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400SB/700R4 compatibility

blazin topless 75

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I need your help folks-will a stock 400SB be to much for a 700R4? I'm not going to be doing too much heavy wheeling-just some trails and mostly DD'ing. I will also be trailering my 3400LB boat.
 

pauly383

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Stock its not a good idea. However if gone through it would be fine. Run a cooler of course. Also do not use the OD with any amount of weight in tow, for that matter you don't need OD in town either. /forums/images/graemlins/thumb.gif
 

shane74

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I don't see why it's be an issue. GM put them in their /forums/images/graemlins/burb.gif as a standard powertrain combo ( my bro-in-law has that combo in his '87 /forums/images/graemlins/burb.gif). I had that exact same combo in a '79 /forums/images/graemlins/k5.gif and I had NO issues. I also had a 19' Reinel that I towed almost every weekend and even on some extened trips. It was on a single axle trailer too. My 79' never even broke a sweat. But, I didn't/don't tow in OD EVER. That makes the tranny slip too much when your pulling a heavy load and can burn it up pretty quick. Maybe the newer rigs are different, but for me towing in OD has always been bad juju.
 

blazin topless 75

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Thanks everybody. I found an '87 donor truck for $500 that has a built 305 and a 700R4 that I was going to drop into my rig until I get my TH350/NP203 rebuilt.
 

CHEVY 4WD

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pull out the stock cooler and get a bigger one... also get a gauge. I think it will be fine what kind of gears are you running?
 

rjfguitar

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I am running a built 406 that is making around 325HP and 425 ft lbs with a built th700R4 behind it. I like the combo a lot! I am running 4.10 gears with 35's and it seems to be ok for right now and I pull trailers all the time behind it without any issues what so ever. If your donor th700 is in good shape and you take care of the cooling issue than I would not worry about it much, even pulling your boat. BTW 3,500 lbs isn't all that much really.
 

rjfguitar

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Almost everything. A LOT of parts have to be replaced to make it a very strong tranny. If your 400 is stock and there isn't any plans for more power than I would say a fresh 87'-later 700 with a good cooler and shift kit should hold up just fine.
 

4X4HIGH

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Just in case you don't already know this I will tell you. If you want to install a 700R4 into your 75 K5 you will need to use a spacer between the tranny and T-case adapter since the TH350 and 700R4 output shafts are different lengths. You will also need to have the drivelines corrected since the 700R4 tranny is 1 7/8" longer than TH350 and also because you are needing the spacer. You will also need to address the TV cable and the TC lock-up. You will need to relocate the tranny crossmember as well.
 

pauly383

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Even if you use the whole drivetrain out of the donor truck some of the issues 4x4high mentioned need addrerssed. The TV cable needs the bracketry from a later truck to hook up to carb/injection. Your older truck does not contain wiring for lockup torque converter, you may have to wire in a switch or use a combination of two wiring harnesses. I also believe, based on my 12 bolt swap , that the 10 bolt u-joints on donor shafts are slightly bigger than the u-joints a 75 has (d44/12b). Hope it helps /forums/images/graemlins/thumb.gif
 

blazin topless 75

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It does help-thanks. I was considering swapping out the entire wiring harness and fuse block because a lot of my wiring was "modified" making the accessories, interior lighting, backup lights, etc inoperable. I would probably just swap out any other wiring that I would need for the tranny at that time.
 

pauly383

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I also want to mention your sig says 9 inches of lift on 35's. You should remove some lift since you only have 35's. This will make it easier to shim you axle for proper u-joint angles. Or you can run a CV shaft. Just a thought /forums/images/graemlins/thumb.gif
 

blazin topless 75

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I have 6" of suspension lift-the rest is in the body. I am thinking of taking the body lift out because I am running 35s, and with the bushwacker cut-outs it looks kind of silly on those "little" tires. I don't want to get bigger tires because I am trailering my ski boat and I don't want to scrape the prop with the additional height.
 

blazin topless 75

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Paul I just looked at your pics-I've never seen the drive angle with the shackle flips-awesome! I think I'll have to invest in those as well... /forums/images/graemlins/peace.gif
 

pauly383

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That angle made mine vibrate with stock shaft, I am running a CV shaft now with NO shims in axle. Basically with stock shafts the axle and transfercase need to point flat in relation to each other. With a CV shaft the axle just needs to point at transfercase. So in my case it worked great for a CV /forums/images/graemlins/thumb.gif
 
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