Who has a newer transmission on their 305 V6

[wcstory]

I love the uniqueness of my big block 305 v6 in my 1966 GMC 2500, but the 45-50 mph top end sucks. First gear is low enough I can turn the step on the gas and turn the key to go from a dead cold stop.

I'd like to switch to a more modern 5 speed manual transmission, but the GMC BB v6 does not use the GM standard bell housing bolt pattern. What is needed to swap to a Borg Warner T5 or a NV3500/NV4500?

I've also been looking at Bendtsen’s Transmission about their adapter kits to run the 4 speed automatic 700r4 and 4L60E transmissions. The idea of just cruising without shifting is appealing.

What are you running and what did it take?

[MusicMan70]

I have the 3:92 rear diff ratio in mine and the SM420, so I was always just using 2nd gear and above to drive around. Running at 65 mph, I was at about 3000rpms and I always felt I was "seconds from disaster" so I never ventured that high too often. GMC V6's do not like high rpm's.

Then one day I read these articles and found several links on the NP440 MY6 new Process Overdrive from mid 80's Chevy/GMC Trucks;
I just followed the Classic Truck's article (not all the photos match the captions correctly), it all went in pretty smoothly. The low torque of the V6 is well suited for this transmission and the .73 overdrive is great on the highway. I think I was turning about 2000rpm's at 65mph afterwards. I did have to have a new driveshaft made and a transmission crossmember for my 61.

The tough part is finding a complete transmission with the correct shifter. I think they had a couple combinations of shifter rods and shifter mounting brackets, so mix and match will be a puzzle. Also you need the one with the mounting ears that does not require the special bellhousing.

http://www.classicjunkyard.com/new_process_a833.htm

http://www.customclassictrucks.com/t...n/viewall.html

The other option I considered was using a factory automatic transmission adapter and going with a 4l80e or something similar. The adapters are hard to find as well but still out there; Here is a photo of one.

[duallyjams]

You can also use the auto trans adapter for a NV4500 bell housing or any other GM bell housing.

If you get the later NV4500 you can use a Dodge input shaft, it's longer and then make a adapter to your original bell housing.

[TJ's Chevy]

Lotta people said my TKO600 wouldn't bolt up to my 292 I6 and it bolted on just fine. Didn't even need a different bell housing. The 305 V6 used the same Sm420 tranny as the rest of the GM crew.....Bet my TKO would bolt on behind my 305 no problem. Common thing to do is put a taller gear in the rear end. 2500 is 50-55 for me...and I hate even being there. lol 2000 is where the engine seems happiest. I'd find a 305 V6 bell housing and match it up with an SBC bell housing and see what's different.

[Captainfab]

Another option would be a GearVendors overdrive unit behind your SM420, although not cheap.

Making an adapter for a Dodge NV4500 as duallyjams mentioned has been done here on the forum.

http://www.67-72chevytrucks.com/vboa...d.php?t=613597

[slorio]

WC:
I have the 3 speed with overdrive (T85N) behind my 351 V6. Overdrive drops RPM's 30%. It was a bolt in swap in place of my original 3 speed (SM318), but you would have to do some drive shaft work to replace your original 4 speed. See the current discussion on overdrive 3 speeds here:

http://67-72chevytrucks.com/vboard/s...d.php?t=313886

Regards,
Steve
New Orleans