What you have described is normal for an air brake equipped truck. There is no feedback with full air brakes and they cannot be compared to hydraulic brakes in that regard. There is a push button valve on the dash that is for charging the trailer brake system. It will be marked "Emergency" I imagine and be yellow. If your not pulling an air brake trailer it is of no consequence to you. There should also be another push/pull button valve for the parking brake. It is pulled out to engage and pushed in to release.
You claim that the trailer part has been removed. Are you thinking about the hoses and valve at the back of the cab? If so it is still just fine and there would be no air to them. Air is only released to the trailer thru the charging valve located on the dash (assuming it has not been removed also). There is no danger of them applying themselves so not to worry. The air brake system is simple and direct. What is important to undestand is that moisture is the enemy of any air system and your truck is no different so be sure to drain the reservoirs daily. If the sludge that comes out of the tanks contains a lot of oil it is from the air compressor which gets it's oil from the engine so don't let the engine oil level get too low. Adjustment to the brakes is made at the wheel on the slack adjuster/cam if not equipped with wedge brakes. It is possible that your truck does not have any front brakes as a lot of older tractors had them deleted.
