My brake light stays on constantly on my '83 W250 and believe my proportioning valve might be tripped or have some air trapped - anyone experience this problem with first gen trucks? Thanks

 

Could try bleeding the brakes, see if you can get it to reset.

 

They have been bleed by the shop but noticed front brake line are ancient, hard and cracked so system will have to be open again to be bled anyway. I have read that a worn/leaky master cylinder can create a constant light too along with the proportioning valve. Master cylinder cheap along with hoses - finicky system

 

Master certainly could cause the issue. Proportioning valve generally just reacts to pressure supplied by the m/c, and pressure held by the brake system.. If there is a fault anywhere, (leak....) valve will be displaced, and turn on the lite in the dash.

 

Not sure about what dodge did in the 80's but the 70's trucks had a terminal on the prop valve, It would trigger the light if the pressure on both front and back where to different(meaning a leak or not building enough pressure on both sides). Also did you check to see if it's switch on the emergency brake?

 

Yep, definitely not ebrake activated

 

are the rear brakes properly adjusted?

 

Yep. adjusters are freed up, newer shoes, drums turned. I picked up a new MC and also noticed that front brake hoses are ancient and cracked. Will remove these and replace and do a thorough bench bleed on new MC, install, bleed again and check proportioning valve. My gut tells me my MC is worn and has some pressure loss -




Yep, adjuster freed u