The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 66 GMC V6 Manual to auto tranny swap

I am pretty sure that GMC had an automatic behind their V6 engines,, MY question is, has anyone attempted to hook up a 700R4 automatic behind a Big Block V6 ?

I have a powerglide behind mine. I too would be wondering about this. I was thinking about a th350.

Sam,

The V-6 have a unique bolt pattern setup. Bendtsens tranmission adaptore is made for this aplication runs about $850 or so, THEN you can mate up just about any automatic. I already had a spare Automatic, and mated it to my new short block.

http://good-times.webshots.com/album/568422172LCyGEI?start=12


Check Jolly's link, scrool down about to half way to see what automatics were used.

http://www.6066gmcguy.org/SM420.htm

Bendstens Transmission adaptor
http://www.transmissionadapters.com/GMC%20V6%20&%20V12.htm

now there is something ive never seen or thought id see a v6 with an auto! i knew odball bolt pattern though very cool to know! timbuk

There is a guy on e-bay selling what you need right now, e-bay name is 327turbofire the kit is selling for 150.00 buy it now price.

There is a guy on e-bay selling what you need right now, e-bay name is 327turbofire the kit is selling for 150.00 buy it now price.http://motors.shop.ebay.com/merchant/327turbofire_W0QQ_nkwZQQ_armrsZ1QQ_fromZ

Thanks For the Help Guys.

I know I have an adaptor plate in front of my powerglide trans but will this work with a th350, when I got the truck, the shift linkage was missing. It's the piece that comes off the frame and attaches to the transmission. I had to make one, it's been working alright for 4 years, but I can only go from park to drive. It's a 2 speed powerglide in a '66 gmc with 305 v6. I've been trying to find this piece for along time in alot of junk yards in my area and on the internet with no luck, plus the thing leaks bad even though I replaced both seals front and back, changed the filter and pan gasket, this was right after I set the rebuilt engine on the frame. Sorry for rambling on, I want to just put a different tranny in it (I have a good th350 laying around). Any help would be appreciated!

Here is the listing for the Adaptor plate, Grab it while you can.

Ebay Number 170335341268

As long as you have the aluminum case Powerglide behind the V6, any other Chevy aluminum automatic transmission will bolt up. The 'glides used a slightly smaller bolt circle on the torque converter than the other automatics, but you can drill the flexplate if neccessary.

The GMC's used an adapter to mate the back of the V6 block to the Chevy pattern automatic.

Thanks for the info, I wonder if I'd have to shorten or lengthen my driveshaft also?
Ted.

Depends on the transmission used. Most TH350's and all 700R4's and 2004R's shound not require driveshaft mods. The yoke from the 'glide uses the same spline so that will work too.

Some TH350's and all the TH400's are longer and would require shortening of the shaft. In addition, most TH400's use a larger yoke with a larger U-joint. (some very early Buicks in the mid 60's were an exception to the larger yoke)

On both the TH400 and the 2004R, the crossmember will have to be moved back about 6 inches. Some 700R4's have the transmission mount on the main case, not the tailshaft housing. You will need the tailshaft mount to use the same mounting location as the 'glide.

If you go with the 700R4 and the one you have doesn't have the tailshaft housing mount, you can change the tailshaft housing. When doing conversions, I would buy the correct tailshaft housing from the dealer for about 35 bucks.

For informational purposes, one of the OD (700R4 or 2004R)transmissions would be the best. Both have lower first gears than any of the three speeds, an overdrive gear (remember, the V6 has a torque peak RPM of 1600 and would get the best economy cruising at that RPM on the highway) and the lockup converters take converter slippage out of the equation.

Powerglide: 1.76:1 first gear
TH350: 2.52;1 first gear
TH400: 2.48:1 first gear

700R4: 3.06:1 first gear, .70:1 OD
2004R: 2.77:1 first gear, .67:1 OD