2000 GMC trans question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Boog** · 02-21-2010, 02:10 PM

2000 GMC
5.3 auto
Z71
133,000 miles

I've been noticing on the first startup of the day on these cold mornings, below 30* there seems to be a delayed upshift until the engine temp reaches 180 or so. The 1-2 shift runs normally but the 2-3 shift doesn't happen until 35 mph. Then the c lockup not until 45 mph. Once the temp gets up to 180 it shifts normally in all gears. On days when this occurs it is usually only when leaving the house first thing in the morning. The rest of the day it shifts normally even if ambient temp is below 30 and the truck has cooled off.
Is this by chance a warmup feature of these trucks or is it maybe a pressure problem developing?

67ChevyRedneck · 02-21-2010, 02:27 PM

I don't know about the 2-3 shifts, but the first winter I owned my truck I thought my trans was going out. I lived immediately off the interstate, so within just a few minutes after startup I was going 65mph, and the truck wouldn't lock in OD, I thought it was slipping. I did some research and it turns out that the trans will not lock until it reaches a certain temp. I think it's 170 or 180 degrees. That was over 60,000 miles ago, it has 123K now. Now, I just leave it in 3rd until the engine is warm on really cold days (which isn't many down here.)

**Boog** · 02-22-2010, 12:14 AM

I hope it is just a warmup aid deal. It makes sense.

miracle whip · 02-22-2010, 01:56 AM

I think its just cause the trans fluid is cold and thicker ive had a couple cars and trucks do this and have had no problems. just take it easy on her till it warms up

**truckdude239** · 02-22-2010, 04:34 PM

it is normal. the computer holds the shifts longer to increace engine rpms and help the engine warm up faster

**Boog** · 02-22-2010, 06:30 PM

Yeah it makes sense. I think my 97 does the same thing on those real cold mornings but it's not as noticeable with stock muffler.

**bwood** · 02-22-2010, 09:33 PM

I don't believe the converter lock up works until the ECT sensor hit 130 which is also when the system begins to go into closed loop. I also don't believe the converter will lock below 45 mph anyway. I know when I leave work and head to the highway, once I get to 70, my rpms are about 400 higher than normal depending on terrain until it hits right around 130 then it drops to 2000rpm like normal.

Huck · 02-23-2010, 10:27 AM

Make sure the TOW-Haul is not turned on as this feature will delay shifting to higher rpm's. Common problem to have the TOW-Haul switch wire broken between the shift stalk and the steering column---two skinny frail wires with a heavier insulator on them that gets way tooo stiff over time.
If everything works just fine when warm, your trans fluid may need changing (couldn't hurt as most guys neglect this) but ---letting your truck warm up a bit is just reall good sense as cold start and takeoff is the worst thing you can do to create premature wear.

86k10 · 10-13-2010, 10:54 PM

It could also be caused by the EPC solenoid having some debris on the screens or just thicker than normal oil for whatever reason. GM did a mod on that subject with larger micron screens to help when cold. But I can't remember off hand what exact year, i'm thinking somewhere after 2000

spudz · 10-28-2010, 10:16 PM

normal... also dont change your fluid....it will last longer if you dont... trust me. This is coming from a gm certified ASE master tech... Unless you change it every 30k dont change it and never change it over 100k. me personaly, I will never change the fluid unless I have a leak and have to. NOW if you come to my dealership.... my opinion may change if you ask me $$$$$

02-21-2010, 02:10 PM	#1
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,514	2000 GMC trans question 2000 GMC 5.3 auto Z71 133,000 miles I've been noticing on the first startup of the day on these cold mornings, below 30* there seems to be a delayed upshift until the engine temp reaches 180 or so. The 1-2 shift runs normally but the 2-3 shift doesn't happen until 35 mph. Then the c lockup not until 45 mph. Once the temp gets up to 180 it shifts normally in all gears. On days when this occurs it is usually only when leaving the house first thing in the morning. The rest of the day it shifts normally even if ambient temp is below 30 and the truck has cooled off. Is this by chance a warmup feature of these trucks or is it maybe a pressure problem developing? __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

02-21-2010, 02:27 PM	#2
67ChevyRedneck Hittin E-Z Street on Mud Tires Join Date: Nov 2004 Location: Greenville, SC Posts: 23,090	Re: 2000 GMC trans question I don't know about the 2-3 shifts, but the first winter I owned my truck I thought my trans was going out. I lived immediately off the interstate, so within just a few minutes after startup I was going 65mph, and the truck wouldn't lock in OD, I thought it was slipping. I did some research and it turns out that the trans will not lock until it reaches a certain temp. I think it's 170 or 180 degrees. That was over 60,000 miles ago, it has 123K now. Now, I just leave it in 3rd until the engine is warm on really cold days (which isn't many down here.) __________________ Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride American Born, Country by the Grace of God 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! Last edited by 67ChevyRedneck; 02-21-2010 at 02:31 PM.

02-22-2010, 12:14 AM	#3
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,514	Re: 2000 GMC trans question I hope it is just a warmup aid deal. It makes sense. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

02-22-2010, 01:56 AM	#4
miracle whip Registered User Join Date: Feb 2010 Location: jackson michigan Posts: 34	Re: 2000 GMC trans question I think its just cause the trans fluid is cold and thicker ive had a couple cars and trucks do this and have had no problems. just take it easy on her till it warms up

02-22-2010, 04:34 PM	#5
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,237	Re: 2000 GMC trans question it is normal. the computer holds the shifts longer to increace engine rpms and help the engine warm up faster __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

02-22-2010, 06:30 PM	#6
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,514	Re: 2000 GMC trans question Yeah it makes sense. I think my 97 does the same thing on those real cold mornings but it's not as noticeable with stock muffler. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

02-22-2010, 09:33 PM	#7
bwood Registered User Join Date: Jan 2003 Location: Denison, Texas Posts: 1,919	Re: 2000 GMC trans question I don't believe the converter lock up works until the ECT sensor hit 130 which is also when the system begins to go into closed loop. I also don't believe the converter will lock below 45 mph anyway. I know when I leave work and head to the highway, once I get to 70, my rpms are about 400 higher than normal depending on terrain until it hits right around 130 then it drops to 2000rpm like normal. __________________ 1998 GMC Sierra SLE 1/2 ton 2WD 305 Vortec -Gibson Stainless Cat Back Swept Side -SS Wheels 2005 Honda CRF250R 2006 Honda CRF150F

02-23-2010, 10:27 AM	#8
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Re: 2000 GMC trans question Make sure the TOW-Haul is not turned on as this feature will delay shifting to higher rpm's. Common problem to have the TOW-Haul switch wire broken between the shift stalk and the steering column---two skinny frail wires with a heavier insulator on them that gets way tooo stiff over time. If everything works just fine when warm, your trans fluid may need changing (couldn't hurt as most guys neglect this) but ---letting your truck warm up a bit is just reall good sense as cold start and takeoff is the worst thing you can do to create premature wear.

10-13-2010, 10:54 PM	#9
86k10 Registered User Join Date: Feb 2003 Location: Bertrand, Nebraska Posts: 355	Re: 2000 GMC trans question It could also be caused by the EPC solenoid having some debris on the screens or just thicker than normal oil for whatever reason. GM did a mod on that subject with larger micron screens to help when cold. But I can't remember off hand what exact year, i'm thinking somewhere after 2000 __________________ 98 Neon 97 Grand Prix GT 02 Grand Prix 40th Anniv. 86 GMC 5.0 77 Olds 98 6.6 REAL AMERICANS, DRIVE AMERICAN

10-28-2010, 10:16 PM	#10
spudz Registered User Join Date: Oct 2005 Location: Branchville SC Posts: 1,647	Re: 2000 GMC trans question normal... also dont change your fluid....it will last longer if you dont... trust me. This is coming from a gm certified ASE master tech... Unless you change it every 30k dont change it and never change it over 100k. me personaly, I will never change the fluid unless I have a leak and have to. NOW if you come to my dealership.... my opinion may change if you ask me $$$$$ __________________ 2004 z71, 96 z71 on 38s, 88 Chevy k5 blazer, 4in lift. 84 swb project, 82 SWB project , 84 chevy 4x4 lwb project, 88 Jimmy beater/highschool ride. 79 c30. 99 tahoe 4x4 project. and a bunch of parts trucks..

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