Topic: Dot 5 brake fluid

[jwurbel]

Did a complete rebuild of brake system.  Caliper seals, brake lines, and master cylinder rebuild kit.  System had been drained of Dot 3 years before as bike sat for 15 years.  Initially, brake system worked very well.  Bike sat for four months as I was doing other work on it.  Went to ride yesterday and no brake lever pressure at all.  Opened cover and fluid level down for some reason.  Filled and tried to bleed.  System will not pressurize.  Like I have a huge amount of air in system.  Not sure if rubber seals in master cylinder are gone due to Dot 5.
Any suggestions would be helpful.  Hate to think I’ll have to do entire rebuild and switch back to Dot 3 or 4.

[BenelliSEI]

Did you replace the tworubber hoses at the front end too.?

What colour is the brake fluid coming out? If it’s clean and clear, keeep bleeding. If it’s dark or black, start looking for what “melted”?

[RAFster122s]

Dot 3/4 and DOT 5 do NOT mix. Contamination from DOT3/4 can cause serious issues for DOT 5 fluid. DOT 5.1 doesn't have these issues. Flushing DOT 3/4 out of system isn't easy from what I have read.
If you put DOT 5 in I bet you are going to have to replace the hoses and rebuild or replace the MC to get a working system again.

[Jerry Rxman Griffin aka MuthaF'er]

I've had no issues with DOT5 in either CB750F after complete rebuilds

[jwurbel]

Fluid is blue.  Replaced all hoses when rebuilt.  Will keep bleeding an let you know.