700r4, gas to diesel difference

[Itali83]

Ok guys, long shot here but has anyone ever put a gas 700r4 behind a 6.2? I’ve come across a super cheap and supposedly good 6.2 I just can’t pass up. Been thinking about swapping a 6.2 into my 76 k25 and running a 700r4 and np208 transfer case. I’ve never cared about gas mileage but this last year has changed my mind a bit. I want to ditch the full time 203 transfer case. I’m getting 22mpg’s from my suburban with a 6.2. So I figure I can get mid teens from my k25 with a 6.2/700r4/208 set up.

Anyway. I know the governor is different for lower shift points. I know the torque converter is different. I’ve been searching the internet and some say the valve body is different. Some say it’s not. That’s my biggest worry. I don’t want to deal trying to find or buy new a diesel valve body. It’s going to cost more than all the rest of the parts for this swap since I’ve got a good 700/208 combo and getting a 6.2 for dirt cheap.

Any thoughts or facts?

Ben

 

[CheemsK1500]

While a 6.2 isn't exactly a power house, I'm not sure if I'd trust a stock 700r4 to go behind it, whether it fit or not. I'd suggest selling the 700r4 and finding a TH400. If you are good with electronics, a 4L80 could work nicely, if adapters exist for it.

The 700r4 was intended for use in 1/2 ton gas trucks and small cars, putting one behind a diesel of any sort would probably be tempting fate. If you never towed anything heavy with the truck, or got crazy with aftermarket performance modifications, you might be able to get away with using one though.

 

[Turbo4whl]

The 700R4 was the very transmission GM used in the 6.2 when it was introduced in 1982. If you have a later model 700 with all the fixes GM did you should be fine. I'm sure the shift points are different between the oil burner and the gas engines.

 

[Itali83]

Yeah, I don’t want to hear how weak or trash the 700’s were. I’ve only ever had 700’s and never had one let me down. I’m not a savage, don’t haul 20k and I make sure the converter lock works on them all.

In my experience, the converter lock system is the fate of all 700’s. Everyone and their billy bob brother love to cut and throw away all “them electro digical gizmos” under the hood they don’t understand and end up never having the converter lock up again. Then a few months later that ends up with “ f’n junk 700r4 done blow’d up again!”

Anyway….. yes the 6.2 couldn’t pull an old lady off a piss pot. I know that. I own one, guess what, it has a 700r4 behind it too…. Factory even.

I’m only looking to make my truck a little more efficient to drive daily and easier on the wallet in these crazy times.

If anyone else has some pertinent replies, love to hear them. Thanks
Ben.

 

[CheemsK1500]

Today I learned the 700r4 was a factory option in a 6.2. I've never owned a 6.2, I always just assumed they were wall equipped with 400s this entire time. Sorry for my bad advice earlier...

 

[Rusty Nail]

I dont know the reason that would be a bad idea if you could bolt it together sans jankiness. Kinda sounds like a match made in heaven if ya do it right. An idea is to be wary of voltage loss in the electrical connections because it prolly wouldnt take much to muck it up.
I'm under the impression that could be real important.
What low speed torque converter is available?

 

[Itali83]

I dont know the reason that would be a bad idea if you could bolt it together sans jankiness. Kinda sounds like a match made in heaven if ya do it right. An idea is to be wary of voltage loss in the electrical connections because it prolly wouldnt take much to muck it up.
I'm under the impression that could be real important.
What low speed torque converter is available?

I would just get a converter specific for the 6.2. As for the lockup circuit, I don’t like the factory throttle switch that my suburban has. It’s very primitive and always unlocks the converter at idle so every time you let off to coast, the converter unlocks. The unlock under throttle is at about full throttle so I didn’t like that either.

So if I end up doing this swap, I’m wiring the lockup solenoid directly to a toggle switch and my brake switch. That way, I can lock it in 2nd, 3rd or 4th. Unlock it when I want etc etc. so power to the solenoid would be easy.

Ben.

 

[Vbb199]

The governor and TC is the only thing that's different.

Nothing else.

 

[Vbb199]

87-92 is the ONLY 700r4 you want.

 

[Matt69olds]

87-92 is the ONLY 700r4 you want.

Install a diesel specific converter and governor. A TransGo shift kit would be a good durability improvement. Make sure the TV cable iscorrrct (close is NOT good enough!!) and make sure the converter lockup works. If your working it, install a hood oil cooler.

 

[Itali83]

The 700 I’m going to use is from my ‘89 parts truck. Was a good running truck. Just rust got the best of it.

Already have a big cooler in the truck. I don’t use the truck for anything but a pickup. May haul a trailer once a year to haul another square I buy or something like that. A load of bark mulch or something from time to time.

I’ve been driving squares since ‘99 and all have been 700’s. Never had one give me problems.

Ben