Adapt 4x4 Th350 in Place of 700r4

[HotRodPC]

Yeah, you want to keep them cool as possible so you don't distupt the heat treat temper. Yes, I cut the one on the left. It does actually appear to be in better shape and look stronger than the one that came in the kit. I have already pushed in the Tcase adapter, nice and snug fit and went in and came out very smooth. I'm planning on using the one I cut and keep the other one for a template. You know thats not an OEM 4wd output shaft. Its the special one that works with the apapter. But doing this one, did bring something else to mind. I can easiy cut down a 2wd 700r4 shaft to be a 4wd shaft.

 

[Swims350]

a word of advice to you, I bet you already know it or thought of it, but change the t-case input seal.

I did not change mine in the 88 and now it leaks trans fluid into the t-case and overfills it.

It's like a front pump seal on the trans, I guess anytime you have converter out you change it to be sure, guess the same goes for the T-case.

 

[crazy4offroad]

I agree, cheap insurance while you're in there. I have a lifetime warranty clutch for my truck and you can bet if the throw-out bearing is bad I would be swapping everything else while I have it apart.

 

[HotRodPC]

I intend on ordering a gasket and seal kit and resealing the whole Tcase. I am even considering bearings and races too. Just not 100% sure yet. It feels good, but I know I want to reseal it just because, and I'm thinking while I'm in it and got it apart, may as well do it all.

 

[Swims350]

wouldn't hurt a bit, new bearings and races is cheap insurance and you'll have a new trans and new t-case then.

I only wished I would have changed my seal, I hate the thing overfilling the t-case.

 

[HotRodPC]

Here is a comparison pic once again. From left to right. The one on the left is the one I cut for the adapter kit to make the th350 the same length as a 700r4 so it will fit both my K1500 and K10 without any crossmember or driveshaft mods since they were both OEM 700r4. I'll keep the Th350 for a back up trans for when I break the 700r4's. The one in the middle is a short 6in shaft which is the size I cut down for the adpater shaft. The short 6in shaft is usually found in passenger cars. The 3rd one on the far right, is the intermediate 9in shaft. Most will refer to it as long shaft, but is actually intermediate since there is also a 12in long shaft which is a bit rarely seen these days and not pictured here. The 9in Intermediate shaft is the size of output shaft used for Squarebody trucks starting in 73 up until the 700r4 replaced the Th350. So I started with a Squarebody 2wd transmission. Cut down the shaft of a passenger car output shaft and put in the OEM squarebody intermediate shaft case to make this Th350 for my 4x4 trucks. So the other 2 sizes of output shafts not picutred for Th350, are the actual 4x4 output shaft that does not need adapted, and the long 12in 2wd output shaft. So there are 4 OEM output shaft sizes, then the adpater 4x4 size that is made from an OEM shaft to match up to the 700r4. Confusing I know. But its actually quite simple.

 

[Zoolo42]

Hey guys noob here, my 700r4 just went out
In my 87 v10. My buddy has a 350/205 for me
If I want it, what I'm asking is will I have to use
This kit and also will it work for a 205 behind the th350?

 

[HotRodPC]

NO, this kit will not do you a bit of good. You'll have to get your driveshafts worked over to fit this this whole new combination. Quite worth it though. The NP205 is about bulletproof being a gear to gear driven unit where the aluminum case NP208 that you have now is chain driven. The Th350 is quite strong too and will tolerate much more abuse than the 700r4. If you can afford the driveshaft work, and don't mind losing Overdrive, you'll have a much stronger combo. Also, ask your buddy if he has the front driveshaft from whatever he got the Th350/NP205 out of, that will save you half the cost.

 

[Zoolo42]

Thanks for the info! I'll ask him about the front driveshaft
And what it came out of.

 

[jelawrfarms7]

oh I have a 700r4 with what I believe is a np203 case and I can get my hands on th350 4x4 trans with or without tcase would this help if I use the current tcase in the truck??

 

[HotRodPC]

Welcome to GMSB Chris.

If you're wanting to convert from a 700r4/NP208 to a Th350/NP208 without any driveshaft mods, exhaust mods, or crossmember mods, the Th350 you actually want to find is a 2wd short shaft. The one most common in passenger cars with a 6in tailshaft. Reason being, you're going to do away with the tailshaft, BUT, you'll have the output shaft long enough for the spacer, then you'll cut that output shaft down about an inch IIRC, to fit your current NP208 and it's apapter. You should be able to easily find a 2wd 6in tailshaft unit.

Now if you're buying the whole space kit with the shaft and all already in the kit, then it doesn't matter, just get any Th350 core you can find, and use that output shaft. Now the 4x4 Units do have the bigger bolts at the bell housing for bolting support rods, but honestly, I Think on the Th350, you can do some some drilling and make the holes bigger, or use smaller bolts and still use the support rods if you wanted. Also with this mod though, you will get to keep your support rod from the 700r4, Tcase to bell housing, so you may not need the under the bellhousing rods. Up to you.

 

[buckethead27]

hey guys quick question, I am running a th350/np203 combo, Im wanting to put in an np241, Ive bought an adapter that ran in the 81-82 trucks that came with the 350/241 combo and I was wondering if there was anything else I would have to do as far as crossmember movement, driveshaft modification and so forth. Ive been searching for days now and hopefully some of you guys will be able to chime in and help me. Thanks in advance, Jordan

 

[HotRodPC]

hey guys quick question, I am running a th350/np203 combo, Im wanting to put in an np241, Ive bought an adapter that ran in the 81-82 trucks that came with the 350/241 combo and I was wondering if there was anything else I would have to do as far as crossmember movement, driveshaft modification and so forth. Ive been searching for days now and hopefully some of you guys will be able to chime in and help me. Thanks in advance, Jordan

NP241 was NEVER mated up to a Th350. NP241 came about in the late 80's but does have the same mounting specs as a NP208. But again, NP208 was never mated to a Th350 either. The Th350 output shaft for a NP203 will be to short to reach the splines for a NP208 or NP241C. So that will be your first problem.

I am not familiar with the mounting location of the rear mount on the NP203, so I'll someone else answer that portion.

 

[bucket]

The 208 was indeed available behind the th350, but it had a longer trans output than the th350 used with the 203 and 205.

 

[HotRodPC]

The 208 was indeed available behind the th350, but it had a longer trans output than the th350 used with the 203 and 205.

Yeah I guess so huh? That would have been 81 for sure and some 82's that weren't 700r4 yet. But still, his output shaft wouldn't work having a NP203 unit.