4l60e tranny

[krunt]

The other nite my tranny was shifting hard between 1st and 2nd. Now it shifts fine. The Tahoe is a 1999 old style body 4x4 with the 5.7 engine. does anyone have an idea what is caused this failure? It was a pretty loud and hard shift.

[777stickman]

Originally Posted by krunt

The other nite my tranny was shifting hard between 1st and 2nd. Now it shifts fine. The Tahoe is a 1999 old style body 4x4 with the 5.7 engine. does anyone have an idea what is caused this failure? It was a pretty loud and hard shift.

Since it is working fine now I would suspect an electrical problem.

The ign sw has 5 contacts in it, one of which, is dedicated to the TRANS fuse in the I/P fuse block.

I would suggest changing the TRANS fuse 1st. If the problem continues randomly you need to check the connector at the tranny and for other wiring problems including the ign sw.

[MT-2500]

Originally Posted by krunt

The other nite my tranny was shifting hard between 1st and 2nd. Now it shifts fine. The Tahoe is a 1999 old style body 4x4 with the 5.7 engine. does anyone have an idea what is caused this failure? It was a pretty loud and hard shift.

Hard shifting is usually caused when engine/transmission computer VCM loses control of shifting.
Engine runnuing computer stufff or transmission computer system can cause the problem.
First step in repair or checking it out is to get it on a engine/transmission capable scanner and checking for past present or history codes.

Then clear codes and drive and see if any codes come back.
If any codes come back repair for them codes.
Post back any code no past present or history or what comes back?

Do not go hog wild and give it a flush job but if it has not been serviced and after checking codes give it a pan drop and filter change.

[krunt]

I did a code check in the cab and the only code is p0300. Nothing else. thanks for the replies

[MT-2500]

Originally Posted by krunt

I did a code check in the cab and the only code is p0300. Nothing else. thanks for the replies

You need to check it with a engine/transmission capable scanner.

[j cAT]

Originally Posted by krunt

The other nite my tranny was shifting hard between 1st and 2nd. Now it shifts fine. The Tahoe is a 1999 old style body 4x4 with the 5.7 engine. does anyone have an idea what is caused this failure? It was a pretty loud and hard shift.

this harsh upshift is common when the transmission slips,,, it is then reported to the pcm where it is commanded to produce max, transmission fluid pressure..hence the harsh shift...this starts out like this then in time gets worse,,,more often...if it repeats,,,shut down the engine and after 10minutes restart and see if it goes away...if so this is mostlikely your problem...

as stated earlier a gm drivetrain specific code reader will extract what drivetrain DTC you have ...this should narrow down what needs attention...

[Jeremy-WI]

Do you have a remote start on the vehicle? I had a hard shift that was caused by a remote start that didn't power the tranny at the same time as the PCM, once I rewired the relays the hard shift vanished. If it happens only after driving at highway speeds, it is probably because the PCM has detected the trans slipping like others have already stated

[pikappkaz]

This exact problem was happening to me yesterday in my 99 Tahoe. I was coming back from CT to VA, and I hit really bad storm in NYC, lots of very deep water on the highway. I was stuck in traffic and had to deal with a terrible shift from 1->2 quite a bit, it felt like the tranny was going to be left on 95 somewhere.

Anyways, the bad shift is gone this morning, after I gave some time for the connector to dry out, I am going to assume that the connection got wet from the excessive water. Does that make sense that it would be the problem?

Any chance you were driving in real wet conditions when the bad shifting was happening?