DOT 5 vs DOT4 Brake Fluid for Linked System (5th Gen)

After installing Galfer braided steel lines in my '98 (challenging, to say the least . . .) I am curious to know if anyone has used DOT 5 brake fluid in their system, whether stock or braided steel? What were your observations/opinions? Is there any downside that you can find (other than the cost)?

For now I have gone with DOT 4 but can't ride it until I fix a sticky center piston on the rear. This bike has been idle for approximately 10 years, so I am working out some bugs. However it's a good low mileage one with good plastics. This brake issue is the last item to fix before going down to the DMV and finally registering it (2 years after purchase). I know, you can spare me the slacker jokes . . . .

Pictures later, gotta get it on the road first.

 

You are stuck with DOT4 do not mix them, you can only swap to DOT5 after a complete brake strip and very thorough clean

 

Umm. When it comes to changing brake fluids be VERY careful - your life depends on it!!!

Dot 4 and Dot 5.1 are both GLYCOL based but with different boiling points - so if you really must, they can be mixed. BUT Dot 5 is silicone based and does not play well if there are traces of GLYCOL in any system. So its fine to use Dot 5 in a brand new system or one with new components throughout, and you will enjoy the improved braking (at the extremes) because of the higher boiling point.

For most VFR riders Dot 4 works fine - assuming its not being used as a track day special where I guess every thousandth of a second might count.

Take care


SkiMad

 

Gycol type only, minimum Dot-4

 

I've used DOT 5 in my FJ because the stupid slave cylinder would leak periodically and strip the paint off the crankcase in the process. Silicon brake fluid solved that problem. It is a pain if you have glycol based and you want to change to silicone. Like everyone says you really need to pay close attention to getting all the gycol based fluid out of the system before adding any silicone based fluid. It will gel if you don't and you'll have little clumps of semi-solid brake fluid in the system. Not a good thing. So even though the lines would be new, you'd still have to pay close attention to the calipers themselves, and ABS if you have it, and the brake proportioning valve, or whatever they call it.

A lot of hassle for little discernible benefit, IMO anyway.

 

Back in '85 I switched to DOT 5 in my VF750 when I put braded lines on. Fast foward to 2015 when I restored the 83 after sitting for 25 years ( did manage to get it running after 10). I took apart everything but the engine, replaced just about every rubber seal and boot. The DOT 5 fluid was still clear without any gunge. My spare calipers with DOT 4 were totally gummed up and unuseable. So I suggest that you totally take apart your rear caliper and replace the seals. Getting pistons out won't be easy, careful not to score them.

I don't see any advantage to switching now, just keep flushing systems on a regular basis.

 

I agree with Allyance, I changed out the front brake master cylinder last year and changed back to DOT 4 brake fluid. I pulled the calipers apart and checked everything out. Brake fluid was good, no rust or corrosion anywhere, and this was after at least 10 years.

 

Partzilla has OEM seals (and most other rubber parts).

 

You can flush the brake system with denatured alcohol to get the DOT 4 out. Bad thing about DOT 5 silicone is any moisture, aka water, that gets in will separate from the silicone and lay in the bottom of the calipers. Which tends to rust after a while. That's why the HP cars like the Vett have an all Stainless steel brake system and lines.

The reason for silicone is for high temps which you will never see on the street.

 

Excellent responses everybody. Thank you! I kinda put the cart before the horse in asking the question after already filling the system. Since this bike will never see a track day, DOT 4 it is (or 5.1 if I get ambitious). Was interested in the silicon based fluid but oh well. Am using OEM parts, including a new center cup on the rebuild, so hopefully should get another 18 years out of it before there's a problem.