Replacing my 700R4 with a TH400 Need Help!

[JESSEGALLEGOS]

I have a 1982 K5 Blazer 2WD. Motor is a crate 350, 290 hp and my tranny went out. I will be replacing my 1991 700R4 with a TH400 and have a couple of questions. The driveftshaft I know is different so I plan on having one custom made, the 400 has a vac. which I would connect to the intake manifold. were does the 4 prong elec plug from the 700R4 go on the 400? Does it get reused. The 400 does not use the same kick down? how do I connect to solenoid from the 400 to the carb??

[JESSEGALLEGOS]

pictures
700R4


TH400

were does this go?

[Lugnut64052]

The four-pin plug from your 700R does not get re-used on the TH400. The throttle valve cable doesn't get re-used either.

The 400 downshifts using modulator vacuum and an electrical switch attached to the gas pedal or a fabbed switch mounted on the throttle linkage. Whichever switch you use connects to the single terminal on the 400.

[JESSEGALLEGOS]

Thank you for the quick answer!!

to the gas pedal or a fabbed switch mounted on the throttle linkage

Do you know what where are can pick up this part or order?

[Lugnut64052]

Any good transmission supply in a bigger town should be able to fix you up with the pedal mounted switch. Transmission Center sells one online for 39 bucks. It's item #79, about 7/8ths of the way down this humongor web page. If you want to mount the switch on the throttle linkage, find a heavy duty momentary contact push button switch and make a bracket. Adjust it so that it makes contact at about wide open throttle.

You want to wire it up so it's B+power---->the switch---->terminal on the side of the transmission.

(the pictured switch is the one that mounts on the gas pedal bracket)

[JESSEGALLEGOS]

I've done some research online and it looks like I have a truck TH400 so the yoke is bolted to the trans and will now need a two piece driveshaft. Going to see if i can find one from a suburban and have it shorten.

[Highsteel]

Subscribed

I just replaced a TH350 with I think this very same TH400 in a 71 C/10. I will be checking tomorrow for the replacement piece for the shaft. Probably just take it to my buddies shop to cut it down and weld the new piece back on.

Thanks to you Lugnut, for the information on the electric kick-down switch. I was eyeballing that terminal today, just before I stabbed the engine/tranny back into its new home, thinking it could be a temp. sensor or some such!

Phew! Dodged a bullet on that one! Thanks again!

Jerry

[meansting04]

for the kickdown on a th400 you can get an intake mounted switch from b amd m. You have to wire a keyed 12v in to one side. The same 12v on the other side down to the 400 and the hook up in the tranny is grounded to the case. Hook up the modulator to the back of the intake and you are ready to go. Hope this helps.

[MylilBowTie]

The th400 will work without it. Electric kickdown is for a 3rd to 1st downshift under 25 mph. It also raises your line pressure to help hold the clutch packs better.

[JESSEGALLEGOS]

Thanks for all the input.

I have a couple of more questions if you don't mind.

Torque converter

here is the one from the 700R4



TH400




I think it would be a good idea to replace the stock converter from the 400 plus I don't think it will work with the flywheel I have right now. In Summit it shows for small bolt pattern only that's the bolt pattern the 700 has right? B&M shows Variable pitch TH400 transmissions must have pump input shaft changed to fixed fixed pitch design. What does that mean and which one do I have?

[Lugnut64052]

Yeah, the bolt circles are different. You'll have to get a different flexplate.

You have a fixed pitch 400. Variable pitch (also called "switch pitch") 400s were only available from 1967 thru 1969 in some full-sized Buicks and few Cadillacs, plus they had a two-pin plug on the side of the case. Yours is a one-pin, which means its a fixed pitch.

[JESSEGALLEGOS]

Thanks for all the help! I have the trans in along with a new torque converter and new flex plate. I also had a custom drive shaft made. If you guys need any pictures I'll be happy to post some. I do need to more items. I need a TH400 trans crossmember from a 2wd Suburban and also the speedo cable for a TH400

[Sugarsdaddy]

Hey, i am building a 4bt - 700r4 right now. U have the same converter/flex plate issues... What did you do?

Cheers,

[geezer#99]

Originally Posted by Sugarsdaddy

Hey, i am building a 4bt - 700r4 right now. U have the same converter/flex plate issues... What did you do?

Cheers,

He hasn't been here for 5 years.
Much easier to start your own thread.