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

It's your engine, transmission, driveline
kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Fri Sep 14, 2018 7:39 am

Well 14 months later, it may be just starting to have intermittent shudder issues. Not positive though. Almost felt like a misfire but it seems to be only when the torque converter is locked, and even then only in 5th, which is the highest load. Plus my engine mounts have been shot so any torque transient will shudder its way through the drivetrain anyway.

That said, I looked at the older post and recall that I still had 25% of the old, nasty Dexron III in there. So the most prudent thing to do would be to drain and refill another ~4 quarts (no pan drop because drain plug!). Math says a 4 quart change would yield only 14.5% remaining nasty Dexron III. It sounds like a small amount but as a percentage of total capacity that is still 1-3/8 quart of crap fluid (down from 2-3/8 quart which I have now), which can't be doing the torque converter clutch any favors. This would be a great application for a flush...

Good news - I actually have 4-5 quarts of Castrol Dexron VI on hand. I will just take care of this tomorrow. This is why it pays to maintain your car properly. Should not have gone 125k on the original Dexron III.

kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Sun Sep 16, 2018 12:17 pm

Drove up the highway a little. I definitely need to suck it up and get this done today.

kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Sun Sep 16, 2018 3:59 pm

~4 qts Castrol Dexron VI. Road testing now. 138,290.

Back. Well, it's better I guess. But not gone. This thing really just needs a full flush. I guess I will do another 4 quarts next weekend...

Let's see. Down to 14.4% remaining old crap or about 1-3/8th quart. If I do it again, that will be down to 8.3% or about 3/4 quart. The fluid was also darker than I expected but not sure if that means anything. TCC particles? Just a year and half of driving?

I probably mentioned this before but if the original fluid is good to 50k, 100k or even 150k, if you drain the pan and refill, you are NOT good for another 50k, 100k or 150k interval, because a lot of the old stuff is still in there.

I could try a DIY flush I guess at the trans cooler. Given how cramped the engine bay is, I think I will pass on that.

I still have the Lubegard additive (somewhere), also. I guess if I got down to 3/4 quart of the old stuff and it was still doing it I might be inclined to add the additive. I repeat: I am not doing a torque converter on this car unless it stops driving.

And speaking of maintenance items, I should really do the transfer case fluid. It does not look that difficult. I just need the right fluid. Which may just be Dexron III.
Last edited by kevm14 on Sun Sep 16, 2018 4:45 pm, edited 2 times in total.
Reason: Added some stuff

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Mon Sep 17, 2018 6:01 am

Commuted in. Definitely still stick-slipping which is the shudder I feel. I wonder if I should drop the pan and do the filter again. I don't really feel like it. It changes a little more fluid (actually another full quart) but that filter is fairly recent and I don't see how it could cause a TCC issue. There, I talked myself out of it.

Bob
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Joined: Thu Dec 19, 2013 7:36 am

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by Bob » Mon Sep 17, 2018 12:40 pm

So what's the next step? Just live with it?

kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Mon Sep 17, 2018 3:57 pm

More fluid changes, possibly another pan drop, and I still have the Lubegard additive. And if that doesn't work, a second tube.

It may be a case where I am just buying more time but I think I can continue to milk it. From what I recall, the clutch isn't so much worn out, but it has an uneven friction characteristic. I think that is exacerbated by the fact that the TCC lockup strategy is actually to have a small amount of slip (so obviously the clutch material was designed to handle that, so I think it is fairly robust). Well, when you have uneven friction around the circumference, and it has a designed/target slip RPM, it is going to slip somewhat inconsistently. I think that is what I am feeling. It is also possible that if I had new engine mounts, I might not even feel it.

bill25
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Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by bill25 » Mon Sep 17, 2018 6:45 pm

I might be inclined to add the additive.
What is the hesitation?

kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Mon Sep 17, 2018 7:58 pm

I dunno, I guess I subscribe to the belief that if you don't need an additive, don't add it.

Adam
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Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by Adam » Mon Sep 17, 2018 8:17 pm

I solved the TCC code in Jenn's Northstar Cadillac by removing and replacing the fluid, seals, solenoid, and the torque converter. I don't recommend any of that 'cause it sucked. It might be easier on RWD, though. Although you have AWD...

kevm14
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Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 Cadillac STS (5L50) transmission fluid & filter chang

Post by kevm14 » Mon Sep 17, 2018 8:20 pm

I don't have a code....yet.

Also totally different problems mechanically. Mine is actually a weird issue with the friction material.

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