The official dealer didn't notice,when renewing fluid, that the previous fluid was DOT 4 (i just bought a used RK). As DOT 4 and DOT 5 don't mixed, the system didn't work well.
Not satisfied i went to a Suzuki dealer who find out where was the problem. The point is he cleaned the whole system and then used DOT 4 fluid.
The system is now working well, but can DOT 4 fluid damage my system or cause any problem as HD standart is DOT5 ?
Thanks
sbkjo

 

What bike do you have? The HD standard has changed from DOT 5 to DOT 4, beginning in I believe 2005.

 

According to HD's web page this is the fitment data:
DOT 5 Brake Fluid

Fits all models (except '05-later Touring models, '06-later VRSC™, Dyna™, Softail® and '07 Sportster® models).

DOT 4 Brake Fluid

Fits '05-later Touring and '06-later VRSC™, Dyna™ and Softail® and '07 Sportster® models.

either should work so long as they are not mixed and if one changes from one to the other then the system and internal parts must be cleaned to prevent cross contamination.

FBL

 

I have a 2001 RK classic.

 

DOT 4, like DOT 3 and DOT 5.1, is a polyethylene glycol-based fluid (contrasted with DOT 5 which is silicone-based). Fluids such as DOT 4 are hygroscopic and will absorb water from the atmosphere. This degrades the fluid's performance by drastically reducing its boiling point. In a passenger car this is not much of an issue, but can be of serious concerns in racecars or motorcycles.

 

DOT 4 brake fluid is NOT compatable with DOT 5 systems. It will probably ruin the whole brake system, seals etc. Plus, DOT 4 EATS PAINT andDOT 5 is much safer for paint. I have DOT 4 from the factory and I hate the paint factor. I wish they would have stuck with DOT 5 on the newer bikes. I don't get why they changed.

 

My 2006 RKc came with dot 4 ,when installing new front master cylinder I changed it to dot5,for sake of my paint.No problems with system

 

The answer is no, it won't hurt your brake parts. Once it's been thoroughly cleaned and flushed, it won't matter. DoT4 is plenty good enough for a street bike. I use it in my track car without any issues, but I bleed it 6-10 times a year.

But I would flush every month or so to make sure there's no residual. No scientific data to back that up; it would just make me feel better.

 

My '06 Heritage came with DOT4,.... I just did some work on the bike and for kicks bled front and rear using DOT4 from Oreilley Auto Parts (Gunk/solder seal); good stuff. works fine. manual says DOT4,..good enough for me.

 

Sorta on this same topic.

We are getting ready to swap the front calipers on my Pops Ultra Classic to th new 2k8 Brembo's.

In the process of moving from DOT-5, to the now favored DOT-4... What are you suggestions for getting the system totally flushed of the DOT-5?

I don't ming re-building the master cylinder, but I don't want to leave any old DOT-5 in the lines...

Suggestions?