4L60E Shift Quality Differences

ComputernerdBD

Original poster
Member
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
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
The tendency for GM has been to make shifts mushier and more undetectable through the years. I know the TB's shifts are adjustable (to a point) for firmness via a tune so whatever GM sets it at, it's likely softer than the '98. Same for TCC lockup that later years went to PWM that we get rid of with either a shift kit or tune.

You should feel the shifts in the '15 Tahoe I drive at work. The shifts are sooooooo mushy, I barely feel them and have to look at the tach to know when it shifts.
 

DocBrown

Member
Dec 8, 2011
501
Most definitely computer changes. I don't believe the '98 had any computer controls on the trans, or very little. I've had 4 trucks with the 4L60E. A '92 GMC Safari, '95 Suburban, '03 Trailblazer, and my current '08 GMC Sierra. All of them had/have the slow sloppy shifts and clunks the 4L60E is notorious for. I fixed that in the TB with a shift kit. All of them felt very different from each other. The 'Burb's trans was rebuilt at 120k. I bought it with 97k and have no idea how it was cared for before that.

My Sierra makes a whirring noise at about 20 mph when shifting between 2 & 3. And it drags for a split second. I had it in the shop and they said there is nothing wrong. Interestingly enough I did not hear this until it got cold out, after I replaced the glass pack with a standard muffler and started having to close the windows because of the cold. So it could have been happening a long time. Shifting from 2 to 3 at speeds higher than 20 are very smooth and fast.
 

AWD V8

Member
Jan 12, 2015
463
I had a '98 Jimmy and when I got a tune I had the guy tighten up the shifting, it made a big difference. The transmission tuning made a bigger improvement than the engine tuning.

When I bought my '03 Envoy 5.3 I loved the power but hated the sloppy shifting. I drove it with such a light foot because I thought the transmission was going to burn itself up with those sliding shifts. With this vehicle I thought I would buy a hand held tuner instead of the mail order tune. I didn't have much chose of tuner as their aren't many companies that make them for my truck. Don't think their is one for the 4.2

The shifting greatly improved, still not quite as tight as I would like it but much firmer and much quicker.

A tune is the way to go as a first step to improve the feel of the transmission.
 
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