Hello all,

I have a 1979 K5 and I'm swapping out my TH350/NP203 for a 700R4/NP208.

I was hoping that before I got too deep into it that some of you might have some helpful tips and tricks for this swap as it seems to be common. If I needed to mod or purchase any new connectors, brackets, or levers etc... that it would be easier to do now than find out midway and grind the work to a halt while installing.

I am aware that the crossmember will have to be relocated back roughly an inch or so as the 700R4 is a bit longer than the TH350, and I have the drive shafts from the donating Blazer as well so driveshaft distance should not be an issue. I have already dropped the TH350/NP203 and would like to change anything else needed while I have the room and ease of access. Any help would be appreciated.

Thanks,

Chris

 

The transfer case shifters are quite a bit different so you will definitely want the shifter from the donor truck. I believe that the NP208 equiped trucks also used a torque rod to support the dropped side of the transfer case.

 

Thanks for the reply.

I do have the torque bar. But I did NOT get the shifter parts. But thanks to your quick reply I called the owner of the donor rig and he still has it in his driveway so I'll be picking it up tomorrow. THANK YOU. It is so much easier grabbing it off his rig than searching around. He will be crushing it soon though (the frame is cracked in 4 places) so if there is anything else anyone can think of let me know.

Thanks again!

 

Hi again. I have the engine, tranny, and transfer case all installed now, and fitted the front drive shaft fine. The rear shaft U joint does not mate up with the rear yoke. It is too big. I spoke to some people and they say there are U joints that have different size caps on each axis for this type of situation. Has anyone run into this before or knows the part number for this type of U joint? '85 model year U joint to a '79 yoke.

I'm going down to the garage to mess with this some, but thought I'd post this question before my hands got greasy.

Thanks.

 

They are called conversion u-joints. NAPA is one place that I know sells them. You need to take both u-joints with you and they should be able to determine the proper conversion u-joint.

 

try autozone part number 3-3130. pretty sure thats the one i used when i went from a th350/203 to th400/208. but as swartk said bring them both up there too to make sure they pull the right one. and remember that part number cause i had to argue with them before cause they said they dont sell anything like that.

also your gonna need some kinda converter lock up device or else you are gonna burn up the trans. dont really know much about them, im usually ripping out 700r4s instead of putting them in

 

Great to know the U joint is something fairly easy to get. I'll remember that number and take the stuff in to double check. Thanks guys.

Thanks for the tips on the trans. This is my first 4x4, so forgive me for not knowing all the lingo yet. I AM catching on quick though. But, what is a lock up device, and what does it do? After all this work rebuilding this blazer, I'd hate for it to get F'd up.

My understanding was that the TH350 was a fairly solid trans, it got bad milage and was mainly a low end torque trans with 3 gears. The 700R4 had a 4th gear and had a great 1st gear torque and actually got decent milage. I didnt really see much negative feedback while researching it. I also got a smoking deal on all the parts too from a guy parting before crushing due to his frame being cracked. $75 for the trans, xfer case, both drive shafts, spare tire carrier, spare tire, 4wd shifter and linkage with boot, and a 4 core radiator, fluid lines and torque arm. I couldn't help throwing a few 24 pks of PBR in there for him too. :-) I've put all that in plus a set of 33's, a 4in lift, refreshing and repainting everything we can while we had access to it, headers, and dual exhaust over the last week and a half with just my 15 yr old son, some patience and a good radio station. ;-) Most everything was fortuitous craigslist finds, but I've been careful.

We have been busy, and are pretty well worn out at this point and wanna see this done and enjoy it! I've taken a pretty good set of documentation pics as well and am planning to post when complete, along with experiences and info for what I've done for others.

Sorry to ramble. I seriously appreciate your help and guidance. THANK YOU!

 

ive never had any problems with the 700r4 but everyone i ever owned have been in street trucks. alot of people complain about them holding up to abuse offroad.

as far as that lock up device goes. as i said i really never had any problems with it so dont know much about it. its something to do with overdrive, it locks up the torque converter other wise it will slip and wear out prematurely. something like that. google around. sorry couldnt be much more help on the matter

 

Sorry for being away a few days. I went back to work, so less time to fiddle in the garage. Gotta pay the bills, right?

Ok, so I have got some picks of the electric line issue I face at the moment.

The trans has a two pole plug that plugs into the passenger side that is routed from the transfer case shifter linkage assembly. It has two wires, one black that is loomed in with the light from the boot casing, and a white-ish one that is not. After looking around the net for some answers, I feel more confused than I started. I'm pretty sure the black is a ground. the white is probably +12V. Is this right, or am I assuming wrong? Also, after researching, I am hesitant that my '79 has the right outputs as I have stock cruise control, and I am finding some confusing info out there as to how that plays into this situation. All that was there to begin with was a two pole flat plug set 90degrees to each other, and probably a vacuum for the CC which I can not confirm was hooked up. I used the CC before once and it seemed fine, but i honestly don't recall pulling off any vac lines when dropping the trans. I honestly don't use it much anyway, but if I don't do it now, I might never get back to it. So I figured I give it a shot at doing things right the first time. Here are the pics for reference.

 

Anyone?