The Stovebolt Site Forums The Parking Lot Big Bolts 1951 4400 Master Cylinder

Trying to solve my brake problem on this truck I thought I would change the master cylinder. When I do a search for the part, I find sites that have a master cylinder for trucks up to 1 ton, or the 3800 models. These all have a 1.25" bore. I took the one off of my 1.5 ton truck (no hydro-vac) and it too has a 1.25" bore. So why don't the parts places include the 4400 in the "works with this truck" column?
Cylinder looks good with no visible pitting or rings and good looking seals. Brake fluid is cloudy. So now I fear all the wheel cylinders need to come off for replacement, rebuild or cleaning. The brake issue I have is the brakes go on but don't come off until the truck sits for hours.

Hy Gazz, a lot of sites don't include trucks over one ton in their descriptions even when the parts are the same and will fit on trucks larger than one ton. As to your brake problem, it sounds to me like the master cylinder piston is not returning to its full at rest position. Is there a return spring on your brake pedal linkage? Have any adjustments been made to the linkage or master cylinder replacement lately? There must be a slight amount of clearance between the brake pedal linkage and the master cylinder piston, I believe the manual calls for 3/4" pedal movement before the master cylinder piston starts to move. If your checks reveal no problems in this area, then I would suspect the flexible brake lines may be "Check valving", good luck

3B, thanks for the input. Yes there is a return spring for the pedal and I have no idea about any previous adjustments since I bought the truck last fall and it was last registered in 2003 or so. The brake lines are newer as are the rubber flex lines so somebody had done this work before I got it, probably when it was last registered. I hadn't done anything with the master cylinder or pedal as far adjustment goes or anything for that matter. I did remove the drums and cleaned with brake cleaner and pressure washer and lubricated the moving parts of each brake assembly as per the manual.
So the other day I did remove the master cylinder and took it apart. It looks essentially new inside. The bore is clean with no rust, pits or rings except for a small amount of crud that had collected near where the piston would be at rest. This was wiped away with my finger for the most part and then some scotch brite type stuff to clean off what was more stubborn. The rubber cups look fine and are pliable so I put it back together. I clamped it in a vise and took a short piece of brake line that looped around from the output of the MC and routed it to empty into the reservoir fill opening and added brake fluid. Pumping the piston in creates a good stream of fluid back into the reservoir but I noticed that when I retract the push rod, there is a slight delay in the piston to catch up, maybe a second or two. I've never done this before and don't know what is normal or correct but guess that the piston with its compressed spring would stay in contact with the push rod always or, maybe the fluid is enough to delay this action. I wish I had done this prior to taking it apart to inspect as that may have told me something, I don't know. I may get to putting it back into the truck today but probably tomorrow.