Previa Automatic Transmission Re-Assembly

Having destroyed the two tabs in the oil pump of my transmission that lock into the torque converter (due to improper torque converter installation and attempting to force the transmission to mate with the block by threading the bolts and pulling them together), I found myself needing to replace it. I got a bell housing from a local pick-and-pull (took the whole bell housing since the pump is pressed into it and you need a special service tool that grips inside the pump to pull it out). Unfortunately, when I took the bell housing off my transmission, the O/D case and front clutch pulled out with it. I'm hoping these pictures and instructions might come in handy for anyone who finds themselves in the same unfortunate situation.

Parts Removed:
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Rear cluch (foreground), O/D planetary gear and input shaft (top right), front clutch (top left)

Center Support
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View of center support that the rear clutch locks into. Don't remove the rear clutch! It typically does not come out with the O/D case and front clutch, but I removed it anyway. It's a pain to get back on (the splines of the rear clutch have to mesh with the flukes (those 3 little sets of teeth every inch or so) and it was very difficult to do. It is fully installed when the splined center of the clutch is flush with the splines of the sun gear shaft.

Rear Clutch Installed
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Rear clutch fully installed. The front side of the rear clutch has 3 sets of flukes that the splines of the front clutch must mesh with.

Rear Clutch - Another View
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Another shot of the rear clutch which shows the splined center of the clutch flush with the splines of the sun gear shaft

Front clutch
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The front clutch has a ring in the center than tends to fall to the bottom. It must be centered in the clutch before installation or it will hang up on the sun gear shaft.

Front clutch - Another View
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Another shot of the ring inside the front clutch, almost in place. Shake the front clutch until the ring is centered.

Front clutch - Ready to install
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Front clutch with the center ring properly positioned in the center of the clutch so it will slide onto the sun gear shaft.

M8 x 1.25 Threaded Rod
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The FSM calls for 2 SSTs which thread into the transmission case for installation of the O/D case and bell housing. Since I couldn't find bolts long enough, I purchased a 1m length of M8 x 1.25 pitch threaded rod, and cut two lengths to 7" each.

Front clutch installed
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Front clutch is installed and the two makeshift SST threaded rods have been inserted. One note on installing the front clutch: I found that turning the output shaft of the trans while pressing on the front clutch allowed it to sink in further than I could otherwise get it in. The first time I assembled this, I didn't get the front clutch in far enough and it prevented the output shaft from turning CCW (no reverse). When properly installed, it should be just slightly recessed *behind* the face of the transmission case.

Installing the O/D case
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Installing the O/D case is facilitated with the makeshift SST alignment rods.

Front side of O/D case
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After installing the O/D case, make sure this gear is pushed in and fully seated on the shaft.

O/D planetary gear, input shaft, and one-way clutch
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Now install the O/D planetary gear, input shaft, and one-way clutch. The FSM instructs to install this as a unit, but I found it much easier to separate the one-way clutch from the planetary gear/input shaft and install them one at a time.

O/D planetary gear and input shaft installed
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Here the O/D planetary gear and input shaft is installed. The flukes on the front of the O/D planetary gear must mesh with the splines of the one-way clutch, which is installed next.

One-way clutch
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Here is the one-way clutch installed on the O/D planetary gear. When installed correctly, the rear of the clutch should nearly touch the front of the O/D planetary gear, with just enough clearance to allow free rotation of the one-way clutch.

Bell Housing o-ring
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Coat a new bellhousing o-ring in ATF and install it on the O/D case.

Backside of oil pump inside bell housing
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Make sure the assembled bearing and race are properly installed on the back of the oil pump in the bell housing. If necessary, coat the back of the bearing with petroleum jelly to keep it held in place. I also coated the inside of the bell housing and the outside of the O/D case with ATF to make them slide together easier.

Installing the bell housing
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Slide the bell housing over the O/D case. I left the threaded rod installed at this point, which may have been a mistake. It was very difficult to get the rods through the holes in the pump, and they actually dislodged the pump from the bell housing a little. I got it pushed back in, but now I have an oil leak from the bell housing and I suspect the pump is probably leaking. In the future, I would remove the threaded rod at this point and just slide the bell housing over the O/D case and bolt it up. The pump should be properly aligned once the bell housing is bolted up, because the pump is typically stuck in the bell housing in the correct position.

Bell housing installed
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Bell housing and oil pump fully seated flush with the transmission case.

All done
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All bolts are in and the the transmission is fully reassembled. Torque is 42 ftlb for the two larger 17mm head (M12) bolts, 25ftlb for the 14mm head (M10) bolts, and 16 ftlb for the pump bolts (12mm head, M8x1.25). Put sealant on the heads of the pump bolts.

Torque converter
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Torque converter installed on the transmission. Make sure the notches on the converter slip over the two tabs in the oil pump (spaced 180 degrees apart, just like the notches in the converter). Getting this is on is a piece of cake after getting the clutches to mesh with the flukes. I coated the nose of the conveter with grease to help it avoid getting hung up inside the flex plate when installing it into the van.

That's about it. If all went well, the output shaft should turn freely in both directions in all gear settings except park. Eric

Thanks for the great pics and the nice write-up. I've been slowly getting my nerve up to pull the auto transmission out of my All-Trac Previa and find out why I get a vibration when it shifts in & out of overdrive. While it's out I plan on putting a 2 speed transfer case on it as well. A couple of weeks ago I pulled apart one of my junk A45DF auto transmissions, disassembled, studied, and successfully reassembled just to familiarize myself with the job and to get my confidence up. It really takes a long time to figure out just how to align and assemble everything for a correct fit. I found myself removing, inspecting, re-installing, removing, re-inspecting things a lot until I finally discovered the correct order of assembly. This type of work requires patience and great attention to detail.

I'm still a little shaky on a few things, but now that I've had a chance to let it sink in, I'm going to do this again at least one more time before I tackle the Previa. I just opened an account with Transtar (transmission part wholesaler), so I can get a good deal on the master rebuild kit. I refuse to pay somebody $1,500 plus to do something I can do myself for under $250. Tim

Hi Tim. You are wise to practice more than once on a junk transmission before taking apart a good one. I had no experience before undertaking the above job, and I had to take it apart and try again 3 times before I finally got it right (the first time I didn't get the front clutch meshed properly and the output shaft wouldn't turn in reverse, and the 2nd time it was leaking a lot of ATF from the bell housing b/c the oil pump o-ring had dislodged in the process of re-assembly). The guys who charge thousands to do a complete rebuild have the advantage of intensive study and practice during trade school. Without the benefit of school or a mentor, us DIYers have to practice and learn by doing, which often comes with many mistakes along the way. The trial-and-error approach can be frustrating at times, but also very rewarding when we finally get it right. I don't know if I'll ever have the courage to do a complete rebuild like you are planning, but I'd be tempted if I were facing a $2000 repair estimate. Luckily, I've put almost 5k miles on that transmission since I slapped it together last spring, and it still shifts smooth and is working great, which is pretty remarkable considering what it went through and that it has almost 320,000 miles on it! Adding a 2-speed transfer to the AWD transmission will be really nice...I'm interested to hear how that turns out. Eric.