Getting near the end of my 69 Dart 340 engine swat with front disc brakes. Putting in a new master cylinder and flushing the lines. Get a lot of opinions on whether to use Dot 4 or Dot 5 synthetic. Looking for advice/thoughts on what to use. Thanks!
Dot 4 or Dot 5 Brake Fliud?
- Thread starter Rover125
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Kendog 170
Let the boy go !
I've heard synthetic is good for keeping moisture out but IDK.
DOT 4 and DOT 5 fluids are completely different creatures.
Oversimplified, DOT 4 is the "HD" version of DOT 3, and basically it just has a higher boiling point than DOT 3. Both of these are glycol based, and are very hygroscopic.
DOT 5 is silicone based, and has a higher boiling point than either DOT 3 or DOT 4. It's also less hygroscopic than the glycol based fluids, which can be seen as an advantage.
Use whatever you feel is best, but whatever you decide, never mix the glycol based fluids with DOT 5.
Oversimplified, DOT 4 is the "HD" version of DOT 3, and basically it just has a higher boiling point than DOT 3. Both of these are glycol based, and are very hygroscopic.
DOT 5 is silicone based, and has a higher boiling point than either DOT 3 or DOT 4. It's also less hygroscopic than the glycol based fluids, which can be seen as an advantage.
Use whatever you feel is best, but whatever you decide, never mix the glycol based fluids with DOT 5.
DOT 5 does not strip paint like others.
Whatever you do, DO NOT mix DOT 5 with any other.
My DOT 5 conversion has been going strong for almost 10 years.
Just a slight bit of sponginess and a slight bit of additional pedal travel.
Whatever you do, DO NOT mix DOT 5 with any other.
My DOT 5 conversion has been going strong for almost 10 years.
Just a slight bit of sponginess and a slight bit of additional pedal travel.
3rd for DOT 5! I only went there because of paint issues and a pretty car. I do not like wrinkled paint on my master cylinder.
I’m on year 3. But let me tell you my system was ALL brand new on the 66’with the 74’ bbp manual brakes. Stops like a champ and never pedal fade or any issues.
Just make sure you always carry a spare bottle on the shelf of it if you goto dot5. Not all places have it. But then again in 3 years I’ve never need to add any.
Syleng1
I’m on year 3. But let me tell you my system was ALL brand new on the 66’with the 74’ bbp manual brakes. Stops like a champ and never pedal fade or any issues.
Just make sure you always carry a spare bottle on the shelf of it if you goto dot5. Not all places have it. But then again in 3 years I’ve never need to add any.
Syleng1
Jeremiah (jd)
Well-Known Member
I have been using DOT5 for 20+ years without issue.
Things to know:
Not all DOT 5 fluid is of equal quality. As a for instance, parts store brand seems to aerate easily wheras the Cartelbrand we eventually switched to did not.
DOT 5 can crystalize over long periods of downtime. Just like any fluid in you brake system it will need routine maintenance intervals.
The two real benefits of DOT5 are paint protection from spills/leaks and that it's not hydroscopic like DOT3.
Things to know:
Not all DOT 5 fluid is of equal quality. As a for instance, parts store brand seems to aerate easily wheras the Cartelbrand we eventually switched to did not.
DOT 5 can crystalize over long periods of downtime. Just like any fluid in you brake system it will need routine maintenance intervals.
The two real benefits of DOT5 are paint protection from spills/leaks and that it's not hydroscopic like DOT3.
junkyardhero
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i've occasionally had instances where dot 5 will find the absolute teeny-tiniest microscopic places to weep where 3 or 4 won't. but other than that, i like 5 for all the above reasons.
the only real down side is that because it doesn't absorb water, whatever water makes its way into the system is now free to wreak havoc. but regular maintenance intervals solves that problem.
the only real down side is that because it doesn't absorb water, whatever water makes its way into the system is now free to wreak havoc. but regular maintenance intervals solves that problem.
We had a master cyl leak onto firewall and bubbled paint. Went right down and got Dot 5. Added it directly and bled brakes until Dot5(purple) came out. Zero issues 11 years later. Factory disc front, rear drum.
DOT5 in all my Darts - drum, factory disc and SSBC discs. Never a problem. Started when I got my first nice paint job in 1999, and have switched over on the other two when brakes needed complete rebuild.
Jeff Seighman
aka jeffnmo
DOT 5 all the way. Redid my whole brake system years ago, not one problem.
DOT4 absorbs moisture. DOT5 does not. The difference other than that is the boiling point and DOT5 will not attack paint, as previously mentioned.
I like DOT3. It's cheap, always in stock and the amount of moisture it absorbs is minimal having to do with operation. Since DOT5 does not absorb moisture, it collects in various places through the system and sits there. To me, a fluid that absorbs moisture is what I want. Besides, I drive my car on the street and don't drive it like a race car, so the temperatures in the brake system are relatively low. Vehicles have used DOT3 for almost 100 years and it works well.
Lastly, be advised, In order to change from DOT3 or DOT4 to DOT5, you are supposed to change the entire system. In other words, all new brake parts. You cannot mix DOT5 with DOT4 or DOT3. At all. A lot of people think you can just flush and go. A complete system changeover is the only correct way.
I like DOT3. It's cheap, always in stock and the amount of moisture it absorbs is minimal having to do with operation. Since DOT5 does not absorb moisture, it collects in various places through the system and sits there. To me, a fluid that absorbs moisture is what I want. Besides, I drive my car on the street and don't drive it like a race car, so the temperatures in the brake system are relatively low. Vehicles have used DOT3 for almost 100 years and it works well.
Lastly, be advised, In order to change from DOT3 or DOT4 to DOT5, you are supposed to change the entire system. In other words, all new brake parts. You cannot mix DOT5 with DOT4 or DOT3. At all. A lot of people think you can just flush and go. A complete system changeover is the only correct way.
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Flushed with 5 and didnt replace a single piece. I think I've bled brakes once since the 5 went in. Everyone's results will vary, but I believe the fear is internet based lol.
If, you are changing to DOT 5 be sure to flush the ENTIRE SYSTEM with at least 95 to 99% reagent grade alcohol. This will flush all of the previous fluid and any other contaminants from the system. When I switched to DOT 5 with Wilwood 4 wheel manual disc brakes, I did the flush and haven't had any problems in over ten years.
I went with DOT 5 years ago after the tireless job of sanding and painting my car. It is great, no spongy feeling, no moisture collection, won't damage paint, etc. But that does come at a slight cost. Be aware, if you take your car on a trip, take brake fluid with you. It's just one of those thing we should carry with us, like extra points or a spare VR or ignition box. You may be hard pressed to find DOT 5 in some stores and the cost is roughly 4x the cost of DOT 4, but it's still waaaay cheaper than painting the engine compartment again. Just my opinion.
Steve, it's not just the internet. It's every single service manual that goes in depth talking about brake fluid differences. That's all I was doing was stating technical fact.
Now, as far as what you said, I agree 100% and that's how I would do it if I ever swapped to DOT5. But I'm not going to recommend someone do it that way.
ir3333
Well-Known Member
Rusty is correct...dot 5 will not absorb moisture so moisture will pool in low spots.
If you build and install your brake system correctly your fair weather driven classic
will never corrode or leak. Dot 3 will be fine and last indefinately.
If you build and install your brake system correctly your fair weather driven classic
will never corrode or leak. Dot 3 will be fine and last indefinately.
I know we are only talking brakes here, but I have seen dot 5 eat the seals out of several throw out bearings. I have nothing to base my opinion on other than a guess, but I would guess a silicon based fluid isn't compatible in every brake caliper out there. Maybe I'm wrong. But I know 5 voids the warranty on more than one TOB manufacturer. Just something to ponder.
That's interesting.
Maybe showing my ignorance here, but why would Dot 5(or any other) brake fluid be used for TOB?
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