Rear brake has no pedal after sitting for a long time

Try bleeding the brake sys

If you need further help, I’m available over the phone at https://www.6ya.com/expert/richard_b59056c0c62ecb00

After reading your description, two ideas come to mind. If you have bench tested your master cylinder and it does not leak down. You have checked all fittings, lines, and master cylinder for leaks, and there are none. Then would suspect an issue with the rear brake caliper. You mentioned that you replaced the rear rotor due to it warping. I am curious to know why it warped? Raise the rear wheel off of the ground and spin the wheel. It should spin freely. Then apply and release the brake, to that wheel (a few times). After releasing the brakes, spin the wheel again. Does the wheel still spin freely? If it doesn't then I would check the brake pedal (see if it is releasing freely or binding), check the brake lines (see if there are and defects, flat spots, or kinks), and check the rear brake caliper (do all the cylinders retract with little resistance?) If the wheel does spin freely then I would check to see if you are using the correct type of brake fluid. Most bikes will require you to use DOT 4 or 5 brake fluid. If you substitute for a cheaper grade, it will affect the braking system. It may sound silly but I would double check that you are not accidentally resting you foot on the brake pedal. If that was happening, it would cause the brakes to fade. I hope that helps but If you have other details or question, let me know.

"pedal all the way down, no movement of caliper"
Sounds like hydraulic problem.

Check if you have enough brake fluid.

If so, it could be a bad master cylinder.
Rear brake light switch won't work without hydraulic pressure (which also works the caliper), while front brake light switch is mechanical.

There are multiple possible reasons:
1. Brake caliper is not adjusted so pads are within 1/8" or so of rim (rim should be straight enough to allow that).
2. Brake pads are old and hardened.
3. Too much friction in brake cable and housing
4. Brake cable housing is too long, allowing too much flex.
5. If brake levers have been replaced wrong levers were installed.

p.a. It is helpful to know whether a problem is new, has developed gradually over time, or has always been there, and if any maintenance or event occurred just before the problem began.

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Just bleed the brake system. That will take the air out of the system it is a common problem when you let a goldwing sit.
First bleed the front left brake then bleed the rear brake they both work off the brake pedal.
When you are done with that bleed the front right brake with the hand brake lever,
Get a service manual for your wing it explains how to do many services and it will save you money.

Check your rear brake resevoir. Fill it with Dot 4 brake fluid and proceed to bleed the brakes, If this does not resore your braking and there is no sign of a leak on the rear caliper, you will have to replace the seals in the master cylinder, or the complete cylinder.

Make sure the rear brakes are adjusted and also make sure there are no leaks. if there are no leaks then you have air in the system or a bad mastercylinder, rebleed the brakes, have someone inside pumping the pedal three times every time, then start at the right rear wheel and bleed it four times, each time have them pump pedall three times and hold it down, then go to left wheel and do the same then the right front then left front. to make sure you dont run master dry top off the fluid after every wheel, then adjust the rear brakes, and after that if pedal is low replace the master but you may just have air in the system, and make sure there are no leaks on any line. hope this helps.

Try putting the bike on the center stand and get the front wheel off the ground with a floor jack. Spin the front wheel by hand and press on the rear brake pedal. The front wheel should stop. Likewise with the bike on the center stand and the rear wheel off the ground you should be able to lock the rear wheel with the foot pedal. On many Goldwings the rear pedal also operates one front disc. This is for people that refuse to use there front brakes to stop or slow there bike (80% to 90% of your stopping power is the front brake). Try bleeding the entire system front and back, you may just have air in the system. If the rear brake still does not work you may have a bad delay valve in the system. If you need to take the bike in to a shop, try to find a mechanic that is familiar with the system so they do not replace parts unnecessarily. That way you minimize your shop time and maximize your riding time.

If it has been sitting on the sidestand, the cylinders on the low side occasionally become fouled - which will clear up pretty fast or after changing the plugs. There is probably gunk in the rear caliper from sitting & dealer may want to check the fronts as well. Dealers are really expensive & I would guess that they would want $250 or so just to fix the rear brake issue. When i needed all my calipers cleaned, my dealer wanted almost $1000., so I did them myselves for about $50. Rick

The taillight should be on at all times. The brakelight should come on when the front or rear brakes are applied. Start by disconnecting the front brake light switch then the rear to see which switch is broken. Also check the bulbs. I have seen them short out internally. The filament inside the bulb break and contacts the other circuit.