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I rebuilt the transfer case air cylinder on the M818 last week. It had the air leaking when it was in neutral or forward gears problem. It had been doing this since I got the truck but I could put it in reverse and let the air pressure build up and then it would seal. The truck sat for a couple of months while I was on a trip and now I couldn't get the leak to stop any more. I decided it was time to just change the seals and be done with it.
The procedure is very easy and is the first thing under transfer case in the TM. It's a good idea to look at the TM for torque specs etc. I was pressed for time so I don't have pictures but it you have this problem and know where the air cylinder is, you are half way there.
I got the seals from White Owl at $17.50 each. I've read the copper washers or gaskets that come with the rebuild kits are the wrong size. I don't know where those kits came from but I thought I would just play it safe and just buy the seals. After taking the cylinder off I can see you don't need the new washers/gaskets because the ones installed are thick and I didn't see any deformation at all. I just cleaned them off and turned them over and re-installed them.
You don't have to remove the front driveshaft or flange. Remove the air line that goes to the end of the air cylinder. remove the 4 bolts that hold the air cylinder on and remove the cylinder end (one bolt doesn't slide past the front drive flange until you remove the cylinder end). There's a nut in the piston; remove this nut. Tap around the outside of the air cylinder to loosen it and once it's out of the transfer case remove it and the piston together.
The copper washer/gaskets are in the bore where the cylinder mounts on the transfer case and in the cylinder end. They come out easily with a small screw driver or similar tool.
I didn't disassemble the piston. I let it soak in a can of diesel to get the crud off. There are 2 flat washers (one on each side) in the piston where the nut and shaft contact the piston. Don't lose them.
The piston is brass and mine had some scoring on the end rings that center the piston in the cylinder. I took a few minutes and sanded these down. The cylinder also had some scoring on each end to match the piston. The actual sealing surface is near the center of the cylinder and the piston throw is short so you don't need to worry too much. I used a brake wheel cylinder hone to hone the cylinder.
Cut the old seals off with a razor knife being careful not to gouge the piston. Clean and dry the piston at this point and install the new seals with the lips pointing to the ends of the piston. The seals are tough to get on the piston so just go slow and use a small screw driver to help work the seal on. Once the seals are in the slots on the piston make sure they are not rolled or twisted.
Wash and dry the cylinder then put some air tool oil or ATF in the cylinder and on the piston. Install the piston in the cylinder (you need to work the seal into the bore with your fingers) and put the washers back in the piston.
If you haven't already done it, clean the cylinder end cap and the bore in the transfer case and wipe off the copper washers/gaskets and re-install them. Slide the piston and cylinder assembly over the shift rod and install and tighten the piston nut.
Now insert the bolt that won't clear the front drive flange in the cylinder end cap and noting the orientation of the air line fitting (should be at the top), install the cylinder end cap and the rest of the bolts. Use a torque pattern and make sure the cylinder and end cap assembly are pulling down straight. Once everything is tight, bend the locking tabs back over the 4 bolts.
Apply thread tape to the air line fittings and re-install the air line.
Start the engine and check for leaks and operation.
The procedure is very easy and is the first thing under transfer case in the TM. It's a good idea to look at the TM for torque specs etc. I was pressed for time so I don't have pictures but it you have this problem and know where the air cylinder is, you are half way there.
I got the seals from White Owl at $17.50 each. I've read the copper washers or gaskets that come with the rebuild kits are the wrong size. I don't know where those kits came from but I thought I would just play it safe and just buy the seals. After taking the cylinder off I can see you don't need the new washers/gaskets because the ones installed are thick and I didn't see any deformation at all. I just cleaned them off and turned them over and re-installed them.
You don't have to remove the front driveshaft or flange. Remove the air line that goes to the end of the air cylinder. remove the 4 bolts that hold the air cylinder on and remove the cylinder end (one bolt doesn't slide past the front drive flange until you remove the cylinder end). There's a nut in the piston; remove this nut. Tap around the outside of the air cylinder to loosen it and once it's out of the transfer case remove it and the piston together.
The copper washer/gaskets are in the bore where the cylinder mounts on the transfer case and in the cylinder end. They come out easily with a small screw driver or similar tool.
I didn't disassemble the piston. I let it soak in a can of diesel to get the crud off. There are 2 flat washers (one on each side) in the piston where the nut and shaft contact the piston. Don't lose them.
The piston is brass and mine had some scoring on the end rings that center the piston in the cylinder. I took a few minutes and sanded these down. The cylinder also had some scoring on each end to match the piston. The actual sealing surface is near the center of the cylinder and the piston throw is short so you don't need to worry too much. I used a brake wheel cylinder hone to hone the cylinder.
Cut the old seals off with a razor knife being careful not to gouge the piston. Clean and dry the piston at this point and install the new seals with the lips pointing to the ends of the piston. The seals are tough to get on the piston so just go slow and use a small screw driver to help work the seal on. Once the seals are in the slots on the piston make sure they are not rolled or twisted.
Wash and dry the cylinder then put some air tool oil or ATF in the cylinder and on the piston. Install the piston in the cylinder (you need to work the seal into the bore with your fingers) and put the washers back in the piston.
If you haven't already done it, clean the cylinder end cap and the bore in the transfer case and wipe off the copper washers/gaskets and re-install them. Slide the piston and cylinder assembly over the shift rod and install and tighten the piston nut.
Now insert the bolt that won't clear the front drive flange in the cylinder end cap and noting the orientation of the air line fitting (should be at the top), install the cylinder end cap and the rest of the bolts. Use a torque pattern and make sure the cylinder and end cap assembly are pulling down straight. Once everything is tight, bend the locking tabs back over the 4 bolts.
Apply thread tape to the air line fittings and re-install the air line.
Start the engine and check for leaks and operation.
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...another air leak at a 3/8" air brake to 1/4" NPT fitting on the forward/neutral hose
. The fitting had a nice hairline crack that would become worse with tightening. Ordered a couple extra and now all is good...no more leaks. Shifts good with a hearty thunk.
