Air Hydraulic Unit

I am thinking about rebuilding my Air Hydraulic Unit. The reason is that When I drive the truck it often makes a howling noise from the rear breaks when I start off from a stop. I think what is happening is that the AHU is letting air continue to hold pressure on the hydraulic line even after I let off the breaks. I don't think it is much but I hate to ruin the break shoes if the AHU is keeping a continuous drag on them. I have seen some posts on SS about the need to rebuild the "Air Pack" Assume that is AKA for Air Hydraulic Unit. In the other posts the symptoms are either little or no breaks or break hang up/lock up. I am thinking that I may be in the early stages of the later category. Does this soud right and can anyone give me any advice about rebuilding the air pack? Do I need to take it completeyly apart or is it that there are only some parts that really need to come apart? As always help or advice is welcomed.

Thanks guys

Strip it down. Rebuild kits are available from a variety of sources including Ebay. Cranetruck did an article in MV Magazine on just this subject.

Of course, the first thing you could do is take off the J pipe that connects to the middle rear side of the air cylinder and shoot a couple of squirts of air tool oil, CLP or something similar in there. Reconnect the J pipe and drive it around a little bit; it just might need a little lubrication to get it working smoothly again. If that doesn't help then you can undertake the rebuild.

Brakes

I agree with lubing the air pack first. Its not a split system so if one brake is are not releasing quickly the same should be true of the rest. I would jack a non-squealing wheel up and if the brakes release properly I would suspect something in the squealing wheel(s). I had a front wheel that was always slow to release. I took it apart several times and looked it over to see if I could see the problem. Nothing. Tried cleaning, lubing spots where shoe contacted backing plate (high temp brake lube) I even tried replacing the front brake lines (rubber) nothing. I finally found the problem and it was the stud that goes through the shoe at the bottom. Being the lowest section of the brakes it sees more dirt and moisture and is the last to dry. Cleaned shoe and stud with sand paper and a small dab of never seize and it has worked properly ever since.

Thanks for the tips guys. I'll try the air tool oil first. Fingers crossed. Then if no improvement I'll dig in to the AHU.

m35a2cowner, one question. How were you able to tell which wheel was giving you the trouble? When mine makes the howling noise I can only tell that it is comming from the rear wheels. But if it is one in particular I can't tell.

Broke Back Brakes - the novel

In my case I was lucky and it was one of the front tires, it made the truck pull to one side. For a rear end noise I would: Make sure all tires inflated to the correct pressure, look for signs of bad or mis-match tire size. A bald or badly worn tire will make a surprising bit of noise. Check oil levels to see if they are full. Jack each wheel up, might have to do more than one if rear shaft connected, and spin each to listen for any dragging noise. Also check for loose wheel berings (look at lug nut/studs as well -- look for rust streaks around nuts- check to see if nuts/stud tight) You might also want to load the mechanically inclined friend , or make him drive, in the back of the truck and drive around in the school/mall parking lot while applying the brakes at different levels to see if he can hear which wheel is loud. Or, have him listen as you drive past. You might also stick a finger (be careful - start doing first thing) on each of the brake drums and see if there is one or more hotter than the rest. Its normal for the front to be a bit warmer than the rear. If your a man of means (notice I have to use finger) or if you have yet to collect your Father's Day bounty you could use one of those high tech infrared temperature measuring devices.
Hope that helps out.