If I have an 86 K5 with a 305-700r4-208, can I swap out the TH400-208 out of a m1009 cucv to leave me with a 305-Th400-208? I would expect this to be almost a direct swap with no driveshaft, crossmember, problems.
I can't find any write ups on this on the web. Only write ups on swaping from 400 to 700 (Who would want to do that ).

I dont have much faith in the 700r4's and also I plan on droping in a 454 in future. If you are wondering why.

 

The TH400 has a higher parasitic drag than the TH350/700R4 and when going to the TH400, you lose overdrive which is what many people want when they do the swap to the 700R4. The 700R4 can be built to handle serious power. The early versions had some reliability problems that were later cured for the most part. The aftermarket really steps up to beef them up.

To determine if they'll swap, you are going to have to get some measurements. I believe that the TH400 case is longer than the 700R4 by a good margin, but the adapter for the 208 may be shorter to give it the same overall length as the 700R4-208 when all said and done, but I don't have any hands on experience with both of these combinations to say for sure.


IMO, if this truck is going to be driven on the road, I would build the 700R4 to handle the power of your intended engine swap so you can keep overdrive to save some fuel. You also get the benefit of the lowest 1st & 2nd gear ratios of all of the common RWD GM transmissions. If it is going to be an offroad only rig, then go with the TH400.


CLICK HERE for a good discussion thread on Priate4x4.com that I found while looking for dimensions.

 

Thanks. That was a good link.

The blazer will be a streetable off road rig. So I'm leaning towards the 400 tranny.
Most poeple say the tranny is longer, have to modify, ect.
But the m1009 cucv is a k5 blazer, so cant i just use the transmission back and have a smooth fit?

 

Axles & all would make for quite the truck. Didn't the M1009 have the D60/14BFF? If so, you would need conversion u-joints to use the drive shafts which likely would be different lengths. Measure things up first to be sure though.

 

A Turbo 400 would be overkill for 305 engine.Not so bad if you have a beefed up 350 or 400small block.The turbo 400 was used mainly behind the 454 big block..Me personaly I would stick with the 700r4 or non electric 4l60 and have rebuilt with stronger kit.

 

M1009's typically came with the 6.2 and 10 bolt axles.
The pickup version the M1008 is the bad boy with the 60/14 combos.

With a 305 there is no reason in the world to step up to a TH400. Now if you do throw in a 454 I would vote for the TH400. If you can fit a big block in a K5 then you shouldn't have any issues with the transmission/t-case fitment.

 

The gear ratios of the TH400 are insanely high,I had a 77 chevy with 454 behind a TH400 and 308 gears.It was dog.I changed the the rear end to 373`s and swapped the 454 with 350 that I built up.It was much better combination than what it came with stock.

 

Transmission ratios:
TGear - ..1st../..2nd./3rd
TH350 - 2.52 / 1.52 / 1
TH400 - 2.48 / 1.48 / 1

1stTJO your ride was s dog because of the 3.08's in the rear end, not because of the transmission ratio. If you didn't know which transmission was in a vehicle you could not tell which based on gear ratio.

 

I know the gear ratio didnt help but the weight of the turbo H 400 didnt help it either.Even with the 350 I put in it my gas milege didnt improve much over the 454.Then again the 350 engine I built wasnt meant to conserve gas either

 

TH400 is only a few lbs heavier than a TH350, maybe 10lbs difference.
Transmission is only a hundred, maybe hundred and a half pounds including a torque converter full of fluid.

I don't understand what you're getting at.