In order to solve the dreaded Saturn “reverse-slam” that automatic transmissions develop over time, you have to replace the valve body inside the transmission. The valve body can be rebuilt, but it must be done with “Sonnax” internal parts – using those quality parts will ensure that this doesn’t happen again in the future.
Overall, this project can be considered a “moderate” difficulty level. Actually, it is pretty easy – but it is time consuming.
So here we go:
1. You’ll need a variety of fluids, parts, and tools to do the job. Most importantly, you’ll need a rebuilt valve body. These can be purchased off eBay for around $200 USD. Although pictured, YOU DO NOT NEED TO DRAIN THE AUTOMATIC TRANSMISSION FLUID (ATF). You can do this procedure in your driveway – heck, you don’t even need to jack up the car! ;)
2. Start by disconnecting the battery (do this first, very important!), then take out the air-box, throttle-body snorkel, and the battery tray.
3. You’ll now see the top of the transmission, and the valve body cover. Remove the upper harness that connects to the top of the cover – it is a 7mm bolt. It takes no more than 60 seconds (60 seconds well spent I might add) to cut up a small piece of cardboard to keep track of where each bolt came from. When you take off the cover, make sure you are careful with the gasket attached to the bottom of the cover. If you damage it, you’ll need to get a replacement, which is $40-$50. In most cases, you can reuse it:
4. The valve body will now be exposed. There are 11 8mm bolts, and they are various lengths. So, like the valve body cover bolt removal, I highly recommend that you make a cardboard template: Once you remove all the bolts, the valve body will come out quite easily. But make sure you have some rags, because lots of ATF will still be inside the valve body:
5. You’ll now see the “guts” of the transmission. It looks pretty cool in my opinion. But enough staring, time to install the new valve body :) My valve body didn’t come with a manual valve shaft, so I removed it and put it in the new one. The manual valve shaft is what your automatic shifter (The P-R-N-D shifter that you shift inside the car) is connected too. It is the only part on the valve body that comes out. Just swap them, and put in the rebuilt valve body. Use the handy template to re-install the bolts:
6. Once you’ve put all the bolts back together, I recommend giving the valve body cover a quick clean. I used some carb cleaner – BUT MAKE SURE YOU DON’T GET ANY CLEANER INSIDE THE COVER, OR THE SIDE EXPOSED TO THE VALVE BODY. If you do, you’ll need to scrub a lot more with a non-solvent because you need that side to be clean/ATF-coated/untouched – any cleaner on that side will contaminate the ATF. Once that is done, re-install is the reverse of the tear-down.
It should take about 30-45 minutes to do this. Once you’ve completed everything, start the car up and let it warm-up to operating temperature. Then shift the car through all the gears with the parking brake on – this gets new ATF throughout the valve body.
Take it out for a spin. You’ll probably get a little bit of harsh shifting – this is completely normal. The ECM must learn the new shifting patterns all over again. You can go up to 50 kilometers before the harsh shifting will stop, but it eventually will.
Pat yourself on the back, you just save about $800 by doing it yourself :)