Zuke says use DOT 4 brake fluid, so what is DOT 5.1 for?

[FloydV]

From what I've read, DOT 5.1 is a silicone based fluid with a higher boiling point than DOT 4. If I recall correctly, silicone based brake fluids do not attract moisture. So, why not use the 5.1?

Also, my understanding is that to change the brake fluid, I should open the reservoir, then attach a vacuum pump and pull all the fluid into a container in between the two. After that, I should pour in new fluid, and pump the brake until no more bubbles appear, and then close the bleed valve. Is that about correct?

 

[Busa1166]

All I do know I was told DOT 5 is a no-no on bikes dunno why. Some on here did give the reason just can't remember

 

[Warputer]

I've read that it's Not a good idea to change to different rated fluids. You cannot get all of the old stuff out & in the end there will be problems.

 

[Warputer]

Copied from the infonet:

Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

 

[AJAY]

It's funny. When I built my cafe Sportster back in 1989, I used the front end from a Suzuki 550 as a cheap way to upgrade to dual disks in front and to quicken up the steering. At that time, I used DOT 5 silicone brake fluid because that's what Harley uses stock, but it did take a lot of flushing to get rid of the old glycol-based fluid. The same DOT 5 is in the system and I've never had a problem with it.

So why do most sport bikes (actually, just about everybody but Harley) come with glycol based DOT4 fluid? As I understand it, the silicone fluid is more compressible than glycol and gives a softer feel to the brakes. Harley seems to always oversize their master cylinders giving less mechanical advantage and their brakes require a very firm squeeze compared to Japanese bikes. No two finger stopping on a Harley and the brakes feel hard as h3ll to me. The brakes on modern sportbikes have more mechanical advantage (ratio of master cylinder piston area to the combined area of the caliper pistons is smaller), so using the stiffest fluid available makes sense.

I have read that there is a difference in the seals between systems intended for silicone vs. glycol fluids. That may indeed be true, but again, I have had no problems with silicone fluid in the Suzuki brakes on my old Sportster. One big advantage has been that the brake fluid still hasn't picked up water and no corrosion has occurred, even though I haven't bled the system in 20 years. YMMV.

 

[dadofthree]

I wonder if the DOT 5 would be good for those upgrading their entire brake system ? Sounds like changing to it is a major no no.

 

[fastblackblur]

Also, my understanding is that to change the brake fluid, I should open the reservoir, then attach a vacuum pump and pull all the fluid into a container in between the two. After that, I should pour in new fluid, and pump the brake until no more bubbles appear, and then close the bleed valve. Is that about correct?

The easiest way I've found to do the brakes on my bikes is with speed bleeders. They are basically a one way valve that make changing brake fluid very easy.

With speed bleeders the process is simple.

Loosen bleeder valve. Have some manner to neatly catch the expelled brake fluid. I used a rubber tube to put the fluid in a container.

Open brake fluid reservoir.

Pump out old fluid, replace with new fluid. It is very important that at no time the brake fluid reservoir becomes completely empty. This is to keep air out of the system.

Once only clean fluid is being expelled through the bleeder tighten the bleeder and repeat the process for the other caliper if present.

Re-fasten brake fluid reservoir cap.




The speed bleeders make the process much easier because without them your having to constantly tighten/loosen your stock bleeders.


This little write up is not perfect...I recomend checking out youtube out to see how simple it really is.

 

[AJAY]

Speed bleeders are awesome, but I'm too cheap to buy them for something I use so infrequently.

 

[jellyrug]

Careful, DOT 5 and DOT 5.1 is not the same thing.

Here is a linky that explains the pros and cons.

http://www.gabma.us/docs/dot5.pdf

 

[karnage]

I was taught in tech school that denatured alcohol is fine to flush out brake lines.Have done it and never had an issue,Of course I havent dont it too many times, but it did work fine.I used dot 3 in my rear brake when i put on the stretch and new braided line.Shop said it would be fine.Dot 4 has a higher boiling point.

 

[FloydV]

Careful, DOT 5 and DOT 5.1 is not the same thing.

Here is a linky that explains the pros and cons.

http://www.gabma.us/docs/dot5.pdf

Really good article. Thanks!

 

[AJAY]

I was taught in tech school that denatured alcohol is fine to flush out brake lines.Have done it and never had an issue,Of course I havent dont it too many times, but it did work fine.I used dot 3 in my rear brake when i put on the stretch and new braided line.Shop said it would be fine.Dot 4 has a higher boiling point.

That's actually a pretty good idea. Over the years, I've used WATER to wash disassembled brake components without any problem. You just have to blow it dry and then wipe down with brake fluid when reassembling. Never had a problem, but alcohol would do as well and would certainly dry more quickly in air.

Before anybody goes all ape$h1t on me, remember that you will get adsorbed water from the atmosphere whenever you coat parts with a hygroscopic material such as alcohol or glycol-based brake fluid and then let them sit in air. This is why we are cautioned to only use brake fluid from freshly opened bottles. Once it's opened and exposed to air, it starts to pick up water. If you wash brake parts in water, you could always put them in an oven to dry more thoroughly. Even 150*F would do an excellent job for these purposes. (all this comes from someone who has done a decent amount of chemistry work for semiconductor materials where water is a major challenge)

 

[FloydV]

I wonder if a solvent like toluene which is not hygroscopic would work better to clean out brake lines. Metallic sodium which reacts violently with water is stored in toluene.