clunking after Dexron VI

[ehall]

Hi guys,

I've got a 1985 Cadillac DeVille with 139k miles that is in solid condition so I've been trying to do a full service to get it ready for the next 20 years. It's got the old-school 440-T4/4T60 tranny, and I recently had Midas drain (not flush) the old Dexron III, and swap in a Wix filter and a fresh batch of Pennzoil Dexron VI fluid while they were doing brake work. Since then, it has made a knock/clunk whenever it goes into gear, but has otherwise been great. It's most noticeable at very low speeds (like in a parking lot) and also when downshifting when I coast up to a red light, but does not do it much when shifting during acceleration. It is worst in reverse, which is always low-speed. It has gotten somewhat better in the last couple of days (I did some engine tuning that probably affected vaccum), but it's still happening.

Reading the forum here it seems that Dexron VI is known to be too thin for some applications, and it seems that I have low-pressure valve noise, so I'm hoping that I only need a different fluid. At this point I am trying to decide whether to add some Lucas to see if that quiets it down, or if I should go ahead and replace the fluid.

FWIW, I pumped out a couple of quarts and put half a bottle of Auto-RX and a small can of Trans-X and plan to run that until I figure out what to do. The prior fluid came out clean and red, and the current stuff came out the same color as it went in, but I figured I would take advantage of the wrong fluid to give it a little scrubbing.

Also BTW, I used Dexron VI in a 334k mile Jeep Cherokee with an AW4 tranny and it has been really good there--just some minor slipping on cold mornings, but otherwise runs like butter. I bought two cases of the stuff to do both trannies and that was a chunk of change... not looking to buy two cases of something else if I can avoid it.

Any thoughts or recommendations on any of this would be appreciated. Thanks

 

[The Critic]

Originally Posted By: ehall
Reading the forum here it seems that Dexron VI is known to be too thin for some applications, and it seems that I have low-pressure valve noise, so I'm hoping that I only need a different fluid. At this point I am trying to decide whether to add some Lucas to see if that quiets it down, or if I should go ahead and replace the fluid.

Dexron-VI has a lower initial viscosity, but it is very, very shear stable compared to Dexron-III(H). In fact, the oil film thickness is actually greater with Dexron-VI than with Dexron-III(H), so viscosity is not the problem.

I would avoid the additives and do a full flush with Dexron-VI. Since the problem started occuring after the service, I suspect that the clunk may have something to do with the filter change. Was the filter installed correctly? Was the o-ring replaced?

 

[JHZR2]

how sure are you of the fact that they did it? Might they have done the lazy route and flushed it, meanwhile claiming that it was done and now the new flid is "cleaning" and cauing the filter to be clogged?

Even if they did drain and refill, if you dont know the histry of the last fluid change, it could be cleaning and junk building up.

Generally on ATs with over 100k and unknown history, fluid chsnge shoul dbe very gradual, with many changes.

JMH

 

[ehall]

I have owned the car since the 90s and have maintained it pretty well. The last fluid came out clean according to the tech. I didn't see it, but they do all my suspension work and have no reason to lie about color. It's always been red on the stick btw.

I don't know if they put the filter in right or if they actually flushed. A flush would explain some of the valve noise, and would also explain why it's getting quieter on it's own (sediment relocating). I was assuming that it was just the fluid and have not really considered beyond that. I should probably take it to a tranny shop and ask them to check the work.

 

[The Critic]

Partial or complete changes should not make a difference, IMO. I highly doubt that new transmission fluid has much cleaning action at all.

Fluid color doesn't tell much. A fluid could be dark brown because it was doing its job. If the filter wasn't installed properly I guess it could cause your problem.

 

[onion]

Critic- I want to know something. What are your qualifications?

Every time a thread regarding Dexron VI is posted, you're among the first posts, loyally defending Dexron VI. That's all fine and good with me- it seems to be a vast improvement over Dex III. But I have a problem with some of the advice you've given (here and elsewhere- it's often nonsense). A screwed-up filter installation will not cause a 'clunk'. Can't happen. Sure, it can cause other problems... but 'clunk' is not among them. Personally, I blame either an over-active imagination or excessively dirty fluid before the service.

So... under occupation, you've listed "sales". It used to say "student". Perhaps you've finished school and now you sell Dexron VI? What exactly qualifies you to parrot advice all over BITOG when you clearly have no mechanical background?

 

[Pablo]

Originally Posted By: The Critic

Dexron-VI has a lower initial viscosity, but it is very, very shear stable compared to Dexron-III(H). In fact, the oil film thickness is actually greater with Dexron-VI than with Dexron-III(H), so viscosity is not the problem.


While what the Critic repeats is essentially true for old style NON-synthetic Dex III of any revision (H and back), it does not necessarily prove that the lower viscosity Dex VI fluid is not the issue. The main assumption here being that the old fluid in the tranny was indeed sheared. I still prefer a modern synthetic (read very, very, very shear stable) Dex III style with Vis in the 7+ range for these transmissions.

When was the fluid last fully changed?

Dex VI in a 334k mile Jeep Cherokee with an AW4? Interesting!

 

[JHZR2]

Originally Posted By: The Critic
Partial or complete changes should not make a difference, IMO. I highly doubt that new transmission fluid has much cleaning action at all.

Fluid color doesn't tell much. A fluid could be dark brown because it was doing its job. If the filter wasn't installed properly I guess it could cause your problem.


An improperly installed filter could indeed cause the issue. With regards to the cleaning and gradual changeover, hundreds of >200k mile MB AT owners with 20+ year old cars cant really be wrong.

JMH

 

[ehall]

Originally Posted By: Pablo
When was the fluid last fully changed?

filter and fluids were previously changed at 96881 miles in 1998

 

[WishIhadatruck]

It seems hard to believe that a fluid being too thin or a poorly installed filter or filter seal would get better on its own. You said it is getting somewhat better. The fluid wouldn't have gotten thicker and the filter won't start sealing better would it? When you changed the fluid in 1998 was it a full flush? Perhaps things were dirtier in there than you think and the new fluid is cleaning things up a little and broke some junk loose? Hard to say. Maybe let the Auto-Rx do its job and do a flush with a filter change? I'd probably try the Dex VI again since it is the approved fluid and you already own it. Otherwise you could take Pablo's suggestion and go with a thicker DexIII type fluid. Dex III is no longer licensed so you're putting your faith in the fluid supplier rather than the auto manufacturer so make sure it is a brand you trust.

Do the older non-computer controlled transmissions like this not handle the switch to a thinner fluid as well? Of course the old fluid may have sheared and could be thinner than the Dex VI was.

I'm just throwing out ideas. I've only tried Dex VI once so far and had zero issues. '96 4L60E

 

[Donald]

You could install an inline filter such as the Magnefine and it would filter out the junk if new fluid is loosening things up.

 

[ehall]

I just did another ~50 mile drive and it is better again. Even reverse has changed to more of a thud than a thunk.

At this point I'm guessing the tranny is just dirty and the low-pressure valve noise is clearing itself up. I'll keep the current mix going until my next oil change in 1.8k miles and will change the fluid and filter again then.

Some of you are suggesting a full flush... don't they usually make things worse?

 

[Donald]

Maybe the new fluid or the Auto-Rx is doing its thing and cleaning things up. I would wait the 1000 miles for Auto-Rx to work and then do a complete fluid replacement. You may want to consider replacing the filter also as it may be somewhat clogged.

 

[WishIhadatruck]

Originally Posted By: ehall
Some of you are suggesting a full flush... don't they usually make things worse?


Maybe, but you've already done a partial change and now you've added some additives that will clean things up further so hopefully in 1000-1500 miles it will be clean enough that a flush won't do any harm. The advantage is that it will flush out all the junk in the old fluid.

 

[PT1]

Originally Posted By: JHZR2
.

Generally on ATs with over 100k and unknown history, fluid chsnge shoul dbe very gradual, with many changes.

JMH


I agree...fluid exchanges are good...gradual ones even better if you have over 100k..but that's JMHO

 

[PT1]

Originally Posted By: ehall
I just did another ~50 mile drive and it is better again. Even reverse has changed to more of a thud than a thunk.

At this point I'm guessing the tranny is just dirty and the low-pressure valve noise is clearing itself up. I'll keep the current mix going until my next oil change in 1.8k miles and will change the fluid and filter again then.

Some of you are suggesting a full flush... don't they usually make things worse?



I would do a pan drop/filter inspection-RR. You may be surprised to find your new filter is already loaded up with crud broken loose by the new fluid. I have had that happen on transmissions that were run 80-100k on factory fill then flushed. The second filter loaded within 5000 miles. Then the fun started. But once that filter was replaced all was fine. So you may want to consider inspecting the filter sooner than your OCI.

 

[Whitewolf]

Originally Posted By: ehall
filter and fluids were previously changed at 96881 miles in 1998


If the last time the fluid was changed was in 1998, then AT BEST what you had in there was a DEXRON-IIIG fluid since the upgrade to IIIG occurred during 1997. If it was old stock, then it could be just a straight DEXRON-III.

That being said, I think your problem is just plain old dirt ... because those older fluids, by today's standards, were not oxidatively stable. The newer fluids have far superior dispersancy, hence it is now probably carrying away the build-up that's occurred over time.

To Pablo's point about viscosity, it's pretty much impossible to run one of those old fluids for 40,000 + miles without getting any shear ... so I agree with Critic, I don't see that as being the issue.
I suggest that you run for a short while then do another change.

 

[ehall]

Originally Posted By: PT1
Originally Posted By: JHZR2
.

Generally on ATs with over 100k and unknown history, fluid chsnge shoul dbe very gradual, with many changes.

JMH


I agree...fluid exchanges are good...gradual ones even better if you have over 100k..but that's JMHO

That's what I did on the Cherokee with 335k miles... drained the pan (but not the cooler), topped off with D6, repeated twice more over the course of a month.

The Cadillac didn't exhibit any problems and the interval did not seem excessive so I just went for the swap. I guess the old stuff wasn't working too good.

 

[unDummy]

But those old fluids were what was recommended at the time. Are we admitting that they were pathetic?

With a pan drop, one would notice if there is a buildup issue. Since the fluid came out clean and red, I wouldn't expect dirt or fluid type as an issue.

If problem occurred at the time after the Midas service, you would be smart to make sure that your ATF level is correct. Grossly overfilled or underfilled by hacks can cause shift issues. Concerning the filter install, it would be smart to have that rechecked or just replaced after your ARX run.

You should also not mix additives.

Have a look into throttle valve adjustment and modulator valve replacement.

There is nothing wrong with doing a flush or a partial change. With that many years and miles on a fluid, a filter change along with a full flush is a must. Stick with DexronVI or any full synthetic Dexron(M1, RP, RL, Ams). Graduals changes are NOT required but simply an option. Lets quit with the scare hearsay concerning full flushes.

 

[Whitewolf]

Originally Posted By: unDummy
But those old fluids were what was recommended at the time. Are we admitting that they were pathetic?


No, what we are saying is that they were the best at that moment in history. Improvement is a good thing. Technology has moved forward since those days. So are you telling us that we should not move forward with the latest available technology?

According to my interpretation of your view we should perhaps revert to horses and carts?