05 Cadillac STS (5L50) transmission fluid & filter change

[Adam]

Then you definitely shouldn't do that job.

[kevm14]

I didn't mention something because I am not sure if it is relevant. The transmission fluid I had on hand was Castrol Dexron VI but the stuff I used before was branded Castrol Transmax Dexron VI. I assumed it was just updated marketing. But if there is in fact a difference I may have introduced another variable into this equation unintentionally. I should order more I guess.

https://shop.advanceautoparts.com/p/cas ... /8140020-P

Still not sure if there is any difference.

https://www.castrol.com/en_us/united-st ... d-atf.html

Kinda seems like they just started calling their transmission fluids Transmax.

All that said, I drove a good distance on the highway today. Maybe 35 minutes on the actual interstate each way. The TCC issue was present but varied. It seemed worse up hills but not positive. The worst NVH symptom is when it sends shudders through the drivetrain. Almost feels like washboard road, that kind of thing. I would think my best approach would be a total flush plus the additive. That would probably eliminate it for a long time and then possibly have to repeat at some point. Still way better than replacing the torque converter. I will keep chipping away at it though - I am still not ready to put the additive in, if I can even find it at this point.

[kevm14]

Did that highway drive again and one commute into work. So far I do continue to feel symptoms but on the other hand, I could probably also just ignore it, too. I will still try to improve it of course. And if it gets worse, well, then I'd probably want to take it more seriously.

[kevm14]

Another commute in. Still does not seem to be getting worse. No check engine light or anything, either.

[kevm14]

Not only is it not getting worse, it seems to be getting better. Almost seems like it is fine now...good thing I didn't add the stuff because I would have surely attributed this to that.

[kevm14]

So basically it went away. Then it came back this month. So I dropped another 4 quarts and filled it. This time I added my LubeGard stuff.

Here it is idling while I waited for it to get to temp after adding ~3 quarts.

20190126_182430.jpg

It's not that hard since they blessed the 5L50 with a drain plug. It totally makes up for the lack of dipstick.

Results? Super smooth shifting and the torque converter shudder seems to be gone...just like that.

I think it's down to like 3/4 quart of the old crap at this point. It smelled great but was on the darker side. The LubeGard smelled like concentrated trans fluid. Probably all friction modifier.

[kevm14]

The torque converter shudder feeling was completely gone on my ride in. One piece of good news...

[kevm14]

So this lasted a while. There has been some construction on my commute which has lead me to hold it in 4th because the speeds end up slower than the torque converter will lock in 5th and that annoys me, so I hold it in 4th and let it lock the converter. Well previously I've found that if I do that all the time and feed engine power, it will keep it locked under considerably more throttle than if I just leave it in D. This eventually leads to a recurrence of some of the shuddering feeling, or has in the past. Well, it has started again. It is very subtle and I probably wouldn't notice if it had good engine mounts but I can almost hear it as a buzzing (unless it's the air compressor riding on my muffler, haha). It is nowhere near as pronounced as it was the day I drove it home like 2-1/2 years ago. That stuff I added really worked.

Anyway, I guess I don't learn my lesson. Of course the torque converter should be fine with this as I am not operating the car outside of its programming (it can unlock anytime it wants). But since there is a deficiency in the design, this seems to make it start to act up. I will probably ignore it for a while longer. In the past, if I stop holding it in gears which make the torque converter lock more aggressively, the behavior sometimes has gone away. So no big deal.

If not, the fix would likely be to drop another ~4 quarts out of it and put some of that additive back in which worked so well since Feb. I may even try to do back to back changes to get more new fluid in and THEN put the additive back.

Almost 150k.

[kevm14]

In the past, if I stop holding it in gears which make the torque converter lock more aggressively, the behavior sometimes has gone away. So no big deal.

I stopped holding it in manual 4th and guess what - the shuddering has gone away and been away for months. I didn't do any more trans fluid service. I just keep it in D.

This trans performs better at 153k than it did at 125k when I bought it.