700R4 and NP205?

I need to swap 700R4 into my 1028 and can get a great deal on a 32sp input 205 with TH400 adapter, or 27sp 205 with TH350 adapter. Found 3 different 4x4 700R4's all from 91 k5 and Silverado's.

It is my understanding that the 4x4 700R4 is a 27sp output (please verify?). Im not dead set on anything at this point other than the 700r4. I want to do 70mph without killing the motor and a twin stick 205 seems like a good idea. I will be on 37's.

What is the input spline count on my 208? Would my current 208 swap straight over to the 700R4 (assuming what I read is correct and it is in fact a 27sp out)?

The primary goal here is to get the 700R4 working. If this is going to require a output shaft change, then Im going to rebuild it and make it a 32sp while Im there, and run the "big bearing" 205. If I can avoid a swap with any of the above combin of parts that would be my first choice ($$). Am I missing any viable alternatives that would get the 700R4 in there and mate to the 205 or 208?

All 700-R4s are 27 spline. The spline count on your TH400 is 32, so the input on the 208 will be the same, 32. The 208 nor the 205 that was behind a TH400 will mate to the 700-R4 without changing the input splines on the TC to 27. If you really want a 205, you will have to find one that was behind a TH350, 27 splines. 27 spline 208s are easy to come by. I have a rebuilt, never installed Northwest fabworks small bearing 27 spline 205, but you are too far from here. You really don't need a 205, the only reason they were installed on the M1031 was to run a generator.

wayne pick said:

All 700-R4s are 27 spline. The spline count on your TH400 is 32, so the input on the 208 will be the same, 32. The 208 nor the 205 that was behind a TH400 will mate to the 700-R4 without changing the input splines on the TC to 27. If you really want a 205, you will have to find one that was behind a TH350, 27 splines. 27 spline 208s are easy to come by. I have a rebuilt, never installed Northwest fabworks small bearing 27 spline 205, but you are too far from here. You really don't need a 205, the only reason they were installed on the M1031 was to run a generator.

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^ Perfect, thanks. For the price of a kit that will allow me to adapt the TC to 27sp I can buy a 205, twin stick it, and a clocking ring.... So Im going to get a TC regardless, might as well get a 205, because its stronger. I agree, I dont "need" it, but I need a TC soooo. Or this is my logic anyways.

Ok so if I pull the trigger on the 27sp 205 with TH350 adapter that I have available to me right now, this will bolt right up to my 4x4 700R4?? I read about this 2" spacer and possibly some redrilling?

That depends on how far the output shaft sticks out on the 700-R4 you have. A stock 700-R4 that had an NP208 behind it will have a long output shaft as they had the round 6 bolt adapter on them. So yes, you will need the 2" spacer and the shaft coupler sleeve to mate to it to the figure 8, or racetrack bolt pattern as it is sometimes called 205.

A short output shaft that sticks out approx 3/4" can be installed in the 700-R4 to simplify adapting the 205 to it. You do not need the 2" spacer in the short shaft installed. Advance adapters has this shaft. the trans has to be completly torn down to install the shaft. Using the 2" spacer will require shortining the rear driveshaft and of course lenthining the front shaft. A 27 spline 208 TC is far easier to put behind the 700-R4, It's a boltup, and no fooling around with driveshafts.

Oh BTW, If you can find the later model 205 with the 6 bolt round pattern, it is also a boltup with no driveshaft mods or input couplers needed. The 6 bolt 205 is hard to find as their production run was short and they were discontinued completly as an option.

The one possible advantage the 208 has over the 205 is a deeper low range. 2.61 to 1.

Yup, and with the 700-R4s first gear ratio of 3.06 to 1, compaired to the TH400s ratio of 2.48, it will crawl pretty well off road fully loaded with firewood or whatever.

How common are 700r4 208s? I see a bunch of 205s for sale. So a 208 from a th350 has the same spline input and adapter as the 700r4 208? How about the 208 output differences between a 208 from a 400 vs 350 vs 700r4?

Tons of half tons, blazers and half ton burbs had the 700R4/ 208 combo. One of the easier finds in the 80s.

Thanks. All the early 90s 700r4s im running across are 241s. Maybe I need to cast a wider net. My thought was the later 700r4s would benifit from years of product development and revisions that would lend to the durability of the trans.

How about the output commonality between 1/2-1ton 208s? Are they the same from a 400 350 and 700r4?

I think the 241 came into play in 89 or 90. I have one of these with a 700 ready for one of my CUCVs.

'92 was the last year of the 700r4, after that it became the 4L60e, electronically controlled. You want an '87-'92 700r4 ideally. There were tall and short adapters for the 700r4/208, you want the tall adapter.

All 80s GM transfer case outputs to driveshaft yoke are 32 spline.

Ill hit the local JY's this weekend and see what I can come up with. Side note, at some point I will likley be asking to borrow a TV bracket from a DB2 IP from someone that has been able to score an OE unit. I need to fab one and Ill make a drawing while Im at it. Of course Im happy to pay shipping and will paypal a few $$ for your trouble. If I cant make this happen maybe some pics of the bracket in lieu of....

What would the tall adapter come out of? Found a 85 208 but its a short adapter.

You guys got me on the right track, thanks.

I found my tall adapter under a k5 at the junkyard. I don't know what year it was. You can also find them on auction sites.

I used the short adapter on my 700R4/208 swap. I simply made a little spacer to raise the shorty adapter. A link to my swap thread is in my sig line

I have found a 208 27sp but it comes with the shorty... im not keen on forking over $50-$100 for the tall adapter for a $100 tc. I guess nothing some square tube and angle can't take care of.

Thats a good score for a TC and adapter. Around here just a TC will run you no less than $150.00.

albersondh said:

I have found a 208 27sp but it comes with the shorty... im not keen on forking over $50-$100 for the tall adapter for a $100 tc. I guess nothing some square tube and angle can't take care of.

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If you look at my install thread, you can see that I used some 1" key stock and a piece of 1/2" bar stock to make mine. 1x1 bar would work as well, but we had the key stock laying around at work. It was an easy thing to make and the 2 1/2" is a perfect height for the adapter

What (if anything) is different about mounting the 241 vs the 208 behind a 700r4? Looks like the 241 is a tad deeper reduction, has revised lubrication, and SYE is available.... Maybe a good option?