Shifts rough... but not all the time..

[kielsa18]

I bought a 2004 Bonneville SLE a few months ago and everything has been just fine with it, until just recently after it is driven for about a half hour or 45 mins in the city it starts to sort of clunk or shift rough into every gear making the whole car jerk, it does not always do this that is why I am very Dumbfounded when it comes to what the solution should be, hoping it might maybe just be the pressure control solenoid?? Any help would be greatly Appreciated. Thank You!

[Archon]

Start by adding some of Seafoam's Trans Tune, run that for a short time, then drop the pan and change the fluid and filter. If the PCS is sticking, that should help. You may also want to consider adding a shift kit when you drop the pan.

While you're checking things, also check the front transmission mount. If the engine is rocking, that can make it feel like rough shifts.

[LeSabre in Buffalo]

+1 on the shift kit.

Also, when you replace the fluid, replace it with Dexron-VI. Then drain the pan again and refill with more Dex-VI.

The combination of shift kit+Dexron-VI in my 4T65 gives me fast, consistently mild shifts.

[wjcollier07]

I've actually been dealing with the same exact issue in my transmission, it only tends to do it when its cool out, and I'm going very gently on it. Then it'll BANG into every gear, whether I'm accelerating lightly, or heavily, and generally will not be present the next time I get back to driving the car after it's been sitting.

I've already run two cans of seafoam transtune through mine, about 1.5 cans in there right now when counting the filter change/pan drop I did about 400 miles ago, and it's still not helping TOO significantly with this problem, but has significantly cleaned up the feel of the transmission in several other ways.

Let me assure you, you do NOT want to be hoping it's the pressure control solenoid, for exactly the same reason I think it's mine, and I'm trying to throw every solution in a can in there to try and fix it. It's a relatively inexpensive part, but you really don't want to be the one replacing it, or the one paying for its replacement. However, with your car being an 04, it is noted in the GM TSB about the PCS that the TSB is only addressing 1997-2002 model years, and because of the differences in the valve bodies and the revision of the PCS itself, the issue is supposedly no longer present?

My next few steps on this quest to get the most out of my transmission for the remainder of its life (100,000+ miles), is to swap to Dexron VI, get a mild shiftkit (might even just go with a transgo), add in a bit of lucas transfix, and throwing a nice B&M 70268 plate type aluminum, thermostatically controlled transmission cooler

Don't overlook Archon's suggestions of engine/transmission mount(s), especially that front one on the 00+...those can mysteriously make the engine/trans like it just fell out on the road.

[00Beast]

Guys, from what I've been hearing, Dex VI isn't all that it's cracked up to be. There are a good number of people having issues with it in the colder weather. I'd go with a high quality Dex III and some Lucas TransFix after a pan drop + filter + shift kit with TransTune.

[wjcollier07]

Would you please care to elaborate on this "cold weather" issue Ed?

[00Beast]

I've just heard from some people on other sites that Dex VI is really poor in cold conditions (under 30* F), in certain transmissions. It was geared towards the Allison, but probably affects most the same way.

[LeSabre in Buffalo]

Hmm, haven't experienced any issues with the Dex-VI in my car at 35* F. So far I'm enjoying the Dex-VI a lot, especially in the cold weather since it starts out much closer to its warm viscosity than any Dex-III out there.

[shredthebonnie]

mine was doing the same i was reading somewhere that the waste spark could be the cause check your spark plugs i found one in my bonnie that had a crack in the porciline soon as i changed my plugs it helped a bunch it doesnt do it at all anymore.

[laxmangl]

I had the same problem and a bottle of Lucas tranny fix helped a great deal.

I also replaced my front motor mount and it hasn't shifted hard since

[wjcollier07]

In the last couple days, I siphoned out about 3 quarts of fluid, added one bottle of lucas trans fix, installed a B&M 70268 transmission oil cooler, and started on the path of swapping to Dex VI, so far two quarts in there mixed with the rest, but just with the Lucas Trans Fix alone, it almost completely stopped the slipping, so now the transmission isn't requesting full line pressure all the time, and is now doing significantly better than before. No chattering off the line anymore, just once i got a HEAVY slip, without chatter, and it caught HARD. A good sign indeed. The issues I'm still seeing might be the fact that my transmission got a little OD'ed on Seafoam TransTune (which I found reaaally doesn't contribute to good clutch friction)

One additional interesting thing is that my trans fluid is QUITE dark again after just 1000 miles of driving after my last pan drop/filter change. This does tell me that the trans tune has successfully done its job by cleaning out the transmission of EVERYTHING...but all that stuff suspended in there obviously doesn't help the functionality, as previously noted.

Shift times are still horrible, and shift firmness is still all over the board, however, it's only 'bang-shifted' a handful of times since I did this, and it was only for about a 2-3 minute period.

One more pan drop, 6 more quarts of Dex VI and just about a 1/4 - 1/2 bottle of trans fix more and she should be doing significantly better.

On the upside, and a reminder to everyone...If you live anywhere that gets above 70 degrees...you need a transmission cooler. Mine was getting near 200 degrees with an outside temp of around 75, and now, even at 90 degree outside temps, the highest I've seen is 172. 175 degree fluid temperatures, even with Dex III, can fully support 100k change intervals (on paper of course), and Dex VI just the same, but a little higher recommended.

[LeSabre in Buffalo]

Yesterday my car was sitting outside in 29* F weather all day. I started it, and it shifted like it has been doing since installing the shift kit. IE, fast and smooth. The Dex-VI seems fine in my car.

Could the people who report problems have a mix of III and VI? My car only has VI after I did a cooler line flush on it.

[likeamojay]

I had the exact same issue on my 2000 Bonneville SSEi about a month ago. I replace the front transmission mount and the motor mount. That solved everything, the rubber motor mount was badly torn. They usually last about 4-10 years depending on how hard the car is driven. If the engine is loose and rocking that usually causes hard, rough, and delayed shifts.

[golfyeti]

likeamojay: off topic question on your mods list: what's NASCAR Oxygen?

[gonzo4191]

off topic, their nascar sensors, oil, oxygen and....

[Melissa]

I had this issue with my 2000 SLE I have right now. It ended up being a mount and sway bar or something of the sort. I'm no mechanic but it wasn't the transmission which is automatically what that feeling makes you think of. The mount was bad so the engine was able to rock around more than usual when the car shifted. Don't know how else to explain it but I guess all I'm saying is don't panic too soon!! It was a relief finding out it wasn't going to cost $1,400 or more!!

[Bvill_GXP]

Humm My 05 GXP with 66k miles tend to do the exact same thing about once every 2 weeks!!! But it's going to the Toyota dealership (warranty is with them) at the end of the month for the creaking in the steering wheel issue and they is going to check out the trans also and replace it if need be!!! But they is going to take it over to the GM delership (chevy) and let them work on the steering wheel and tranny...... Don't care whats going on with the car b/c it's covered 100% with the warranty till 100k miles... I just hope they don't keep it long b/c i will be driving a loaner car from Toyota dealership!!!

[LeSabreUltra]

Could the people who report problems have a mix of III and VI? My car only has VI after I did a cooler line flush on it.

Just to update on this, my car has a mix of III and VI...mostly VI. It's been 20* here the past few days and my trans shifts better than ever. No issues.
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[wjcollier07]

You've got a 60 though Dan. I think we're after the 65 here.

[LeSabreUltra]

True, I don't know if the 65 responds any differently to VI than the 60.
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