Just did a trip, NOT towing the 1962 Shasta trailer, that was long enough to do an MPG check. Truck not loaded with any thing except me and the wife.
This is on my '65 300 six, T18 4 speed, Gear Vendors OD, 3.50:1 rear gears.
Mostly highway, some of it hilly, some at 55 mph, mostly at 65-68 mph(you'll get runover on the Nor Cal Hwy 280 if you are slower then that), some stop and go through San Fran(19th ave), some hills of hwy 17 and hwy 9.
16.55 MPG

 

Couple of questions, what is the OD ratio, can you start from a stop easily with the OD engaged? Thinking of running straight 3.00 rear in mine.

 

I believe the OD ratio is .78.

I need to be above 30 mph to kick the OD in. I really only use it in 3rd & 4th. I think with a auto trans it can be on all the time, GV could answer that.

My 300 I6 has enough torque that I could go to a taller rear gear than the current(orig) 3.50. I might do that some day but then I would probably need to make my starts in my non-syc very low 1st gear. 99% of the time I start 2nd gear, even towing.

 

It does sound like with an automatic if you set the control module to "Auto" that it can start out in overdrive mode, but I think it changes automatically, not that it is engaged all the time.

https://www.gearvendors.com/f2wd3s.html

Chad

 

So your is essentially 2.73, so I should be fine with the 3.00 all the time.

 

 

true, but tire size is easily changed, so unless he's running something in the 28" range I should be good.

 

I'm running 235-75-15 tires with 28.9"

 

Very interesting! Out of curiosity how was the mileage calculated? Via odometer or GPS? If it was odometer is your speedo correct?

 

Odometer. I have checked the speedo with a phone app. It is pretty much dead on up to about 65mph. After that it gets a little off at 70 on the speedo the phone waffles between 68/69.

 

I have the same exact setup on my truck minus the overdrive..... where would I purchase one?

 

Here: https://www.gearvendors.com/index.html It will be around $3,000(plus Tax & shipping) to buy it all new which does not include the drive shaft.
or
look around for a used or never installed setup or some of the parts and buy from GV what you need to finish it off.
I bought off of from a private party, off Craigslist, what was a complete never installed system for 4R70/AOD. The guy bought for a Fox Mustang. The ad I had printed was over a year old and I called to see if he happened to still have it. He did the car was long gone, so I got it all for $1,000, found a T18 adapter on ebay for 300, bought the other T18 specific parts from GV, had a drive shaft made locally, sold all the 4R70(the adapter being the most valuable part) stuff for $900(ebay). I'm into it for about $1,800 total.