apix17
Contributor
Posts: 199
Loc: San Francisco Area
Reg: 12-22-07
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10-09-24 09:46 AM - Post#2874532
I have a 2000 4.3L 2 wheel drive blazer with just under 200k miles. Runs very well, I have had it almost since new and maintained it very well. No codes. When I am driving up a hill at about 40 mph or more and it is starting to slow down and needs to downshift it downshifts fine but then quickly, after maybe 2 seconds it upshifts. After upshifting it will downshift and quickly upshift again. Only happens above about 40 mph. All other functions of transmission and engine are good. Fluid level and color are okay
I talked to a transmission guy who said it does not sound like a problem these transmission normally have. He didn't offer any other thoughts.
Any input appreciated. Thanks.
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gchemist
Member #271 Senior Chevytalk Moderator
Posts: 26159

Loc: Austin, TX 78748
Reg: 05-09-00
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10-09-24 05:05 PM - Post#2874539
In response to apix17
What is your rear gearing? Yes, 4L60E are known to hunt gears under certain conditions. 3.08 gears are the worst. 3.55 gears are better. The torque converter will also lock and unlock too. If you have a lot of hills, drive it out of OD. Third is a good gear to try.
'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE
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Edited by gchemist on 10-10-24 03:52 AM. Reason for edit: No reason given.
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toro455
"9th Year" Gold Supporting Member
Posts: 1515

Loc: Western NY
Reg: 06-15-02
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12-13-24 04:02 PM - Post#2876250
In response to gchemist
Around that year I believe the standard ratio for the automatic, with the 4.3L, was 3.42:1. My truck is a 4.3L with a 5spd manual and the standard ratio was 3.08:1 with the heavy duty rear axle (the HD axle was a forced option when you ordered the 5spd and 4.3L together).
It seems like a lot of GM transmissions had logic such that the smallest amount of increased pedal pressure would down shift. So when I read the description, if it was light acceleration to maintain 40mph while climbing a hill, I thought probably normal.... and one reason I wanted the manual transmission.
I doubt it's related but I would also not that a torque converter normally engages/disengages around 40 to 45mph. Once you get tuned into the feeling, if you are trying to maintain a speed exactly at the engagement speed, it can drive you nuts. I had a 1984 where it occurred at 45.. very annoying and you will see a small change in RPM. I doubt it would be confused for a up/down shift though.
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gchemist
Member #271 Senior Chevytalk Moderator
Posts: 26159

Loc: Austin, TX 78748
Reg: 05-09-00
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12-14-24 05:46 AM - Post#2876256
In response to toro455
toro455's experience is correct. My '95 had 3.08 gears. It was gutless until it was above 50 MPH. It would do 80 MPH on the toll road easily. '95 was the year the 4.3 made the most power too. My '96 had 3.42 gears. The 3.42 gears pushed some 17" wheels really nice. It could pull a 1500 lbs popup camper to 70 MPH. I towed a camper several times over long distances. Both had rebuilt transmissions put in. The 4L60E were upgraded with better parts and shift kits.
'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE
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