Bill Ball

Here are the intended shiftpoints from the A-28 transmission guide.

My car is an 89 (2.54). Using the RPM to speed graphs in my owners manual, here are the shiftpoints in RPM. This is with the shifter in D. I believe holding the shifter in 2 or 3 alters this. I will go through that later.

Full throttle:
1-2: 4300-4900 RPM
2-3: 5300-6200 RPM
3-4: 5300-5800 RPM

Kickdown:
1-2: 5000-5300 RPM
2-3: 6000-6300 RPM
3-4: 5600-5800 RPM

borland

The kickdown relay delays the shift points under full throttle.

Here's from my prior post...

The earlier kickdown relays hold the upshifts longer based on engine RPM before interrupting the solenoid with the relay.

But for 89’+, there is a special interrupt just for the 1-2 upshift, which makes the shift at a lower engine RPM. In that case, they use the speedometer pulse to determine if 1st gear is engaged.

Here’s the wording from the Porsche guide which explains the earlier, and later (89+) relays.



Here’s the diagram showing how the hydraulic up shift program is held longer with the kickdown solenoid.



You can see, without the solenoid activated, the hydraulic shift program shifts earlier.

And here’s the corresponding speed/rpm/gear graph.



I opened up the kickdown relay removed from my 90’ S4 during the GTS dynamic kickdown mod. This has the later circuit especially for the 1-2 shift. Here’s a photo of the insides.





There using a couple of identical hybrid boards, each carrying a Philips HEF4538BT. Here’s the datasheet link..

http://www.nxp.com/acrobat_download/...538B_CNV_3.pdf

There are two resistors that were hand soldered in place during assembly, apparently to calibrate the two shift points. Just guessing, it must be using a low-pass filter for the speedo and two high-pass filters for RPM to trigger the upshift hold limits.

RngTrtl

I know for sure that the my throttle plate is opening fully under WOT, and I know that my KD switch and selonoid are working as well. So, that should only leave the bowden cable Many thanks to all for the kind advice, I will post again sometime this week when I have a chance to play with the car again.

Bill Ball

borland's information updates the shiftpoints for 89+, whereas my table was more generic for the 4-speed tranny, showing larger tolerances in RPM ranges for the 1-2 upshift. Thanks! Also, all this information is for "automatic" shifting - i.e., the lever in D. Here is some generic information about the effect of lever position with the 4-speed A-28. Note the zero throttle is the highest, providing for engine braking.

JHowell37

I have a '85 as well and I had the same problem up until a few weeks ago. Behind the gas pedal there is a rod that attaches to the lever that connects to the throttle cable and also activates the kick down switch. The ball joint on the lever broke one night so I had to replace the lever. Luckily I had a spare so I didn't get raped on a replacement. Anyway, check the rod that goes from the back of the pedal to the lever. It is adjustable. Mine was short enough that it wouldn't activate the kick down or allow it to red line in first. I adjusted it out almost all the way. Also check to see if the lever is actually pressing down the kick down switch with the gas pedal to the floor. Even after adjusting the rod, mine still wouldn't press the switch. What I did was slip a piece of thick fuel hose over the end of the rod to make it fatter so it would contact and depress the switch, which then forces the transmission to remain in first gear. That "mod"/adjustment was good for a bigger performance boost then a set of chips.