If this is posted in the wrong spot please let me know. I recently purchased a 67 C50 farm/grain truck. Original 327 - 4 Speed - Hi/Low rear axle. I wouldn't say I am restoring it but definitely doing a re-fresh.
One thing that has me completely baffled is that the engine pulls vacuum continually from the cab filter (near the back of the seat on drivers side) regardless of whether you push on the brake pedal or not. The vacuum booster is working (pulls brake pedal down when you start the motor with slight foot pressure) and it actually has good brakes and pedal. Has original firewall mounted brass check valve. I can hear the valve under the floor switching when you throw the two speed switch up/down. Now whether it's actually switching lines I have not confirmed but it sure sounds like it is. All lines and hoses look good.
So I know this pulling of constant vacuum can't be correct because it will and does make the motor run wonky but I'm not sure where the issue is or how to correct it. My thought is that it should only pull atmosphere vacuum when stepping on the brakes like every other farm truck I have seen.
Seems like the problem is in the valve under the cab. Can someone confirm? Appreciate any feedback!
