Original 1982 RV TH400 - Dexron 3 or Dexron 6???

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leroyd92

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I'm crossed between running full synthetic atf in an original AT.

The last few time I added full synthetic oil to an old engine or trans I got bad leaks.
Can
The pan gasket is seeping right now, but it hasn't been touched for many years.

What are your thoughts?

Btw, the TH400 has under 70k on it
 
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Gaskets and seals are very different.

When discussing seals such as in engines, transmissions, and other driveline components, the context is that of using flexible, elastomeric materials to keep fluids contained within the mechanical system that have rotating components exiting the system, such as protruding rotating shafts.

For a gasket, the context is that of using a material (such as silicone or cork or composite), or some other material to keep fluids contained in and around stationary objects, such as the valve cover gasket on an engine or the pan gasket on an automatic transmission.

Both seals and gaskets "prevent" loss of fluids...

Conditioning seals refers to the following actions:

1) Seal swell due to Seal elastomer molecular replacement
2) Seal cleaning,

Today's synthetic formulations have pretty much solved the seal "shrink-swell" problem.

I would use a Dexron VI in that HD transmission.
 
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I had a turbo-hydramatic 125C(3T40) rebuilt about 18 months ago because it lost reverse. Rear brakes were locking up/dragging after it sit all night with parking brake on. Backing up a hill into main road with rear brakes locking up and dragging is not good My wife never told me until it was too late.

I asked the shop manager if he could put Dex 6 in it. He said they would not warranty it, and do not recommend it. I asked why. He said the turbo-hydramatic transmissions in general have worked with Dex 3 for the longest time, and he was not going to go against something he knows that works good. I said Dex 3 it is then.

18 months later, and the Dex 3 still looks very good on the stick/paper towel when I check it.
 
I started using mercon 5 (I was working at a ford dealership) in my 86 TH700R4 and my 87 TH2004R about 15 years ago. Then I started using dexron 6 in the 2004R soon after it came out. I still have dexron 6 in the same 2004R now and it has over 280k miles on it now. Mostly highway miles since I got it but I did used to take it to the quarter mile track and few times a year and I swapped a 350 in to replace the original 305 12 years ago so the transmission has seen some stress and never been rebuilt. The previous owner did put a shift kit in because he pulled a boat with it up to 120k miles when I bought it.

I think my winter beater also has dexron 6 in it and it's a 2004R with 275K miles on it.
 
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I would go Dex III/Mercon in it, I use it in my '93 4L80E and it's done well with towing, etc. (with a secondary cooler and oversize aluminum pan)-just use a gauge and don't let it get too hot (highest I've seen is 220F).
 
Originally Posted by leroyd92
I'm crossed between running full synthetic atf in an original AT.

The last few time I added full synthetic oil to an old engine or trans I got bad leaks.
Can
The pan gasket is seeping right now, but it hasn't been touched for many years.

What are your thoughts?

Btw, the TH400 has under 70k on it


Drop the pan, change the filter and the gasket. Put extra magnet in the bottom corner of the pan. Refill with Dex III and be on your way. Use HM Dex if you want. It'll be fine
smile.gif
 
Seems like everyone is recommending dexron 3 just because that's what they had back when they were new but I have real doubts that my transmission would have held up as long as it has without the better dexron 6 and 5 I've used over the years.
 
I changed the ATF in my 2000 4Runner with 245k miles last Summer when I bought it. Was not shifting well and no history of it being changed. When the old oil came out it was pretty nasty and smelly so I doubt it was ever changed. I didn't use Dexron III (recommended) but a newer spec oil and after about a month of driving it shifts nice and smooth. I won't mention what I used because I was boo-hood on another thread but it was, supposedly, a full synthetic. I'll probably do another drain-and fill next summer since Toyota doesn't recommend changing the filter, ever!.
 
Your transmission would actually be a TH475 that was later renamed 3L80-HD in the late 80's, It has straight-cut planetary gear sets compared to helical-cut gears found in the TH400. This was to keep "Thrust-Load" to a minimum in heavy vehicles.

The TH400/TH475 units don't really care what ATF is put in them, They were living long lives in the Dexron I, II, IIE days. I DID see some front pump seal failures when Dexron VI first came out on pre-1988 Hydramatic units, The lip seals were Orange in color on the older units, The newer units with Black/Brown seals didn't seem to suffer any damage from Dexron VI.

To be clear.....The 700R4 & TH350 are NOT Hydramatic Division produced or designed transmissions, The 700R4 was designed by the Chevrolet division & the TH350 was a Buick/Chevrolet joint venture......These two units didn't seem affected by Dexron VI.
 
Originally Posted by clinebarger
Your transmission would actually be a TH475 that was later renamed 3L80-HD in the late 80's, It has straight-cut planetary gear sets compared to helical-cut gears found in the TH400. This was to keep "Thrust-Load" to a minimum in heavy vehicles.

The TH400/TH475 units don't really care what ATF is put in them, They were living long lives in the Dexron I, II, IIE days. I DID see some front pump seal failures when Dexron VI first came out on pre-1988 Hydramatic units, The lip seals were Orange in color on the older units, The newer units with Black/Brown seals didn't seem to suffer any damage from Dexron VI.

To be clear.....The 700R4 & TH350 are NOT Hydramatic Division produced or designed transmissions, The 700R4 was designed by the Chevrolet division & the TH350 was a Buick/Chevrolet joint venture......These two units didn't seem affected by Dexron VI.





Any thoughts on the 2004R in regards to fluid usage or failure patterns? Feel free to PM me if you think this is too off topic. I also have a non functioning lockup you may have some input on. I've assumed it just needs a rebuild for the past few years.
 
The 200-4R is a Hydramatic unit & had the obsolete orange front pump seal through 1987. I don't often see virgin 200-4R cores much less operational original units anymore, The front pump was a big weakness on otherwise good units.

What I'm getting at is.....Your 200-4R most likely has a updated front pump seal.
 
Mine was a 1987 car but the tag on the transmission says it was built in 86. No idea on the pump seal color. The only leak I ever had was the pan gasket but the lock up had to be disabled a couple years ago when it kept disengaging after warmup. Originally the problem would arrise after 20-30k miles on the fluid...change the fluid and it was okay again. Eventually that stopped working. I assume it needs a rebuild to fix that because I remember reading a tsb saying something about excessive end play on some shaft. But it shifts perfectly and fluid looks perfect still after 40-50k.

The 2004R in my 83 Caprice had the output shaft seal start leaking a few years ago and we replaced it a couple years ago. I assumed it was because of the high mileage.
 
I remember the TSB, It advised that loose internal torque converter end-play can cause the unit to fall out of lock-up "Hot". This was for brand new cars at the time.....Some torque converters had loose end-play from the factory.

The Lock-Up solenoids on the 700R4 & 200-4R were not that great when they were new & haven't aged well either.....Even a small amount of leakage can cause Lock-Up to fall out when hot, Sheared/Dirty fluid will aggravate the symptom. Eventually it will no longer Lock-Up at all.

1996 & up 4L60E Lock-Up solenoids on the other hand are VERY robust & rarely fail, They can be retrofitting to 200-4R's by spacing the solenoid body down using washers/spacers. 700R4 solenoid "snouts" are a little longer than the original 200-4R piece. Splice the 2 wires to your harness.....They ARE polarity sensitive! The polarity is marked on the solenoid body.

The pressure switch (If equipped) could have a ruptured diaphragm, Test it with shop air....If air escapes the bleed hole on the back of the switch, The diaphragm is ruptured.
 
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