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Discussion Starter · #1 ·
I have a '91 4.3l with 4l60E tranny, 103,000 miles. I bought the truck at 100k. It was a one owner truck and the po said he never changed the tranny fluid. Age old debate here, can I get some input please ?
I have heard adamant opinions from both sides and am trying to make the best decision I can. The question is :

Should you change tranny fluid and filter at 100k or has it been too long and you are safer leaving it alone ?

From what I have read everywhere the consensus is do NOT flush the system but some say it is safe to just change the filter along with the fluid in the pan. I have been building hot rods 40 years, but I am a die hard TH350 man and know nothing about the 4L60E. When this tranny fails I will put in a TH350, make a custom crossmember, and have a driveshaft made, better tranny and bye bye carrier bearing lol. Thanks in advance for any advice.
 

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4l60e is vastly superior to 1970s th350 tech in every aspect.
that being said, filter and fluid change is fine, just like you would do with the turbo-hydramatic..
you can install a one piece shaft if the carrier bearing bothers you so much.
 

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I have the same situation in mine. I'm watching closely to see what type of responses we get.
Looking forward to all recommendations with differing opinions.
 

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4l60e is vastly superior to 1970s th350 tech in every aspect.
that being said, filter and fluid change is fine, just like you would do with the turbo-hydramatic..
you can install a one piece shaft if the carrier bearing bothers you so much.
Ditto that. going bak to th350 from 4l60e is same league as returning to steam power from diesel.
 

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Fluid and filter change should be fine, giving the trannys not slipping already. replace the little seal where the fluid filter pushes up into. If I remember correct you have to push it up on one side with a screw driver or something to knock it loose before you can pull it out. Don't scratch the tube.
 

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Ironduker please provide a picture of some of the fluid on paper towel I want to compare it to mine which has 123,000 miles possibly original fluid.
 

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By all means change it, should follow routine maintenance recommended by manufactures. Too many wait too long or they start having trouble or darkening (burnt) fluid and it's really too late. You wouldn't let your engine oil for 10's of thousands of miles.
 

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Discussion Starter · #9 ·
I never said the TH350 was better, nor did I say the 4L60E was junk, just said the 350 Turbo is what I know :)
My fluid is a little dark, not burnt nor does it smell burnt. My tranny is working fine. I will take gladly take a pic in the morning of the fluid on a paper towel. One thing I will add, from all the research I did, in this situation you do NOT want to have the system flushed. They say if you have over 100k on the original fluid and have the system flushed there is a good chance it will cause problems. Evidently there is clutch material in the fluid and when you flush the whole system, it turns out the clutch material in the fluid was the only thing keeping the clutch pack from slipping lol. But half the sources I researched said it is safe to change just the fluid in the pan and the filter. The other half say that can cause problems too, and to just leave it be. Right now I am leaning towards leaving it be, if it ain't broke don't fix it deal. Amazing the PO bought this truck new in 1991, put 100k on it in 30 years, Changed the oil every 3k and kept every receipt, but never changed the tranny fluid or rear end oil......Thanks everyone for the input and help it is much appreciated (y)
 

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I never said the TH350 was better, nor did I say the 4L60E was junk, just said the 350 Turbo is what I know :)
My fluid is a little dark, not burnt nor does it smell burnt. My tranny is working fine. I will take gladly take a pic in the morning of the fluid on a paper towel. One thing I will add, from all the research I did, in this situation you do NOT want to have the system flushed. They say if you have over 100k on the original fluid and have the system flushed there is a good chance it will cause problems. Evidently there is clutch material in the fluid and when you flush the whole system, it turns out the clutch material in the fluid was the only thing keeping the clutch pack from slipping lol. But half the sources I researched said it is safe to change just the fluid in the pan and the filter. The other half say that can cause problems too, and to just leave it be. Right now I am leaning towards leaving it be, if it ain't broke don't fix it deal. Amazing the PO bought this truck new in 1991, put 100k on it in 30 years, Changed the oil every 3k and kept every receipt, but never changed the tranny fluid or rear end oil......Thanks everyone for the input and help it is much appreciated (y)
Yea do not flush it, unless a transmission has been flushed regularly during its lifetime I am strongly against flushes. Now if it has been flushed regularly then no problem.

I will be doing a drain/fill with a new filter on mine because I do not know the service history. I will be using Valvoline Dex/Merc.
 

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Discussion Starter · #11 ·
Ironduker please provide a picture of some of the fluid on paper towel I want to compare it to mine which has 123,000 miles possibly original fluid.
Yea do not flush it, unless a transmission has been flushed regularly during its lifetime I am strongly against flushes. Now if it has been flushed regularly then no problem.

I will be doing a drain/fill with a new filter on mine because I do not know the service history. I will be using Valvoline Dex/Merc.
Sounds like we are in the same boat, and I ONLY use Valvoline oil and fluids (y) I will post a pic of my fluid as soon as the sun comes up, but I have pretty much decided to not change mine. I can see why you decided to do it, you don't know the history, it might have already been changed before. Mine I KNOW hasn't been changed, plus you can probably tell from looking at the pan gasket when you take it off, not sure. My truck works great, no need to chance it, I just don't believe the benefits outweigh the risk. I already have a fresh TH350 and sbc ready to go in her, that's what I bought her for. Not my fault this dam 4.3 has me liking a dam V6, my first one. Of course the 4.3 is a sbc with 2 cylinders chopped off so it's a BABY sbc !! lol. Dam thing runs GOOD ! Has me wondering how good this thing would run built.....omg thinking about building a V6, it's official, I have lost my mind.
 

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Sounds like we are in the same boat, and I ONLY use Valvoline oil and fluids (y) I will post a pic of my fluid as soon as the sun comes up, but I have pretty much decided to not change mine. I can see why you decided to do it, you don't know the history, it might have already been changed before. Mine I KNOW hasn't been changed, plus you can probably tell from looking at the pan gasket when you take it off, not sure. My truck works great, no need to chance it, I just don't believe the benefits outweigh the risk. I already have a fresh TH350 and sbc ready to go in her, that's what I bought her for. Not my fault this dam 4.3 has me liking a dam V6, my first one. Of course the 4.3 is a sbc with 2 cylinders chopped off so it's a BABY sbc !! lol. Dam thing runs GOOD ! Has me wondering how good this thing would run built.....omg thinking about building a V6, it's official, I have lost my mind.
Preventive maintenance !! Changed my Daughters truck @ 109,000 - cleanest trans I have ever seen. Closing in on 175,000 and plan on changing it again.
 

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Sounds like we are in the same boat, and I ONLY use Valvoline oil and fluids (y) I will post a pic of my fluid as soon as the sun comes up, but I have pretty much decided to not change mine. I can see why you decided to do it, you don't know the history, it might have already been changed before. Mine I KNOW hasn't been changed, plus you can probably tell from looking at the pan gasket when you take it off, not sure. My truck works great, no need to chance it, I just don't believe the benefits outweigh the risk. I already have a fresh TH350 and sbc ready to go in her, that's what I bought her for. Not my fault this dam 4.3 has me liking a dam V6, my first one. Of course the 4.3 is a sbc with 2 cylinders chopped off so it's a BABY sbc !! lol. Dam thing runs GOOD ! Has me wondering how good this thing would run built.....omg thinking about building a V6, it's official, I have lost my mind.
The main reason I want to do a drain/fill and new filter in my S10 is because again it possibly has 123,000 original miles I do not have any history on it and that filter probably has all of that break in material from when it was new and also due to age the filter probably caught a lot of clutch material from normal wear and could be getting close to clogging up.

So we already know the outcome of not doing it and that is a failed transmission at some point, but also there is the possible risk of changing it. Anyways I have spoken to multiple transmission experts who rebuild these transmissions and they said that mine is safe for a drain/fill with a new filter and every one of them said to stick with Dexron III and do not use Dexron VI so that is why I am choosing Valvoline Dex/Merc because it is Dexron III.

The 4.3 is a good engine and honestly it is a shame everyone does V8 swaps, there is a few people out there who have proven the 4.3 is capable and some are pushing over 1,000hp. I plan to in the future have some fun with my truck on the drag strip but the 4.3 is staying I will modify it. Mine is an LU3 4.3 pushing 190hp according to GM.

The TH350 is an excellent transmission and is one of the most reliable transmissions ever made along with the TH400 there is a reason they are a common transmission for drag setups. But they aren't a good option if you plan to daily the truck or drive long distances because of the lack of overdrive. The 4L60E can become a beast as well with a heavy duty rebuild and you have the best of both worlds with it.
 

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The main reason I want to do a drain/fill and new filter in my S10 is because again it possibly has 123,000 original miles I do not have any history on it and that filter probably has all of that break in material from when it was new and also due to age the filter probably caught a lot of clutch material from normal wear and could be getting close to clogging up.

So we already know the outcome of not doing it and that is a failed transmission at some point, but also there is the possible risk of changing it. Anyways I have spoken to multiple transmission experts who rebuild these transmissions and they said that mine is safe for a drain/fill with a new filter and every one of them said to stick with Dexron III and do not use Dexron VI so that is why I am choosing Valvoline Dex/Merc because it is Dexron III.

The 4.3 is a good engine and honestly it is a damn shame everyone does V8 swaps, there is a few people out there who have proven the 4.3 is capable and some are pushing over 1,000hp. I plan to in the future have some fun with my truck on the drag strip but the 4.3 is staying I will modify it. Mine is an LU3 4.3 pushing 190hp according to GM.

The TH350 is an excellent transmission and is one of the most reliable transmissions ever made along with the TH400 there is a reason they are a common transmission for drag setups. But they aren't a good option if you plan to daily the truck or drive long distances because of the lack of overdrive. The 4L60E can become a beast as well with a heavy duty rebuild and you have the best of both worlds with it.
1000hp??? Show me.
 

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Discussion Starter · #15 ·
The main reason I want to do a drain/fill and new filter in my S10 is because again it possibly has 123,000 original miles I do not have any history on it and that filter probably has all of that break in material from when it was new and also due to age the filter probably caught a lot of clutch material from normal wear and could be getting close to clogging up.

So we already know the outcome of not doing it and that is a failed transmission at some point, but also there is the possible risk of changing it. Anyways I have spoken to multiple transmission experts who rebuild these transmissions and they said that mine is safe for a drain/fill with a new filter and every one of them said to stick with Dexron III and do not use Dexron VI so that is why I am choosing Valvoline Dex/Merc because it is Dexron III.

The 4.3 is a good engine and honestly it is a damn shame everyone does V8 swaps, there is a few people out there who have proven the 4.3 is capable and some are pushing over 1,000hp. I plan to in the future have some fun with my truck on the drag strip but the 4.3 is staying I will modify it. Mine is an LU3 4.3 pushing 190hp according to GM.

The TH350 is an excellent transmission and is one of the most reliable transmissions ever made along with the TH400 there is a reason they are a common transmission for drag setups. But they aren't a good option if you plan to daily the truck or drive long distances because of the lack of overdrive. The 4L60E can become a beast as well with a heavy duty rebuild and you have the best of both worlds with it.
Wow, great post, I know the TH350 inside out, I can put a shift kit in one in the vehicle in 20 min lol. Thanks for all the info on the 4L60E. I went out and got tranny fluid and YIKES, lol. Guess it was worse than I thought. Made my mind up for me, not changing it. I have this TH350 sitting here freshly rebuilt I will just drive this tranny till it drops. Do me a favor MrUnkown and post pics of your Tranny fluid at 130k, we should be able to tell if yours has been changed because I am positive mine has not.
The left is Valvoline Dex/Merc out of new bottle.
350421
oilchecks10.jpg
 

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Wow, great post, I know the TH350 inside out, I can put a shift kit in one in the vehicle in 20 min lol. Thanks for all the info on the 4L60E. I went out and got tranny fluid and YIKES, lol. Guess it was worse than I thought. Made my mind up for me, not changing it. I have this TH350 sitting here freshly rebuilt I will just drive this tranny till it drops. Do me a favor MrUnkown and post pics of your Tranny fluid at 130k, we should be able to tell if yours has been changed because I am positive mine has not. View attachment 350421 View attachment 350421
It will probably take me 1 or 2 years to reach 130,000 miles on my S10. It isn't driven much I only drove it 1,000 miles since I bought it last summer.

350422
 

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Actually 1073 HP @ 7700 RPM Twin Turbo 4.3L V6
Yep thats a beast. I wouldn't want to push that much though I think a more respectable 500-600hp is good enough, which there is a few pushing that as well.

As for the transmission fluid yours and mine are pretty similar, yours is maybe just a tad more brown so I think mine is also original fluid.

Good thing is they both aren't black/burnt and if they don't look burnt and smell burnt and the transmission has no issues it is most likely safe to drain/fill with a new filter.
 

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Something tells me that 1000+hp engine isn't running a production 2-bolt block or cast iron offset rod journal crank.
Since there's plenty of room, go ahead and add the two missing cylinders and get more! If 1000hp is good, then 1250 has to be better!
 
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