- Aug 24, 2014
- 189
Hey everyone. I have been driving my old truck (98 GMC Jimmy) more often lately and have noticed how different the transmissions have been performing in terms of shift quality but not sure why.
Both trucks have DEXRON VI in them, Dorman deep pans with AC Delco deep pan filters and heavy duty transmission coolers installed between the radiator return line and the transmission. I rarely see them higher than 120-140F using an IR thermometer but never more than 160-170F in summer on mountains. Both have had frequent fluid changes and other than a pressure control solenoid on the Jimmy, two throttle position sensors (which improved shift quality on that truck) and previous use of Lucas Trans Fix (many years ago used once, but by now completely gone and that was preventative but no longer used due to online research) and Lubeguard a couple years ago in the Trailblazer (also long gone) both are more or less untouched and unmodified. Both trucks had transmission fluid changes a few months ago and nothing of concern was found (never is other than some particles on the magnets but not excessive). Both pans and filters were fairly clean and even got positive comments from the mechanics about that. Also no issues found when driving them. Never any codes in PCM also. U-Joints and trans mounts are original on both.
I noticed that on the Trailblazer over the past year or two that the shifting has been consistently "slow" between 1-2 and 2-3 like the engine throttles back further for shifting and there feels like more slack in the drivetrain during a shift. But not delayed or anything like that, just does not fit any of the top 30 failure modes for a 4L60E. No slipping, no flaring, no noise, cannot see any issue looking at the RPMs and shift completes within a second. Just slow and more sloppy than the Jimmy, but can feel the shift in the floor. This truck has 52K miles. On the Jimmy with 130k miles the shifting for the most part is tight even at higher RPMs and speeds. Less noticeable actually.
I know there are other variables such as the Trailblazer having more than 100 additional horsepower and a few hundred pounds higher weight at a lower center of gravity but did GM make changes to the computers from year to year or use different type parts between 98 and 07? I know, crazy but is this type of shift behavior natural or am I just making a big deal out of a differently programmed transmission behind a different engine? Thanks
Both trucks have DEXRON VI in them, Dorman deep pans with AC Delco deep pan filters and heavy duty transmission coolers installed between the radiator return line and the transmission. I rarely see them higher than 120-140F using an IR thermometer but never more than 160-170F in summer on mountains. Both have had frequent fluid changes and other than a pressure control solenoid on the Jimmy, two throttle position sensors (which improved shift quality on that truck) and previous use of Lucas Trans Fix (many years ago used once, but by now completely gone and that was preventative but no longer used due to online research) and Lubeguard a couple years ago in the Trailblazer (also long gone) both are more or less untouched and unmodified. Both trucks had transmission fluid changes a few months ago and nothing of concern was found (never is other than some particles on the magnets but not excessive). Both pans and filters were fairly clean and even got positive comments from the mechanics about that. Also no issues found when driving them. Never any codes in PCM also. U-Joints and trans mounts are original on both.
I noticed that on the Trailblazer over the past year or two that the shifting has been consistently "slow" between 1-2 and 2-3 like the engine throttles back further for shifting and there feels like more slack in the drivetrain during a shift. But not delayed or anything like that, just does not fit any of the top 30 failure modes for a 4L60E. No slipping, no flaring, no noise, cannot see any issue looking at the RPMs and shift completes within a second. Just slow and more sloppy than the Jimmy, but can feel the shift in the floor. This truck has 52K miles. On the Jimmy with 130k miles the shifting for the most part is tight even at higher RPMs and speeds. Less noticeable actually.
I know there are other variables such as the Trailblazer having more than 100 additional horsepower and a few hundred pounds higher weight at a lower center of gravity but did GM make changes to the computers from year to year or use different type parts between 98 and 07? I know, crazy but is this type of shift behavior natural or am I just making a big deal out of a differently programmed transmission behind a different engine? Thanks