My 2004 Road King uses DOT 5 (silicone) brake fluid. The used Brembo calipers & master cylinder I got on eBay use DOT4. I know we don't mix the two brake fluids.

My used Brembo calipers & master cylinder have leftover DOT 4 residue in them. My bike's front brake line has DOT 5 residue in it. You see where I'm going now.

Here's my question: Is there a good way to flush all the DOT 5 out of the bike's old front brake line, or should I just buy a new brake line and start clean with the new DOT 4?

Any suggestions/ideas much appreciated.

JR
P.S. Before we go there, yes, I got the larger Brembo rotors to match the Brembo calipers too.

 

You could squirt brake cleaner through the lines to get the old fluid out. I'd use it as an excuse to get fancy-shmancy new braided lines.

 

I ran into the same issue during my build when I'd wanted to run DOT 4 and the used front master cylinder I bought had DOT 5 in it. The caliper which I also bought used had who knows what in it. So I took the caliper apart and cleaned it with denatured alcohol.

Then I drained as much of the DOT 5 out of the master cylinder as possible and filled it with more denatured alcohol. Then I ran the denatured alcohol through the master cylinder and caliper just like I was bleeding it. I filled and drained the master cylinder several times with the alcohol. Lastly I filled the master cylinder with DOT 4 and bled the air out. It's been about a month now and the front brake works fine.

If, in your case, you're positive the caliper had DOT 4 in it to begin with you could just skip to the second step . . .

 

Just flush the DOT 5 out of the brake line as a couple have suggested and you'll be fine.

 

The issue with the fluids is a seal compatibility issue in the brakes. I am assuming the brake hose material is copmpatible with both but that would be worth check for sure. If there were small traces of 1 or other you really shouldn't have a problem. Flush the hose and you're good to go

 

Let us know how the Brembo conversion with calipers and m/c works when using the OEM, non-Brembo brake lines. The Brembo system is a higher pressure system than what you are replacing and the brake lines on the '08 and newer bikes reflect the pressure change. HD could have used the same brake lines but didn't.

I re-used the stainless brake lines I had on my '04 since HD used the same part no. for the Brembo model. I'm not saying you won't see an improvement with the conversion while retaining the OEM lines, just curious to see if you have increased lever travel as the rubber lines swell with the increased pressure.

Carl

 

If there is an elevated brake pressure issue then this is an extremely important point

 

Be as rigorous as you can in cleaning out all traces of whichever of them you want out. I have first-hand experience of mixing them and it can get nasty, with irrepairable corrosion in the master cylinders and calipers. I would dismantle the master cylinder and caliper to clean them, rather than just flush them.

 

Wow, lots of great responses & info.

Let's see here...

1) I can explore the joys of mixing DOT 4 and DOT 5, and
2) Learn of the corrosive effects of various brake fluids in my brake system, and
3) Test the old H-D front brake line & see if withstands the increased pressure of the Brembo master cylinder.

Or,

1) I could spend $77 on a new 2008 front brake line and ride carefree.


I'm thinking it might be a while before we learn what happens when mixing old & new brake parts & fluids.

Thanks again all!

JR

 

A very accurate summary indeed. From a seal compatibility perspective the key thing then remains to use the fluid that was spec'd for those brake components