2WD Transmission into a 4X4 Truck

[Milblazer]

Found a 2WD 86 C10 with a 6.2 and 700r4. After reading a few things I'd like to confirm them here.

-2WD have a longer output shaft that needs to be switched to a shorter 27 spline shaft
-Input shaft on the 208 that is currently mated to a TH400 will have to be swapped to a 27 spline shaft
-I'll need a different driveshaft. Will a driveshaft out of any K5 with a 700r4 and 10 bolt work?
-Different flex plate and torque converter
-Wiring harness
-Will the th400 speedometer work or do I need to take a 700r4 cluster? I believe the gear that drives the speedometer cable is in the transmission correct?

I've never done this before and I'm probably forgetting a few things. Can I tackle this myself or should I let a professional do this? Thanks everyone

 

[HotRodPC]

You got some more splaing to do. So what do you have in YOUR TRUCK now? I gather you have a 6.2/Th400/NP208 ??? And you're wanting to swap out to a 700r4 Trans?

If that's the case. Yes, the whole transmission will have to come apart. All the valve body, and everything in the tunnel will have to come out to swap to the shorter 4x4 output shaft.

You are also correct, if you currently have a Th400/NP208, the NP208 you have now will be 32 spline and you need that changed to a 27 spline. I recently traded a guy who needed a 27 spline NP208 for the 32 spline NP208 that a buddy had given him. You can put an ad on CL for the same type of swap and may very well get a hit on that, since the 27 spline is much more common. The 32 spline was used on Th400 and late SM465 transmissions. There were many more 700r4 K10's produced than Th400 models.

You will need a different drive shaft, but you're not telling us if this is going into another K5 or a truck, so no way to say for sure. If it's going in a truck, cuz of different wheel bases, NO, the K5 shaft will not work due to length difference, but the yoke will work.

Flex plate likely going to be fine. Torque Converter obviously needs to be one that goes with the 700r4.

Wiring harness if for TC lock up only, so you can either go with an aftermarket lock up kit, or get you the OEM Vac switch and harness out of a DIY pull it yard or ask someone here would probably has that set up.

Speedo should be fine in the years you're talking about since you it's not into the late 80's when it's gone to VSS. The trans won't matter anyway. The Tcase is what matters. Just be sure to get a Tcase with the manual speedo gears and not a reluctor wheel. The speedo gear 27 spline is most common in fact it's hard to find the VSS model NP208's.

 

[Milblazer]

You got some more splaing to do. So what do you have in YOUR TRUCK now? I gather you have a 6.2/Th400/NP208 ??? And you're wanting to swap out to a 700r4 Trans?

You are correct, that is what I have.

You will need a different drive shaft, but you're not telling us if this is going into another K5 or a truck, so no way to say for sure. If it's going in a truck, cuz of different wheel bases, NO, the K5 shaft will not work due to length difference, but the yoke will work.

This would be going into my K5 from the C10. Think this project is going to be put on hold as I found a crack in my frame today.

 

[HotRodPC]

You are correct, that is what I have.



This would be going into my K5 from the C10. Think this project is going to be put on hold as I found a crack in my frame today.

A crack in your C10 frame? Where at? Post pics? It can likely be repaired.

Orrr, are you going to be having a good K5 frame left over?

 

[Milblazer]

The C10 is a truck being parted out locally. The crack is in my K5's frame.

 

[HotRodPC]

Very Common. Easily fixed, then get the support bracket to beef it up and it's better than new.

 

[HotRodPC]

OK, now it makes sense. I smell what you're steppin in now. Duh,, MilBlazer = CUCV M1008 with a 6.2, 400/NP208 and 3.08 10 bolts. I sure hope you're plan is to get rid of the 3.08's cuz you sure don't a 700r4 with the 3.08's and more than likely going to kill the 700r4 with 3.08's.

 

[Swims350]

in my 88 they had a 2wd 700r4 trans with the tailshaft removed, and had a spacer plate used to commonly make a th350 go in place of a 700r4 in 4wd applications, and then slide the crossmember back or up whichever it was drilled new holes and bolted it down. I replaced it with a th350 when I got the truck, so it could be an option, although t-case still needs to match up. I have a np241 in mine being a gmt400 and electric speedo. I would think the np208 that comes behind a 700r4 would work just fine also since the th350 and the 700 have the same 4 bolt tail ends. Then both share the 27 spline setup.

lol yes 3.08's and a 700r4 sucks big time, same thing our 86 k10 had.

 

[Milblazer]

Is this what you're talking about HotRod?

http://www.offroaddesign.com/catalog/steeringkit.htm

I didn't know the 3.08s and 700r4 were not a good combo. What would be a good gear ratio to use with a 6.2 and 700r4?

 

[HotRodPC]

Is this what you're talking about HotRod?

http://www.offroaddesign.com/catalog/steeringkit.htm

I didn't know the 3.08s and 700r4 were not a good combo. What would be a good gear ratio to use with a 6.2 and 700r4?

yes, that's it. I think there are others too in the aftermarket world.

Yes, 3.08's are horrible with a 700r4 and the OD is really not needed at all.
As far a good ratio, I'd normally say 4.10's but being your working with a 6.2 and they don't like higher rpm, 3.73's would probably be good. As far as taking stress off the 700r4, go 4.10's and even 4.56's if you're running 35 or bigger tires. You'll really need to decide what all you are wanting to accomplish, what lift and tire size you want to go with, then choose your gear ratio and trans around that.

 

[Swims350]

aint sure about diesels and gear ratios but I'd think 3.73's or taller depends on tire size too.

f course for me I like tall gears like 3.73's or 4.10's on cars and 2wds. I want 4.56's on my 88 with 35's or 37's and then I have a th350.

 

[HotRodPC]

I go nothing higher than a 3.73 gear no matter what the tire size cuz then you're getting into strain on the trans. 3.73's and 31s, 33 max would probably be OK.

 

[Milblazer]

I'm running stock suspension, rims, and tires. I dont plan on altering the suspension ever as I like the way the truck sits. Plus I keep finding things like this crack to put a nice hole in my budget.

aint sure about diesels and gear ratios but I'd think 3.73's or taller depends on tire size too.

f course for me I like tall gears like 3.73's or 4.10's on cars and 2wds. I want 4.56's on my 88 with 35's or 37's and then I have a th350.

I just want something that will make it a little easier on the engine when I get on the highway. The 6.2 does not like the th400 when everyone around me is doing 65+. I hate getting passed by a Prius.

 

[HotRodPC]

In that case, some 3.73's would be about perfect. Actually, with 3.08's and a Th400, I don't see why you'd want the 700r4. The Th400 is a very strong and reliable transmission. The 700r4 does have the advantage of an OD, but it's weaker than ****, and has been known to be problematic. What you will gain by going to 3.73 and 700r4, you'll notice a huge difference in pep. The 3.73's will help with the pep, then add the fact the 700r4 has a 3.06 first gear, and the Th400 has a 2.48, so the 700r4 does have a deeper first gear to help get it moving. Then you have the OD to compensate for the lower rear gear that get's you moving. As far as top end, The 3.73 and OD isn't going to add much. Of course the 700r4 does also have a locking conveter.

Just so you know all the details to make your choice....