My brake lever that is...finished installing dual Brembo GP4-RS calipers and my lever is not as firm as I'd like. I haven't ridden the bike (and won't for several months), so I don't know about actual breaking feel, I am just talking about lever feel and travel. I am confident that there is no air in the system so my next step might be replacing the master with a different size. When the bike was a single disc with 9/16 master my lever feel was great, very firm and readable. When I went with the dual FXDLS setup a couple of years back I also added the stock 11/16 master and that's where I lost the feel. No matter how much it was bled it's mushy and there is too much travel before engagement.

It looks like I have 3 options for stock style master cylinders, the 11/16 (that ain't cutting it), going back to the 9/16 or the Harley Touring Brembo caliper @15mm, any other suggestions? I really would like to keep my control setup looking stock, so I don't want to swap to a Brembo master if I can get around it. This is about the only sizing information that I've found and the authors reference for feel is racing Front Master Cylinder Ratio Chart (vintagebrake.com)

EDIT: I forgot to mention that these Brembo's have 4, 30mm pistons each.

 

Man I thought you were talking about your dick. I was going to tell you to keep pulling.LOL

 

Yeah, just some Monday word play

 

I've used the hold the brake handle in the "applied" position", cover the master cyl. overnight and if there are bubbles in the system they work their way up. This is on a single brake system. I used a rubber band to hold the brake lever back.

 

Didn't work, I tried it overnight twice, that's one of the reasons I'm pretty confident when I say it's not a bleeding issue.

 

cmon man im browsing these forums on my work computer!

 

I don't know if this will help or not. When I have trouble getting the lever to feel good, I will crack the line at the master cylinder and bleed from there first. It seems like I always get bubbles from the master cylinder when I crack the line with the lever pulled back. I always do this until I get no bubbles. Now I bleed the calipers. This method always gives me a good firm feel if you know what I mean!

 

This is worth a try...

You said the 11/16 master has never had proper feel... That leads me to think it's a bleeding issue, or maybe a bad seal in the 11/16 master.

I always bench bleed a new master cylinder before hooking it up to the "system".

Did you bench bleed the master cylinder when you first added it to the system..?

There are also many people, who on tricky bleeds, will use pressure to force the brake fluid up through the caliper to the master. The flow of fluid in the direction any air bubbles will want to flow, is also helpful on a troubled bleed.

Does your bike use DOT 4 or DOT 5...?

I have had to use the "tie the handle overnight" trick on my DOT 5 bikes, because of DOT 5's tendency to form micro bubbles. I've never had to resort to that with my DOT 4 bikes.. This trick works best if you psoition the handlebars so the brake lines to master are in aa straight as an upward line as possible... I hope that make sense.


All that being said, I have never changed calipers from OEM. I am unexperienced in how different size calipers may require more fluid movement to function properly..

You might give Brembo a call. See if they can offer a definitive assessment on whether the two HD master cylinders would work well with their specific caliper you are using... If they say one should work, then you will know to focus on a bleeding issue


Keep us posted on the remedy...

 

I'll give it a shot, thanks.

No, when the new master went on 2 years ago, I could not figure out how I could bench bleed it. It is a DOT4 bike and has had everything from normal bleeding to speed bleeding to power bleeding done, including cracking all the connection points last year and the rubber band trick, and tapping on the lines and splitter, etc., and nothing has really changed.

I HAVE NOT tried going reverse though, that might be worth a try before going to a new master. I'm going to try and find the stock caliper bore size for comparison too, I bought the 30mm Brembo's specifically because they were smaller than other models.

I HATE bleeding brakes. Seems like no matter how careful I am I get fooking fluid everywhere!

 

What size are the stock pistons?
Also, if you hold them face-to-face, do the new pads have about the same surface area as the stock ones?
I'm all in for giving Brembo a call. This ain't their first rodeo so they may have the info you need to ensure that you have the correct master-to-slave ratio before you proceed down other avenues.