THM400 ATF Recommendations
Thread Starter
Instructor
Joined: Oct 2012
Posts: 222
Likes: 11
From: Johnston, Rhode Island
THM400 ATF Recommendations
I have a leaky transmission oil pan gasket and am going to replace it with a Fel-Pro TOS-18621 one. Since the engine is out of the car being rebuilt this seems like an opportune time to do this. I am considering using the Mobile 1 synthetic ATF fluid as I believe synthetic oils perform better than conventional oils. Does anyone think this is a bad idea or think I should use a different ATF?
Thank you.
Thank you.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Mobil 1 synthetic for me for years. Never had a tranny problem. I do change it & filter ever 35k miles which is probably overkill. One advantage to it is it handles heat better which is damaging to tranny's.
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
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I wouldn't be so fast to add synthetic to an old trans especially if you're not hammering it hard. Old Dexron is good, Type F will firm up the shifts a little or race guys like John Deere Hy-guard hydraulic fluid for really good shifts. But they usually have better linings to handle it and want super firm shifts.
JIM
Pro
Joined: Sep 2022
Posts: 651
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From: Ohio
Race Director
Joined: Jan 2000
Posts: 13,018
Likes: 2,262
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Original Dexron was considered a "high lubricity" fluid to provide calmer shifts. Type F is considered a "high impact" fluid. They have different properties based on the trans design. If you defeat some of the features a T-400 has to calm the shifts it will bark the tires going into 3rd gear at 30 MPH at part throttle and jar your teeth.
For years Type F has been spec'd by places like B&M when installing a shift kit.
JIM
For years Type F has been spec'd by places like B&M when installing a shift kit.
JIM
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Team Owner
Joined: Jan 2006
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From: Crossville TN
Synthetic oil is the way to go for ALL moving part systems. Just make sure it is meant for transmissions. Also, make sure you change the tranny filter while you are in there.
You WILL see lots for fine, black "silt" in the pan. That is just normally worn-off clutch plate facing material.Just clean it out.
If you find shiny metal particles, Hmmmmm .... might be a problem brewing. Also, make sure the oil pan gasket surface is smooth and flat...particularly around the bolt holes. People over-torque pan bolts...to "help" them seal. This usually distorts the pan rail and makes it difficult to seal the next time.
You WILL see lots for fine, black "silt" in the pan. That is just normally worn-off clutch plate facing material.Just clean it out.
If you find shiny metal particles, Hmmmmm .... might be a problem brewing. Also, make sure the oil pan gasket surface is smooth and flat...particularly around the bolt holes. People over-torque pan bolts...to "help" them seal. This usually distorts the pan rail and makes it difficult to seal the next time.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Not so quick. Too many people jump on the synthetic band wagon because it works so great in their 2000s daily driver.
Some of those 40 - 50 yr old parts are not so convinced its the greatest lube ever invented.
And lots of gaskets & seals dislike the syn.
Some of those 40 - 50 yr old parts are not so convinced its the greatest lube ever invented.
And lots of gaskets & seals dislike the syn.