Change Original Transmission Fluid or Not?

[Ryan5O]

Ref: 72 C10 Automatic turbo350 105,000 miles

Ever since I picked up this truck from my G'pa, I've been systematically going through and changing all the fluids, filters, seals, etc. The transmission fluid has been next on my list, but Ive been reading alot of opinions about how the fluid change can damage the tranny.

It shifts fine. Doesnt leak and doesnt give me any indication that it needs repairs. Im also assuming that the fluids have never been changed.

Should I be hesitant to change the fluid, or go ahead with the change and just treat it as regular maintenance?

Thanks in advance
R

[webfoot]

An even better way to damage the tranny is by not changing the fluid. Not sure where you heard that but I'd diagnose it as pure BS.

[stich626]

Originally Posted by webfoot

An even better way to damage the tranny is by not changing the fluid. Not sure where you heard that but I'd diagnose it as pure BS.

a automatic that never been serviced like it should've (every 35k)
at 105k changing the fluid can kill the tranny,,
call it b/s all you want.. any tranny shop knows this.. it's not new knowledge.. most good shops try to talk owners out of it.. if they never been serviced..
it's hit and miss,, mostly miss.. owners don't like it when the car drove in and now can't leave

[Already Gone]

Originally Posted by stich626

a automatic that never been serviced like it should've (every 35k)
at 105k changing the fluid can kill the tranny,,
call it b/s all you want.. any tranny shop knows this.. it's not new knowledge.. most good shops try to talk owners out of it.. if they never been serviced..
it's hit and miss,, mostly miss.. owners don't like it when the car drove in and now can't leave

That is a very interesteing point and one I've never heard. Do you know why changing the trans fliud in a high mileage vehicle hurts the trans, it kinda goes against logic ??

[kSStamp0182]

Originally Posted by Already Gone

That is a very interesteing point and one I've never heard. Do you know why changing the trans fliud in a high mileage vehicle hurts the trans, it kinda goes against logic ??

i was taught this as well.

the way i understand it, is as time and miles go on, the seals begin to deteriorate, but as the fluid gets older, it gets "thicker" and continues to work just fine.

new fluid is added, which is much thinner than the stuff removed, and it blows right around the seals.

[R.L.]

Change the fluid and don't forget the filter.

[mrein3]

Originally Posted by R.L.

Change the fluid and don't forget the filter.

I'll second that.

I did a million turbo 350 fluid and filter changes and never once had that service "wreck" the tranny.

Modern service is to hook the tranny up to a machine and completely change out the ATF. I've seen this "wreck" a transmission.

If it were my 105,000 mile truck that still had the original fluid and filter I'd drop the pan, replace the filter, and fill it back up. It takes about 3 quarts to re-fill after this service.

I have seen turbo 350s with that many unserviced miles have a hole in the filter. The filter is a simple screen. Passing pieces of clutch material through a th350 because there is a hole in the filter can't be good for it.

If you're afraid to attempt this service yourself, look for an older shop and ask if they will do an old style fluid and filter change, NOT the modern way by hooking it up to a machine and never dropping the pan.

[mrein3]

Originally Posted by kSStamp0182

i was taught this as well.

the way i understand it, is as time and miles go on, the seals begin to deteriorate, but as the fluid gets older, it gets "thicker" and continues to work just fine.

new fluid is added, which is much thinner than the stuff removed, and it blows right around the seals.

It isn't a seal thing. It is a friction thing. The clutches in an auto tranny have clutch material on them. It wears off. Your transmission begins to "slip" when there is no clutch material left on the clutches. In an auto transmission that is circling the drain, the clutch material floating around in the transmission fluid is helping the clutches stick. When you flush out all that material with a modern service and replace it with new, it is game over for an amost failed anyways transmission.

[hjewell2]

Originally Posted by kSStamp0182

i was taught this as well.

the way i understand it, is as time and miles go on, the seals begin to deteriorate, but as the fluid gets older, it gets "thicker" and continues to work just fine.

new fluid is added, which is much thinner than the stuff removed, and it blows right around the seals.

Yes your statement is very true. I may get criticism for what im about to say but I know it works and lowers temps. found this out by mistake-long story short was at race track tranny hot on transbrake blew fluid out of vent now low on fluid, did not have any tranny fluid. I used 10w-30 I use for the tow vehicle. put it in and went back to racing, right away I notice my temps went down and stayed down for the rest of the day. tranny shifted better also.
so anyway when you change the fluid add 1 to 1 1/2 quarts of motor oil and this will not happen. later I was told what I did was the same effect as trick shift fluid. victim was TH-350 . hpe this helps

[a_barth]

If it were me I would change it. The key thing that you have to think about here is that changing the fluid won't wreck a good transmission, but a worn tranny on its last leg. You may change the fluid and and it won't leave the garage, but that is alot better than a month down the road leaving a car show, work, or anywhere else and having the tranny let go. My suggestion is to change the fluid and feel things out, if the tranny starts slipping by a rebuild kit and a Haynes tranny book and rebuild it yourself if you can. I know that most are scared of the inside of an auto for the first time but I just took my time and rebuilt one over the course of a weekend, success.

By the way I have heard the same things about old Briggs and Stratton engines that have never had the oil changed, change the oil and it dies.

[1967wannabe]

Originally Posted by mrein3

It isn't a seal thing. It is a friction thing. The clutches in an auto tranny have clutch material on them. It wears off. Your transmission begins to "slip" when there is no clutch material left on the clutches. In an auto transmission that is circling the drain, the clutch material floating around in the transmission fluid is helping the clutches stick. When you flush out all that material with a modern service and replace it with new, it is game over for an amost failed anyways transmission.

Bingo!

When dealing with a high mile/never been serviced transmission I always warn my customers that servicing the trans may wipe it out. But if it does, it was likely on it's way out the door anyway and it's a whole lot more convenient to have their trans fail in my shop than it is on the road.

[eightbanger]

Originally Posted by mrein3

It isn't a seal thing. It is a friction thing. The clutches in an auto tranny have clutch material on them. It wears off. Your transmission begins to "slip" when there is no clutch material left on the clutches. In an auto transmission that is circling the drain, the clutch material floating around in the transmission fluid is helping the clutches stick. When you flush out all that material with a modern service and replace it with new, it is game over for an amost failed anyways transmission.

Bingo x2

It may be working fine now, but on that old fluid it won't stay like that forever.

If your prepared should worst come to worst for a rebuild to replace the clutches & seals, then drain it and fill that sucker with clean fresh fluid, you may want to go further and pull the Converter off and drain that also.
Remember to add a quart back into the Converter before you reinstall.

[Ryan5O]

lol, you guys are killing me. Not really a simple yes or no answer it looks like; which is what I was afraid of.

[1967wannabe]

Originally Posted by Ryan5O

lol, you guys are killing me. Not really a simple yes or no answer it looks like; which is what I was afraid of.

Service the transmission (filter & fluid) as soon as you are prepared to overhaul it.

There.

Oh, and happy Veterans Day, thank you for your service.

[fastwillie 696969]

Originally Posted by 1967wannabe

Bingo!

When dealing with a high mile/never been serviced transmission I always warn my customers that servicing the trans may wipe it out. But if it does, it was likely on it's way out the door anyway and it's a whole lot more convenient to have their trans fail in my shop than it is on the road.

b i n g o x3 rebuild it its cheaper in the long run

[MARKDTN]

In your case, if it isn't burnt, I would not change it. My understanding is that the new fluid will introduce new detergents that will loosen up gunk and foul it all up. Especially if it is the original Dextron (1) fluid from 1972.

http://answers.yahoo.com/question/in...3050113AAyS9XE

http://www.explorerforum.com/forums/...d.php?t=244309

http://www.gm-trucks.com/forums/inde...howtopic=68337

Now, all that said, on anything you have control of-CHANGE IT REGULARLY!

[too much stuff]

If it is working fine and doesn't leak like you say and it isn't burnt, i wouldn't touch it.

[68gmsee]

"The transmission will start acting up." I have heard this so many times in 50 plus years that it is ingrained in my brain. I have a deRanger with 255,000 miles on it. My daughter owned it and it had some high miles when I got it (IIRC over 100K) and fluid had never been changed.

Rather than take a chance (remember ingrained in brain) I siphoned off half of the fluid and replaced it with clean fluid and ran it for about 6 months like that. Then, I repeated the procedure and drove it for several more months. Finally, I went whole hog and drained it all out an put a new filter...

Wouldn't you know it!!!! The d@mn thing started slipping while going into reverse when it was cold. It would catch but hesitated before engaging. It's been a few years now and so far the reverse thing has disappeared but now it's ready for another change....

[Ryan5O]

Makes sense, looks like I'll ride it out and leave the old fluid in. Do you think this applies to the newer generations of trannys being built?

[MagmaJct]

Look at the logic side of things:

If a transmission is in otherwise healthy condition, then replacing the fluid should cause no harm.

However, if the transmission is failing, I've heard that what's in the old fluid will "keep it going" for some time. Which begs the question. Do you intend to keep the old fluid indefinitely? Because if you are concerned about replacing the old fluid "breaking" things, then you should also be concerned that things are already broken.

Plan for a rebuild, when life permits replace the fluid. At that time, you'll be prepared, and may find a rebuild is not needed after all.

[Vintage Windmills]

My 4l60E went out after changing the fluid at 140,000 miles. It wasn't acting the best before I changed the fluid though.

Now I need to figure out what do do on my 72,000 mile '01 4l80e. Want to switch to synthetic but the fluid is probably original. Shifts like new.

[68gmsee]

Originally Posted by Vintage Windmills

My 4l60E went out after changing the fluid at 140,000 miles. It wasn't acting the best before I changed the fluid though.

Now I need to figure out what do do on my 72,000 mile '01 4l80e. Want to switch to synthetic but the fluid is probably original. Shifts like new.

If you want to do it try what I did. Read my post above.

Buddy of mine is the one that actually tried it first and it worked for him so I tried it also. His car had around 150K on it.

As I mentioned, my truck started slipping in reverse when first started but for some reason it's not doing it anymore.

[sbc10guy]

i have not had a problem with the couple times i drained and put new fluid and filter in but i would not recommend a fluid flush. This has wrecked the transmission i have had it done on and i have heard it from quite a few others as well.

[kSStamp0182]

if it aint broke dont fix it.

[redbaron69]

Originally Posted by kSStamp0182

if it aint broke dont fix it.

x2. drive and enjoy your truck.