'95 C4 LT1 automatic - kickdown mode

[Oliver S.]

I'd like to know the stock shift mode / kickdown mode of a '95 LT1 Automatic. At which mph should it down- or upshift? As far as I know there was only one rear axle ratio 2,59:1 available.
Background: a buddy of mine drove such a Corvette that I'm interested in and it didn't downshift during a kickdown at around 55 mph. We thought it should but aren't sure.
As I have read the used 4l60e automatic transmission doesn't have a TV cable and, hence, in case of a problem no easy adjustment would be possible as a first option to check.

Oliver

[Terry M.]

Re: '95 C4 LT1 automatic - kickdown mode

The 4L60E is an electronically (computer) controlled transmission, thus there is no TV cable. Downshifts are controlled by the computer and are dependent on road speed, engine RPM, and throttle position.

[David H.]

Re: '95 C4 LT1 automatic - kickdown mode

You are correct that the car should have both Part Throttle Detent Downshift and Full Throttle Detent Downshift in fourth gear at speeds of 40 to 55 mph upon quick increase in throttle angle. (1995 Service Manual page 7a-14a-19) Both descriptions of full/part note the TCC (Torque Converter Clutch) should release.

The service manual has a comprehensive Auto Trans description of the 4-3 and the 3-2 downshift process on pages 7A-14A-58 thru 61.

Any DTC set? See pages 7A-14A-14 & 15 for a list of transmission codes.

BTW: is the trans fluid level ok?

[Edward J.]

Re: '95 C4 LT1 automatic - kickdown mode

Oliver there are many hand held computer programmers that will let you play around with a lot of different functions for engine and transmission that the factory set they limits on, other wise it is the natural of the beast so to speak. It sound the guys above have pretty much spelled it out for.

[Oliver S.]

Re: '95 C4 LT1 automatic - kickdown mode

Edward,
'95 Corvettes have an OBD2 socket but use the GM proprietary GM OBD1.5 protocol. As far as I understand the cheaply available OBD2 data scanners can't be used. Furthermore the OBD2 cables might not work, too. The cables required are ALDL (with 16 pins) ones. Visually the same but different cable/pin settings afaik.
Since I live in Germany and pre 1996 GM cars (except Opel with another protocol) are not that common I would have to order the cable in the US. But the shipping takes some time. I could ask the owner to go to a Corvette mechanic who should have one but this needs to be clarified. It is possible to bridge pin 4 and 12 (if I recall correctly) and error codes would be shown in the display. But I'm not sure if the seller would agree to do so. And I'm not sure if - in case of an actual problem - the error would be shown. This GM OBD 1.5 protocol is very limited compared to OBD2, which has been used since 1996 (a '96 C4 would hence be easy to check cheaply).

Oliver

[Edward J.]

Re: '95 C4 LT1 automatic - kickdown mode

Oliver, I think your talking about scan tools and I am talking about programmers, there are companies that programmers that will let you play with engine control functions such as Gas octane being used, MPH , red lines, injector on time, engine timing curves, cooling fan temp. on time, transmission shift points, torque convertor apply. and much is a simple yes or no.

if the corvette is not experiencing and warning lights on the dash, chances are everything should be fine.

[Oliver S.]

Re: '95 C4 LT1 automatic - kickdown mode

OK, apparently it was a mechanical issue with the non-existing downshift - the floor mat was under the pedal preventing a fully depress.