700r4 to th400 swap in '84 6.2 K10

[mathias]

The 700r4 gave up in my '84 'burb. I have only had it a year, and it appears that the previous owner drove it with the tv cable out of adjustment.

I want to tow my tractor with the truck (8000#), so I think the th400 is a better choice for me. I don't have much money to throw at it either, so a $2k-$3k 700r4 rebuild is out of the question.

What will be involved in the swap? Will I end up spending just as much finding all of the pieces to finish the job? I currently have a 700r4/NP208 combination. I know the input spline count is different, so I need a th400 with transfer case. What about the driveshafts? Are those different as well?

It also looks like the th400 is a different physical size, so maybe the shafts have to be a different length anyway?

If I find a used th400 was originally bolted to a 6.2, should I replace the torque converter?

Edited to add: I am open to other trans. options if they would be easier/cheaper. Wouldn't mind a manual at all...

Seems like several people are going the other way -- anybody in central NC want to swap drivetrains?

[SimonUK]

Done the swap both ways myself a few times.

First off make sure you get a th400/np208 combo as the 208 on the 700r4 has a different adaptor and the splines are different.

You'll also need the flexplate, tc, kickdown switch and wiring, vacuum lines and throttle position valve on the ip.

The oil cooler lines, drive shafts, speedo cable etc were all a straight swap on my cucv's anyway.

[mathias]

Thanks! That doesn't sound too bad. Just gotta find the right donor...

[Edahall]

Since you mentioned that you would consider a manual, you might want to look strongly into swapping in a SM465 4 speed manual in it. The SM465 is a very tough transmission and cheap on the used market. The advantage of this transmission over the TH400 is that there is no torque converter slippage so you put more power to the ground and with a 8000 lb load behind a 135 hp 6.2 diesel, you're going to need as much advantage as possible. Also, you won't have to worry about the transmission heating up. The TH400 is notorious for building heat due to the lack of a lock up torque converter. However, the installation will be a bit more complicated since you'll have to install the clutch pedals and cut a hole in the tunnel for the shifter.

Also, I notice that your Suburban is a K10 1/2 ton and you're wanting to pull 8000 lbs. I've even done a little more than that with my 6.2 Suburban but that's a pretty heavy load for that truck and it's going to be very slow on the road behind any 6.2 diesel. What gearing are you running? I hope it's not 3.08's.

[mathias]

Not afraid of the install if I can find the parts cheap enough.

Axle ratio is 3.73. Current have 31s on it, but I need tires, so I'm willing to put whatever tire would work the best on it.

I know it will be slow, but that's okay. Just want to get there safely without damaging my truck.

Where I drive, top speed is 60 mph about 95% of the time.

Towing breakdown is probably:
5% tractor (8000#)
25% single axle 6'x10' enclosed trailer (<4000#)
20% 5x10 open (<2000#)
50% none

[Edahall]

You should be alright with 3.73's. However, heat will be the biggest enemy with that 1/2 ton rear end when pulling heavy loads. I would put some good synthetic oil in that differential and get an extra capacity cover with fins to help dissipate the heat.

Nothing wrong with 31x10.5 tires. Just make sure you stick with heavy duty LT tires or it'll sway badly.

The SM465 transmissions are low cost on the used market. There's plenty of them on the used market because they usually outlived the truck.

Another option would be the NV4500. It's a 5 speed manual transmission and 5th gear is an overdrive. The overdrive would tame the engine rpm's at highway speeds like the 700r4 and gain a few extra mpg's. If you go this route, make sure you weld the 5th gear nut so it doesn't back out. These transmissions usually go for more money than the SM465 but I notice that there is one locally in our classifieds for $200.

[mathias]

Thanks for the advice! The 5 speed would obviously be preferable, then I would be ready if I ever decided to swap in a 6bt (but that's a whole other can of worms, and I won't be opening it anytime soon). I'll just have to keep an eye out for whatever is available.

[Edahall]

Thanks for the advice! The 5 speed would obviously be preferable, then I would be ready if I ever decided to swap in a 6bt (but that's a whole other can of worms, and I won't be opening it anytime soon). I'll just have to keep an eye out for whatever is available.

Yes, a 6BT would require an overdrive behind 3.73 gears althout there's always the option of 3.08 or 2.73 gears. It would also pull your load without a sweat. And believe it or not, they fit into our square bodied Suburbans as if they were meant to be in there.

[ronniejoe]

I did this swap for a guy with a 1982 several years ago. He was disappointed in the result because the first gear ratio is very steep in the 700R4 as compared to the TH400. He couldn't pull as heavy of a load with the 400 that he could with the 700. It seems his 6.2 needed that extra first gear ratio. I think he had 4.10's in the diff's IIRC.

[Edahall]

I did this swap for a guy with a 1982 several years ago. He was disappointed in the result because the first gear ratio is very steep in the 700R4 as compared to the TH400. He couldn't pull as heavy of a load with the 400 that he could with the 700. It seems his 6.2 needed that extra first gear ratio. I think he had 4.10's in the diff's IIRC.

This is an excellent point regarding swapping from a 700r4 to a TH400. It'll really struggle to get that heavy of a load started. For this reason, it makes even more sense to go the SM465 or NV4500 route. Both of these transmissions have a granny low.

[mathias]

This is an excellent point regarding swapping from a 700r4 to a TH400. It'll really struggle to get that heavy of a load started. For this reason, it makes even more sense to go the SM465 or NV4500 route. Both of these transmissions have a granny low.

ronniejoe -- thanks for that input.

Edahall -- I agree. Guess I should retitle the thread. I am going to put a NV4500 in it.

So, I need:
NV4500
NP208 with 32-spline input
flywheel
clutch
stock pedal assembly and clutch master
possibly an adapter for the speedometer, if it has electronic sender.

Anything else?

[ronniejoe]

I didn't really mean to scare you away from it. My uncle has a 1984 K2500 truck with 6.2 and TH400 with 4.10's from the factory. It has worked well for him. I may be remembering incorrectly on the axle ratio in the truck that I did the swap in. That guy had chewed up two or three 700's and wanted a stronger transmission. That's why he went to the 400. His engine may have been a weak one as well. As I recall, it had a lot of miles on it. His main complaint after the swap was that he couldn't get up a local hill anymore with comparable loads.

In the end, there is a big difference in first gear ratio between the two transmissions. That should be considered when doing this swap.

[mathias]

I had already decided I wanted the manual, so that is just confirmation. I am in the same state, as my engine is pretty tired. Hopefully my engine will last another year or two. Whenever it dies, I will probably put a cummins in it.

[Edahall]

I had already decided I wanted the manual, so that is just confirmation. I am in the same state, as my engine is pretty tired. Hopefully my engine will last another year or two. Whenever it dies, I will probably put a cummins in it.

You'll have a very unique Suburban with the manual. A few were sold with the SM465 manual but none with the 5 speed. I've got an NV5600 6 speed manual in my 1990 Suburban and I couldn't be happier. Best of all, it's plenty strong enough to handle the power of the Cummins.

In the mean time, you can do some cheap mods to wake up that anemic 6.2 that came with about 130 hp from the factory. The first thing on the list would be to open up that exhaust then the second would be to install a "J" code intake manifold. Or you could do like what I did and just modify your existing intake manifold for free. I took mine off and chipped away at the EGR apparatus in the center of the intake. Once that's all done, turn up the injection pump and feel the power.