Soft front brakes

82 750ltd - this bike has the twin front rotor setup. I fitted a master cylinder from a 94 ninja after putting shorter, lower bars on as the ltd master would not fit right. The ninja master is 5/8. I was expecting the lever to be a little stiff with the larger bore master, but it's opposite. The front brakes do work, but engagement doesn't occur until the lever is close to the grip. It feels like air in the system, but I have bled about a quart of fluid out of the calipers. Any ideas/suggestions? Should I rebuild the ninja master cylinder or look for a smaller bore master?

5/8" is the correct bore for dual disks; I definitely would not try a smaller bore master cylinder. You probably still have air in the lines. Some folks have had luck getting air out of the lines by strapping the brake lever as close to the grip as possible and letting it sit that way overnight. Ed

650ed wrote: 5/8" is the correct bore for dual disks; I definitely would not try a smaller bore master cylinder. You probably still have air in the lines. Some folks have had luck getting air out of the lines by strapping the brake lever as close to the grip as possible and letting it sit that way overnight. Ed

I can second that. It has worked for me before.

Watch your brake lines and see if they bulge. Also you may have to clean out the M/C . There might be some crud in there.
Steve

If your bike still has the stock rubber brake lines you should consider updating them. For one thing they are 33 year old rubber parts with all that goes with that, AND unless the brake fluid has been changed every couple years during those years there will be some scale/grunge buildup on the inside of the line which will contaminate your brake system.

Strapping the brake lever back to the grip may help, but not so much to help bleed the system, rather the constant pressure will encourage your caliper pistons to move closer to the disc.

And speaking of calipers, if they have never been cleaned out now is a good time. Use compressed air to pop the pistons out so you can clean out the grunge. Like the brake line there is very likely some sludge build up inside the caliper. Flushing the fluid doesn't dispel this crap. You need to tear down the system to do that.

If the lever itself is bent slightly or its travel is limited in some way you could replace every other part of the system and still have soft brakes. A new lever is about $10. Something to consider before spending $$$ on new lines.

The fluid was really bad. I do plan on getting braided hoses and caliper rebuild kits soon. I suppose I just wanted to make sure the new master was going to be compatible before i went any further. Im going to try doing a vacuum bleed to see if that makes a difference, and try the lever zip tied to the grip trick.

JaFlo wrote: The fluid was really bad. I do plan on getting braided hoses and caliper rebuild kits soon. I suppose I just wanted to make sure the new master was going to be compatible before i went any further. Im going to try doing a vacuum bleed to see if that makes a difference, and try the lever zip tied to the grip trick.

This is probably what should be my next project after my lazy rear gets the motor back in from the starter clutch fix...... had the braided lines all picked out and the caliber, fluid and master cylinder kits bought so I'm mostly ready just need to get it done.