be needed to run through the lines first? I understand that if the 2 different types come in contact with each other it can turn to sludge???

Thanks

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  • 1 month later...
Guest rocketguy

I have four wheel disc on my 442 and have used .5 for 12 years with no problems. It was basically a new system when I installed it though, and I would reccomend purging yours with something to rinse out the dot 3 if you do use dot 5. Dot 3 and .5 are not compatable liquids and will coagulate if put together.

The thing I 've read about .5 is that it does not absorb moisture. Therefore .5 will allow H2O to be a separate liquid in your brake system. If your brakes get REALLY hot, the H2O can then boil, introducing air into the system. This leads to a very undesireable situation. This is probably why OldsmoREO had the situation at high altitude. If you use .3, the H2O is absorbed into the fluid, therfore cannot boil under extreme heat.

Best of luck with your car! ;)

.

Edited by rocketguy (see edit history)
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I have four wheel disc on my 442 and have used .5 for 12 years with no problems. It was basically a new system when I installed it though, and I would reccomend purging yours with something to rinse out the dot 3 if you do use dot 5. Dot 3 and .5 are not compatable liquids and will coagulate if put together.

The thing I 've read about .5 is that it does not absorb moisture. Therefore .5 will allow H2O to be a separate liquid in your brake system. If your brakes get REALLY hot, the H2O can then boil, introducing air into the system. This leads to a very undesireable situation. This is probably why OldsmoREO had the situation at high altitude. If you use .3, the H2O is absorbed into the fluid, therfore cannot boil under extreme heat.

Best of luck with your car! ;)

.

Thank you, but my question is what do I run through first to purge the DOT 3????

Thanks again

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  • 2 months later...

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@ Hurst Olds : To clean your brake lines I would use brake cleaner spray until pure brake cleaner comes out of the lines. Blow out than the lines with water and oil free air. You have to change all the rubber parts in the cylinders and the brake hoses. Than you should be sure to use a 100 % DOT 5 brake system.

I still use DOT 3 or 4 in my cars and all 2 years I change the brake fluid. It is important after rebuilding brake cylinders, to use a brake cylinder paste when installing the new rubbers and pistons to avoid rust in the cylinders. And you should also press down the brake pedal several times, once or twice a month when your are not driving the car.

Tom

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  • 4 weeks later...

So what happens to the small rubber brake lines or if there is a little residue from the DOT3 when the DOT 5 is introduced? Does it sludge up really? To Joe Padavano, did you notice any problems with sludging when you didn't change out the lines on the 71? I want to use 5 on my Toro. Every last part is new but DOT3 was put in about a year ago although the car has not been used as I'm still restoring it. I was hoping to just force out the 3 with air and bleed out a DOT 5 chaser.

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  • 1 year later...
Guest dennis g

After putting it in my 65 mustang 30 years ago the requirement for brake system work stopped. I also have a jeep that has had it in for 36 years no problems for either of them.

If you put it in a system which has had conventional brake fluid in it the old fluid has to be drained, flushed with alcohol and dried out. Then you add the dot5.

I did have a system in a motorcycle "jelly" but it was my fault for not getting out all of the old dot 4.

I use the old lines, just get them clean. Really clean.

The pedal feel will not be as hard for dot5.

Dot3 or 4 or 5.1 has one advantage: when you flush the system, water is removed. Of course the disadvantage is that it must be flushed regularly and if it is not it corrodes, badly. With dot 5 it will probably never corrode so for a vehicle which is infrequently used, dot 5 is the brake fluid of choice.

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Dot3 or 4 or 5.1 has one advantage: when you flush the system, water is removed. Of course the disadvantage is that it must be flushed regularly and if it is not it corrodes, badly. With dot 5 it will probably never corrode so for a vehicle which is infrequently used, dot 5 is the brake fluid of choice.

-------------------------------------------------------------------

Just a small word of advise on the dot 3 or 3/4. The complete flush every two years ( I do once a year ) is very important. People get into more problems if they wait say five years, than if they never changed fluid until a leak. The reason is after five years all this moisture and crud builds up in the portion of the master cylinder where the piston dosen't normally travel. When you bleed the system and push the pedal to the floor it pushes the cup/cups on the piston right through all this crud and cuts them up and now you've got a master cylinder problem. If you don't know how long it's been since it was last done look at the color of the fluid. Dot 3 or 3/4 will turn golden in about two years, then light brown, and finally dark brown. I would not attempt a flush on a system with any brown colored brake fluid unless I rebuilt the hydraulic system.

Don

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  • 2 months later...
Guest dstaton

I concur with OLDSMOREO. I ran a 67 Vette with a Powerglide with DOT 5 over Engineer Pass and, yeah, went really fast leeside. Harrowing memory.

Doug

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  • 1 month later...

Robsf37-

Looks like you're already registered with your own title, so here's how. Open the Forums main page and select which forum you want to post in. When the Forum opens up, you'll see a button at the top left of the page that says "New Thread" right above the "Threads in Forum". That button will open the forum for your new post.

Good luck and welcome.

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  • 4 years later...

Living in a humid environment, I've used DOT-5 in several of our cars, but only after a complete rebuild. DOT-5 is less hygroscopic than DOT-3 so you will not have the eventual rust problems.

 

First flush solid lines with denatured alcohol, and allow them to AIR-DRY naturally. Then replace all flex hoses and wheel cylinders and master cylinder. Fill with DOT-5 and bleed the system. Carry spare with you, but you'll likely never need it. At least that is my experience.

 

Good luck!

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  • 3 years later...

As noted above DOT 3 & 4 will absorb moisture....the moisture not only rust and corrodes parts in the brake system, but the moisture lowers the boiling point of the brake fluid.

pretty sure 2% moisture lowers the boiling point 100 degrees (F)  this can be critical if you live in hilly or mountainous country.........what you think is brake fade is actually the fluid boiling.

There are test strips available that will show you the moisture content.

DOT 5 does not absorb moisture,  but if you live in a humid area, condensation can form and moisture can get into the system....the moisture is not absorbed by DOT 5,  so it is likely to puddle in low areas

giving the risk of rusting only in those areas.

DOT 5 is not recommended for brake systems with ABS....the fast cycling of the antilock valves can create air bubbles in the fluid.

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On 9/7/2015 at 1:05 AM, JFranklin said:

Flush the lines with denatured alcohol. I used a livestock syringe with lines in place, then air.

 

I was advised to allow lines to dry naturally, and to allow alcahol to evaporate naturally, not with compressed air, as it can contain moisture -

then use DOT-5 which is synthetic, and cannot be mixed with either Dot-3 or Dot-4

 

Dot-3 and Dot-4 may be mixed with each other when necessary, but Dot-4 is the better, if slightly more expensive alternative, since it is less hygroscopic, less absorbent of water.

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