Brake Fluid Type (DOT 3, 4, 5, 5.1)

[Xeilos]

This should be a good topic for all younger FSAE teams and this post will hopefully become some sort of reference for any teams asking this question. That is provided they know how to use the Find button http://fsae.com/groupee_common/emoticons/icon_biggrin.gif (sadly this is lacking these days).

I am looking for people to weigh in on the advantages and what they prefer for each of the types of brake fluid. DOT 3, 4, 5, 5.1.

The big contention of course is over the silicone versus glycol based fluids and what is preferred in an FSAE environment (which we all know is different from a 'real' car).

We have ran DOT 5 for the past couple of years due to availability for our team. But I am impartial to either silicone DOT 5 or even "downgrading" to a DOT 4 (glycol) with the relatively quick replacement rates of brake fluid on our car.

[Xeilos]

This should be a good topic for all younger FSAE teams and this post will hopefully become some sort of reference for any teams asking this question. That is provided they know how to use the Find button http://fsae.com/groupee_common/emoticons/icon_biggrin.gif (sadly this is lacking these days).

I am looking for people to weigh in on the advantages and what they prefer for each of the types of brake fluid. DOT 3, 4, 5, 5.1.

The big contention of course is over the silicone versus glycol based fluids and what is preferred in an FSAE environment (which we all know is different from a 'real' car).

We have ran DOT 5 for the past couple of years due to availability for our team. But I am impartial to either silicone DOT 5 or even "downgrading" to a DOT 4 (glycol) with the relatively quick replacement rates of brake fluid on our car.

[Drew Price]

1) (This is #1 for a reason) SEAL COMPATIBILITY. Shouldn't be a problem, just double check with whatever you buy for the car that it's compatible.

2) Dry boiling point.

3) Cost - FSAE cars don't hold much fluid, so it shouldn't matter a bunch.

ATE 'Super Blue' fluid is compatible with nearly everything, has 95% the boiling point of the expensive Motul or Wilwood fluids, and is readily available at something like $18/liter. It will take you a looooong time to use a liter of fluid in an FSAE car.

I like to alternate my fluids when flushing with something clear and the Super Blue (which is dyed blue) so I can tell when I have flushed all the old fluid out - the fluid coming out changed color, very simple, even simpler than measuring the volume of fluid you drain out.

There are some articles to read about how many times a fluid will tolerate being boiled if I remember right too.

We used Wilwood 570 racing fluid in our brake system partly because used Wilwood components and partly because we got it in the same order from the same vendor as our brakes, it's also not very expensive.

We also didn't have issues overheating the brakes, so I can't comment on it in that respect.

[RANeff]

ATE superblue is the best bang for the buck, and is highly compatible (as stated by Drew).

To add to Drew's idea of replacing ATE Blue fluid with a clear one: ATE makes the same fluid in clear type, its called TYP 200.

So, you alternate between Superblue and TYP 200, its the same fluid, different colors. This allows you to know when the brakes are fully bled and not worry about compatability, easy peasy

[TacoPete]

I agree with Drew that the number 1 reason for choosing a brake fluid is the seal compatibility. DOT 3 4 5.1 are compatible with one another to the best of my knowledge, so a seal compatible with one is compatible with all.

I'd argue that the "wet" boiling point is more important than the "dry" boiling point, especially in a FSAE (and Baja SAE) application. The "wet" boiling point is measured when the fluid absorbs 3.5% water (by vol or weight I'm not sure) and is always lower than the "dry" boiling point. The glycol based fluids absorb water from air- so every time the cap is left off the reservoir or the fluid container (both happen frequently in my experience), the fluid is absorbing water. Side note- This is why I prefer buying smaller containers so that there is less time with the cap off. Typically, the higher the DOT #, the higher the boiling points. However this is not always the case since the boiling points are not the only criteria in determining DOT #- viscosity and compressibility are two of the other criteria.

I also remember reading that the DOT 5 fluids were developed for military applications- they don't absorb water (or absorb as readily as the glycol based fluids) increasing their service life. However, they are more compressible than the glycol based fluids (does this make a noticeable difference in FSAE- I don't know but would be interested to hear from someone who does).

The Bosh Automotive Handbook has a good section on brake fluids.

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by TacoPete:
DOT 3 4 5.1 are compatible with one another to the best of my knowledge, so a seal compatible with one is compatible with all.

</div></BLOCKQUOTE>


This is technically not correct, for example in classic European cars (especially English ones), but for the sake of FSAE I would wager it's impossible for you to even get your hands on seal kits that were designed to only accept DOT 3 fluid, so for the sake of this thread it doesn't really matter, but you should still check and know the requirements of your system.

Read up about how DOT 5 silicone base fluid is is not miscible with DOT 3 or 4 fluids.

DOT 5.1 CAN be mixed with 3 and 4, but DOT 5 will just float on top of the 3/4/5.1 fluids.

I would say just use what you can get that's meant for racing use, change it every once in a while, and you'll be fine.

[Stocky Fast 1]

Interesting points being made here. I used to use Motul 600, I chose this over the Motul 660. The higher wet boiling point was prefered over the higher dry boiling point. As mentioned above, during all the work on the car sometimes the fluid may be left open to atomosphere, even for a short time. The minor loss in dry boiling point for a similiar gain in wet boiling point was always security to me.

It really depends on the team and how well thought out things are if you will be often tearing things apart on the car and properly maintaining the car as well.

[MegaDeath]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Stocky Fast 1:
Interesting points being made here. I used to use Motul 600, I chose this over the Motul 660. The higher wet boiling point was prefered over the higher dry boiling point. As mentioned above, during all the work on the car sometimes the fluid may be left open to atomosphere, even for a short time. The minor loss in dry boiling point for a similiar gain in wet boiling point was always security to me.

It really depends on the team and how well thought out things are if you will be often tearing things apart on the car and properly maintaining the car as well. </div></BLOCKQUOTE>

GET BACK TO WORK MIKE!!!!!