Mystery Transmission Problem

[rhoward2]

Hi,

First post here; hope someone can help. I have an '06 C6 with an A6 and my car has been having a shifting problem for just over 6 months now. My car shifts great in D-mode. The problem only occurs in S-mode and it will occur with or without using the paddles. While shifting from 4th to 5th the engine rpms will climb and speed drops momentarily before shifting into 5th gear. It "feels" as if on the way from 4th to 5th it momentarily grabs 3rd. I had the car up at LG Motorsports in Dallas for service recently, and they spent several days trying to figure it out, but could come to no conclusion as to the cause. They told me all my shift parameters were as they should be per GM, and they were stumped. I hope someone here is able to shed some light on the matter for me. I have a GMPP plan, but I live in a rural area and my local dealer has limited experience working on vettes. Any advice would be greatly appreciated. Thanks in advance.

Mods are LG long tube headers, Halltech Cold Air Intake, Wheels and tires are stock. 60,000 miles on the car. All fluids changed regularly: Mobil 1 oil, Red Line Transmission Fluid (car was exhibiting this problem prior to transmission fluid and filter change) and new AC Delco transmission filter. I have approximately 60,000 miles on the car. It's never been tracked.

[c4c5specialist]

Hi there,

We would need to know all modifications that are on the vehicle.

Tire size changes, programming changes, different fluid used in the transmission and the mileage.

Allthebest, c4c5

[rhoward2]

Mods are LG long tube headers, Halltech Cold Air Intake, Wheels and tires are stock. 60,000 miles on the car. All fluids changed regularly: Mobil 1 oil, Red Line Transmission Fluid (car was exhibiting this problem prior to transmission fluid and filter change) and new AC Delco transmission filter. I have approximately 60,000 miles on the car. It's never been tracked.

[c4c5specialist]

Hi there,

So you did NO tuning to the PCM for the headers and transmission calibration for increased shift firmness ????

Allthebest, c4c5

[rhoward2]

Tune was done for headers, but that was in '08, and this issue began approximately six months ago. I have lived with it until I took the car into LG for trans fluid and filter, differential change and new plugs. They spent several days going over the car and were unable to find any problems related to tune or otherwise. No metal or parts in transmission pan, and problem does not occur at all in D-mode, and all shift parameters are stock.

[c4c5specialist]

HI there,
First, it sounds like you have pressure leaking, creating your condition.

When you are in 4th, you have the 1234 clutch and the 456 clutch turned on.

5th gear requires that the 1234 clutch turns OFF prior to the 35R clutch turning on. The shift timing of the transmission would dictate how this engagement feels.

HOWEVER, if you have either a pressure souce bleeding into the 1234 clutch, this condition may occur.

Personally, I would be looking for shift timing as the data from a Tech2 will give you the actual shift solenoid on/off sequence along with bleed off control solenoid function as well.

If you look at the picture below, 51 is the assembly for both the 1234 and 35R clutches so if for some reason there is a problem with the housing or the seals within it, this issue may occur.

The reason why you have this only in S may be due to the fact that there is higher pressures being put to the clutch, therefore pushing past whatever part has failed.

BUT I STRESS, your Tech 2 data will tell you EVERYTHING ABOUT HOW THIS TRANSMISSION FUNCTIONS.

You can see pressure changes, you can see solenoid functions and I can tell you first hand, you will be able to SEE what is going on PRIOR to opening your transmission.

Allthebest, c4c5

[rhoward2]

Thanks, I will share that with the service tech I am seeing tomorrow. I'll let you know what they find.