chevy 700 R4 swap

Heck, I do that all the time; thought it was normal. And I swear, the older I get, the worse it gets. :>)

You made a very good point though, those 400s take that electrical kick-down switch and all the associated wiring, connectors, etc. that goes with it.

Plus the fact that the 400's upper kick-down speed is limited by governor pressure and depending upon the truck's gear ratio, this limit could really be kinda cumbersome.

That's why a lot of those heavier trucks with the 4:11 or 5:56 rear ends (after a 400 conversion) won't ever drop back down into 2nd at any speed higher than around 35 to 37 mph.

Have a good one,

Allan

You may not be a transmission expert, but you sure know what you are talking about. That vacuum control probably looked something like this one? I can't remember if I yanked this one from a 6.2 or 5.7.

And you are right; a lot of those original 700 equipped trucks wouldn't even back themselves down off the transport. They were a real headache for many years.

Additionally, remember how they used to blow those front converter seals out? Took a number of years for GM to get that one right; we were drilling oil passages for what seemed like forever.

Regards,

Allan

That 400 will require a special adaptor to marry to your transfer case. It is the part that bolts to the cross member & also to the front of the transfer case body.

The back of the 400 case has a different bolt pattern than the 350, 350C or 700's do. It's kind of a round gizmo instead of square.

Allan

long story short-a 350 makes a dog out of a driveline set up to take advantage of overdrive.

7-8 months later, a transmission shop reinstalled my rebuilt 200 and I've since put over 60,000 miles on it. (and the rebuild cost less than the rebuilt 350+ the conversion kit).

I whole-heatedly agree. It is kind of a 'shocking' step down.

The reason that little 200 gave you so much better mileage is because even though it is still just a 3-speed, it has the added lock-up converter, which locks in after 3rd gear applies and it will add about an 8% increase in overall fuel efficiency.

The fastest tranny job I ever did was on a 200 in a little Olds Cutlass, I think it was. The car jockey pulled it on my hoist, I yanked it, overhauled it & threw �er back in the car and it was 5 1/2 hours later that I pulled the car out for a road test. Job paid me something like 11.5 hours flat rate, if I remember right.

And those 200s were pretty darned tough too.

Regards,

Allan

Just had a thought. It is hard to imgine that that old original tranny is still in the truck; they just did not last very long. Maybe the little guy has already been updated.

What is the truck doing? What are your symptoms?

Tryin' to help,

Allan

All rested up from your trip? :>)

The trouble with the 200 idea is that he has a 4X4.

A 200 won't marry up.

Allan

I wasn't very clear on my post.While the early TH700 had the same splines as the TH200R4 I would never consider swapping a 700 for a 200. What I intended the TH200R4's were no prize. And the later TH700's with more splines and a host of other internal improvements were a decent transmission. I think the TH4160 ancestors are the TH350 and TH700? I had to back to work for a rest. The other guys on the trip are 60yrs with diabetes, 65yrs and 82yrs. Made for some lugging and slugging through some thick wet country. To get the two moose out. Field dressed, quartered, hauled back to camp, hung, loaded onto the airplane, unloaded and loaded into the trailer, hung in the garage, that hauled again to the butcher shop. Plus doing the firewood and cooking. Then came back to the place to find more labour to repair stuff busted/wrecked by the kids.

No the 4L60 is a 700. It is just GM's new designation.

It stands for 4 speeds, mounted longitudinally & with a power rating of 60. Likewise, that overdriven 400 is a 4L80(E) and those transmissions in a lot of the full sized front-wheel drive cars were 4T60's (transversely mounted overdrives).

Those little 125s were then named 3T40s and the larger Eldorado and Rivera�s tranny, which was nothing more than a 400 mounted crosswise, became either a 3T80 or a 4T80 (overdrive model).

When they went electric, they then became the 4L60E, etc., etc. with the �E� designation on behind the string of numbers and letters.

Okay, off my soapbox before I slip and lie again. I hate it when I do that! :>)

Glad ya had fun up there,

Allan

Those 700s from 83 thru 86 were a nightmare and the worst tranny GM ever built.

I can see where you would like to save some cash since this is your old beater, but are you sure you want to drop down to that old 350?

In 1991, GM bullet-proofed that guy so you might consider a used unit? (Pretty iffy, I know).

However, the absolute best fix as far as reliability goes, is to drop in a SERTA. Expensive, but they are nice.

Hope ya get 'er goin',

Allan

You use a THM-350 with a short 4X2 tailshaft, and cut off a bit. This will still be longer than the stock 4X4 THM350 tailshaft.

If you can't find a local supplier, contact Advance Adapters through the "contact" link on their website. They should have what you need, and be able to put you in touch with a dealer near you.

(Also, a local wrecking yard might have a used kit.)

The adapter kit is not cheap though, and, if you have to pay much for a good THM350, plus the kit, you'll be getting up to the price to repair the THM700R4.

As I'm sure you're aware, highway mileage will suffer without the overdrive tranny you know have.

• advance adapters

The 700 and the 350 are exactly the same length.

Allan

The case length is about 1-3/4" longer on the 700R4.

Here is a link to a Hot Rod Magazine story that backs me up in this:

Link

Look at the "mount position" specs. This is measured from the bellhousing face to the C/L of the rear mount bolt holes.

The rear mount bolt holes are NOT USED on the 4X4 application, but are in the same position relative to the rear flange of the tranny case. The THM350 dimension is 19.5" and the THM700R4 is 21.25"

Hey! What's with this "ampacity" thing anyway. LOL!!!!

How come that feller is doggin' me and a following me around all over the place like smell on a skunk? :>(

'Twasinit' my (so-called) word. My Webster's is rejecting it too. :>)

You're probably right 'bout the case lengths; I think I was thinking 350 vs MV-4 (350C).

Sorry, should have kept my yap shut yet once again. (Boy, this is gettin' to be a habit, eh?) :>)

Thanks Pard,

Allan

Looking at it another way, you say you don't want to put much money into it. Well, it isn't worth anything without a trans. Can you buy a replacement vehicle for $700? Probably not.

With the proper adapter which probably cost $700 there is no change in the drive line. Shifter, kick down cable and vacuum line are not hard to do either. The detents are in the trens. I put a TH350 in my 65' Sub and didn't have to do much. Used a drive line from one of those old Chevy station wagons.