I just installed new handlebars on my 2004 Low Rider. The new bars required a new front brake line. The local parts guy lent me one temporarily so I could get on the road while my new one was on the way. After installing the temporary one, we had a very difficult time bleeding the line. We just could not get any pressure. After double checking things multiple times, we finally started getting some pressure and finished bleeding the line. When my new line arrived a few days later, I installed it and started trying to bleed the brakes. Again I have had a difficult time getting any pressure. Been working on it for an hour or 2 after work for the last 3 days. I even filled up the Master Cylinder and bungied the brake lever and let it sit overnight-no good. Finally I bought a vacuum pump in hopes that would work. After about 45 minutes I finally started getting some pressure but the lever feels soft. It does stiffen up near the throttle. The Master Cylinder says to use DOT 5 and that is what I used. I have read a number of things about DOT 5 vs DOT 4 on this forum. I know that DOT 5 is silicone based and others have had issues with a spongy lever.

My questions are:
1) Is there any reason I can NOT put DOT 4 in my bike? I know I need to completely flush the DOT 5 out of it. Is there any more to this than draining the fluid completely out and re-filling it with DOT 4?
2) Will DOT 4 do anything to the brake system (Lines, seals, etc.) that will affect the performance of the brakes?

I have also read about people cleaning up the pistons on the calipers and getting a better feel in their lever. Haven't tried this yet but, since i should change the pads, I probably will.

If anybody has any suggestions, please feel free to comment. I don't know what else to try. I really want to get this resolved-I'd love to try out my new bars!

 

1. Your problems are nothing to do with which fluid you use, so stick with the correct DOT. Changing DOT will not solve your problem.
2. There is a risk that the traces of DOT5 left will react with the DOT4 and cause brake problems, as the two fluids do not mix, but can create a yucky jello-like substance.
3. There are two Stickies at the top of this section which should help you sort this out. Above all else stick with it!

 

Sounds like you need to bleed a little more. Try bleeding through the banjo bolts. Instead of using the bleeding nipple when you pump up the system crack the banjo bolt instead. Sometimes air can hide in there.

If the brakes are working take the bike out for a ride and get them warm. Between the heat and the jolts the road gives it could knock an air bubble out. Get home and do a quick bleed.

 

Thanks for the encouragement. I went out this morning and had some lever. Pumped up the brake and did a quick bleed. The lever still feels a little soft but does not hit the throttle. Gonna take it for a spin this afternoon. Maybe things will feel a little better on the road. Will probably bleed the entire system again when I change the pads. I'll also take the opportunity to clean up the caliper pistons. Hopefully, all of those steps will give me a better feel.

I am still concerned about the DOT 5 fluid. It seems as though the DOT 5 has the ability to compress within the system because of the silicon in it. That does not seem like it would make for a very good brake fluid since the premise of the system is that the fluid actuates the caliper. The last thing you want is for the fluid to compress in the event of a panic situation. Am I missing something?