I have a 1996 CE, LT1, with automatic electronic trans (M30). It has 63k miles on it it and was in Nevada for years before coming home to Calif (it was originally sold in Calif). I plan to just pull the trans pan, drain fluid, replace filter and button back up and refill. I don't want to drain the fluid in the torque converter. Is there any chance that by just pulling the pan the tq converter might drain? If so, is there any way to prevent it from draining? Thanks. Randy PS I have seen many utubes that say don't change trans fluid. I'm well aware of that controversy.

 

On an automatic transmission, of any big 3's brand, the best way to change fluid is way more involved than draining the pan and refilling, as you mentioned, torque converter, but also the cooling system. When you get into 3/4 & 1 ton trucks the pan will have 4-5 quarts, but the system will hold 21 quarts. A pan job there would be the equivalent of doing an engine oil change, but only replacing the oil filter and the amount of oil it contains and leaving the rest of the old oil in the engine. What's the point of changing any oil like that?

The best way on an auto is to disconnect the return hose at the transmission, shove clear tubing over the line and have that go to a 5 gallon bucket. Do the normal pan drop/filter job, and refill it. Then start the engine and continuously refill the transmission at the same rate as the bucket accumulates. When the clear tubing starts pumping bright clean new fluid shut it off. Reconnect the return line, top off the dipstick level, and start the vehicle again. Once it's up to operating temps you can fill the transmission to its "full" level on the dipstick.

That's truly the only way to ensure you have changed all the fluid out vs just mixing in a percentage of new fluid with the old. Yeah it can be a little messy, and it will take more time, and you will need more fluid. But you know it will be done properly

My FiL went thru 2 transmissions in his Duramax by 279k miles. He was really ticked the second time cause he always did the pan drop and refill every 30k miles. But his truck held like 21 quarts, and he was replacing 4. On a PowerStroke it's 28 quarts... I'm not sure how many the autos in a C4 hold since I own a 4+3. But the same logic applies across all platforms. You'll want at least 2 more quarts than the C4 system holds to do it this way due to losses in the clear tubing before shutting off the engine and a little mixing pushing the old with the new.

 

Post above is probably better way to do it. Dropping pan and changing filter will do you no harm - and is the way most transmission shops used to do it. < 2 cents

 

There is nothing wrong with dropping the pan and replacing the filter and fluid. I do mine every 30k miles and it does a good job of keeping the fluid fresh.

 

OK, so maybe you can answer my question. When you drop the pan, does the torque converter drain too? How much fluid do you end up putting back in (that will tell me)? What I don't want to do is a full flush as recommended earlier.

 

Not a bit sure as to why you are concerned with the torque converter draining but the short answer is no - taking the pan off would not by itself drain the TC.

 

When I first bought my 96 I was busy and took it to a dealer to have the trans fluid flushed. They disconnect the cooler line at the radiator and pump out all the fluid and replace. It was not until I picked it up did I find out they do not drop the pan and replace the filter. A few weeks later I got the car on jack stands and dropped the pan and replaced the filter and refilled. I wanted a new filter as the old one was 25 years old and maybe just maybe they have made some upgrades in filter media in the last quarter century. I now think I did it the best way possible but cost a few bucks. Dan

 

not sure how the 96 differs to an 85, but when i (filter) service my 700R4, seems to me it's around 4 quarts. i did a full flush at 100K - presently 170K - zero issues with the transmission. BTW, filter service every 30K-40K miles.. only use ac delco filter kits - tried another brand once - didn't fit for schitt.

 

As already noted, Dropping the pan does not drain the converter, after replacing the filter and pan gasket add 4 quarts and run the shifter through all the selections pausing at each one for a few seconds. Then top off the fluid level. I am sure everyone knows but has a former HS Automotive teacher I’m going to say it anyway. Fluid level is checked with the car on a level surface with the engine running and the gear selector in park. If the fluid is cold (room temperature). The fluid should be at the bottom of the checkered indicator and when the trans is warm (after driving) the level will come up to the full mark.

 

That said, the converter DOES drain. It's slow, but does so, as in days. This is partly why we have to check the tranny fluid level after driving for a bit and with the engine running.

So if you think you can cheat, like I did, by checking the fluid correctly then re-checking after it's been sitting for a while cold, make note of the time span and match it next time.