Power Take Off drives originally mounted directly on the back of the transfer case. With an overdrive installed in the PTO port, a special adapter was used to drive the PTO from the back of the overdrive. The overdrive has a conical shaped cap (for the rear bearing) which must be removed. This exposes the end of the overdrive shaft, which can now drive the PTO via a special 15 tooth "Drive Flange" sprocket.
To understand how the PTO is driven, look at this picture. This is the gear inside the transfer case on the aft end of the transmission mainshaft. When you remove the flat sheetmetal cover (secured by five bolts) from the transfer case, this is the gear you will see. This is the gear that is removed to install the Warn overdrive. The 6 splines inside fit on the transmission shaft. (The factory V6 CJ-5/6 had 10 splines) The 26 teeth around the perimeter (Later vehicles use 29 teeth) deliver power to the rest of the transfer case and the drive axles:
The PTO unit has an internally splined collar that is shifted forward to engage the 15 tooth Drive Flange inside the transfer case. Or in this situation, with an overdrive, it will engage the 15 tooth PTO Drive Flange added to the rear of the overdrive.
The next three images are courtesy of Bill Magee. The front of the vehicle would be towards the right. The first shows the sliding collar extended to the engaged position. The internal splines can be seen inside the collar. To the right of the picture is the Transmission Main Gear, held back so the PTO drive flange is visible. Note the mounting face of the PTO drive. Without an overdrive and PTO adapter, this would bolt directly to the aft face of the transfer case:
The next image shows the sliding collar retracted. Note the gap between the units. When installed, this gap is approximately .060". The shift fork is controlled by a lever sticking up through the floor:
This picture shows how things look with the collar extended and the Transmission Main Gear held in the proper relationship. When the transmission gear is turning, it will power the PTO drive:
The next two links, courtesy of Rick Grover's website, show the adapter sold by Warn allowing a PTO to be used behind the overdrive. These Warn images are slightly misleading because the portion of the PTO that would have projected forward into the transfer case was not shown for clarity. Note the special PTO drive flange added to the rear of the overdrive unit. It has the exact same 15 teeth as on the Transmission Main Gear Also note how the PTO drive is relocated aft with the overdrive and adapter:
Jeff Gent has an overdrive and Warn-manufactured PTO adapter on his Willys wagon and kindly supplied some pictures. The Warn overdrive, with the rear bearing cap removed, is shown bolted behind the Dana 18 transfer case in this image:
The OD/PTO adapter is shown bolted to the rear face of the overdrive, using the four bolts which originally secured the rear bearing cap. The special "Drive Flange" sprocket (not shown in this test fit) is secured on the aft end of the overdrive shaft :
The aft face of the adapter has the same pattern as the PTO port on the transfer case, allowing the PTO drive to bolt right up. Note that the Koenig PTO drive for the wagon is a different design than used on the CJ series:
Warn stopped production of the adapters years ago and I would have had to find a used one, generally only available at a price comparable to a king's ransom. As I have a Scotsman's wallet (A Velcro flap that screams when opened) I had the bright idea at the time to make my own adapter. Faithful reproductions, including the special Drive Flange, can now be found at HermTheOverdriveGuy.Com at a very reasonable price. (Disclaimer: I am his web designer) My semi-brilliant plan at the time was to use five long mounting bolts, securing the PTO drive, custom adapter and overdrive to the transfer case all in one fell swoop. Mostly this was chosen for ease of machining.
The following is a cross section of my homemade adapter. The details inside the overdrive and PTO drive are not shown. The front of the vehicle would be towards the left.
The cross section of the overdrive as seen above is not entirely accurate. Since the overdrive's main housing has a teardrop shape, one of the stock mounting bolts passes right through the inside of the overdrive case. Warn used a washer with a seal for that mounting bolt. The other four bolts pass within the wall of the overdrive case and don't require a seal. Sealing this one bolt proved to be a problem, due to the fact that the adapter must also secure the ball bearing in the rear of the overdrive. In the cross section image, note the recess for the stock OD mounting bolt heads. A seal washer, not shown, had to be added in the exact thickness so the bearing was held securely and the gasket also compressed properly. Since seal washers don't come in very many thicknesses, I had to machine the recesses slightly deeper to match what was available. Compensating with thicker gasket paper between the OD and PTO adapter was not practical, as it would have had to have been quite thick. The seal washers were needed on all five bolts. Oil can migrate under the bolt heads inside the PTO drive and travel forward. Without seal washers on all five bolts, there would be a leak. I could have added the seal washers under the five bolt heads instead, but that one bolt will still need a seal washer between the overdrive and adapter.
It has been some time since I built my PTO adapter. Sorry that I have no pictures of it, but I installed it for a test fitting, and before I knew it I was driving around. The adapter is relatively simple, but it taxed my limited machining skills. It is made from 6" diameter aluminum bar stock approximately 4" long. Appropriate holes were added to match the oil passages on the overdrive's rear plate.
The PTO drive flange, on the rear of the overdrive shaft, was made from a transmission mainshaft gear with a broken tooth. The six splines for the T90 mainshaft match the overdrive rear shaft. I cut away the bulk of the gear, leaving just the 15 tooth PTO drive flange and a short section of the splines. Since the gear is induction hardened, I cut away the bulk of the material using a cutoff wheel in a die grinder. That reduced the amount of hardened material that had to be removed using the lathe.
Were I to do it over again, I don't know that I would have used the design with the long bolts. One unforeseen problem was installing these long bolts. Immediately aft of the PTO is a hat channel under the body tub. This hat channel was deep enough to interfere with installing the top bolts. I had to unbolt the crossmember and let it down (on a jack) about 2" so the bolts could be installed. This would add extra work should any field repairs ever be needed. But overall, I am very pleased with the PTO adapter and how it turned out.
Here are the details of my PTO shift lever. Note how it doesn't come up through the stock location in the body tub due to the overdrive and PTO adapter. I had originally planned to make a remote lever that would utilize the stock PTO lever hole in the floor. However, the top of the PTO is nearly touching the floor so there wasn't much room. Also, the stock lever would stick straight up. I was concerned that it might get bumped aft to the engaged position. This custom lever is bent forward 90 degrees. If it gets stepped on, it will be to the disengaged position. At the original PTO lever hole, I made a cover plate with a spring-loaded latch to hold the lever in the disengaged position. I've heard too many horror stories of folks driving off with the PTO engaged and the winch cable ripping the bumper loose or worse.
Here we see the lever raised to the engaged position. The shift boot came from a Pontiac Fiero and fit perfectly:
Here is an image with the shift boot removed. The stock PTO lever oil seal was a piece of felt. Before I installed the shift boot, I discovered the felt seal didn't work very well. Gear lube sprayed up around the PTO lever during a test drive, but not enough that it was noticeable right away. That was only a minor problem. The big problem is that my formerly-devoted wife liked to set her purse right behind there. The next day I made an oil seal from the dust boot on a brake wheel cylinder:
Here is an exploded view of the stock felt seal. The piece of felt will be sandwiched between the two plates. Note the notch in the lever which engages the shift rod inside the PTO drive:
Here is the stock felt seal assembled. The dimpled profile of the upper plate is a little easier to see. You cannot see the felt between the two plates. When installed, the plates retain the lever pivot shaft in a recess in the top of the PTO drive:
After the purse soaking incident, here is what I made. The new plate uses the same four screws for mounting. The oil seal is a dust boot from a brake wheel cylinder:
Here is the new seal installed on the lever. The dust boot has been turned inside out in this image. When I installed this on my PTO drive with a different handle bent at 90 degrees, I found it worked better when I put the dust boot back to its original inverted shape:
