Adapt 4x4 Th350 in Place of 700r4

[HotRodPC]

As most of us know already, Tranfer Case adapters for 700r4 usually fit Th350 also, and vice versa. This is because the tailshaft housing bolt pattern is the same and so is the output splines meaning, they'll share the same driveshaft yoke.

Here is where the 2 differ and why you simply can't swap a Th350 in place of a 700r4 and vice versa. The reason is, because the 700r4 is longer in the main case before it gets to the tailshaft. So what happens, is the crossmember needs to come forward if your using a Th350 instead, and also you'd need a new driveshaft since it would be short.

Today I happen to be at Pull a Part and seen a 4x4 Burb. It was gutted, except I could see the trans and tranfer case hanging down from a distance. I looked inside the Burb and seen the gear shift indicator was D 321 telling me it was originally a 700r4 which is correct for an 85. Just happened to look under it and seen a Turbo 350 and NP241C. Walked off and then all of a sudden it him me. I bet there is an adapter for Th350 to 700r4. There sure was. Its an expensive adapter. I've been told about $225. It took me about 15 minutes total to get it and I bought it for $5. I also got the hardware that goes with it.

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[HotRodPC]

So what's the purpose of downgrading to a Th350 from a 700r4??? Well, calling it downgrade is a matter of opinion, and actually depends on what your intend to use the truck for if its actually a downgrade. Most will make this conversion for 1 of 2 or both reasons as I am going to for both reasons. #1, the Turbo 350 can be buillt stronger than a 700r4 and much less prone to failure, espeically in an abusive use situation.
#2, the cost to build and beef up a Th350 is much cheaper than building and beefing up a 700r4.

What are you losing by going to Th350 from a 700r4? You're losig a lower first gear. 700r4 is 3.06:1 while Th350 is 2.52:1 first gear. But you do gain a better transition to 2nd gear where 700r4 is very wide ratio to get to 2nd gear. Also of course you lose overdrive, so if its a vehicle intended for alot of highway driving, I'd avoid this conversion.

 

[HotRodPC]

What does this adapter do? It equals the length of the T350 to the 700r4.

Here is a pic of the ends of the cases. Pics don't show it, but the bell housings are matched up side by side. Notice the black Th350 case is shorter than the silver 700r4 case.

 

[HotRodPC]

Now the adapter is in place. Its not up tight since the bolts are not tightened, but you see the difference and what's going to happen here.

 

[HotRodPC]

Are you wondering about that output shaft yet on the Th350??? Notice its to long compared to the 700r4? This is because that is a 2wd Short output shaft for a passenger car. Remember the output shafts on 4x4 transmissions are shorter stubs, just long enough to marry the splines of the Transfer case. With the adapter, an OEM 4x4 Th350 output shaft would be to short. So what's going to happen next, when I get to it, is this 2wd passenger car output shaft will be cut off approximately 1 1/2 inches, so that it will match the overal length of the 700r4 4x4 output shaft. Even with the cut-off, there will be the same or more spline length into the tranfer case and all will be well.

With this adapter, the Th350 will use the same Tcase, Tcase mount, Tcase linkage, crossmember, OEM crossmember position, and also the same driveshafts and yokes both front and rear. Now I'll be able to install either this Th350 or a 700r4 without any other modifications. Man, I love having options without grief. All for Fi Dolla !!! It does pay to pay attention and check things out. Sure glad I tripped over that part because I sure wouldn't have spent that kind of money to buy one.

 

[Swims350]

they make a kit for this with the right length shaft, northern auto parts has it and somebody else tci i think. It's what I bought. Kit is like $150-200 but it has a dipstick, kitdown cable, the adapter, gaskets, bolts, nuts, flexplate dust cover, the shaft, and maybe other things I forget. I did this in my 88 k1500.

 

[HotRodPC]

Glad to hear such kit exists for those who need it. When I hear or see the word "KIT" that usually tells me its to much money. They are usually charging for assembling what you'll need to make a conversion. I got the hard to find part for $5, the rest of it i'll gather the parts up myself and make my own correct length output shaft and save a bundle. I'll run this Th350 in this truck, then the 700r4 I have set aside for this truck, I'll put in the other K10 with the 4.10's when I'll want that OD and the lower first gear. But now, this will take some pressure off me. I've been debating whether or not to pull the 700r4 K case apart for a build, even though it doesn't need it, to beef it up for strength. Now, I can do that since I won't be using it in the 85 K1500 and the rush is off.

 

[89Suburban]

Good ****!!!!

 

[Manbearpig]

Looks like whoever swapped a TH350 in my K5 used the stock 700r4 driveshaft lol

Not sure if it has that adapter

 

[HotRodPC]

I assume you might suggest that because 6 feet of yoke is showing??? Really, its only an inch and half or so differant, so if the yoke is long enough, I can see someone might make the stretch. That's all fine if your rear end doesn't drop down to low and pull the driveshaft yoke out, or get the to the point you're barely grabbing splines.
What normally would happen to make the swap, move the crossmember forward, so now your Tcase shift linkage is to long. Front driveshaft is now to long, rear driveshaft is now to short. The mods can certianly be made to make it work and be safe and functional. But, I prefer the adapter because then there is no other mods that would need to be done. I just prefer to do it the right way, so that I have more options. When I finally get this truck running, I am likley to be like I was when I was younger. I changed engine and transmission combinations like I changed underwear. So I love the idea of interchangeability. I might just put the 4.56 CUCV rear end in this truck if I find a 4.56 D44 or 10 bolt 8 lug front axle. If I do that, then I'll go back to a well built 700r4.

 

[Swims350]

ok here's some links for ya on the swap kits....

http://www.summitracing.com/parts/TCI-329900/?rtype=10

http://www.bulkpart.com/Merchant2/m...oduct_Code=7-35A&Category_Code=350-350Cswitch

http://www.compperformancegroupstor...Screen=PROD&Store_Code=TC&Product_Code=329900

 

[HotRodPC]

Great info Swims. So its not as expensive as I was told. I was told $225. Maybe so with shipping and the $204 kit. But I was also told that didn't include the output shaft. I know I can cut an output shaft to work, but now maybe I should go back and get that output shaft out of that trans. Here is the bad deal. At our Pull a Part, they will not sell transmission or motor parts. Example, an output shaft, or a rod and piston. Apparently its against the rules to disassemble engines and transmissions. Someone has already jacked the valve body of the transmission, so I sure don't think I shuld have to pay for a full transmission.

Here is the aluminum adapter only. You'd still have to modify an output shaft.

http://www.summitracing.com/parts/add-7q-35a

 

[HotRodPC]

I went ahead and went back to PAP today. I gutted that Th350 to get the shaft out of it too. Knowing they wouldn't sell to me if it was a trans part, the girl asked what it was, I said a driveshaft yoke and she sold it to me for $8.

But as I had said before, I intended on cutting down a short output shaft. Obviously it'll work, so while I have the shaft to the kit out now too, I'll go ahead and match them up, and cut the 2wd short shaft to match so I have a spare incase for a really wierd event, break the output shaft. Of all the years, I've never seen a Th350 break an output shaft, but you never know. Better safe then sorry.

 

[HotRodPC]

With my precision set of power tools.....

I was able to cut off the 2wd short output shaft, and make me another modified 4wd output shaft for the Th350 adapter. It doesn't look it in the angle of the pic, but rest assured, its cut square and is the exact same length.

 

[crazy4offroad]

As long as you went really slow and didn't overheat it, it should be fine. A wet saw is the best way to go. If the one you cut is the one on the left in the last pic, WOW it has some good, deep splines.