HarleyTechTalk

On the 06 Softail rear brake I'm not able to get fluid moving through the caliper bleed screw. Previously, the rear caliper worked when the bike had front controls.
The bike has been switched to mid controls and now the rear brake system is hybrid at best.
The rear master cylinder is from an 86 FXRS. The reservoir canister is from Wilwood. The steel braided lines are 3 AN. I've tightened the lines so there are no leaks.
When the bleeder screw is open no juice will flow through. 
Currently, the reservoir canister is sitting to the right of the starter and under the oil tank. Could the position of the canister (not being high enough) be the source of the problem?

These ydraulic systems don't usually care  as long as the drain back works, have you tried a vacuum on the bleed nipple? A big syringe from the auto store or even a dedicated brake bleeder kit

Can you loosen the line at the master and get fluid to flow there?
If so, loosen the line at the caliper and see if you can get it to flow there.
Or vice versa.

I have tried a pneumatic brake bleeder on it without success. I'll try loosing the line going into the master cylinder. 
I appreciate the suggestions.

Assuming you're flowing okay at the Master and the Caliper, maybe try removing the bleeder completely to ensure it's not blocked itself. Sillier things have happened.

Quote from: Tacocaster on March 13, 2025, 12:59:38 PMAssuming you're flowing okay at the Master and the Caliper, maybe try removing the bleeder completely to ensure it's not blocked itself. Sillier things have happened.

That might be the easiest place to start.

I plan to get started on finding the reason the brake fluid is not flowing today. I'll update everyone on what I find out.

You might try a bench type bleed on mc .

I'm getting fluid out of the rear caliper now mixed with air bubbles. Still no brake pedal pressure. 
I removed the banjo bolt going into the master cylinder, put my thumb over the hole and pressed the pedal. Fluid came out but not a lot of pressure was present.
 
Could the rod going into the master cylinder be too short to adequately depress the piston in the master cylinder?

Can you tell a bit more about this 40 year old master cylinder from '86 FXRS? Did you take it apart and confirm the bore is solid and maybe do a piston cup replacement?

-JW

The master cylinder is the problem. I'm going to replace it with a different style. Hopefully, I'll have better results.
Thanks for all your help.

A fairly common prblem with the rear master cylinder as a result of bleeding occurs when the pedal is pressed too hard and allowed to bottom the piston out in the bore.  The piston will wedge itself into the end of the bore and stick there.  Any subsequent pumps on the pedal will be useless because the piston doesn't return with the pushrod.  The piston can be pushed back by removing the line and or a light shot of air into the fitting hole.  If this turns out to be the problem and the pushrod can't be adjusted shorter to prevent this from reoccuring (bottoming) just be aware of the issue and DO NOT push the pedal until it stops or use too much force. Leave a little clearance and then close the bleeder.

Thanks, i was not aware of the piston potentially sticking.