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Old 01-17-2016, 05:59 PM   #1
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TH-400 rebuild or new

Front and rear Oil seal are leaking on my TH-400 and I found a good amount of metal dust and a few small chunks (size of very small nail heads) in the pan when I replaced it recently. Someone also messed up one of the threats under the crossmember and did a fairly successful helicoil thread repair job, which appears to be holding.
Should I have the trans rebuild and just buy a new one?
I don't think I want to go with the 4L80E at this time, unless I would know someone that could deal with all the associated issues, especially the fuel injection.
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Old 01-17-2016, 07:43 PM   #2
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In general I think you are better off rebuilding what you have unless it had a catastrophic failure that tore up a lot of parts. Most of the time automatics quit working because of a rubber part like an O-ring or a seal. That is why trans oil temp is important, a little too much heat and the rubber parts harden and then you start burning up clutch plates and pretty soon your vehicle wont move. Most of the time a rebuild is just what is called "soft parts" gaskets and O-rings and clutch plates. If you have a good transmission guy he will know what "hard parts" will need to be replaced like gears or bearings. You have to trust the judgment of the re-builder weather you get an exchange transmission or get yours overhauled. I guess you just pay the money and hope the re-builder was good. To get the most life from your transmission just try to pull forward onto leveling blocks instead of backing on because reverse is a higher gear ratio than first and it is easier on the transmission to go forward. Leland
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Old 01-17-2016, 07:56 PM   #3
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I would swap for a rebuilt unit with a good warranty
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Old 01-17-2016, 08:58 PM   #4
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Find a TH 400 specialist and have him rebuild yours. There are many clutches, bands and other parts from other transmissions that can be used to really build up the TH 400. Find a guy that really knows the TH 400 and have him build you a great trans.
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Old 01-18-2016, 07:09 AM   #5
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Peter, if you exchange you need to make sure you get the 475 version with the straight cut gears.

Or like the TBI you could go with the 4L80e and we can work out the bugs together
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Old 01-18-2016, 01:13 PM   #6
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The 4L80E is a good tranny, but it's computer-controlled: shift switches inside the side cover; torque converter lock-up solenoid; valve body (electronic shift control switch) ; electronic speedo output; etc. You may hafta relocate the cross member. And you'd also hafta shorten the drive shaft.

Frankly, the TH400 is a damn good transmission. Take it to an old-school tranny guy and let him build it properly for you - to your specs. The heli-coil can be heli-arced, drilled, and tapped. So that's no big deal.

BTW - I'm an old-school back counter Chevy parts guy and I'm skeptical of what's "new" out there. I'd much rather take it to a bona-fide tranny guy I trust and (at the very least) let him do a tear-down and get his opinion.

BTW - I'd go to an old-school, independent tranny shop. Today's dealership techs are a generation removed, and have no clue how to build a TH400.

If you're thinking "overdrive," research Gear Vendor. Their unit bolts directly to your TH400 case and thus, replaces your tail shaft housing.

Tom
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Old 01-18-2016, 02:24 PM   #7
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Are there any "Old school" TH-400 guys still out there? After all G.M stopped installing them in 1975. That's 40 years ago. Most are retired by now traveling in their Airstreams.
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Old 01-18-2016, 04:46 PM   #8
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LOL, if you can't find an old guy, try Jasper. Good work, good people, great warranty.
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Old 01-18-2016, 05:47 PM   #9
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You might look into a prepped 700R4 it is used in a lot of street racers due to durability and performance.You will pickup a overdrive (4th gear) and that may be helpful in your application.Your turbo 400 was a good transmission but there have been some improvements since its introduction.
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Old 01-18-2016, 06:32 PM   #10
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1984 34.5' Airstream 345
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Rebuild

The trans on my 345 had a LARGE crack in the bell housing
I pulled a running trans out of another motorhome
That trans (I was told) ran fine (it was attached to a broken motor)
But I figured if it was out I might as well rebuild it I just brought it to a AAMCO trans place near me (I did some research and picked a shop near me with good reviews) then I had a truck repair shop pull the bad and put in the good I haven't taken any really long trips in it but I think I've put about 500 miles on it without a problum
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Old 01-18-2016, 07:04 PM   #11
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Th 400

Stay with a TH 400 one of the best ever made for our style of motorhome Malcolm
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Old 01-18-2016, 07:54 PM   #12
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The THM 400 was used in production vehicles through 1989, and longer in military Hummers.


Brevi tempore!
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Old 01-19-2016, 07:48 AM   #13
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Peter, I'd personally have it rebuilt by a reputable tranny shop. Same sentiment as many above. reputable, knowledgeable etc.. You might be hard pressed to find another TH-475, so I'd stick with what you have.

Keep us posted!
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Old 01-19-2016, 09:48 AM   #14
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The trans is better than that 454 and worth the rebuild! Im just sayin
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