A4 Trans Gurus: Can someone explain...
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
A4 Trans Gurus: Can someone explain...
Assuming an A4, what is the difference between downshifting with the gear selector lever and letting the trans downshift itself via your right foot? How can the former be harder on the tranny than the latter?
TIA,
-Ed
TIA,
-Ed
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
Let's say that you're cruising down the road at about 60 mph in 4th gear. You decide to mash the gas, and the car downshifts itself into second and takes off. Typical.
Okay, same scenario, except that you manually move the gearshift lever to force a downshift into 2nd gear (you wanted to accelerate hard and also hold 2nd because there are some twisties ahead).
I was under the impression that scenario #2 was hard on the tranny and was not something that you should do on a regular basis. I don't understand why that is (unless my presumption is wrong in the first place). What is the difference between shifting with you hand or with your feet?
Okay, same scenario, except that you manually move the gearshift lever to force a downshift into 2nd gear (you wanted to accelerate hard and also hold 2nd because there are some twisties ahead).
I was under the impression that scenario #2 was hard on the tranny and was not something that you should do on a regular basis. I don't understand why that is (unless my presumption is wrong in the first place). What is the difference between shifting with you hand or with your feet?
Drifting
Joined: Mar 2004
Posts: 1,504
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From: Byron Center MI
I'm not a trans guru but I have a GM service manual for the 700R4. The fluid flows thru the valve body in a different route when you manually control the trans versus letting the trans do the work. Maybe it is bad for the trans to hold a gear because the fluid may heat up. Just some thinking out loud. Tim
Instructor
Joined: Jun 2004
Posts: 249
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From: clinton ut
There would only be a problem in DOWNSHIFTING and then only when you are using the transmission to slow the car down. Consider coming to a stop sign or a curve at 60 and instead of using the brakes you down shift to 2nd then 1st to slow the car down. If you want to stay in the power band for twisties like you mention, you gotta do it, letting the auto do its thing does not work for this type driving and you obviously know it. This can be hard on an auto and hard on a manual (mostly the clutch) so you decide is it worth it? I think so if abuse is not included. I am curious for others to give opinions.
Burning Brakes
Joined: Nov 2003
Posts: 844
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From: Cape Cod Ma
Originally Posted by 89vert
I'm not a trans guru but I have a GM service manual for the 700R4. The fluid flows thru the valve body in a different route when you manually control the trans versus letting the trans do the work. Maybe it is bad for the trans to hold a gear because the fluid may heat up. Just some thinking out loud. Tim
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
The only difference that I can see is that when you mash the pedal to cause a down shift the engine is speeding up which better matches input and output shaft speeds, whereas if you just manually down shift the car will lurch due to lack of engine speed (the same will happen with a stick shift if you let out the clutch before getting onto the throttle).
When I do the manual down shift of my A4 it is in one of several circumstances:
- I have my foot on the brake going into a corner and want additional braking going in with more pull comming out
- I am going down a hill and want some additional braking, in which case I always tap the brake pedal first to unlock the TC clutch for a second or two before moving the shifter
- I am about to "play in traffic" and anticipate the need for shortly being in the power band; this one is rare however
BTW, I do have a built up A4 with a TransGo-like shift kit, a 12" lockup 2,000rpm TC and only stock cooling.
When I do the manual down shift of my A4 it is in one of several circumstances:
- I have my foot on the brake going into a corner and want additional braking going in with more pull comming out
- I am going down a hill and want some additional braking, in which case I always tap the brake pedal first to unlock the TC clutch for a second or two before moving the shifter
- I am about to "play in traffic" and anticipate the need for shortly being in the power band; this one is rare however
BTW, I do have a built up A4 with a TransGo-like shift kit, a 12" lockup 2,000rpm TC and only stock cooling.
Burning Brakes
Joined: Sep 2001
Posts: 1,013
Likes: 9
While I wouldn't say it's bad for it to manually put it in a lower gear . . . at full throttle, you will get a little more clutch and band holding power with the lever in OD.
Why? Because when the lever is in OD, The valve body's TV (throttle valve) circuit is actively controlling line pressure (more throttle = more line pressure, light throttle = low line pressure). When you put the transmission in 3/2/1/R ranges, the line pressure is controlled by a fixed fluid circuit, and is not influenced by the TV circuit. This fixed fluid circuit is a relatively high line pressure. The line pressure is then much higher than you will get at low throttle positions with the trans in OD ... BUT it is usually 10-20% lower line pressure than you will get at full throttle in OD.
Why? Because when the lever is in OD, The valve body's TV (throttle valve) circuit is actively controlling line pressure (more throttle = more line pressure, light throttle = low line pressure). When you put the transmission in 3/2/1/R ranges, the line pressure is controlled by a fixed fluid circuit, and is not influenced by the TV circuit. This fixed fluid circuit is a relatively high line pressure. The line pressure is then much higher than you will get at low throttle positions with the trans in OD ... BUT it is usually 10-20% lower line pressure than you will get at full throttle in OD.
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Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
Originally Posted by Mr6spd
While I wouldn't say it's bad for it to manually put it in a lower gear . . . at full throttle, you will get a little more clutch and band holding power with the lever in OD.
Why? Because when the lever is in OD, The valve body's TV (throttle valve) circuit is actively controlling line pressure (more throttle = more line pressure, light throttle = low line pressure). When you put the transmission in 3/2/1/R ranges, the line pressure is controlled by a fixed fluid circuit, and is not influenced by the TV circuit. This fixed fluid circuit is a relatively high line pressure. The line pressure is then much higher than you will get at low throttle positions with the trans in OD ... BUT it is usually 10-20% lower line pressure than you will get at full throttle in OD.
Why? Because when the lever is in OD, The valve body's TV (throttle valve) circuit is actively controlling line pressure (more throttle = more line pressure, light throttle = low line pressure). When you put the transmission in 3/2/1/R ranges, the line pressure is controlled by a fixed fluid circuit, and is not influenced by the TV circuit. This fixed fluid circuit is a relatively high line pressure. The line pressure is then much higher than you will get at low throttle positions with the trans in OD ... BUT it is usually 10-20% lower line pressure than you will get at full throttle in OD.
ps... I have WAY more questions than I have answers. :o
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by eschoendorff
Assuming an A4, what is the difference between downshifting with the gear selector lever and letting the trans downshift itself via your right foot? How can the former be harder on the tranny than the latter?
TIA,
-Ed
TIA,
-Ed
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 7,625
Likes: 4
From: Director of Bands
St. Jude Donor '08
CFI-EFI: I was hoping you'd get in on this. I enjoy reading your posts. 
So, am I correct in assuming that manually downshifting at will is no less harmful to the car than downshifting with your right foot (for the reasons detailed above)? I had always thought that manually downshifting a stock trans was hard on it, but that was just based on what I had heard in the past...
Thanks everyone!
So, am I correct in assuming that manually downshifting at will is no less harmful to the car than downshifting with your right foot (for the reasons detailed above)? I had always thought that manually downshifting a stock trans was hard on it, but that was just based on what I had heard in the past...
Thanks everyone!