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2004 Chevy Tahoe 2WD 5.3 Flex
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Discussion Starter · #1 ·
Have a 2004 Tahoe with a rebuilt engine. With prior engine and new engine (both engines) the transmission seems to slip or shifts slow from 2nd to 3rd. It does not occur all the time. There is no noise or grinding or jerking It’s perfectly smooth and feels as though it is a slow drug out shift. I changed the transmission filter and fluid a year ago. I also torqued down all valve body bolts per specs with pan off. ATF fluid is Valvoline Max Life Synthetic and levels are good.

I have decided to try Lucas Stops Slip additive. First anyone see and reason not to try it? Second the bottle I have is 24 oz and directions indicate to add entire bottle. Do I need to pump out any existing fluid before adding the bottle?
 

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2004 Chevy Tahoe 2WD 5.3 Flex
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Discussion Starter · #3 ·
Thanks. Added today and drove about 150 miles normal driving. Next weekend going to take it out on interstate to see if there are any improvements.
 

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Lucas works when a transmission is just starting to go out, it does help with slipping. But if the transmission is too far gone don't expect any real results from it.

Lucas claims it can be added without draining the transmission however I would still drain some out personally.

Did it do this before or after you changed your transmission fluid and filter?
 

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2001 Suburban 5.3L, 296k miles
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You need to be aware of the conditions that make it slip shifting from 2nd to 3rd.
1. During normal acceleration?
2. During medium acceleration?
3. During hard acceleration?

If it slips during medium to hard acceleration, you may need to baby it from now on to make it last.
If it slips during normal acceleration, you better save up for a rebuild. Can't drive it like you stole it anymore, haha.

If it slips, apply piston has a blow-by, 3-4 clutches are getting thin, or line pressure is not enough for clamping friction clutches.
 

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2004 Chevy Tahoe 2WD 5.3 Flex
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Discussion Starter · #6 ·
Lucas works when a transmission is just starting to go out, it does help with slipping. But if the transmission is too far gone don't expect any real results from it.

Lucas claims it can be added without draining the transmission however I would still drain some out personally.

Did it do this before or after you changed your transmission fluid and filter?
thanks. I did remove 24 oz of fluid before adding it. Then is was so thick I poured about 3 oz of fluid in behind it to clean the funnel and dip stick sleeve.
It has slipped like this both before and after the fluid and filter change. My engine blew a lifter in summer of 2019 and the camshaft lobe was chewed up. My rear main seal was leaking also I was already $1500 in so I just had a rebuilt motor installed and kept the old motor for a project. (I have never rebuilt a motor and want to try it). After the engine swap I changed the fluid and filter on trans.
 

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2004 Chevy Tahoe 2WD 5.3 Flex
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Discussion Starter · #7 ·
Update: The Lucas stop slip has helped some but I can still feel the gear change drag out (I think this is called a skip) between 2-3 gear. Like if on a manual clutch I let it out slow and long. It’s happens with normal to medium acceleration. I am 56 so never gun or drive aggressive. Just normal driving. So likely at 250K miles my clutches are worn and taking longer to grab and mate up if that’s the correct terminology. BTW does this drag also cause even more wear on the clutches escakating

So I will drive to failure and then get a rebuild or buy a new transmission and keep mine for a learning project.

Heck I feel I am 30 years late to the party as in 10 years most vehicles will be electric.
 

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2001 Suburban 5.3L, 296k miles
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When it starts slipping, better start saving up for a rebuild or replacement. How long? Depends how you baby it.
Just like a manual transmission, the pressure plate applies pressure to the clutch disc. When the clutch material is below min thickness, pressure plate loses clamping force, then it slips.
In an auto transmission, clamping force is coming from a hydraulic piston pressurized by the pump, pressing on the clutch packs. If piston seals leak, due to hardened seal or cracked piston, it loses clamping force, it slips. If clutch pack is below minimum thickness, it also slips.
At WOT, high rpm, apply pressure is increased, but since clutches or pistons are worn, it will still slips.
I don't use transmission additives. No amount of additive will fix a slipping tranny.
 
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2004 Chevy Tahoe 2WD 5.3 Flex
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Discussion Starter · #9 ·
Thanks bazar01. I am going to baby it (basically old person driving, normal driving). The fluid is new with the fix additive.

So far no noises, no slipping out of gear, no smells. Just the occasional 2-3 drag delay. I assume once I hear any noise or it is dragging and slipping consistently it’s time to replace.

My hope is to get about 15,000 more miles of suburb driving out of it. I promised my wife a new 2024 Tahoe (August of 2023). After that it’s my vehicle for projects. It’s a 2WD and I was thinking of converting it to 4WD myself (if doable).
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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The frame probably isn't compatible for 4WD conversion. Definitely something to look into closely...

My transmission in my 04 Burb didn't make it 6mo after starting to slip 1 to 2. It very quickly started affecting 2 to 3 and then started slamming into gear after highway driving. (And I mean SLAMMING.) Fluid changes didn't prolong the inevitable...

Just my experience.
 
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