I have noticed that my tranny refuses to downshift to 2nd-gear at any speed greater than about 65-70mph. When I mash the throttle at those speeds on the highway, it downshifts to 3rd, but not 2nd :confused:

I've checked my shift point for the 2-3 upshift when accelerating WOT from low speeds and it changes up at about 95mph. So, how come it doesn't downshift to 2nd from a 70mph roll??? The only way I can do this is to manually downshift (which works fine). Is this normal?

Cheers,
Ian.
:cheers:

 

Thats just about right ,70-75 mph.It will shift out at 84mph back to 3rd. Downshift from 60mph and watch your tach to see if it shifts past it's normal shift point 58-5900 and if so it could be slipping.

 

My tranny shifts at about 5,800rpm exactly as it should.
Why does the factory programming prohibit a downshift to 2nd past 70mph??? :confused:

Cheers,
Ian.

 

Without checking the SM my guess would be that it would bump the rev limiter. The PCM knows that grabbing second would put the engine over the limit and therefore refuses to drop down a gear.
I've noticed the same thing dropping to first. I can drop to second under 60 and then put it in first, without it dropping. But as soon as I brake the speed and it drops to the set level, first will then engage. Has to be the same thing for what your trying to do.

later,

 

That's just it though... it DOESN'T bump the limiter changing down manually to 2nd at 70mph... there's still about 1,000rpm of headroom left! Just means I have to remember to change down manually if I want to get maximum acceleration from a 70mph+ roll. I don't understand why the PCM prohibits the downshift when there is useful acceleration to be had without bumping the limiter.

 

Maybe it doesn't drop because you're past the torque peak at that RPM?

 

Even though I'd be past the engine's peak torque, the torque multiplication offered by the gear ratio in 2nd would (and does) still mean better acceleration than leaving it in 3rd.

Still confused! :confused:

 

If you have it in 3rd during your acceleration, instead of 'D', will it drop to 2nd? It may be a balance chosen by GM since the shift you're looking for would be a rough one, and it would likely increase wear on the transmission. Don't get me wrong, I don't like the transmission shifting map the PCM uses, either. Since I don't want to pay for LS1 editing simply for tranny shift changes, I've decided to go the Transgo shift kit route. Hopefully, it will address the shifting issues that bug me :cheers:

Merely speculation, but thought I'd add my two cents.

 

The tranny has been my biggest complaint about the car since I bought it... It's never in the right gear when you need it. You've got to go WOT to get a downshift which puts you back into the seat or manually downshift when needed. Seems those things would cause more wear and tear than anything else. I can't wait to get mine tuned with LS1-Edit, the Hypertech only controls upshifts at WOT.

 

I_York,

Here's the long version, hope it helps you find what you're looking for, just don't ask me to explain, I just copied and pasted.

later,
++++++++++++++++++++++++++++++++++++++++ ++++++
Overdrive Range, 3-2 Downshift

Similar to a forced 4-3 downshift, a forced 3-2 downshift can occur because of minimum throttle (coastdown conditions), heavy throttle or increased engine load. In order to achieve a forced 3-2 downshift, the PCM energizes the 2-3 shift solenoid valve and the following changes occur:

Energized by the PCM, the normally open solenoid closes and blocks the signal B fluid from exhausting through the solenoid. This creates pressure in the signal B fluid circuit at the solenoid end of the 2-3 shift valve.

2-3 Shift Valve Train
The signal B fluid pressure from the shift solenoid moves both valves to the downshift position against AFL fluid pressure acting on the 2-3 shift valve. This causes the following changes:

The AFL fluid is blocked from the D432 fluid circuit and the D432 fluid exhausts past the 2-3 shuttle valve.
The 2nd fluid is blocked from feeding the 3-4 signal fluid circuit and the 2nd fluid is routed into the servo feed fluid circuit.
The 3-4 signal fluid is exhausted past the valve. The 3-4 clutch fluid and the 3rd accumulator fluid, which were fed by the 3-4 signal fluid, also exhaust.
3-4 Clutch Releases and 2-4 Band Applies
3-4 Clutch Piston
The 3-4 clutch fluid exhausts from the piston and the 3-4 clutch plates are released.

3-4 Clutch Exhaust Checkball (#4)
Exhausting 3-4 clutch fluid seats the #4 checkball and is forced through orifice #13. This orifice controls the 3-4 clutch fluid exhaust and the 3-4 clutch release rate.

2-4 Servo Assembly
The 3rd accumulator fluid exhausts from the servo assembly. The 2nd clutch fluid pressure moves the 2nd apply piston against the servo return spring force in order to move the apply pin and apply the 2-4 band.

3-2 Downshift Valve and 1-2 Upshift Checkball (#8)
The 3-4 clutch fluid exhausts from the valve and the spring force moves the valve into the second gear position. However, before the spring force overcomes the exhausting 3-4 clutch fluid pressure, the 2nd fluid feeds the 2nd clutch fluid circuit through the valve. This bypasses the control of orifice #16 at the #8 checkball and provides a faster 2-4 band apply. Remember that the #8 checkball and orifice #16 are used to help control the 2-4 band apply during a 1-2 upshift.

Downshift Timing and Control
At higher vehicle speeds, the 2-4 band apply must be delayed to allow the engine speed RPM to increase sufficiently for a smooth transfer of engine load to the 2-4 band. Therefore, exhaust of the 3rd accumulator fluid must be delayed. However, at lower speeds the band must be applied quickly. In order to provide for the varying requirements for the 2-4 band apply rate, the exhausting 3rd accumulator fluid is routed to both the 3rd accumulator checkball (#2) and the 3-2 control valve.

3rd Accumulator Checkball (#2)
The exhausting 3rd accumulator fluid seats the #2 checkball and is forced through orifice #12. This fluid exhausts through the 3-4 clutch and the 3-4 signal fluid circuits and past the 2-3 shift valve. Orifice #12 slows the exhaust of the 3rd accumulator fluid and delays the 2-4 band apply rate.

3-2 Control Solenoid Valve and 3-2 Control Valve
These components are used to increase the exhaust rate of 3rd accumulator fluid, as needed, depending on the vehicle speed.

The 3-2 control solenoid valve is a normally closed On/Off solenoid controlled by the PCM. The PCM controls the solenoid state during a 3-2 downshift according to vehicle speed.

Low Speed
At lower vehicle speeds, the PCM operates the 3-2 control solenoid valve in the Off position.
In the Off position the solenoid blocks actuator feed limit fluid pressure from the 3-2 control valve.
With no actuator feed limit fluid pressure, the 3-2 control valve spring force keeps the valve open to allow a faster exhaust of 3rd accumulator fluid through orifice #14 into the 3-4 clutch fluid circuit.
A faster exhaust of the 3rd accumulator exhaust fluid provides a faster apply of the 2-4 band, as needed at lower vehicle speeds.
High Speed
At high vehicle speed, the PCM operates the 3-2 control solenoid valve in the On position allowing actuator feed limit fluid to pass through the solenoid. This pushes the 3-2 control valve into the closed position.
This action permits a slow apply of the 2-4 band by blocking off 3rd accumulator exhaust fluid from entering the 3-4 clutch fluid circuit through orifice #14.
This allows the engine speed to easily come up to the necessary RPM before the 2-4 band is applied.
3rd Accumulator Exhaust Checkball (#7)
After the downshift is completed, the #7 checkball unseats and allows the residual fluid in the 3rd accumulator fluid circuit to exhaust.

Pressure Control (PC) Solenoid Valve
Remember that the PC solenoid valve continually adjusts torque signal fluid in relation to the various PCM input signals (mainly the throttle position).

 

here's a dumb question: :jester

Since the computer will not allow the transmission to downshift into a gear which would cause the engine to over rev, is it "safe" to just slam it down into first and punch it from a 70+ roll (or whenever for that matter) when you want to be in the "optimal" gear? I get the jibblys thinking about dropping the selector into 1 at 100mph, but technically it should be OK, right?

 

The PCM is supposed to keep the tranny from shifting into 1st at speeds that would over-rev the engine. I assume the same is true for 2nd. So if you slam it in 1st at 100 MPH, it might shift down to 2nd but not down to 1st.

 

Thanks for the info, but that just explains how, mechanically, the tranny engages the appropriate gear. It doesn't explain the programming that is applied via the PCM in relation to gear selection based on road speed, engine speed, throttle position, etc.

I'm still at a loss as to why the A4 tranny will not downshift to 2nd past 70mph (unless manually forced)!

C'mon guys, there must be someone here that has the answer!

Cheers,
Ian.
:cheers:

 

Last night I put it into 2nd at 70mph (my auto wont go down into 2nd by itself over 65 or so) and wow, I've never pulled that hard up top as long as I've had the car. The downshift limits definatly need to be bumped up 15mph or so.

TopCat: Thanks for the reply. Sometime I've got to find out for sure if the downshift protection applys to all the gears or just first before I try anything like that. Even if I did find out for sure I'll probably never do it :D

 

Look at the http://www.carputing.com/ website for LS1Edit and checkout the user guide http://carputing.tripod.com/ls1edituserguide.zip

There are tables for upshift and downshift. From the manual look at the section
"3.1.1 Shift Speed
This table controls the Part throttle shift speed. The entries are in MPH. There is a separate curve for each upshift, and each downshift. The curve is shift MPH vs Throttle position."

I have adjusted my tables so that it downshifts the way I want it. You should consider getting LS1Edit. It gives a lot more control than the HP3.