'07 Lacrosse Tranny Slipping

[Pete O]

Ok, so '07 isn't an antique, but it is post-war!  You guys have so much Buick knowledge, I figured I'd give you a chance because my Buick dealer can't (won't?) figure it out.  Maybe you've had the same thing happen to your car and you got it fixed.  The symptoms are that after idling at a traffic light for say a couple of minutes, when you take off, the car will move a little, but then wham bam, something grabs and makes a thunk, and then everything is back to normal.   Happens most when the car is partially warmed up.  It's like the bands are slipping and then suddenly tighten. The car shifts beautifully once it's in motion, and if you're stopped for a short time only, it won't do it when you take off.  Oh, I have the 3.8 engine in the car.

 

Dealership flashed the software to install an update and  changed the fluid and filter.  But it's not throwing an OBDC error code.   And because there are no real mechanics left out there, if there's no error code, they don't know were to begin to make a diagnosis. 

 

I searched the internet for this symptom, and found a suggestion to clean the mass airflow sensor.  Gunk on the filament can give a false reading causing the transmission fluid pressure to be too low.  I cleaned it carefully with a swab and some alcohol.  No change in behavior.  

 

Thanks for your insights!

[EmTee]

Weird behavior approaching or accelerating away from a stop always make me suspicious of the torque converter.  There are no other noticeable symptoms when driving along?  How many miles are on the car?

[Pete O]

Around 84K miles,  and no other symptoms. 

[60FlatTop]

It is a FWD 4l65E, kind of an adaptation of the 4L60E. For 20 years GM has been using a sun gear shell (we called them a drum, but these things break like egg shells) that is so bad an aftermarket company makes a durable one that is a standard replacement in all but dealer shops, 'cause the dealers don't know yet. Duh.

 

Yours may be partly stripped or cracked on the spot welds, causing the clutches to grip erratically. When the shell breaks completely you will lose reverse, it will shift from first to third skipping second, and will not go into fourth.

 

It costs about 2,000 bucks to learn that but an aftermarket drum is included with the course. So you only have to fix it once. Complete failure, when it happens, is about 110,000 miles. Yours might come early because "mysterious" symptoms are showing.

 

Amazing, aftermarket companies are actually in business making internal transmission parts, intake, and exhaust manifolds. Stuff we never imagined would ever need replacement.

 

Here is the replacement for the factory part that goes bad:

http://www.americanpowertrainwarehouse.com/4l60e-4l65e-4l70e-4l75e-700r4-transmission-sun-gear-shell-the-monster-with-washer-hardened-steel-fits-82/

 

Bernie

Edited December 28, 2016 by 60FlatTop (see edit history)

[NTX5467]

RATHER, 4T65E in fwd cars.  4L65E is the electronic THM700 rwd trans.

 

I don't know how the MAF sensor wire could have ANY connection to trans control!  It's only hooked to the fuel mixture control functions, last time I looked.

 

This issue comes up every so often with the 4T65E transaxle, it seems.  When I did the dealer training ride and drive for the then-new 2004 Grand Prix, we were instructed to NOT use normal throttle after a full stop on the road course.  Otherwise, it'd damage the powertrain mounts, which meant "no more driving that day".  In this case, the stop was after a long sweeping rh curve ("at throttle", as it was a road course and we were supposed to be exploring the car's handling characteristics).  So, we were advised to "feather the throttle until the car moved", then "as normal" once it moved.  He said the engineers were advised of the issue and they were seeking a fix . . . in 2004.

 

I have a 2005 Impala that will try to move and then "wham" it fully engages and moves normally, usually sitting on a slight incline on a warmimg-up engine in the morning.

 

On an electronic valve body automatic transmission, all of the spring-loaded shuttle shift valves have been replaced with electric solenoids or "actuators", which control pressure to bands and clutches, etc.  If, for some reason, one doesn't react normally, it can cause "issues".

 

Otherwise, I'd suspect a leaking valve body gasket (between the two halves of the assembly) which can cause one circuit to temporarily lose pressure, as if going into "N" while it's still in "D", then when the pump gets a little more pressure, everything re-engages "solidly".  I think I found a thread on this in a fwd Chevy Impala forum.  Fixed when the 4 solenoids were replaced, I believe.  It can be done "in car", I believe.

 

Key thing is to NOT use any real amount of throttle until everything engages or proves to be engaged!  The "lower" motor/transmission mounts usually have some damping fluid in them, but when the rubber breaks, it gets messy.  When that shockload "hits", the upper torque straps might limit that movement, but the engine will try to pivot on the axles and push those lower mounts into places they don't like to be.  So, if you throttle into the car after a stop, you notice it doesn't move IMMEDIATELY, IMMEDIATELY get out of the throttle until it hooks up and moves, to do the least damage to the mounts.

 

I'm driving a company Sierra (2014) with the 6L80E automatic.  Same delayed engagement when going into "D", not all the time, but I've learned to feather the throttle if it doesn't creep immediately when put into "D".  Sometimes it acts normally, other times not.  I've learned to deal with it as it's been there since new (now with 130K).  I'd rather have it driving rather than fixes attempted, personally.

 

At the dealership level, unless a trouble code is in the computer, everything's fine.. . . allegedly.  BUT there is some GM-required test equipment which should be able to check "apply" actions of the shift valves. Unfortunately, if "no codes" are found, many dealership techs are conditioned to not go any farther, especially on normal warranty issues (which might not apply here, unless there is possibly an extended warranty?).   With the Chrysler transaxles, they time that "apply" event to see how much the frictions are worn (the longer it takes, the more wear)!

 

That particular transaxle had been in use in almost all of GM's fwd "larger" cars for years, other than just Buicks.  It's a good transaxle, but sometimes, ''things" creep into certain production runs that cause issues in an otherwise very good mechanism.  Finding somebody willing to "look", blindly without codes, but with a working knowledge of the possible causes, can be the KEY.

 

As the memory capabilities of GM's ECMs and such have increased exponentially from even 10 years ago, if there was a "soft malfunction" which didn't set a code, it might still be "in memory", accessed by the GM hand-held computerized test equipment.  There might also be a TSB in the mix, too!  And, all things considered, it could be a wiring problem in the harness which controls the solenoids . . . OR a connector in the harness (in its entirety).

 

Please keep us posted  . . .

NTX5467

[EmTee]

3 hours ago, 60FlatTop said:

It is a FWD 4l65E, kind of an adaptation of the 4L60E. For 20 years GM has been using a sun gear shell (we called them a drum, but these things break like egg shells) that is so bad an aftermarket company makes a durable one that is a standard replacement in all but dealer shops, 'cause the dealers don't know yet. Duh.

 

Yes, I'm familiar with that problem.  That exact failure was the 'last straw' that killed my wife's 2001 Century.  The symptoms described didn't sound exactly like what i experienced, but it could be an early manifestation.  I couldn't tell at first whether it was engine or transmission in my Century, as driving along it felt like either an intermittent 'miss' like a cylinder dropping out, or a buck/surge like a transmission issue.  Dropping the transmission pan and changing the filter led to the true cause.  I opened the old filter and found brass shavings.  I am told that the planetary set is the only place that brass is used.  I wound-up disposing of the car at that point, as it would have cost as much (or more) to rebuild the transmission than the car was worth.

 

I hope it's not that problem in your case...

[NTX5467]

I sold lots of the "sun shell" for THM700-style automatics in the 1990s, at the dealership, to outside shops.  It was a regular failure point.  I suspect that particular shop also knew how to keep it from failing, as I sold him other parts not spec'd for the vehicle he was working on (as valve body gaskets for Corvettes rather than pickup trucks).  We kept several in stock, but this might have been before the ready availability of the aftermarket parts.

 

If we had an automatic in the shop that needed more $$$ to repair than a GM  SRTA trans cost, it got the SRTS (Service Replacement Transmission Assy), which also included ALL of the updates to the then-current model specs.  Plus a GM warranty on the item.

 

NTX5467

[60FlatTop]

Think they kept those updated transmission parts on the shelf next to the steering intermediate shafts they used for 20 years as well.

 

I can understand a part needing a redesign, but a reputation of failure year, after year, after year, until it runs into decades seems common.

 

From a hobbyist and preservationist standpoint, at least a lot of things are predictable. And I like GM cars. Knowing these and other long standing issues has been a deciding factor in some collector car opportunities. But abstinence, though my best choice, has not always been the one I was happiest with.

 

Bernie

[Pete O]

Thanks Guys!  I'll print out your replies and show them to the counter guy!  Sorry state of affairs when the laymen seem to know more than the professionals!

 

PS  When the dealership changed the fluid, they told me that they didn't find any metal fragments or filings in the oil, so I'm hoping it might not be the sun gear cage!

Edited December 29, 2016 by Pete O (see edit history)

[avgwarhawk]

Instead of the MAF sensor, take a look at the MAP sensor.   Also, inside these transmission are shift solenoids.  These cause issues and are replaceable.  Also, as much as we think the dealer knows it all some just don't when it comes to transmissions.  Have you take it to a good transmission shop?    

 

There are several GM bulletins regarding two common problems.

#06-07-30-023C...Shudder on Acceleration
#PIP4188 Delayed Shifts Harsh Engagement

 In either case with those two bulletins, the transmission must be disassembled for repair.

 

FP# 24225825 (valve sol 4.265)

Edited December 29, 2016 by avgwarhawk (see edit history)

[60FlatTop]

" As the memory capabilities of GM's leadership and such have decreased exponentially from even 10 years ago" 

 

My company will be 10 years old in November... but we don't do transmixers.

[NTX5467]

Rather . . . should be "increased exponentially" . . .   Sorry about that!

 

For those who like to put aftermarket programs in their ECMs, the later ones will keep track of that, too . . . EACH change from the original factory software.  LOTS of things in that memory!  Plus some "secret" codes that can really "tell on the customer's actions"! 

 

Reason I know what I do is that I've been in GM parts for 37+ years, paying attention to "things" and learning how things work.  At the dealership level, what's usually seen is "warranty repairs" with fewer customer-pay transmission repairs.  Post-warranty coverage, the better private shops usually get the work.  In the mean time, dealers have moved FAR past the 4-speed OD automatics to the 9-speed transaxles (which have their own unique set of problems) . . . PLUS the upgraded ATF to attempt to keep them alive.

 

In transmission design, there are many parameters which must be met to get things "inside the case" and "into the car", which having adequate torque capacity for the planned powerplants.  The THM200 was originally a 4 cyl and 6 cyl automatic, but later was used in GN Regals.

 

In the case of the sun shell for the RWD THM700-family automatics, there is probably a certain dimension which dictated a certain metal thickness for the shell itself.  Then costs might dictate the alloy of metal to make it.  Obviously, there would need to be an alloy with a certain amount of flex that would have decent service life in MOST uses.  Some customers, it's been observed, could tear up an anvil in a sandpile.

 

Electronics might control things (in many cases, better than "analog"), but a basic knowledge of what circuit (fluid and electrical) does what, when, and why is STILL important to know and understand.  Whether engines, transmissions, transaxles, fuel systems, or whatever.

 

NTX5467