Transmission Slipping

impala
chevrolet

#1

2007 Chevy Impala
3.5L 6-cyl Flex Fuel engine w/ 4 speed auto trans
52,800 miles

Extreme driving conditions maintenance schedule kept.
Transmission standard service done @ 32,800 miles which was 20k ago.

PROBLEM:

  1. Twice in past three days, when shifting from reverse to drive the transmission has slipped, revving hard with rpms spiked above 3,000 for about 2 seconds before engaging the forward drive gear.

Normally I come to a complete stop of all reverse motion with foot fully on the brake pedal before shifting. Admittedly, I got sloppy the first time noted and still had very slight reverse motion when I shifted.

  1. Several times late today, while driving uphill at approx 35 - 45 mph, when the car downshifted there was an extremely brief moment of transmission slippage with spiked rpms. It was so brief each time that at first I thought I’d imagined it until it happened again. Then it did it once on a level surface in a parking lot when having shifted from reverse to drive without problem and was gently accelerating the transmission again slipped for just the briefest moment when the normal automatic shift point was reached. So far, all incidences while driving have been so extremely brief that it was the merest hint of a hiccup.

  2. When bringing the car to a complete stop, such as at a stoplight or when parking, as the transmission automatically shifts for the braking of speed, sometimes there is a minor but noticeable thunk sound seeming to come from underneath the car, I’d judge to be somewhere about under the level of the dashboard or slightly forward of that. Could that be from a worn or broken transmission mount? And, if so, could that be somehow causing the slippage problem?

  3. This transmission has always, even since new, allowed more roll after being shifted into park, the engine shut off and my foot taken off the brake than any other car I have ever driven. If I forget to engage the parking brake quite tightly, the car will roll forward quite a few inches before the parking pawl holds it, even on the level. I’ve been told both by the dealership shop and the independent mechanic shop that there is no problem and that this particular engine/transmission combination tends to do this although my particular car seems to do so somewhat worse than average.

ACTIONS TAKEN SO FAR:

  1. Have made an appointment to take the car into the mechanic.
  2. Will check the transmission fluid level per instructions in the owner’s manual tomorrow when I have daylight to see what the fluid level and color on the stick looks like.

NOTE:

  1. I periodically check the transmission fluid level and it has never been low or discolored. The shop checked it for me, along with making sure everything else was road trip worthy, for an emergency 1,000 round trip in late November, just three months ago. No problems then.
  2. No evidence on the garage floor of any leakage. Garage floor is dry.

QUESTIONS:

  1. I presume the first step is for the mechanic to check the fluid level and examine for any leaks?
  2. If the mechanic cannot duplicate the problem in a test drive, then what?
  3. If the problem cannot be duplicated and no apparent cause found, I presume that the prudent course of action is to go ahead and have standard transmission maintenance done (i.e. drop the pan, check for debris, drain and replace with fresh fluid) then see if that halts the slippages?
  4. Given that this car has already had failures of the power steering pump, water pump, and part of the wiring harness, and has a fuel pump starting to get noisy, despite aggressively maintaining all standard/preventive maintenance, that perhaps it is time to think of replacing this car, especially if there proves to be any truly major transmission problem found?

Marnet
…still reading, still learning, and at this point finally losing her patience with this machine despite liking its configuration and that it is paid for!


#2

Did the trans filter ever get changed? Most likely hopeful source of the problem.


#3

@Barkydog: Thank you for the feedback. I’d LOVE for it to be nothing worse than needing a new trans filter.

The trans filter was changed when the transmission was service 20k ago.


#4

Marnet, I am so sorry for your trouble. If it was me, well I have been on this board for a long time, and most people do not even care about a tranny till it fails, my first thought would be why am I having trouble, and neglectful drivers do not. I do all the changes and suff, at 155k now, so why are you having trouble. Is it possible the wrong fluid was put in? sure, but not probable, is it possible there is another issue yes, so let me give you my waguesses
1a. rpm of 3000 is out of the norm, 600 to 1200 is normal
2a. Spike in rpm not too unusual between gears, but above the norm
3a. A broken mount will not cause slippage, but seems more in tune with a bad u joint.
4a A few inches roll after putting it in park is not unusual.

I feel you are a concerned conscientious person, and done all that you can do for this car, but I think it might be time to trade it in and go on with your life hopefully worry free in a new vehicle with an extended warranty depending on the miles per year. (as many will say wasted money but if you can get an extra 4 years and 40 k with no worries for $1300, I think you need it)


#5

I’ll just say this. Shifting a vehicle from reverse to drive while the vehicle is still moving is abuse. I’m glad you owned up to it but it’s not the way to properly shift an automatic transmission. I’ve done it before as well when I was very young but transmissions cost an arm and a leg these days so I’m careful with them now. Besides…modern transmissions will not take the abuse that older transmissions could take.


#6

I don’t think #1 is slippage, but delayed engagement. Either way, until something is sorted out, do make the R to D transition more slowly - wait until you feel the pull of the trans before going

#2 might actually be normal - it depends on the RPM rise. These transmissions operate with a weird TCC design where the TCC is not on/off or locked/unlocked. It is applied by percentage. So the TCC can “on” to one degree or another anywhere from 2 through OD. The TCC has this weird special lining in it to keep it from being destroyed by heat. Anyway, TCC release generally comes with a little RPM hop. My understanding of that whole thing comes from owning a vehicle with the same trans but from an earlier year. So things could have changed.

#3 is a generally symptom of mount problems and/or ramped up line pressures. The causes of ramped up line pressure are many - from internal problems (solenoid issues, actual slipping detected etc) to squirrely TPS or MAP/MAF

#4 - probably just is what it is.

Hopefully when the transmission was serviced Dexron VI went into it - not Dex VI “compatible” or something - but Dex VI.

You’re going to have to get that classic, old, elusive, competent and independent, local transmission shop. Good luck. I don’t have one. A good tech probably ought to drive it with a scantool hooked up, and probably take a peek at the pan.

For your general reference, this is one of the best places on the web I’ve ever found for looking into problems with those transmissions - which are many:


#7

Your problem sounds electronic rather than mechanical to me. But that’s just a stab in the dark since over the web I can’t see, hear, or feel the car or what it’s doing. First thing I would do is have a mechanic scan for fault codes, then road test while recording some scan data during these odd shifts and then look at the data back at the shop. This should tell a competent guy whether the trouble is mechanical or electrical. Electrical issues could be a bad pressure sensor, pressure regulator solenoid or shift solenoid.

You could have a host of fault codes you don’t know about, that’s the first place to start. Don’t think that because there is no engine light everything checks ok. Remember, the check engine light is an emissions device, not a general diagnostic tool.


#8

On the tail end of asemaster’s advice, I would emphasize that a big part of my frustrations that I had with one of these transmission is that there certainly are plenty of transmission-related error codes that won’t trigger the check engine light, and will not be picked up by generic OBD II scanners. So rather than knowing when a code got set and being able to pull them myself I always had to cough up for the diagnostic charge. This would have been fine with me because I know what the charges are for - except that I never found anyone who wanted to be bothered to tell me what they actually found in the course of diagnosis. I could get them to tell me what the codes were. But never what was done to find the causes. All I ever got was a blank stare and shrug and a quote for a rebuilt transmission. Hence, the need for the ever elusive competent transmission shop.


#9

Missileman brought up an excellent point, one that I’d also like to know the answer to. Have you been shifting from reverse to drive without letting the car come to a stop?

Occasionally I see someone doing this and I cringe. They think that since the tranny didn’t drop out of the car and onto the pavement they must be doing no harm. They’re wrong. They’re relying on frictional devices that are designed only to engage and disengage the drivetrain to slip sufficiently to allow the entire weight of the vehicle to change direction. It will do that for a while, but the frictional devices will wear out prematurely and begin to fail to provide the friction necessary to even function properly. Envision, if you will, the amount of energy it would take you to reverse the direction of the vehicle while pushing and pulling on the bumper. That’s the amount of force you’re placing on the tranny.

So, have you been doing this?


#10

@tsm: No sir, I have not been shifting from reverse to drive without letting the car come to a stop in the 7 years I’ve owned it since new except for the two recent occasions and the reverse momentum was almost at a full stop even then.

I know what I did was sloppy driving and detrimental to the transmission. Both times I was in an extreme hurry and mentally distracted. Both instances of negative response from the car were like a slap in the face which quite got my attention and focus back on my driving. And since then I’ve not allowed myself to be that distracted nor hurried in my driving habits even if in a hurry. I’ve been driving for 39 years and can honestly say the only other time I’ve made this same dumb, careless mistake was when I was learning to drive and got myself thoroughly told off by my instructor (who happened to be my mother.)


To everyone else, thank you so much for your informative feedback. You are very kind and I do appreciate the information.

Hopefully I haven’t done too much damage to the machine. Either way, I get to pay the financial cost to find out and fix whatever needs fixing. And THAT will decidedly keep my attention more focused on my driving habits.


#11

Thank you for your quick and understanding response. Often an OP will think I’m criticizing when in fact I’m only trying to get to the root of the problem.

I wish you only the best and hope the answer is simple. How was the fluid level when you checked it?


#12

@Marnet, I would not in any way assume that, if there are real problems, that you had anything to do with it. Those 4T65E’s are total Jekyll and Hyde systems. When they work they’re great, and many people get long and easy lives out of them. But they do have some very common problems and they’re not about the owner’s abuse of them. They also seem to be notoriously difficult to deal with once problems start, so here’s hoping that’s not where you end up.


#13

@tsm: I’m afraid I’ve been a sloth and haven’t used the car yet today, so haven’t yet checked the fluid level. The sun has finally come out and temps warmed up, so will check it in a little while.

I did not assume you were criticizing. I’ve been reading here on the forum enough years to understand the attitudes and styles of all you regulars. And, frankly, my error in shifting from reverse to drive without being at a total, complete stop first is worthy of criticism. Trust me, I can hear my dad’s and mother’s voices in my head even now. (Doesn’t matter that I’m middle aged and they long gone!) But, as Dad taught me, you make the best decision you can at the time and hope you make more good ones than bad ones. And when you make a bad decision, whether from not doing your best or even when doing your best, learn from it and go forward.


#14

@cigroller: Well, this won’t be the first GM transmission to give me problems. Much as I liked my previous car, a 1987 Cutlass Ciera with the 3.8L engine, the transmission on that car was always trouble with leaks and slippage even when new it ended up being replaced at only about 75k. The replacement/rebuilt trans is still going strong in that car for my nephew who now has about 200k on it as far as I know. The reason I’m now jumping on even the slightest hint of a problem with this transmission in my current Impala is in hopes of avoiding a similar experience with this car.


#15

@asemaster: I hadn’t even thought about the fractional hesitation being electronic. But then one of my few gripes about this car has been the way the electronic throttle always has such a long lag time from when I try to accelerate and when it finally decides to have the engine do so. What is new is that when the transmission automatically hits a shift point under steady throttle, such as driving uphill, there is now a hesitation in the auto shift engaging and once when undergoing gentle acceleration on the level in a parking lot. That along with how it failed to engaged when I erred in how I shifted from reverse to drive.


#16

@missleman: Point fairly given and taken about even a rare instance of such sloppy shifting habit being abusive to the machine. I appreciate you and others taking the time to respond.


#17

@Barkydog: Can you, please, elaborate about the u-joint being connected to the thunk I hear when the car is coming to a stop? Could that in any way get back to un-diagnosed damage from when I hit the road hazard about 18 months ago and bottomed out the car at 70 mph on the highway? That impact cost me four new struts, four new tires, one wheel bearing and, more recently, rear bushings.


#18

After an incident like that, my goodness. Most typical ujoint thump in my experience is when you accelerate from a stop, but in drive train issues certainly a very probable cause of a clunk or thump. After hearing above wondering if an engine mount might be an issue, if the engine shifts enough the linkage may be putting it into neutral explaining the rpm spike.

If you have the option try driving it in the gears below the normal drive, and see if it mis behaves. if not could be a mount.

Here is a picture of a ujoint, it handles a change in angle of the drive shaft. The bearings can wear causing looseness resulting in a thunk.


#19

I don’t believe a FWD Impala has any u-joints


#20

It doesn’t. It only has CV joints. The inner joint could conceivably cause a thunk, but to do so without noise on turns would be highly unllkely.

95% of thunks are caused by worn bushings. Usually the ones that hold the sway bar to the chassis.
4% are caused by strut mounts.
The remaining 1% are caused by other things.