Possible solution for 4t60e transmission issues

My 1994 base model has 157k miles on it, and started having problems with the transmission around 135k. At the time, I thought it was engine problems, because of the way it acted. But between trying a bunch of parts swapping with the engine that didn't help the problem, and tons of research, I think I've stumbled (pun not intended) on a solution.

I started noticing the problem on a vacation trip to the Blue Ridge Mountains. It acted like it had no power, and I would have to manually downshift to lower gears to keep my speed up. After I got back home, it still had a noticeable problem. I would drive about 40 miles each direction on rural highways to visit my parents every weekend. I used my cruise control to save gas, and stayed around 55mph because the highway patrol loves that route. The problem I was having was that the engine settles in at about 1500 rpm around 55 mph on level ground. if there is any slight grade, the transmission is supposed to disengage from overdrive and let the rpm go up slightly, but it wouldn't. I thought it was problem with the engine because it felt like a motor mount was broke, and the engine would vibrate and shake. This was from lugging. I would blip the throttle, and it would temporarily kick the trans back to 3rd.

After replacing spark plugs, wires, O2 sensor, MAP sensor, crank trigger sensor, etc, hoping this would give the engine more power, and none of it working, I started hitting the forums. Turns out this is a common problem with these vehicles. It seems to start around 100k-150k miles. I've read of people replacing torque converters, and whole transmissions.

Before you do all of that work, try this. GM has replaced Dexron III transmission fluid with Dexron VI. They did this in 2006. I haven't really noticed it as commercially available until the other day. My transmission was about a pint low when I was at the parts store. I tried the Dexron VI because it was 'backwards compatible.' I didn't really think anything of it. A few days later, I made a 100 mile round trip, and on the way home, it started actually shifting somewhat normally. It wasn't perfect, but it was better. This got me wondering, so I did some research on Dexron VI. Turns out, that it's a much better fluid than Dexron III was. It was used in the 4t65e that replaced the 4t60e. I had the transmission flushed right around the time I started having my problems, and I started theorizing this may have been part of my problem.

This is the info I have on Dexron VI vs Dexron III ; http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=526448#Post526448

Yesterday, I got 8 quarts of Dexron VI, and a new filter, and today, I did a fluid change. I pulled the pan, and it was full of sediment. I cleaned the pan. I used dish detergent and water. I didn't use cleaning fluid because of the possibility of contamination. I pulled the old filter off, and it was coated with the same sediment. I put a new filter in, and after I made sure the pan was spotless and dry, I re-installed the pan. I added about 4 quarts of Dexron VI to fill the pan, before I cranked the engine. I started it up, and with my foot on the brake, I cycled through the gears a couple of times. I left it running, and rechecked the dipstick. It was at the bottom. I wound up adding a total of 7 1/2 quarts to fill it back to the top.

I did a test drive after a cleaned up, and put away my tools. I had to go to the parts store to get a radiator petcock to fix a leak, and had to dump the fluid and oil from an earlier oil change, so it I made good use of my trip to town. I kept tabs of how it drove. I noticed that it accelerated more smoothly, it seemed to shift much more freely, and it didn't lug and vibrate when it was in cruise control. I don't know if this is going to last forever, but it seems to work fine for now. I've always heard the old wive's tale about not replacing the filter, or cleaning the pan, but I think that's a bunch of crap, personally.

I can't say this will work for everyone, but it worked for me. I would definitely give this a try before I invested $1500 in a new transmission. It was $50 for the fluid, and $25 for the filter and gasket. I would up using the factory gasket, because it was one of those rubber coated metal 'reusable' ones that was better than the cork gasket that came with with filter.

If your transmission is having overdrive problems, or is shifting funky, I'd try this before I sunk some serious money into it.

If someone else tries this, please let me know your results.

Update.

The next couple of days after the change, I've driven to town a couple of days in a row (20-30 mile round trip) and it did much better. When I use cruise, it shifts more smoothly and upshifts when it's supposed to. It stumbles once or twice when it's cold, but otherwise, runs properly. It accelerates smoothly, instead of stumbling and doesn't try to shut off like it had been doing.

Yesterday and today, I took longer trips to my parents houses. Each about 100 miles round trip. Before, I used the cruise at about 55mph most of the way, and it would stumble. Now, it shifts pretty much normally, and doesn't feel like the engine is trying to come through the hood. It had gotten to where the check engine light was coming on about 1/2 way each direction, and it didn't do that on either trip, in either direction.

So far so good.

I'm a flat-lander. Every time I drive in mountain areas, whatever vehicle I am driving feels like there is something wrong with it. When I get back home it feels normal again. My 94 always gets a little jerky in OD because the TC is locked up at 1300 rpm and the engine doesn't like it climbing hills. At 1500 rpm it pulls any hill smoothly. I don't think any vehicle would like to climb hills in high gear at 1300 rpm unless it was a torque monster. I switched to Dex VI a few years ago and it did seem to help things a little bit.

My vehicle seems to shift better on slight grades better at 45 than it does at 55. At 45 its around 1300 rpm like you say, and when it hits a grade, it bumps to about 1750, or drops to 3rd, and bums to 2000 rpm. At 55, it's running 1500 rpm, and seems more 'reluctant' to switch gears. I haven't hit the interstate yet and tried running 65. I have a feeling it will run pretty smoothly at the higher speed. When I do take it on the interstate, I'll report back, and let everyone know how it performed.

I really would like to hear more! 🙂 My transmission has a delay sometimes, when putting it in Drive, Reverse, or the other gears. I think I still have the original fluid in so I want to change the filter and fluid. I am now 'searching' for Dextron III but if VI is better I will do that.

That's actually what started me on this little journey. I was going into town, and when I started my car and backed out of my driveway, when I put the car in Reverse, it didn't go right into gear. I had to rev the engine a little for it to engage. When I got to town, I went straight to the parts store, and checked my fluid. That's when I noticed it was low. I usually go to NAPA unless It's something specific that I'm getting from another source, or they just don't have it (rare). My fluid was low, so when I went to the fluid isle, that's when I first found out about the Dexron VI. They had several options, unlike most other stores. I settled on the Valvoline Synthetic base Dexron VI. It was $7.99 a quart. After reading that it was the upgrade replacement for Dexron III, I figured it couldn't hurt anything. I didn't notice any real changes immediately, other than it would engage as soon as it was put in gear. It didn't notice the changes just 1 pint made until I took a 100 mile round trip, and it had circulated through the system. That was when I really started doing the research, and decided on changing out the fluid and filter.

I will admit, I didn't use the Valvoline Synthetic for the change. I used the NAPA 'regular' Dexron VI. It was $4.99 a quart instead of $7.99. I made that decision due to budget constraints. If I had the money, I would have sprung for the Synthetic. Even the 'standard' fluid has made a huge difference in the way my transmission acts.

It may be harder to find in the Netherlands, but if you have a GM dealer, I'm absolutely sure they have it available, because that's what they superseded Dexron III in most vehicles with in 2006.