New Transmission Fluid TR3650

Candy10

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I know there’s probably a thread on this already somewhere, but I searched and didn’t find one.

Output shaft seal on my trans has been leaking for quite a while. It ain’t TOO bad, one or two drops every few days. Sometimes it looks like it doesn’t leak at all (tshirt on the garage floor). But I know the longer I put this off the higher the chance it suddenly gets worse.

The transmission is the only stock part left on the car (ticking time bomb lol) and just turned 77000 miles. I assume when I remove that seal I’ll lose all the fluid. Is it bad to drain and refill this trans at its current mileage? I hear some people say new fluid in a higher mileage transmission, without a rebuild, is a bad thing. I’d like y’all’s opinion before I change out this rear seal.
 

Midlife Crises

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New fluid in your 3650 isn’t going to heart anything. Possibility it could help. I recommend Mobile 1 full synthetic all brand ATF or Tremec‘s own synthetic HD MTF.
 

stkjock

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lots of threads on this topic




probably more, found these in a few moments.
 

1950StangJump$

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The stuff about not changing old fluid is an old wive's tale, IMO. Might have mattered 50 years ago, I don't know.

As for the type of fluid, back when I had a 3650, I did Mercon, Mobil 1, and Pennzoil Syncromesh all back-to-back-to-back. The Syncromesh was the best, hands down.

Tremec only recommends the Mercon or the Mobil 1 these days; I called them. Allegedly, they also recommended Syncromesh back in the day, but the dude reading from a script couldn't tell me why it's not on the list any longer. Could be 1001 reasons NOT about what's best for the transmission.
 

Candy10

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The stuff about not changing old fluid is an old wive's tale, IMO. Might have mattered 50 years ago, I don't know.

As for the type of fluid, back when I had a 3650, I did Mercon, Mobil 1, and Pennzoil Syncromesh all back-to-back-to-back. The Syncromesh was the best, hands down.

Tremec only recommends the Mercon or the Mobil 1 these days; I called them. Allegedly, they also recommended Syncromesh back in the day, but the dude reading from a script couldn't tell me why it's not on the list any longer. Could be 1001 reasons NOT about what's best for the transmission.
Great info thanks. Question about the Pennzoil; did you add Lucas oil stabilizer as well? It’s just upon further research I’ve seen that mentioned in some forums (though some threads are 10-15 years old!). 3.2 quarts?
 

moooosestang

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I know there’s probably a thread on this already somewhere, but I searched and didn’t find one.

Output shaft seal on my trans has been leaking for quite a while. It ain’t TOO bad, one or two drops every few days. Sometimes it looks like it doesn’t leak at all (tshirt on the garage floor). But I know the longer I put this off the higher the chance it suddenly gets worse.

The transmission is the only stock part left on the car (ticking time bomb lol) and just turned 77000 miles. I assume when I remove that seal I’ll lose all the fluid. Is it bad to drain and refill this trans at its current mileage? I hear some people say new fluid in a higher mileage transmission, without a rebuild, is a bad thing. I’d like y’all’s opinion before I change out this rear seal.
That's with autos, never heard anyone say that about manuals. you won't loose all the fluid, but you might as well change it. get one of the syncromesh fluids. I think i used valvoline.
 

1950StangJump$

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Great info thanks. Question about the Pennzoil; did you add Lucas oil stabilizer as well? It’s just upon further research I’ve seen that mentioned in some forums (though some threads are 10-15 years old!). 3.2 quarts?
I think the use of the stabilizer was a hail mary by someone that was having issues, IIRC. I can't say for sure it's helpful or not. I only used the Syncromesh.
 

moooosestang

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Great info thanks. Question about the Pennzoil; did you add Lucas oil stabilizer as well? It’s just upon further research I’ve seen that mentioned in some forums (though some threads are 10-15 years old!). 3.2 quarts?
I used the lucas stuff, but not very much. The stuff is a royal pain to get into the transmission. It's like honey and kinda sticky too. I think i did 3 quarts of syncromesh and about 1/2 a quart of the lucas. you should be fine with 3.2, i just wanted to be safe that i got enough in there. No shifting issues at all.

Edit: I stand corrected. After 2 days of 32F low, it did not want to shift into 1st gear after backing out of the garage. Temp was in the 50's. If you live where it's cold and drive when it's cold i would not add the lucas stuff. It was fine after about 10 minutes.
 
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