We should keep the JollyRoger rebuild sticky as a learning thread and put your solutions on one of your original threads Brad. It's all good information that we like to keep for future "Brake Problems", so we'll link your solutions over here
http://www.steelsoldiers.com/showthread.php?159330-never-ending-M135-brake-problems!!-Need-advice so we can find you.
The Air-Pak challenge might be solved with a simple cleaning and lubrication of the large diameter "Air" side of the Air Pak but there is a way to determine if it's a hydraulic or air problem. Draining the air-tanks each time you drive it may help keep this from happening.
We were fortunate enough to have 2 trucks go through the "Brakes lock and don't unlock when pedal pressure is released" symptom. We started to do forensic work on the Air-Paks to see if we could nail down the problem.
There is one easy step to see if the large piston is coming all the way back which allows fluid to flow 'away' from the wheel cylinders. 3 steps if you haven't already opened the valves on the air-tanks.
1) Open valves on air-tanks to be sure there is no air pressure in the system.
2) Remove small plug at back of air-pak.
3) Insert measuring device into hole and see what your dip depth is.
The depth on a fully seated air piston is 1 1/4"
If the large piston is properly seated then it is possible the valve that allows 'brake fluid' to return through the air-pak is hung up, sticking, not moving properly.
This next step needs to be done once the brakes are properly set up which means jacking up the truck and following more simple steps listed on page 439 of the 9-8024 TM.
Once the brakes are set properly you just open the valves on the air-tanks and test for proper operation of the brakes without air assist. The way this landscaper is reading things, the fluid flows into "G" inlet line and out through "H" the outlet line as long as the rod "MM" is in the fully returned position. If the brakes return properly without air, then the problem is in your "Air" side of the system, which
can be an easy fix.
If the fluid does not return properly and release brakes, then the problem is likely with piston "GG" which is more difficult to get at or "A" which sits at the start of the air supply line. .
Get the brakes set back up properly, test the beast without air and dip the air side, large piston to see what you're dealing with before you do another tear-out.
There could also be a slight deflection/ dent/ deviation in the shape of the large canister which will hang up the large piston and prevent it from returning to the 'full open' position. This Plate/Packing assembly (H&G), shows a slight oval in the housing which could be a part of our problem on Gizmo, the M135. Gizmo's owner suggested using a pipe with the same outside diameter OD as the inside diameter ID of the canister to help round things out.
If the problem is just with the air side of the Air-Pak then it's only the air pipe and the large canister that need to come off for cleaning. We still need to be careful with dismantling the large canister. I'm tearing down 2 air-paks and on one of them the canister to housing rubber seal appeared soft and stretched out when I pulled the canister off. We need to check if one of the 'newer style' air-pak kits has this seal or find an alternative.
