Automatic Transmission Downshift Problem

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Mar 30, 2011 | 08:41 AM

cdcman

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1st Gear

Joined: Mar 2011

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Automatic Transmission Downshift Problem

Hello, I just recently purchased a 98 C5 (like last week).... I noticed while driving at speed, if I wanted to "punch it" to increase my speed, the transmission seems to have difficulty downshifting out of top gear. I noticed that the RPMS will bounce between 1800-2200 at which point I let off the gas.

Hopefully somebody else has had a problem similar to mine and has a fix.

Thanks

Mar 30, 2011 | 04:08 PM

Paul Wood

Pro

Joined: Aug 2010

Posts: 593

Likes: 9

From: San Antonio Texas

Find a good tuner and see where the torque converter locks up. On stock A4 it is 41 MPH. I had mine configured to lock up progressively as a function of the accelerator position. A tuner can change all of this with a few strokes of the keys on a laptop. It is worth doing and will make the driveability of the car much better IMHO. It cost me about $100 to have this done. Good luck.

Mar 30, 2011 | 04:29 PM

Bluefire

Le Mans Master

Joined: May 2006

Posts: 7,866

Likes: 249

From: Hillsboro OR

Quote:

Originally Posted by cdcman

Your trans needs a tune. For a downshift to happen, three things must be met. The preset speed (MPH), throttle position, and RPM must be met before the shift will take place. A tuner will first set the max RPM for each gear change (i.e. 1>2, 2>3, 4>3, 3>2, etc.). Then you can choose the MPH (and throttle position) for each upshift and downshift to occur at.

As far as TCC settings go, usually people will set it to lock (mechanically lock eng to trans.) in 4th gear only for driving on the highway. Locking the TCC eliminates slip and reduces heat bulid up.

Hope that helps.

FYI, a tuned A4 will

Mar 30, 2011 | 04:39 PM

Bluefire

Le Mans Master

Joined: May 2006

Posts: 7,866

Likes: 249

From: Hillsboro OR

Quote:

Originally Posted by Paul Wood

Find a good tuner and see where the torque converter locks up. On stock A4 it is 41 MPH. I had mine configured to lock up progressively as a function of the accelerator position. A tuner can change all of this with a few strokes of the keys on a laptop. It is worth doing and will make the driveability of the car much better IMHO. It cost me about $100 to have this done. Good luck.

Interesting concept. It annoys me in city driving to have the TCC apply/release constantly. Can the TCC be set to apply only as a function of throttle position in any gear? For example driving around town 35 - 45 mph (TPS 0 - 12% range), if I all of a sudden I set the throttle position to 75%, will the TCC lock? It could be tricky timing between this and the downshift.

Mar 30, 2011 | 04:59 PM

Paul Wood

Pro

Joined: Aug 2010

Posts: 593

Likes: 9

From: San Antonio Texas

Quote:

Originally Posted by Bluefire

My true understanding of this is limited but I know that after my tuner finished his magic the car was so much more enjoyable. The formula that he used for the TTC to lock up was based on throttle position so at a dead stop if you put your foot into it the transmission would not lock up until you reached 100 mph. If you backed off the throttle it locked up at where ever it was set for the current conditions. I also believe that RPM and speed are factored into the formula as well. Bottom line the car performed extremely well after the tune and was worth the money for sure.

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