< Part Three >
+ Part 1: The original setup
+ Part 2: Adding a Pilot Bearing (After initial test drives):
+ Part 3: Transmission/Transfer-Case swap (Update)
-- The need for a new transmission
-- Removing the old units
-- Preparing the new units for installation
-- Changing the transmission mount
-- Installing the new units
-- Disassembling the motor
-- Replacing the motor bearings
-- Putting it all back together and results
« June 2005 »The need for a new transmission
When I originally started my JeepEV conversion almost two years ago, replacing the transmission and/or transfer case was never included as part of the original project. I'd assumed that my Jeep's stock transmission and transfer case were still in good shape and would provide years of future service. I was wrong. Over the past months my transmission had started to die slowly but surely. I guess in retrospect I'm not surprised as the vehicle and stock drivetrain had about 409,000 miles on it before I started the conversion. Thus, the parts weren't new and were likely nearing the end of their expected life even before I finished the EV conversion.
Though, it wasn't until recently that my transmission really began to exhibit symptoms indicating it was dying. For one, my transmission began making a very noticeable whining/whirring sound in all gears, especially at higher motor speeds. Sometimes it wasn't so bad, but other times it sounded like I had a jet engine strapped to my Jeep. Another problem that developed was that the transmission wouldn't allow the vehicle to come up to speed smoothly. When accelerating from a dead stop, the Jeep would have a noticeable lurching feeling, as if the transmission was holding back and the transfer of torque from the motor to wheels was occurring in short bursts instead of ramping up smoothly. A last symptom to alert me of transmission problems was that the transmission began heating up very quickly... it would get quite warm to the touch even after just a few miles of driving.
These problems finally convinced me that I needed to replace my Jeep's transmission. However, I had several options to choose from. I could buy the same model transmission and do a direct swap, or make a few modifications and upgrade to a better transmission. The reason why I even considered upgrading to a better transmission is because I own a 1988 model year Cherokee. Unfortunately, Cherokees made from 1987 to mid-1989 used the less-than-great Peugeot BA-10/5 5 speed manual transmission. This transmission is light-duty and has a reputation for short service life (especially due to problems with the synchronizers and 5th gear breaking). Most other model years of the Cherokee used the Aisin Warner AX-15 5-speed transmission for the manual transmission setup. Not only is the AX-15 a heavier duty transmission than the BA-10/5, but the AX-15 is generally said to be more robust and longer lasting than the Peugeot.
So I decided to upgrade to the AX-15 transmission, which is almost a drop in replacement for the BA-10/5. The only major difference between the AX-15 and the BA-10/5 is that the BA-10/5 has a 21-spline output shaft while the AX-15 has a 23-spline output shaft. This means that my Jeep's stock New Process 231 transfer case would not mate up to the new AX-15 transmission. So I had two choices; I could replace the main-shaft in my old transfer case to match the new transmission, or I could buy a new NP-231 transfer case already equipped with the 23-spline main-shaft. I decided to go ahead and buy a new NP-231 transfer case along with the AX-15 transmission. I figure that if I'm tearing the drivetrain all apart again, I'd might as well replace both the transmission and transfer case and cross my fingers the new drivetrain will last a very long time. A couple of weeks later a brand new AX-15 and NP-231 were delivered to my garage. I enlisted the help of some friends/fellow EVers, and so the swap begins...
Removing the old units
The first thing we had to do was remove the old transmission and transfer case from my Jeep. Although this task is generally straight forward, it is quite time consuming. Here's a mostly complete list of what all had to be done to free the transmission and transfer case:
- Remove front drive shaft
- Remove rear drive shaft
- Remove shift console and boot
- Remove transmission shift stick
- Disconnect transfer case shift linkage
- Drain hydraulic clutch system
- Disconnect clutch hydraulic line
- Disconnect reverse light wiring
- Disconnect speedometer cable
- Remove bellhousing bolts
Although at this point the transmission and transfer case should be able to be removed, this isn't the case with my Jeep. Normally, the idea is that you can slide the transmission and transfer case towards the rear of the vehicle until the transmission input shaft slips out of the clutch components, then lower the transmission and transfer case to the ground. However, in my Cherokee you also have to remove the motor before being able to remove the transmission and transfer case. This isn't how it should be, but was a negative side effect of the position I chose to mount the electric motor in when converting the Cherokee. So, after doing all of the above we got to work removing the batteries from the front of the Jeep so we could remove the electric motor. Once done, we removed the bolts holding the transmission cross-member to the frame of the Jeep and lowered the old transmission and transfer case. Once on the ground, I slid the units out from under the Jeep.
I'm now going to be chronologically incorrect for a minute. Here are some pictures comparing the old units to the new units so you can see them side by side. Obviously, the nice shiny silver units are the new AX-15 transmission and NP-231 transfer case, which in these photos are assembled together. Ok, I'll stop interrupting now, and get back to telling my story in pseudo- chronological order. :-)
After we removed the old transmission and transfer case from my Jeep, I drained the fluids out of them and separated the two units. I then put them on the pallet that the new units were delivered on so they could be shipped back to the manufacturer as core returns. Needless to say, I was happy to get the old grease-caked units out of my garage!
« June 19th, 2005 »Preparing the new units for installation
Before we could install the new transmission and transfer case, there were a few things that had to be done to get them ready for installation. The new transmission and transfer case were pallet shipped as two separate units. Also, they came without some of the needed accessories like a mount, speedometer gear assembly, throwout bearing, clutch slave cylinder, shift stick, etc... The only "extra" thing that came pre-installed on the units was the reverse light switch and wiring on the new transmission.
The first thing we had to do before installing the new transmission was modify its pilot shaft (the end of the input shaft). We had to do this so the motor would mount up to the new transmission as it did to the old transmission. If you read Motor, Clutch, and Drivetrain parts 1 and 2, they contain more information about why I ended up shortening the pilot shaft of my old transmission in the first place. Chris Robison took the electric grinder to the new transmission's pilot shaft, and made a nice clean cut, making the pilot shaft 3/4" shorter. I then slipped the new pilot bearing I bought onto the remainder of the pilot shaft to verify it slipped on and off smoothly.
Next, we stood the motor upright in the garage, and lowered the transmission onto it so I could verify that the transmission pilot shaft wouldn't hit the motor shaft. Luckily, as stated before, Chris did a great job cutting the pilot shaft, and it cleared the motor shaft by just the right amount.
With all of the pilot shaft concerns taken care of, I moved on to the next item of preparation for the new transmission and transfer-case: the speedometer gear. My Cherokee's speedometer and odometer are driven mechanically off the output shaft of the transfer case, through a plastic gear that spins the speedometer cable. The new transfer case didn't come with a new speedometer gear, as there are different sized gears used depending on your specific vehicle. So I unbolted the speedometer gear housing from the old transfer case and transferred it to the new transfer case. I was surprised that the little plastic gear looked to be in great shape... perhaps it had been replaced at some point or they just don't wear like I'd imagined a plastic gear would.
« June 27th, 2005 »Changing the transmission mount
The last item on my list before installing the transmission was the transmission mount. The old Peugeot transmission in the Jeep used a very strange, bulky mount to hold the transmission to the drivetrain crossmember. Needless to say, the new AX-15 transmission uses a completely different mount than the old Peugeot. So I went in look of a new mount. Luckily, the Cherokee's crossmember was pre-drilled to accept several different transmission mounts (as the Cherokees were available with several transmissions depending on model year, engine size, and if they were 4x4 or not). I was looking for an AX-15 mount that would also have the correct studs to bolt right up to my crossmember; this turned out to be a harder part to find than I anticipated. Nonetheless, I finally tracked down the mount I was looking for.
I determined that while the new transmission mount fit my crossmember, the new transmission would sit a tad off center towards the driver's side of the vehicle, which would cause the shift stick to not line up the way it should with the body of the Jeep. To remedy this, I decided to elongate the crossmember-to-body mounting holes on one end of the crossmember. The other end of the crossmember already had oval shaped holes, so by elongating the other two, I'd be able to slide the crossmember (and thus the transmission and transfer-case) into just the right position to better center it under the Jeep. I took the jigsaw to the crossmember, and the issue was solved.
« June 30th, 2005 »Installing the new units
With the transmission mount situation taken care of, I was finally able to install the new transmission and transfer-case into the Jeep. The install wasn't particularly interesting, as it was basically the same as any other transmission installation. With the electric drive motor removed, I was able to use a large floor jack to lift the units straight up into place under the Jeep. Of course, I did enlist the help of some of my family members so we could be sure the transmission was lining up properly as I lifted it in place. After bolting the transmission in place, it became apparent to me just how nice and shiny the new units were compared to the body of the Jeep.
!! Sorry, but as of 02/11/06 This page is still a work in progress !!
Remember, More photos are in the Photo Gallery!