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Old 07-13-2006, 10:15 AM   #1
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1984 31' Limited
1983 31' Airstream310
Oriental , North Carolina
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Question Lockup Torque Converter???

My '84 310 turbo diesel has a GM TH400 transmission (3-speed, no lockup). The slip produces a lot of heat. Has anyone found a torque converter with a lockup feature that can be installed on the TH400 - or better yet, has anyone found a 4-speed tranny with lockup that can be substituted?

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Old 07-13-2006, 10:54 AM   #2
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1993 21' Sovereign
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You can get a TH400 with a lockup converter. I have found after a lot of research, it won't help much as far as RPM's as the stall of the converter is below the engine speed you are traveling at.

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Old 07-13-2006, 12:09 PM   #3
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Lockup Torque Converter

The lock up torque converters lockup after the transmission has shifted into third(in the case of the TH400 which has no overdrive to my recollection).
The 700R4 or 4l60 which ever your prefer calling it has the torque converter lock up after third but before overdrive.
In either case,you will gain nothing if you are pulling hard because the torque converter sill unlocks (feels like a downshift) after you start to give it more accelerator.There used to be a provision in the 700R4 (may still be there) that will cause the torque converter to lock if the transmission gets too hot. Trouble is, by that time your torque converter locks up, you are already damaging your transmission.
If the heat is excessive(transmission fluid is too hot) try installing an oversized cooler with its own fan back under neath the truck(run the fan all the time that you are pulling). Run the hottest fluid comming out of the transmission to the cooler then to the radiator. The oversized cooler cooles the oil too much then the water in the radiator warms it back up to where it needs to be.
This also will add more cooling capacity to your radiator as your radiator is dumping heat into the cool transmission fluid.

This set up has been working well for me for over 20 years.
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Old 07-13-2006, 03:42 PM   #4
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The 4L80E is basicly a 400 trans with overdrive and lockup torque converter. It is strong enough to run in a motorhome. Its the trans you get with the 8.1 in the 3/4 ton Chevies if you don't get an Allison. The 700R4 or 4L60E will not last very long. They are light duty car transmissions.

You would either have to have an aftermarket controller (expensive) or a controler out of a diesel truck to make the 4L80E work. (The "E" means it is electronic and won't work without a controller.) It is probably longer than the 400, so the driveshaft would have to be shortened, and if the parking brake is on the back of the trans like the 310 that I had, you would have to deal with that.

There is also a device available that will let a 4L80E shift the od in and out in 1st and 2nd as well as 3rd, giving a 6 speed. Much like a Gear Vendors, but with lockup.

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Old 07-14-2006, 08:58 PM   #5
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1983 31' Airstream310
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Thank you all for the information. I already have the oversized transmission fluid cooler, and plan to add a fan soon. It looks like I now need a 4L80E and possibly also a Gear Vendors over/underdrive. Any suggestions about who to go to in the southeast for these kinds of things?
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