How to Replace the Transmission in a Cadillac Catera.

How to Replace the Transmission in a Cadillac Catera.

The Cadillac Catera was designed a sport grand touring car. It is actually an Opel Omega built in Germany. When it was introduced, the automotive magazines sang its praises loudly. The car drives and handles well. However, they have proven to be rather high maintenance and unreliable. Also, parts are hard to get and they are expensive.

The transmission is a GM 4L30E. This same transmission is used in BMW’s and Isuzu Troopers. I found some useful information in some of the Trooper forums.

The owner of this particular Catera found a replacement transmission on ebay. I had it delivered to my office parking lot. We swapped it on to my little utility trailer in the parking lot rather than having the truck negotiate the long gravel driveway to my shop.

With the car on the lift and the battery disconnected, I began by draining the fluid. Fluid is added through a hole in the side of the pan. There is no dipstick or filler tube like on other GM transmissions. I only drained the amount that comes out when the engine is off. The level in the pan is lower when the transmission pump is running. For this reason, the transmission fluid level must be checked with the engine running. Which is interesting considering the exhaust pipe runs just a couple of inches from the fill hole.

To release the torque converter from the pressure plate, I removed the rubber plug from the bottom of the bell housing. I used a long screwdriver to slowly rotate the flex plate until a bolt was visible through the front hole. An assistant with small fingers was helpful in removing the bolts through the access hole. There are six bolts that hold the torque converter to the flex plate. They all had 15mm heads.

**See update below on turning the crank by the damper pulley bolt instead.

I next disconnected the drive shaft at the coupling. I should have dropped the exhaust pipes at this point. It would have made removing the oil cooling lines much easier. Next I disconnected the electrical connectors and the oxygen sensors and removed the exhaust pipes. Be careful with the sealing rings at the front as they are very expensive from the GM dealer if you damage one. You can likely get them cheaper at a muffler shop but I was able to reuse the ones on this car.

Note: I was later able to find the sealing rings at Advance Auto but they are marked as discontinued by Fel Pro. They we still over $20 each which seems a lot for a simple gasket.

With the pipes out of the way, disconnect the shift linkage and anything else that might be connected. You may have to cut some wire ties on the wiring harness. Next, support the transmission on a jack and remove the cross member. The transmission mount was broken on this car so the cross member fell off when the bolts to the body were removed. The body bolts had locktite on them and were very difficult to remove.

Two of the main transmission bolts come in from the front of the engine and the rest come in from the transmission side. They all had 19mm heads. There are also four small bolts that hold the bottom of the bell housing.

I removed all the bolts and carefully slid the transmission back off the dowels and let the converter nose slip out of the crank. Then I lowered it out form under the car.

I set the two transmissions side by side on the floor and made sure everything was a match. All the sensors were in place on the replacement transmission so I did not have to move any over.

I then secured the transmission on the jack and set it level as that was how the engine was sitting. The sticker on the replacement transmission warned that the front seal needed to be replaced. I did not see any evidence of leakage but I pulled the torque converter any way to see how the seal looked. Sure enough, there was a visible worn spot on the seal.

The owner picked up one at Auto Zone that did not fit. He tried to get one form the Cadillac dealer but it was going to take two weeks. We found one on ebay but I decided to try one from Advance auto. That seal was made different but fit fine. The original seal has three bolts that hold it in place. The instructions say not to drive the seal in but to use the bolts to pull it down to a seat. The replacement seal from Advance did not have the three bolt holes so I had no choice but to drive it in. I did so carefully.

[Important Update! About three months later, the pump seal popped out of place. The transmission had to be removed from the car and a new seal fitted. This time I took the time to order the correct seal form a supplier on Ebay. This seal had the correct three retaining bolt tangs on it. It may be possible to fabricate some retaining clips for the Advance Auto seal, but I think it would be better to just use the correct seal. Note: do not use a seal without some means of mechanically fastening it in place!]

I had a lot of trouble getting the torque converter indexed back on the pump drive splines. I thought I had it once but when I went to set the transmission in place, it contacted the flex plate way too soon. I had to set it back down and try again. After much spinning of the torque converter, it finally dropped into place on the cogs and then there was plenty of room.

I made sure the transmission was lined up with the engine and carefully slid it into place. Everything slid into place easily. However I took my time and made sure that the bolts drew the transmission up evenly.

Ideally you would spin the torque converter a few times to make sure it is centered in the crank before bolting it to the flex plate. However, due to the design of the bell housing, all I could do was rock it back and forth a few times. I was glad I had pre aligned one of the tabs on the converter with a hole in the flex plate because it is very difficult to turn the torque converter through the tiny access hole.

I use a magnet and a small fingered assistant to work the bolts into place. Between bolts, I again used my long screwdriver to slowly rotate the flex plate to the next position. Once they were all in, I spun it all around one more time and torqued each one down tight.

Update: I found a 16 mm 12 point socket would fit the reverse torx crank bolt and allow me to rotate the engine form the front rather than awkwardly using the screwdriver on the starter ring.

Next I reconnected the wires and the shift linkage. I then reconnected the cooling lines being careful with copper washers on the rear banjo fitting. I fitted a new mount and reattached the cross member and exhaust hanger. There is a helpful arrow on the cross member to show which way is the front.

With all the bolts in place, I then reconnected the drive shaft. I had to use a soft hammer to get the shaft to slip over the output shaft of the transmission. I did not want to try to pull it down with the coupler. The local dealer wanted $220 for the coupler, so don’t damage it.

I set the left side exhaust pipe in place and reconnected the oxygen sensors. I then dropped the oil pan and installed a new filter and gasket. It was much easier to do this job under the car than with the transmission on the floor. I reinstalled the pan and filled it with fluid. I then put up the other exhaust pipe which limits access to the fill hole.

To fill the entire transmission, the pump must be turning. That means that the engine must be running.

Based on advice from a friend, I built a device to quickly put fluid in the transmission. I used a length of ½ inch clear tubing and a gallon transmission fluid jug. I drilled a ½ hole in the cap of the bottle and slipped the hose inside and down to the bottom. I used my heat gun to help straighten the hose. I then drilled a 3/8 hole near the handle of the jug. I put fluid in the jug and slipped the hose in the fill hole. I then used my air blow gun to pressurize the jug and force the fluid up into the transmission. A quart of fluid will transfer in seconds so be careful if you use this method.

Once the transmission was filled, I plugged the hole and lowered the car. I shifted it into all the gears and drove it forward and backwards. I could hear the pump whining so I knew it still needed more fluid. I picked it back up and filled it again. It seemed to stay full after having moved all the solenoids by selecting all the gears and moving the car.

I gave it a test drive and brought it back and checked for leaks. Finding none, I drove it back to the happy owner.

See update on pump seal here

9 Replies to “How to Replace the Transmission in a Cadillac Catera.”

  1. I found your post and thought I may be replacing my sons catera tranny. Wondering if there were any particular difficulties other than mentioned. I hate doing changeouts laying on the ground but thats probably how its gonna be. Did you have the car raised high or up on ramps? Ive done a few tranny changes in my time. but I dont look forward to this one. Gatta save some money doing this so figure I can handle it. I will need to read up again on changing and filling the fluid but also was wondering how long it took to get it changed out and any particular advice before I jump into it. I still have to find one for a good price and get it here. Seen avg 650 used under 100k miles. Seen some even cheaper no warranty like on craigslist. But probably goin with somethin from a resellar with a warranty. havent checked on a rebuilt one but they are probably more than what I paid for the car in the first place.

  2. The owner got this one off Ebay for $400. It had a warranty. I did the job on a lift but it would be easy enough to do on jack stands except for the getting up and down part. I spent about ten hours total on the job. That included pick up and delivery and doing a few other minor repair while I had the car. Getting the right seal for the front pump and getting the torque converter to index properly on the pump drive were the two most difficult parts. Also, remove the exhaust pipes before you start. They have to come down anyway so get them out of he way early.


  3. Hey mike, I found a transmission that is brand new. The guy has a few and thought it was for a trooper, I found it by looking for a 4L390E I called about the torque converter that is mounted on the transmission and found the converter matches what is for a Izusu rodeo,trooper and honda passport. I tried to call around with the tag that is on the transmission but nobody really knew how to tell me what it was out of. I’m trying to determine if it is for the makes above will the tranny it fit a catera? I did a search on rebuild kits for the trooper catra and passport and they all take the same rebuild kit. What I dont know is if it will mount up to the engine and rear connection. One thought I had is if all the guts are the same being they all have the same model and kits, I could take all the parts from the new transmission and put them in my trans that I take out. Lots of thinking and figuring the possibilities on this one. Any info you may have will be helpful.

  4. Form what I have read, I think the transmission is the same. You might be able to just reuse your torque converter if they turn out to be different. I have not been able to find a lot of info on these transmissions. I got a rebuild manual from some Isuzu forum when the owner was considering a rebuild. None of the local transmission shops would touch it he said.

    The Catera has an odd yoke on the output shaft. Make sure the Isuzu trans has that as well.

    Good luck and let me know what you find out. These comments may help some one else.


  5. Hey Mike . What I have found out going to a salvage yard. I took pics and by all markings and stamps and location of sensors and such everything seems to match up. I do know the bell housing that is removable is different and now trying to confirm with the the other trans is that the input shaft is the same. Looks like I change the bell and the yoke from my trans to the new trans I should be in business. I haven’t checked on a new converter or whether I need a new converter. With this design and if all the sensors are the same. stands to reason that the 4L30E that goes into Izusu trooper, rodeo, Honda passport, BMW and catera are all possible to retrofit to one another. I haven’t nailed down the electronics to see if they are the same like the rebuild kits are, but the reason I am looking so deeply into this other than labor and expense is that the guy I am working with has a couple of these transmissions that are brand spankin new from GM and has had them for a couple yrs and only wants 425.00 each. So I figure if my local junkyard wants 400 for theirs its worth looking into to try to get the brand new one. I considered rebuilding my trans, but with all thats involved in getting it done is a little more labor intensive and time consuming. O once I know how it all works out I will let you know. Enjoyed your column and I also have a Jeep Grand that may soon need a tranny too but that’s a whole other project.

  6. Wow, some excellent info here. Just in time for my swap. Thanks for all the advice. One question, how would I be able to verify if the seal is bad? I was wanting to do this this weekend, but it looks like I’m going to have to wait a week to get a seal in.

  7. OK, I’ll check it over real close & hope for the best because it’s gonna get cold next week.

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