V-Twin Forum banner

1 - 2 of 2 Posts

·
Registered
Joined
·
278 Posts
Discussion Starter #1
Hi. I came by some new 6-piston PM calipers. I installed them on my Road King. I already had braided-steel lines. Everything else is stock, 11.5" discs, master cylinder.

The problem I'm having is that they 'feel' like I don't have them bled properly, though they are. I even took the bike to the dealer, who didn't have any better luck. The first pull on the lever, the lever travels to within about 1/4" of the grip. The next and subsequent pulls are a little better, maybe 1/2" from the grip, but still somewhat spongy. At 1/2" from grip, the front wheel can be locked. But the feel of the lever is crappy, too much travel, and 'spongy'.

The stock calipers didn't have this problem, the lever was solid, and not nearly as much travel before action.

Only DOT 4 was used, so it's not a fluid issue. And once again, with the original calipers and all things being equal, brake feel was good. Immediately after changing to the 6-pistons, things went 'south'.

The Harley wrench and I thought either the master cylinder (which he put a rebuild kit in to no effect) can't handle dual 6-pistons, or maybe the brake pads are too thin (their material is only about 1/8" thick)--the wrench thought the pistons looked like they were sticking out of the calipers too far, supporting this last idea.

If anyone knows what might be going on, I'd appreciate any ideas.

Thanks a bunch for any insights, Alan
 

·
Registered
Joined
·
278 Posts
Discussion Starter #2
Since I posted (above), I found that PM does have an installation guide on their web-site. It calls for DOT 5 fluid. I used DOT 4, which is what the bike came with, and what was in the system. But I don't think this is the issue. (The calipers had never seen brake fluid, so there's no issue of mixing glycol with silicone based fluid).

From what I'm able to gather, brake system rubber components are as at-home with DOT 3-4 as with DOT 5. The problem arises when attempting to mix the two types (glycol and silicone), or if a system that's used one is converted to the other type. In the latter case, the rubber seals should be changed.

It's interesting to note that DOT 5 is more compressible than DOT 4. This translates to the fact that DOT 4 provides a more linear feel, which means it's easier for a rider to gauge what small changes in pressure should (will) do, in turn resulting in better 'feedback'.

Advantages to DOT 5 are higher boiling point, and it won't harm paint/plastics.
 
1 - 2 of 2 Posts
Top