Lockup torque converter for a TH400?

As far as I know if a transmission was not built to have one you cant install one on it. The valve body and other internal components do not have the needed control valves or oil passages designed into them that control the torque converters internal clutch system.

It may physically fit but there is no way to lock up the internal clutch system.

Tcmtech is correct. They never came with one. You'd be better off going to a 700R4 to get lockup and enjoy a .70 4th gear. The amount of time and expense to get an lockup torque converter to work in a TH400 would be more than making the conversion to a 700R4. It can be done and has, primarily in some 4L30's, but I couldn't verify that. Non-the-less, what a lot of work! Good luck with your project.

What you could do is switch to a TH350 with the lockup converter and add a manual switch inside to lock and unlock the converter.

I worked with a guy many years ago who did that with a early 80's Olds Cutlass with a 350 Chevy engine. Worked very well for him. Just don't forget to switch it off coming to a stop!

..knew a guy that hooked his TH350 lockup to his brake light switch such that it locked when he released the brakes...worked cool on this drag racer!

Aha! So there is a lockup TC for the 350. Wonder if it could be rigged to lock at a preset speed and unlock below it? Sounds like a perfect low-buck setup.

As far as I know, every new car sold in the USA with electric door locks has an auto-lock feature that actuates at very low speeds; at least some also unlock automatically when the key is turned off (on some Chrysler products at least, ONLY the driver's door unlocks, VERY annoying!).

I suspect that the trigger wheel used for ABS brakes supplies the signal; something quite similar could certainly do the job. Using a "watchdog" function would permit using the same signal - or lack of it - to unlock when speed dropped low enough. Here's a possibility: http://www.edn.com/article/CA265502.html. Or check out Maxim MAX6369 (an integrated circuit).

Could it just be your stall speed is higher then your engine and gearing setup really needs, especially for just cruising down the highway?

Seems to me that swapping out the converter for one with a lower stall would be the least expensive route.

If you're looking to improve fluid temp, there are a number of low-buck fixes (coolers, finned pans, etc). If you're looking to improve economy, you picked the wrong tranny (the TH-400 has the same drivetrain losses as any automatic, but it also weighs more then a TH-350 or 700R4), but there are a few vendors out there who sell overdrive units which bolt to the back of the TH-400 and "split" the gearing, effectively turning your 3 speed into a close ratio 6 speed with a final ratio of about 0.7 (overdrive). These units are a bit pricey, but sometimes you can find them used on Ebay.

If you could give us more information about your car, it would go a long way to finding the best bang for your buck

2100 lb T-bucket, SBC with maybe 400 hp. I had a lower stall TC in it, and you had to stand on the brake or it would idle at 20 mph! So around town it was no fun. The TH400 was handy, or I would have used a TH350 or even a Powerglide. With a 3.0 rear, it only makes 2000 rpm at 50 mph, so it must be slipping. A lockup TC seems to make sense, but I dont want to spend big bucks on a new tranny.

Im guessing that a 400 HP SBC would likely be a moderately "built" 350 or 400 (or some stroked/destroked combo in between, like a 383). Both of these engines typically develop peak torque at relatively low RPM. You optimally want to pick a toque converter 500-750 RPM lower then where peak torque occurs, so in most applications, a 2500 rpm stall speed converter is more then enough. How much duration does your cam have @ 0.050" lift? My guess is your high idle with a lower converter may have just been a poorly adjusted carb (If Im not mistaken, those old beasts liked to idle around 700 rpm, give or take), or an improperly sized/jetted carb. Or are you running FI?

3.0 gears in the rear eh? Im guessing with a car that light it would be nearly impossible to hook up with a 3.73 or 4.10 gears hehehehe.

Put in a 4L60E or 4L80E with a stand alone controller. if your going to change out the trans get one with an overdrive and adjustable shift points via the controller.

It would cost you more to try to convert your th400 to a lockup as you would have to fabricate a lot of parts $$$. You could convert to a th350 with a lockup converter from a salvage yard. If I'm not mistaken you can use a short tail shaft th350 and would just have to change the front yoke and add one circuit using a vacuum switch that controlled the lockup converter and they are referred to as lockup converter vacuum solenoid. By using a th350 it will also help with your mileage as they were a much lighter load transmission. You could also use a 700R4 as it was built on the th350 case and almost all of them were lockup type. If you are worried about it holding the power that is not a concern as the TH350 was capable of dealing with about 450-500 horsepower and around 450 ft.lbs torque. The only fabrication that might have to happen would be the modification of the driveshaft.

Jspeop, thanks for great info. I think that is the perfect solution to my situation.

If I remember correctly, the lockup converter is activated by an electronic solenoid buried in the tranny. There is a (four pin, I think) sealed electrical connector on the side of the case.

Yes, I did a little research last night. B&M apparently no longer has their lockup kit. It seems a brake switch and vacuum switch connect to the tranny and somehow control lockup. Anyone have a wiring diagram or experience with this mod?

B&M offers two different kits to lock up the converter at a preset speed that is able to be determined by you and is very easy to install. The part numbers for the two kits are 70248 for electronic speedometer and 70244 for the mechanical speedometer. I have used several of these kits in street rods that I have built for customers and have not had a single failure from the kits. One customer drives his 42 Chev.coupe everyday and has put about 75000 miles on it in the last 3 years and he's pushing a 383 small block with f.i. and dyno'd 467 hp. It is definitely a fun car to drive and the kits are very easy to install.

Good luck

Thanks again, Jim. I see you too are in Dallas. Do you have a shop?

Kerry

I'm actually in Tyler and am in the process of building a new shop and am right now doing most of my work mobile except for my long term projects which I am doing in my old maintenance barn.

I am just moving from Carrollton to Ardmore. Don Ross of Garland built my car. Can you recommend a reliable source of a TH350C in Dallas? We are preparing to redo the motor mounts, move the motor a little and redo the driveshaft; this would be a good time to replace the tranny too.

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