What is an electronic th-400?

[TexAndy]

I've been cruising craigslist for a replacement transmission and I found one that says it's an "electronic TH-400"

Huh?

It also says it is a "lockup tranny." What is that? Does it have to do with how it attaches to the transfer case?

 

[rlwm211]

Lock up equals lock up torque convertor

A lock up transmission is one that the torque convertor can lock once a cruising speed is attained and you are neither accelerating or de-accelerating. These were initially introduced in cars in the early 80's and are commonplace on all vehicles these days. Typically these types of tranmissions require at least a control module, if not an ECM.

If I am not mistaken your truck is not designed for that type of torque convertor. Your truck has a mechanical speedometer which would make installing the necessary sensors and such difficult if you were to decide to try to add this feature to your truck.

If you are looking to replace your transmission, you might consider trying to find a person who rebuilds the THM400 as it is a very simple transmission and is very reliable once rebuilt. The labor as far as replacing the transmission will be the same as well, and you may be better off to have the one you have rebuilt in the long run. If you are at all capable with a wrench and tools, the THM400 is not a particularly difficult transmission to rebuild yourself.

Hope this helps
RL

 

[nhdiesel]

The electronic version of a TH400 would be the 4L80E. There are stand-alone controllers for them which require no other modifications to use the electronic transmission. The 4L80E also has overdrive, which would be a benefit for economy and highway cruising.

Combined with a lockup torque converter, a 4-speed automatic can artificially be made into a 5 or 6 speed, depending on how many gears the lockup feature operates in. Some transmissions allow lockup in 3rd gear, so you end up with essentially a 6-speed: 1, 2, 3, 3lockup, 4, 4lockup.

For simplicity and cost, the TH400 is hard to beat. Cheap to buy (although they are getting more rare as the old vehicles are scrapped), cheap to maintain and rebuild, and they last a long time.

Jim

 

[TexAndy]

Thanks, I guess I'll just try rebuilding it. I'd like to learn how to do it, anyways.

 

[jwaller]

there are some 400's that were built with a locking torque converter but there were very few of them.

 

[cucvcan]

Whats the purpose of the lock up feature??

 

[nhdiesel]

The lockup feature is for both economy and to reduce heat in the transmission by reducing slippage. To understand what a lockup torque converter does, you have to understand how one works. Although not quite 100% accurate because of the principals of turbines, this is a very close explanation. Inside the torque converter are 2 vanes. One is powered by the engine, one is hooked to the transmission input shaft. The torque converter is filled with transmission fluid. Picture taking a household fan, and place an identical fan as close as you can in front of it. Turn on only 1 fan, and it will cause the other fan to turn.

You can make the 2nd fan turn pretty fast, but never as fast as the powered fan, because there will always be slippage. That slippage is minimal in a torque converter, but it is always there unless it has a lockup feature. That slippage also creates a lot of heat. Lockup torque converters use a hydraulically activated clutch inside the torque converter to lock it together solid. This eliminates the slippage, and acts like having another gear added to the transmission.

Lockup torque converters are hydraulic, but most transmissions use an electric solenoid to control that hydraulic action, so the computer can control when it happens, so it doesn't happen in every gear. One transmission I know of that does it without any electronics is the 727 used in Jeep Grand Wagoneers. Its one of the few 727s with a lockup torque converter, and uses no electronics. The GM TH700R4 is a hydraulic transmission but uses an electric signal to lock up the torque converter.

Jim

 

[southdave]

700r4 can have mech. lock check out b&m part number 70244 runs off the speedo cable imput

 

[84cucv1ton]

i dont know how to do it, got a th400 rebuilt with a b and m kit. also , a **** kit 400 bucks. was told that a ok price

 

[jwaller]

if you get a locking TQ you will reduce your highway rpm's by 300-400.

 

[TexAndy]

So what rebuild kit would ya'll recommend?

What seems to be the consensus on which brand to buy?

 

[nhdiesel]

A TH400 is bulletproof with any stock rebuild. There really isn't anything that needs upgrading, unlike some other autos. You can get a good rebuild kit from Napa, Summit Racing, or many other sources. If you choose, you could install a shift kit, but make sure you look for one recommended for RVs, as they will give a more positive shift without the hard shifts muscle car shift kits leave you with. But even just going with a stock rebuild would give you years of trouble free use.

Jim

 

[hg adams]

What about the transmission in the military humvees. I think it is called a 3L80E. Would this be a 4L80E without the overdrive, but still have have a lockup torque converter?

 

[ODdave]

What about the transmission in the military humvees. I think it is called a 3L80E. Would this be a 4L80E without the overdrive, but still have have a lockup torque converter?

yes.

3 - speeds
L - mounting configuration
80 - torque rating
E - electronic controls

 

[hg adams]

So, are there any 3L80E transmissions floating around?

 

[bguy193]

The E designation on the GM metric 4L80E, 4L60E, etc means that it contains shift solenoids that are controlled by
theECM (computer) in your vehicle.The ECM monitors the RPMS, speed sensor, and engine temp it then shifts the
transmission and locks the torque converter when necessary. For instance, the TC will not lock up until the engine is
up to normal operating temp. A bad thermostat that doesn't allow the the engine to get to operating temp can keep the
ECM from locking the TC. Although its possible to use in your truck it would be extremely pricey to set up.

A 700R4 can be used in anything, I've used them for years in 80's mud trucks. I simply ran the lock up off of a toggle switch but only when at cruising speeds from place to place. You just have to remember to turn it off before slowing down to your next stop. If you're not use to this set up it can be tricky. If you did decide to go with this set up make
sure you get a 700R4 with a "K" cast into the bell housing. These were used in the larger trucks and have a heavier casting

I would have to agree with nhdiesel about going with a TH400, they are tough and are a fairly easy overhaul. You
should be able to find a good overhaul manual at your local parts store. You can also usually get a rebuild kit through
a local tranny shop at a reasonable price, that is if they are reasonable guys.
Happy Trucking