700r4 to th400 swap

[project 67 sub]

I have a 1990 GMC Sierra with a tbi350/700r4 in it. Had the trans rebuilt back in 2013. All gears still work, but it's never shifted right. I've just kinda dealt with it. But I've been increasingly grown more and more annoyed by it. Lol So I picked up a used and working th400, out of a 1972 motorhome with a 402 BBC in it. What I need to know is what do I need to make it work with the tbi 350? I already know about everything else like driveshaft needs to be longer, etc. Just don't know about making it work with the tbi computer or whatever. Any help appreciated. And thanks in advance.

 

[90halfton]

I've never done this swap. Computer won't care though, 700r4 does not rely on it. For no more than a 700 costs seems like you'd be ahead to spend it, save some fab work, and retain overdrive ( the most important part to me )

 

[BIG_KID]

The 400 will need engine vacuum source for the modulator, a kick down cable mounted to the TBI and a generator conversion for the speedometer

I'd slide the 402 in there too. Get a BBC TBI intake, drill/tap the exhaust manifold for the O2

 

[project 67 sub]

I've never done this swap. Computer won't care though, 700r4 does not rely on it. For no more than a 700 costs seems like you'd be ahead to spend it, save some fab work, and retain overdrive ( the most important part to me )

Hmm. So the computer doesn't rely on a speed sensor (vss signal) or anything to let it know the vehicle is moving or anything for more fueling like the newer fuel injected vehicles? Also, why would I waste another $700 of my money on getting the ****** 700r4 rebuilt again? Lol. The only "fab work" that would need done is having a new drive shaft made, or find a longer one and have it cut down. Overdrive isn't really a big deal for me since I'm running 33"tires with the stock 3:42 gears, which kinda sucks. May even gain some gas mileage and whatnot out of the swap. Lol.

The 400 will need engine vacuum source for the modulator, a kick down cable mounted to the TBI and a generator conversion for the speedometer

I'd slide the 402 in there too. Get a BBC TBI intake, drill/tap the exhaust manifold for the O2

Engine vacuum for the modulator is easy. Th400 doesn't use a cable kick down, they're electronic, which I'm not even really worried about having. As far as the generator conversion for the speedo, where could I find one that would work with the stock gauge? Now as far as the 402BBC goes. That engine wasn't mine, it was a friends, and he traded it for 2 "LS" 5.3 engines. I got the transmission from him for helping him remove it from the running and driving motorhome.

 

[project 67 sub]

This is a pic of said vehicle in question for the th400 swap.

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[BIG_KID]

I think this is what you need

https://ls1tech.com/forums/automatic-transmission/1660957-th400-speed-sensor-plug-id-source.html

PS I confused the cable with the TH350

 

[90halfton]

Hmm. So the computer doesn't rely on a speed sensor (vss signal) or anything to let it know the vehicle is moving or anything for more fueling like the newer fuel injected vehicles? Also, why would I waste another $700 of my money on getting the ****** 700r4 rebuilt again? Lol. The only "fab work" that would need done is having a new drive shaft made, or find a longer one and have it cut down. Overdrive isn't really a big deal for me since I'm running 33"tires with the stock 3:42 gears, which kinda sucks. May even gain some gas mileage and whatnot out of the swap. Lol.




Engine vacuum for the modulator is easy. Th400 doesn't use a cable kick down, they're electronic, which I'm not even really worried about having. As far as the generator conversion for the speedo, where could I find one that would work with the stock gauge? Now as far as the 402BBC goes. That engine wasn't mine, it was a friends, and he traded it for 2 "LS" 5.3 engines. I got the transmission from him for helping him remove it from the running and driving motorhome.

The "new fi vehicles" didn't get a 700r4. And I'm pretty confident the speed sensor is only for the speedometer, though it's possible I'm wrong. And the 700 is a good transmission behind a stock 350, despite the incorrect hate they seem to get. Never shifting right after rebuild is not the fault of the design, but the builder, or parts, or adjustment of TV cable, etc. 400 is a good tranny, not having overdrive would drive me nuts though, and it seems like dropping in another 700 would be much easier (if this one was done properly lol)

 

[Tzfbird]

I currently have a 3/4 ton with a factory TH400 and 4.10 gears. I was looking at swapping to a TH700r4 because mileage is terrible but I decided to get a different truck instead. The TH400 will be a direct swap and you can install a reluctor ring AcDelco PN 24202711 and associated VSS sensor. You'll want to first figure out what style VSS it currently uses because there were 4 different styles that GM used in vehicles.
The kickdown solenoid is run off the ECM on the same output as the TCC solenoid and you can find most of the diagrams online. Besides that you already mentioned the driveshaft length and vacuum for the shift modulator.

The truck looks great and you definitely need a heavier duty transmission if you are truly using the truck for the way it appears it's built. I would prefer a modded 5.3 swap with a 4L80e for something like that. You will keep/increase the fuel economy of the 350/700r4 and handle the same power as the TH400.

 

[CRF450R]

Why in hell would you go from a 4spd overdrive to a crappy TH400. Go to a perfesional transmission shop and build up your 700r4 your mpg with show in the back wallet. TH400 aren't as good as there bragged up to be. If you do the swap your definitely not upgrading the truck your down grading it screw the TH350 abd TH400 with all the tough overdrive transmissions on the used market these days why in God's earth would you want to go to old technology 3spd auto transmission. The TH350 and TH400 transmissions belong in the same place as carburators in the trash.

Sent from my Nexus 5 using Tapatalk

 

[Blackwater]

Get a 4l60 or 4l80. or better the 6l60E and add a TCU.