TH350 to NP208?

[398HBX]

I did a quick search on the forum but could not find what I was looking for. Mainly advice from people who have "been there, done that". I'm hoping that you guys can help. I am rebuilding my father-in-laws (Stan)73 K5. I am using an 86 K20 Burb as a donor. I would like to use the NP208 out of the K20 instead of the NP203 out of the K5. I have a new B&M TH350 for the K5. The K20 has a TH400HD/NP208 combo. I am swapping the axles from the K20 to the K5. I would like to have kept the TH400/208 Combo intact but Stan made a valid point: why put a 26 year old transmission with over 100k miles on it instead of a new B&MTH350 Competition?

Here are my questions:
1. Where can I buy and adapter kit to connect the TH350 to the NP208? Other than Advance Adapters (Expensive).
2. Would I use the W crss member out of the K20?
3. Will the frame cross member bolt up to the same frame holes?

I could use the NP203 with a part-time kit but then I will have to change output shafts to match up with my 14BSF rear axle and 10 bolt front axle. I think?

Any help is greatly appreciated.

 

[obijuan]

to put a 208 where a 203 was you need to swap out that output shaft on the trans. thats reason enough to not put the 350 in it.

th400 32 spline, th350 is 27 spline.


there are factory 350 208 combos but still use the different output shaft that you have. they are the tall adapter so you have use your flat crossmember.

if you do end you with the 86 400/208 in the k5 you can use the W crossmember, might have to drill new holes though.

 

[398HBX]

Thanks! I did some more research and it seems like my best option ($wise) is to stick with the TH350/NP203. Go to know about the cross member, I would probably used the W and then realized that I f'd up. The part-time kit from Mile Marker is only about $50 and would give me the part-time that the NP208 would. The only thing that I think I will need to change is the output yokes to match up with the driveshafts for the 3/4T axles.

 

[79rustyk10]

Should be too bad to swap the tail shaft of the TH350, or have it swapped.

I would just find a 27 spline 208 to go with it though.

I have a TH350/203 setup in my truck now. I have a core th350 Ill put together for it and drop the longer output shaft in so I can use the 208 with that one. Kills 2 zombies with one bullet, get a better built transmission and a better transfer case at one time.however Ill have to get a new rear shaft built to work with that.

 

[1BEATK5]

i would sell the t350, use that money to overhaul the t400 with a shift kit and what not. sell the 32spline 208 and get a 241.
but thats my opinion.

 

[4X4HIGH]

I would run the 400/208 combo. The front driveshaft from the burb will work and the rear shaft from the burb would need to be shortened. Goin this way you get a much lower low range gear than the 203, you get a part time t-case, a much lighter t-case. As long as you're not plowing over rocks the aluminum t-case will hold up just fine. At this point you could sell the B&M 350 and use that money for something else on the rig after you used a portion of it to have the rear shaft shortened. Don't forget that you would also need to use the t-case shifter from the burb.