Tow vehicle 4L60E won't downshift when towing. - Third Generation F-Body Message Boards

rayar · 08-23-2009, 06:15 PM

Not a Camaro but thought I would toss out this problem to you guys. I have a 1994 GMC K1500 that I use as my daily driver and also tow my Race car(3000lb car 2000lb trailer) or a small popup camp trailer(Maybe 2500-3000 lbs). I tow in 3rd gear and it has started to not downshift when going over the many mountain passes in the area. That dosen't bother me much because it seem to pull most grades easily allthough I could sometime use a little more on some of the longer steeper grades, but it will not downshift even when I come to a complete stop and I have to manually downshift it to 1st.
The tranny works fine when not towing, shifts fine, and downshifts on fairly easy grades but as soon as I hook up a trailer it starts to not downshift. The first time it happened I thought maybe I had the selector halfway between 2nd and 3rd but since then I have made sure It isen't. It works fine for a little while after I manually downshift but a half hour later it goes right back to not downshifting.

Anyone have an idea of what it might be? I do need to change the fluid and filter and that might solve the problem but if someone has an idea or suggestion it would be nice to change that while I am changing the fliter.

Thanks

Pro Built Automatics · 08-24-2009, 06:04 AM

Go to www.fastchip.com Talk to Ed Wright about this. He is very knowledgeable on this. It sounds like it is going into limp mode, and then coming back to normal, but this does not sound right. Changing filter and fluid will do nothing for this, unless your fluid is bad.... Dana

rayar · 08-24-2009, 04:59 PM

So you might be thinking it is an ECM or PROM issue? That has also crossed my mind. I wonder if someone has changed the PROM? The truck is pretty peppy and the 1-2 shift is very solid. I will try Ed

Atilla the Fun · 08-27-2009, 04:37 PM

sounds electronic to me.

Fast355 · 09-07-2009, 09:49 AM

Quote:

Originally Posted by Atilla the Fun

sounds electronic to me.

Sounds electronic to me too.. Are you sure its not going into Overheat Protection mode. That will lock the converter almost immediately and drastically changes the shift-points.