[Terry Rogers]

When i was Bleeding tha rear brakes on my father-in-laws 1988 1500,
I was drawing brake fluid through the bleeder valve before I opened the valve up. The built up pressure from the Mityvac pump sucked fluid out.
Does the bike have a bad caliper or bad bleeder valve. The brakes did work (although they had a spongy feel) no visible signs of fluid leaking
either.

 

[Red]

The bleed valve must have been just finger tight. When you put the Mity Vac hose on the bleeder you had to loosen the bleeder a hair. If the bleeder valve had been open before you touched it, hitting the rear pedal on the 1500 would have blown fluid all over the place.

Tighten the valve and see if it seals itself.

The 1500 brakes will probably feel spongy to you, because they are. The hoses get soft after 17 years!

Good Luck...