Switch from DOT 4 to DOT 5...problems?

[g356gear]

I recently installed Willwood disc brakes on all 4 corners and switched out the master cylinder. Willwood recommends a DOT 5 fluid for daily driving with their systems. Will there be any issue if I fill the new resevoir with DOT5 and then flush out the whole system to get rid of the DOT4? I wasn't sure if there would be a reaction between the 2 since it is not recommended to mix the 2 together.

[parsonsj]

DOT 5? Are you sure? Please check again, because I'll be astonished if that's what Wilwood recommends.

jp

[Apogee]

DOT 5.1 would be a much better choice since it's also a glycol base and compatible with DOT3/4 fluids. I'm with JP on this one...Wilwood does not recommend using DOT5 silicone based fluids per it's FAQ page on their website:

"Q: Can I use Dot 5?
A: DOT 5 Silicon Fluid is not recommended. In addition to being easily aerated which leads to a spongy brake pedal, it is not hygroscopic, which permits moisture accumulation in the brake system, lowering the boiling point.

Note: To maintain a high dry boiling point and maximum performance, change the brake fluid often, especially after high heat cycles."

Tobin
KORE3

[g356gear]

DOT 5.1 would be a much better choice since it's also a glycol base and compatible with DOT3/4 fluids. I'm with JP on this one...Wilwood does not recommend using DOT5 silicone based fluids per it's FAQ page on their website:

"Q: Can I use Dot 5?
A: DOT 5 Silicon Fluid is not recommended. In addition to being easily aerated which leads to a spongy brake pedal, it is not hygroscopic, which permits moisture accumulation in the brake system, lowering the boiling point.

Note: To maintain a high dry boiling point and maximum performance, change the brake fluid often, especially after high heat cycles."

Tobin
KORE3

I did see that. Later on they do say minimum DOT5 for street applications. DOT6 was for race use only.

[megaladon6]

IIRC doesn't DOT5 destroy most rubber seals? but 5.1 doesn't?

[parsonsj]

Gear,

I've never heard of DOT 6.

Read this.

An excerpt (emphasis mine):

General Recommendations:

1.If you have a brake system that doesn't leak or show any other signs of failure, but has old seals in it, don't change fluid types as a result of reading this article. If it isn't broken, don't "fix" it -- you may simply break it instead!
2.Flushing of the brake system every couple years to remove any absorbed or collected water is probably a good idea to prevent corrosion, regardless of the type of brake fluid used.
3.DOT3 is dangerous to use in cars with natural rubber seals, and thus should not be used in such cars, except as a temporary "quick fix to get me home" solution. (If this is used as a "get-me-home" solution, bleed the system as soon as possible, and be prepared to replace all your seals.)
4.DOT3 is an adequate brake fluid for use in later cars, although it is rarely preferred. My recommendation would be to simply not use it.
5.DOT4 fluid, for a slight increase in cost, will give significantly increased resistance to moisture absorption, thus decreasing the likelihood of corrosion compared to DOT3.
6.DOT4 fluid has a higher boiling point than DOT3, making it preferable for high performance uses such as racing, autocross, or excessive use of the brakes in mountainous areas. For even greater braking performance, consider going to DOT5.1 or a high-performance version of DOT4 fluid.
7.DOT5 is a good choice for the weekend driver/show car. It doesn't absorb water and it doesn't eat paint. One caveat is that because it doesn't absorb water, water that gets in the system will tend to collect at low points. In this scenario, it would actually be promoting corrosion!
8.DOT5 is probably not the thing to use in your race car although it is rated to stand up to the heat generated during racing conditions. The reason for this recommendation is the difficult bleeding mentioned above.
9.When changing from one fluid type to another, as a minimum, bleed all of the old fluid out of the system completely. For best results, all the seals in the system should be replaced.

[Apogee]

I've never heard of DOT6 fluid either aside from the article JP linked to mentioning that it would've saved some confusion if they had gone that route instead of DOT5.1. The DOT only rates a fluid based on it's dry and wet boiling points, hence DOT5 and 5.1 fluids have similar temperature ratings and are thus classified similarly. They however are completely different from a chemical composition standpoint, glycol based versus silicone based. Racing fluids that exceed the DOT5.1 ratings are not typically geared towards street use and as such, don't typically claim any DOT standard from what I've seen, only a temperature rating. That said, none are silicone based to the best of my knowledge due to it's tendency to readily aerate.

I've read the the US military is the number one consumer of DOT 5 silicone brake fluid due to it's better lubricity at extremely low temperatures. That said, I've also heard that they've been looking for better alternatives almost as long as they've been using it. The only OEM that I can think of that uses DOT5 fluids from the factory is Harley Davidson...not sure what their reasoning is to be quite honest, but I would guess that it has to do with it not eating paint, similar to why a lot of hot rod guys use it.

Tobin
KORE3

[robscar]

The Post Office also uses Dot 5 in their little turd heap mail trucks.

[sam 74]

i use dot 5.1 in my car and my sport bike, it holds up pretty well to the high heat.

[MonzaRacer]

Just use a quality DOT 4 brake fluid, many stores carry it or can get it. The one thing is different brands have different boiling points. But for 99% of us any one with over 400 to 450 deg F boiling point is plenty. Finding a local repair shop that uses BG service chemicals can source you with DOT4 fluid. AND if you start out bleeding brake system with it you can save cash. I have seen DOT5.1 costing upwards of $20 a quart. I got a quart of DOT4 from BG sourced at local Meineke (sp) shop and paid like $6.99.
But then I also still have 2 steel,sealed up cans of Performance Friction HP brake fluid ,not sure if its DOT3 or 4 but its supposed to be high boiling point.
May use it in Monza after installing the Vette brakes.
BUT DO NOT USE DOT5 SILICONE. IT SUCKS!

[72'Monte]

don't use dot 5.i loss all brakes from it before.it well eat rubber lines.

[Skip Fix]

My 78 TA has had DOT 5 silicone fluid in it for 20 years with a good pedal. Might be with the funky rear ratchet calipers have not locked up like most do with regular fluid-why the 81 has the brakes all apart right now and the rear out.

[SLO_Z28]

DOT 4 and 5 fluids will actually change quite a bit under heat, and gain a ton of undesirable qualitys. I use DOT 5.1 in the police cars I maintain, with a 40,000 mile replacement schedule and Ive never had problems with it. Ive never had the fluid boil over before the pad catastrophically fails, and its not uncommon for a pad to get to 950 degrees fahrenheit or so in street use. The important part here is the .1 in 5.1, its MUCH better than any silicone based fluid. The reason wilwood sells mostly DOT4 is that most customers have good paint jobs, and DOT 4 and DOT 5 are very forgiving if spilled on paint. If its just a street car then DOT 4 or 5 will be fine, just have it flushed out every 2 years at least.

[dontlifttoshift]

DOT 4 is not silicone based and is very similar in make up to DOT 3 so I am not sure why it would be any easier on paint than DOT 3. Here is a good aritcle on brake fluid. http://www.stoptech.com/technical-su...rs/brake-fluid

DOT 5, which is silicone based, has no place on any car unless it lives in a museum.

[Skip Fix]

Admittedly my 78 has not seen roadrace track time since the swap the rear discs and the silicone fluid but 5 years of hard autocrossing in CP with road race slicks and 20 years of drag racing the last 10 years slowing down from 124mph or so has great pedal feel and good braking I can make the first turn off if I want. Friend who usually won class in his C4 autocrossing liked the brakes also.

So to say it gives bad compressability & bad pedal feel in all situations is incorrect -come drive the thing! Pedal feel is as good as the manual setup in the Camaro project.

[RSX302]

Ok..this thread made me nervous.

I put Dot 5 in my elect power system that was recommended by ABS brake systems. So far it's been just fine.
Napa silicon dot 5 back label reads:
Napa's DOT 5 brake fluid is formulated with silicon and provides superior performance over conventional glycol based fluids (DOT 3 and DOT 4). Napa's DOT 5 brake fluid will not absorb moisture and can be used in most brake fluid applications.
Exceeds federal MVSS no. 116 and SAE J-1703 specs. Minimum wet boiling point: 356degF

$35/qt

[SLO_Z28]

One of the main draw backs of the silicon based fluids is its reduction on the durometer of ethylene propylene rubber. It all boils down to what seals you use on your brake pistons. The other problems you can see are volume differential at temperature, and compressibility change at altitude. A good driver can fell the difference.

[RSX302]

So since my Camaro sees 95%+ street at the same location and I have Wilwood/ABS Electric Master, my system should be ok?

I looked at Wilwoods site which states that they do not recommend DOT 5 for racing applications. Ok, how about mostly street with the occational weekend warrior?

So far, no issues on the street what so ever. I've also run in a local autocross with no issues. I will hopefully get back to a bigger road course this year and test. (Willow Springs, Big Track) But then again I don't do more then 5-7 laps. That is because I realize that it isn't a full blown race car and will go into full melt down if I do. (Power steering temp, oil temp, water temp, street tire temp, etc) I'm sure many street cars fit this description.

As for a good driver feeling the difference? I guess I'm not a good driver cus my DOT 5 ABS electric power system with Wilwoods BP20's feel very close to the manual 3/4 master, race 'H' pad system with DOT 4 that I had. (Which I'm very happy about because the H pads were chewing the crap out of the rotors)

So the moral to this story I'm catching is, If you run mostly street with the proper seals, DOT 5 is just fine. If you are running more serious race set-up with longer compitition stints on the track, stay away from DOT 5.

The Bonus I absolutely love is that DOT 5 does not hurt painted surfaces.

[Skip Fix]

Here in Texas none of the tracks I race at are above 300 ft(heck I think Baytown is below sea level) so maybe that is why I've never had an issue.