Replacing Transmission Checklist

So my 2-3 third gear is now slipping (flare shifting) and I'm pretty convinced the tranny needs to go. 200k miles on her.

I'm looking around and I think the cost of a new/refurb 4L60E isn't worth it for a '03 Yukon with 200k miles. I called a local junkyard and they offer a 90 day warranty for a used trans with "approx" 75k miles for $650.

Is there anything specific I should look for on the used trans? Upgrades I can perform to help extend the longevity?

dwinters14 said:

So my 2-3 third gear is now slipping (flare shifting) and I'm pretty convinced the tranny needs to go. 200k miles on her.

I'm looking around and I think the cost of a new/refurb 4L60E isn't worth it for a '03 Yukon with 200k miles. I called a local junkyard and they offer a 90 day warranty for a used trans with "approx" 75k miles for $650.

Is there anything specific I should look for on the used trans? Upgrades I can perform to help extend the longevity?

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I'm not sure where you are from, but you might try a few other yards -- you might get a little more warranty. That said, there is a write-up on here (for which I am too lazy to search at the moment) for installing a transmission fluid filter. In addition to filtration, if you have a transmission fluid cooler, keeping your transmission cooler will make it last longer. Other than those things, and regular maintenance, I can't think of anything else. Good luck!

no matter if a new or used trans, I would always install an oil cooler, always pay attention to the installation direction, always in the return to the trans.
ideal is also to integrate a thermostat, as shown in the drawing, so that the trans quickly reaches its operating temperature, but never gets too warm.
as in our experience a temperature of 160 - 175 F is ideal, good working temperature, condensation water cannot form and the oil cannot burn

the additionally drawn thermostat is a "Racimex 50100", which I have installed in all my cars.

https://www.amazon.de/Racimex-50100-Thermostat-Schlauch-Chrom/dp/B018LOES4K

Bandit-66 said:

no matter if a new or used trans, I would always install an oil cooler, always pay attention to the installation direction, always in the return to the trans.
ideal is also to integrate a thermostat, as shown in the drawing, so that the trans quickly reaches its operating temperature, but never gets too warm.
as in our experience a temperature of 160 - 175 F is ideal, good working temperature, condensation water cannot form and the oil cannot burn
View attachment 258996
the additionally drawn thermostat is a "Racimex 50100", which I have installed in all my cars.

https://www.amazon.de/Racimex-50100-Thermostat-Schlauch-Chrom/dp/B018LOES4K

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That’s interesting considering GM started using thermostats in the new vehicles in order to increase fuel mileage which has resulted in more failures so people are now bypassing these thermostats. When you say “our experience” who are you referring to? I agree 100% with the cooler but not the thermostat unless you live in a very cold climate.

Rocket Man said:

That’s interesting considering GM started using thermostats in the new vehicles in order to increase fuel mileage which has resulted in more failures so people are now bypassing these thermostats. When you say “our experience” who are you referring to? I agree 100% with the cooler but not the thermostat unless you live in a very cold climate.

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the experience we gained in our german forum, because we also repair our trans ourselves (I have already done 2 of them) and have a specialist who repairs trans every day
the climate in germany may be a bit colder than yours, but it takes several miles until the temperature in the trans is optimal and if you go through the oil cooler it takes even longer.
so we install a thermostat and there have been no negative experiences yet

Who is we? Are there that many 4L60s running around in Germany?

Bandit-66 said:

the experience we gained in our german forum, because we also repair our trans ourselves (I have already done 2 of them) and have a specialist who repairs trans every day
the climate in germany may be a bit colder than yours, but it takes several miles until the temperature in the trans is optimal and if you go through the oil cooler it takes even longer.
so we install a thermostat and there have been no negative experiences yet

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Actually, the oil goes through the radiator first where it heats up along with the engine coolant. There’s a coil inside the factory radiator that’s bathed by the engine coolant. I’d like to know how you would determine if you’re doing harm. Anyway, adding a thermostat isn’t suggested over here unless you’re in the frigid north where it’s frozen for a good part of the winter. Be careful suggesting people do something that may actually shorten the life of their transmission which is the case in the newer vehicles with the factory thermostat, where owners here are deleting them instead of adding them. Here’s a YouTube video that explains the reasoning.

Okay so I should be good to go then? I'm going to do some more research as well.

I would install a Tru-Cool 40k trans cooler and a Corvette servo since it’s easier to do the servo while the trans is out, and also while the trans is out I would replace the rear main seal and rear cover seal on the engine since the trans has to be removed to replace these. You can buy the rear cover/ main seal combo for that which is what I did when I was replacing my trans. It would be a shame to have the rear main start leaking in a few months after you had the trans out. There might be other stuff I’m forgetting, hopefully others will chime in.

Rocket Man said:

I would install a Tru-Cool 40k trans cooler and a Corvette servo since it’s easier to do the servo while the trans is out, and also while the trans is out I would replace the rear main seal and rear cover seal on the engine since the trans has to be removed to replace these. You can buy the rear cover/ main seal combo for that which is what I did when I was replacing my trans. It would be a shame to have the rear main start leaking in a few months after you had the trans out. There might be other stuff I’m forgetting, hopefully others will chime in.

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Thanks Rocket Man.

Another question for you... as I was driving tonight I noticed the rough 1-2 shift and flare were somewhat inconsistent. The flare would be a 500-750 rpm jump at certain throttle inputs and then 250 at others. I also did a WOT pull and didn't notice any shift hesitation and got up to about 70MPH.

Before I go ripping the trans out, I'm wondering if the TPS or throttle body itself may be causing these issues?