A little worried about my tranny

[Benzadmiral]

Did a search for this, but couldn't find anything.

At odd times the autobox in my '03 Buick Park Avenue will suddenly shift hard from 1 to 2, then hard again as I decelerate and it goes back into 1. Usually when this happens, if I pull over, shut the engine off, wait a few seconds, and turn the car back on, the problem vanishes. It seems to happen more often in the afternoon as I come home from work, usually after about 15-20 minutes of driving. It never seems to happen on the way to work in the morning.

The fluid and filter were changed 19,000 miles ago, at 49K. Last night when I got home after about 30 minutes' drive, I checked the fluid in the manual-approved manner (engine running, level surface, shift through each gear with about 3 seconds in each, then back to Park, leave engine on). The fluid was clear, with pinkish color at the tip of the dipstick, and was certainly within the cross-hatched proper area, but there was also some on the stick above that point.

If the fluid were low, I could see this happening; but wouldn't it happen more often? And if the tranny were overfilled, wouldn't it slip -- and more often as well? The first year I had the car, this didn't happen at all. And it occurs only rarely now.

Any ideas?

 

[Bill in Utah]

What fluid did you use?

I've found some ATF fluids are not the same as others....

Automatic transmissions these days are PICKY about fluid.

Bill

 

[Benzadmiral]

As I recall, it was Dexron III, which my mechanic (and people here) said was the right stuff. I was planning to go synthetic when I have the fluid changed again at 79-80K miles.

 

[saberz]

Sounds like performance shift(Grand Prix GTP's have the button). Where if you enable it, the transmission will force into 1st during hard acceleration for a few seconds and shift into overdrive etc. But I doubt the park avenue has that, S/C?

Oh wait, it shifts into 1 hard upon deceleration. Hmm, did they re-install the pan/filter properly. ATF levels ok? It may be a Dex III/Merc III clone, meaning it may or may not be quality stuff.

 

[Benzadmiral]

No, I don't think it has anything like that. Mine is the normally-aspirated model, and has the shift lever on the column instead of on the tunnel.

The only button on it is the one to enable/disable the traction control, and I leave that on (it's on by default). If I disable it during a drive, a light shows on the instrument panel.

ETA: The level seemed okay when I checked it last night. My usual mechanic did the job back in early '08, and no issues cropped up until earlier this year. Do you think another fluid/filter replacement is called for?

 

[Johnny]

Could it be some kind of electronic control module causing this? Sounds like they used the right fluid and the level is correct. Have you asked your mechanic about this?

 

[saberz]

Thats the other thing I was looking at. The transmission is electronically controlled, the ECM may be wonky. My BCM in the impala bought the farm and I lost Cruise Control, Power Locks, everything electronic. The car thought it was being STOLEN!! and the security light would flash and it would refuse to start. BCM is a common issue on the impala's, maybe take it to the dealer and have them check your ECM(diagnostic fee).

 

[sciphi]

Could be the pressure control solenoid on its way out. That's a known issue with the 4T65 of that vintage. It will cause the random hard shift.

The 4T65 in my 1999 LeSabre with 68.5k miles on it had the odd hard 1-2 shift when it was warm before a $5 homemade shift kit and a flush with Dexron-VI. Now all the shifts are faster, a little bit firmer, and the hard, banging shifts are gone.

Another test to see if it's the pressure control solenoid is to floor the car from a stop. If it shakes violently without moving, it's the pressure control solenoid failing. The fixes are either a new pressure control solenoid ($$$) or a shift kit that will mechanically determine the line pressure, working around the defective solenoid.

 

[ryan2022]

Just the fact that you can shut the car off for a minute or two and restart it to have the problem disappear, would make me think that its not a serious internal tranny issue.

GM tranny's have a good reputation for reliability in most cases.

 

[Benzadmiral]

Originally Posted By: sciphi
Could be the pressure control solenoid on its way out. That's a known issue with the 4T65 of that vintage. It will cause the random hard shift.

The 4T65 in my 1999 LeSabre with 68.5k miles on it had the odd hard 1-2 shift when it was warm before a $5 homemade shift kit and a flush with Dexron-VI. Now all the shifts are faster, a little bit firmer, and the hard, banging shifts are gone.

Another test to see if it's the pressure control solenoid is to floor the car from a stop. If it shakes violently without moving, it's the pressure control solenoid failing. The fixes are either a new pressure control solenoid ($$$) or a shift kit that will mechanically determine the line pressure, working around the defective solenoid.

These sound like the same symptoms I have. What's involved in this shift kit? You say homemade -- it's not a fix I can purchase somewhere? And just how much $$$ for a pressure solenoid?

 

[sciphi]

The shift kit is made up of 4 spacers that go into the shift modulator. You can buy a kit online for $40 or so that's the same thing.

A new pressure control solenoid is about $500-800, depending on your area. It's a bear to get to.

 

[RedDart]

I recommend that you take your Buick to a transmission shop you trust and let them test drive the car and see if there are any powertrain codes stored in the PCM. The 4T65 is known for developing harsh 1-2 gears shifts when they get older for various reasons. Only testing will determine the extent of your problem. If you can repair the transaxle and new fluid is needed, I recommend Dexron VI. It is back specified for your transmission and most likely much better than the ATFs on the shelf that are "suitable for use in vehicles previously serviced by Dexron III". Good luck identifying your malady. Transmission problems are stressful and expensive.

 

[eljefino]

The 4T65 in my brother in laws olds intrigue made it to 226k, in the last 15k it had all sorts of solenoid issues (TCC and or 4th gear) yet it lived through the abuse.

Was going to fix it until I found the subframe had to drop to get the side cover off. Maybe your bigger Lesabre will be easier. I agree with the pressure solenoid idea above. On saturns there's a fuse for it you can pull for instant hard shifts; the default is max pressure which will knock your fillings out.

Since the solenoids are about $60 each and there are around 4 in there I'd have them all done if the labor to get in there is a pain.

 

[sciphi]

I'd get your transmission diagnosed. The fix I have proposed is for a pressure control solenoid. It could be something else entirely.

You have to drop the subframe to get at the transmission on the H and C bodies. Not for the faint of heart.

The shift kit needs the transmission pan to come off, and the danged module by the filter (I just did this, I should remember what it's called) unbolts. You then open it up, put the spacers on the shafts inside, close it back up, and reinstall. This can be done with the car on ramps or on a lift. Much easier.

However, the shift kit is a workaround for a damaged part. Having a diagnosis done and the part replaced is the true fix.

 

[Benzadmiral]

Originally Posted By: RedDart
I recommend that you take your Buick to a transmission shop you trust and let them test drive the car and see if there are any powertrain codes stored in the PCM. The 4T65 is known for developing harsh 1-2 gears shifts when they get older for various reasons. Only testing will determine the extent of your problem. If you can repair the transaxle and new fluid is needed, I recommend Dexron VI. It is back specified for your transmission and most likely much better than the ATFs on the shelf that are "suitable for use in vehicles previously serviced by Dexron III". Good luck identifying your malady. Transmission problems are stressful and expensive.

I can ask my regular mechanic who he'd recommend. No, I don't plan to cheap out; the car is worth keeping and doing things right, and now that the payments are done, investing some money in it will be easier.

 

[sciphi]

I didn't want to shell out $$$ for work on a car that's rusting away, so my workaround works for me.

 

[Benzadmiral]

Update, all,

I stopped by my regular shop, since he says he has the ability to read the tranny codes. Result: No DTCs (Diagnostic Trouble Codes" were in memory.

He printed out a sheet from Alldata regarding code P1811, for the 4T65-E Automatic Transaxle. Apparently if the 1-2, 2-3, or 3-4 shift takes longer than .65 seconds and the adaptive modifier can't shorten the time, a counter is incremented by 1. If this happens twice in one trip, the code is set.

Then the PCM (??? control module?) commands max line pressure, freezes the transmission adaptive functions, and records the code in the history. It clears the code if the vehicle completes 40 warm-up cycles without the condition returning again; and it cancels the default actions when the ignition switch is off long enough to power down the PCM.

Now the issue recurred on Monday afternoon (and went away when I made a stop and returned to the car after about 10 minutes). Certainly that was less than 40 warm-up cycles before he read the codes this morning, Wednesday. So the code should still have been there . . . but he didn't get anything.

Thoughts?

 

[AcuraTech]

Are the transmissions in this car known to be durable? Or do they often need repairs?

There are so many poorly designed transmissions out there that it's amazing.

Engines have gotten amazingly more reliable in the past 30 years but it seems that transmissions have actually gone backwards. Transmission fluid hasn't improved much in 30 years either.

TH-400 was the highpoint of automatic transmission design for simplicity, reliability, and potential for frequent abuse and still keep going.

These newer 5, 6, 8 spd autos are mostly junk. Baby em all the way along and they still fail. I guess that's what happens when you jamb so many forward gears in such a small space while trying to shave off weight and keep it confined within a small hot engine bay. Add in the 30 or so electronic solenoids, sensors, and valves on the modern A/T and you have a recipe for early failure.

 

[demarpaint]

Originally Posted By: AcuraTech


These newer 5, 6, 8 spd autos are mostly junk. Baby em all the way along and they still fail. I guess that's what happens when you jamb so many forward gears in such a small space while trying to shave off weight and keep it confined within a small hot engine bay. Add in the 30 or so electronic solenoids, sensors, and valves on the modern A/T and you have a recipe for early failure.


+1 My father has a similar problem in his Buick, it is intermittent but just enough to be annoying. He's had the transmission serviced and even brought it back to Buick to no avail. He was told on the QT that unless he wants to spend a lot of money searching for a problem to live with it until a code is stored. Not exactly what my father wanted to hear, or what the OP wants to hear, but I thought I'd pass the info along.

 

[demarpaint]

To late to edit, even though my fathers and the OP's transmissions are 4 speed units, they can still be difficult to locate intermittent problems. Unless you happen upon the right mechanic, or there is a bulletin which applies to the exact problem, without a code or the right mechanic you could be totally in the dark.