Dot 4 or Dot 5?

[Tor-King]

I will be changing all my brake and clutch lines soon to Russell Renegade lines and have a question as to what brake fluid to use.  Should I be using Dot 4 as per the manual or Dot 5 as suggested by the manufacturer of the new lines I will be installing?  Would there be a problem using Dot 5 and what is the difference between the two?  I will also be rebuilding both master cylinders and clutch slave cylinder so there should be no problem with contamination...

Again, thanks for the help in advance!

[SlowOldGuy]

I changed my brakes to DOT5 in about 1987. That fluid stay in the front brakes until I swapped to monoblocks sometime around '02.  Never flushed or bled them during that time.  When I inspected the old pistons after the swap, they still looked brand new, no signs of contamination or corrosion.

After rebuilding my clutch slave 3 times when using DOT4, I bought a new slave and switched it to DOT5 also.  That was around '00, haven't touched it since.  The first thing I did to my '93 when I got it in '00 was swap everything over to DOT5.  Haven't touched the brakes or clutch since then.

Do it right and DOT5 will last a long time, at least for me.

DavidR.

[rktmanfj]

Do not mix DOT5 with any other kind of fluid.  It is silicone based.  All the others are glycol based.

DOT3, DOT4 and DOT5.1 are somewhat compatible, with the boiling point being biggest difference.

http://en.wikipedia.org/wiki/DOT_5

I've been using DOT5 in my FJ for a long time now.  I just rinsed everything out with contact cleaner (per advice of Motorcyclist magazine), let dry, and filled 'er up.

[Tor-King]

Do not mix DOT5 with any other kind of fluid.  It is silicone based.  All the others are glycol based.

DOT3, DOT4 and DOT5.1 are somewhat compatible, with the boiling point being biggest difference.

http://en.wikipedia.org/wiki/DOT_5

I've been using DOT5 in my FJ for a long time now.  I just rinsed everything out with contact cleaner (per advice of Motorcyclist magazine), let dry, and filled 'er up.

Would that mean that I should change all the seals in my front and rear calipers or simply drain them out before making the switch?

Thanks for your expertise!

[rktmanfj]

Do not mix DOT5 with any other kind of fluid.  It is silicone based.  All the others are glycol based.

DOT3, DOT4 and DOT5.1 are somewhat compatible, with the boiling point being biggest difference.

http://en.wikipedia.org/wiki/DOT_5

I've been using DOT5 in my FJ for a long time now.  I just rinsed everything out with contact cleaner (per advice of Motorcyclist magazine), let dry, and filled 'er up.

Would that mean that I should change all the seals in my front and rear calipers or simply drain them out before making the switch?

Thanks for your expertise!

I just rinsed everything out with contact cleaner (per advice of Motorcyclist magazine), let dry, and filled it up.

No need to change any seals unless they are worn out or you just want to do it as PM.  If you still have the OEM rubber lines, they should be replaced ASAP, IMO.

[ELIMINATOR]

Found this:

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

[glfredrick]

I've found over the years that there is a general misconception about the various DOT brake fluids, as if a higher number equals a higher grade of fluid.  The numbers are for TYPES of base oil used, not necessarily that they are "better" and each has a preferred range where they work best.  

Here are a couple of articles on the issue that may help:

http://www.gomog.com/allmorgan/brakefluid.html

http://www.ebcbrakes.com/automotive/brake_fluids/index.shtml

https://mossmotors.com/forum/forums/thread/5556.aspx

[Tor-King]

Thank you ELIMINATOR and glfredrick for those excellent links.  Very interesting reading on the differences between DOT 3, 4, 5 and 5.1!  Manufacturers sure have to make things difficult.  After reading all I think that I will just stick with the glycol based (5.1) and change out every two years.  I did not know that 5 was incompatible with ABS systems.

You all are great!  Thanks again.

[rktmanfj]

Yep, I learned again about how 'spongy' brakes are with DOT5...     

[Pat Conlon]

Yep, I learned again about how 'spongy' brakes are with DOT5...     

I have DOT 5 in my '84, and I have DOT 4 in my '92. Same exact braking system on both bikes, Spiegler lines, FZR 14mm m/c, R-1 calipers and Galfer wave rotors and HH pads.

I would not say my brakes are "spongy" in my '84 but they *are* softer than the '92. No doubt about it.
There is a definite difference in the lever feel between the bikes, it's not too bad... but the difference is there.
Randy if you come to Colorado, I will have both bikes there for you to sample.

DOT 5 is non hygroscopic (does not absorb water) so if you ride in wet climates I recommend DOT 4. When you get moisture in your system (and you will) it will be absorbed by the hygroscopic DOT 4 fluid and thus you can easily flush it out with your annual maintenance.

Cheers!

[rktmanfj]

Yep, I learned again about how 'spongy' brakes are with DOT5...      

I have DOT 5 in my '84, and I have DOT 4 in my '92. Same exact braking system on both bikes, Spiegler lines, FZR 14mm m/c, R-1 calipers and Galfer wave rotors and HH pads.

I would not say my brakes are "spongy" in my '84 but they *are* softer than the '92. No doubt about it.
There is a definite difference in the lever feel between the bikes, it's not too bad... but the difference is there.
Randy if you come to Colorado, I will have both bikes there for you to sample.

DOT 5 is non hygroscopic (does not absorb water) so if you ride in wet climates I recommend DOT 4. When you get moisture in your system (and you will) it will be absorbed by the hygroscopic DOT 4 fluid and thus you can easily flush it out with your annual maintenance.

Cheers!

Hey Pat, I think we are on the same page.  While I think they are softer than the glycol-based fluids, they are far from 'spongy'.

I actually like it, especially  when I have to hit the brakes really fast... they seem easier to modulate to me.

[Pat Conlon]

..... While I think they are softer than the glycol-based fluids, they are far from 'spongy'.
I actually like it, especially  when I have to hit the brakes really fast... they seem easier to modulate to me.

Yep, I agree with you. I very much like the softer rear brake on my '84. The pedal feel is much more forgiving.

I wish I had a dollar for every time I splashed DOT 5 on my paint work! Heh heh..

[SlowOldGuy]

There were a few things I do not agree with in one of the referenced articles.  The author states that the braking system is not sealed; I believe his words were "see that little notch?"

Yes, there is a notch, but it's for allowing air ABOVE the expansion diaphragm, NOT BELOW.  If the gasket/diaphragm and cover are installed correctly, the fluid is NOT exposed to air.

His other claim that DOT 5 requires more maintenance is also opposite compared to my 25 years of experience with using DOT 5.  I've had far less "required" maintenance (read repairs) using it than I did with glycol based fluid.

I agree with Randy on the "squishy" brakes.  The lever may not be as rock solid as glycol, but it's far from being anything I'd call squishy. 

And like most things, it comes down to personal preference.  I've never been a big fan of one-finger brakes.  If I had those on my bike, the first true panic stop would find me grabbing a handful of lever and throwing me on my face.  I can still lock up either end, I just prefer the threshold of lockup to be more on the dumb side.  Braking performance is far more influenced by the choice of pad materials than the fluid used.

I was also damn glad I had DOT 5 when I changed my brake lines.  I got fluid ALL over the bike during that process.  The result: nice shiny silicone covered paint!  :-)

DavidR.