NP 208 swap

[wpdozer]

Hi all, Im swaping out the NP 205 to a 208 on my M1031 so I can install a newly rebuilt 700R4. I don't want to tear down two transmissions to swap the Advance Adapter 32 spline output shaft from the old trans to the rebuilt one to bolt up the 205. Will I be able to retain the 205 shift linkage? There is no provision for the linkage pivot on the 700R4 to NP208 adapter/trans mount. Does this sound crazy, or should I swap the 32 spline shaft and stay with the far superior and bullet proof 205? My only other option is to put a far superior/bullet proof TH400 back in the truck, but to do that and be able to run this truck at highway speeds I would have to lift it 6in and run 37in tires. I hate the 700, My Banks 6.2 is killing these transmissions.

[Robyn]

Hi

You are in a spot that many folks have been before.

The 700R is IMHO a real POS.
Now this said, it does do a much needed job, sadly GM built it a tad too light to handle the diesel.

OK all is not lost. Transgo came to the rescue many years ago.

Install a transgo "Dash 2" shift kit along woith a good cooler and your "little gear box the could" will live.

Choose the harshest settings that are provided in the kit. (they give several options of springs and other calibration changes.

As I say, set the damned thing on "KILL" and hang on.

The 1-2 shift will scare the heck out of you, but the tranny will live.

Be very careful to get the TV cable bracket from a 6.2 and to get the TV settings correct.

This makes the difference of having a long life tranny or a quick failure.

The cable on the 700 is what controls the line pressure during operation.
Actually Throttle valve pressure.
This alows the clutches/band to recieve the proper pressures to be able to hold duirng the various operating modes (light or heavy throtttle)

Too many folks believe the cable is only a kick down, OOOOPPs NOT, this is a MUST have, and have adjusted right item.

With the throttle WIDE OPEN the cable must be fully extended.

The cable has a great little adjustment. you press the little button, slide the cable housing rearward, then mash the throttle and the unit will self adjust to just the right spot.

To test the setting, do a very light throttle upshift (1-2) and then mash the pedal, the tranny should drop back to first gear.

If it does not drop the TV is not right.

Using the GM factory TV cable bracket and cable, this is pretty much a no brainer and works right every time.

OK now for the T case

The 208 uses a different shifter assembly and the one from the 205 will not work.

The 205 is probably the best case GM ever used in a rig as far as being nearly indestructible.

The 208 is of course nowhere near the box, but will as you know bolt up to the 700R easily.

Use a shifter from a rig that had the 208 (Burb, Blazer or pickup)

You may need to make a sheet metal adapter for the floor to mount the 208 shifter in, but this is an easy task
The 208 shifter ues a single rod (IIRC) and is snap to set it up.

The shifter assembly has a neat little housing that will sit down into the floor (hump) and you can adjust its position accordingly to get things right.

I would start by setting the T case in the 4 HI spot, then set the shifter in that location as well.

Next locate the shifter assembly in the floor and coonect the shift rod, from here you can make any changes needed to allow the unit to work as it should.

The old TH400 is the gold standard of trannies, but as you mention, highway speeds are tedious at best.

Swapping in the 700 requires a slighty longer front drive shaft and shorter rear shaft and most 205's used a different output yoke as apposed to a slip yoke style of the 208

all workable.

The biggy to keep the 700 alive is a good shift kit (tansgo dash 2)

Now if you want to really get a great 700, go back and read my post on building a 700R

There are tons of great HP parts for these gear boxes, that will allow them to handle far more than the factory stuff could ever dream of.

The biggest issue with the 700 is the size of the internal components and the design of the TV system.

The forward clutch drum is aluminum and subject to spine failure.
The sun shell fails
The planetary units fail
The sprag and roller locks fail
There are too few clutch plates in the high clutch
The 2-4 band fails

Sounds grim, but the aftermarket easily solves all these problems.

I have built several 700R4 boxes for 4x4 application and they will do fine, BUTTTTTTTTTTT they need to be done right if they are to live.


For light duty use (non towing) the shift kit will help a lot.


Hope this helps

Missy

[wpdozer]

Hea Missy. Many thanks for the always positive feedback! I'll try not to drone on about this 700R subject, but Ill give you a little history on my trans. As you well know, the 700R was never ment to be put in a 1ton or my truck a 1-1/4ton CUCV. The previous owner did the TH400 to an 82 700R swap without rebuilding it, it's old. he just shoved the $400 and some change adapter shaft in it to mate it to the 205. He also had the wrong tv cable on it wich I did not know at the time. I had it rebuilt in Dec of last year, $1739.00 and all of $900.00+ in parts alone, and thats with me removing and installing it. I was dissapointed with the rebuild as the shifts were inconsistant and it was all over the place. According to my invoice, It does have the Transgo stage 2 kit along with all the HD red? clutch parts, harness, all the good stuff. After installing the proper tv cable, about 6in shorter, the shifts are clean and positive and yes the 1-2 is impressive with no ill effects of having the wrong tv cable for three monthts. Proof of a quality rebuild I guess or just dumb luck. Your right about proper tv cable adjustment. With the lower 1st in the 700R and 4.56 rear I have to be light on the throttle from 1-2, if I don't i'll send engine parts through the hood. Sooo I found a rebuilt 89 700R out of a K2500 with less than 100 miles on it. I'll have to put a 27 spline 208 behind it to simplify a quick swap out if need be as I plow snow with this truck. Guess I did end up droning on and thanks again for your imput on the 700R-208 swap. I just wanted to share my experience with others to save them some of the BS I went through. Regards, Wayne.

[Robyn]

Glad its working out.

The early 700R had even more issues than the later ones. The input shaft was smaller and far weaker than the late ones.
The later "K" case 700R is the unit of choice to build up.

I owned an 82 K5 that had the 6.2 with the 700R behind it, the 700 scattered all over the street one day, so I looked over my options, and at that time the 700R 4x4 boxes were going for a premium, even used, so I opted for a TH 350 with an adapter kit.

The rig was used for daily commuting to work and with 3.42 gears I did not really miss the OD much.

Many years later I purchased another early K5 with a 6.2 and a 700R, this truck also lost the tranny and that one got a well endowed "K" case 700R with all the aftermarket goodies I could put into it.

I really wish that GM had done an OD automatic that used haydraulic controls to run the OD rather than electronics.

Mopar did this with their early OD autos and they were great.

The computer controlled stuff is OK, but leaves few simple ways to get an OD auto in an older rig.

have fun and good luck

Missy

[wpdozer]

Hea Missy, yea, I have known for some time that the ultimate solution is to loose and forget the 700R like an old crazy girlfriend and go with a 4L80. When the stand alone controllers get below $500.00, i'll go that route. At the end of the day, with cost of all the swapping, adapting and rebuilding, I should have done the 4L80 swap when old crazy blew up the first time. It's a road im going to have to cross someday.