I have a 300cid six in my 68 F100 w/a three on the tree and I am looking to retrofit w/a three speed w/overdrive has anyone done this or does anyone have one similiarly equiped. I am looking for improved economy and lower engine speed without spending a fortune so I am wondering if its worth it. How hard are 3-speeds w/overdrive to find and are they pricey? Thanks for your time,
Richard.

 

Welcome to FTE!
Ford used two different styles, one was really weak, and the other was ok, but neither could be recomended for a truck. Plus, both of those trannys were set up with a slip yoke and were quite long, wheras your tranny has a fixed yoke and very short length. You may be best off just changing the gears in the rear end. If you have the 9" rear, try looking around in the junkyard for an 80-83 F-100 with a 300-6 and overdrive. Usually, those trucks came through with a 3.00 or 2.73 rear gear, really lame with od, but probably ok without. You should be able to get the center section for around $100, just swap it out with yours and go. Be sure to regear your speedometer or at least calculate the difference so you don't get speeding tickets.

 

Two different things here:

A 3 speed with OD is what you have with an OD bolted on the back. This was a factory offering in the '60s. You might be able to find one.

A 4 speed OD trans is what was offered in the late '70s and up to mid '80s. There were several. Look here:

http://www.davidkeetoploaders.com/imposters.htm

These are modeled after the toploader 4 speed, but are lighter and 3rd is direct with 4th over. Not as strong as a toploader, but they work ok behind stock 6's like yours and mine. They are a floor shift, so that may cause and issue in your truck. 2nd to 3rd is like the grand canyon, but that's probably how your 3 gear is now, ain't it?

These were built by Tremec and go under the designations SMOD, SROD, T170 and a few others. SMOD is what's under my E150. Side Mounted Over Drive, as the linkage is side mounted external just like an old toploader. Single Rail Over Drive, uses a single internal rail shifter.

These trannys were in pickups and vans and everyone hates them, so you might be able to get one cheap. Tiger Dan has one in Northern Cal, and as soon as I get $1500 to throw at my van, I'll have an extra. (don't count on that anytime soon)

The other option for you is a ZF (bucks, change to juice clutch) 5 speed, or a T18 or T19 with the real low first, which would allow you to change to a much higher diff as suggested earlier.

 

My dad bought an 84 model 1/2 ton truck with that 4 speed O/D behind a 302. He put well over 200,000 miles on that truck with no major mechanical issues. I wouldn't recomend it for any type of hot rod, or big mootor, but a 300 that is just a daily driver should be ok for a long time.
I don't know about other parts of the country, but the local U pull it here gets 300 a piece on that transmision.
The other thing, is like Ford 6 says, it is a different length and yoke. You can count on swapping the drive shaft if you make this swap.
I have a 460 in my truck and I had 3.50 gears. I swapped to 3.00 gears as recomended above and it worked realy well. However, there is a bunch of cubic inches between 460 and 300. Judgeing from the way my 460 responded to that change, and other engine and rear end combonations I have had.....I would strongly advise going any higher than 3.25.
Out of curiosity and to be able to give a more detailed response....what rear gears do you currently have?
Doc

 

I just bought this truck and I don't what the rearend ratio is or what size ring gear it has. The guy I bought it from says its all stock. My truck is a shortbed model with a single piece drive shaft. I rather like having a three on the tree because three people can sit on the bench seat comfortably without having that pesky stick in the way. I went to several old Ford truck websites and it seems as though it was a factory option for these trucks to have a three on the treew/overdrive. From the schematic/exploded view I saw it looks like a standard 3-speed column with a separate ****, lever or switch, mounted on the dash to kick it in to overdrive but I am not sure because I have never seen one in person. I dont really want to cut a hole in the floor for a four speed and the rearend swap option might be the ticket because its easier and cheaper. Like you said though
you loose some real low gear pulling power. But I guess its all about what you intend to use the truck for. I was planning to hop-up my big six with some bolt on power stuff like headers, high perfomance intake and four barrel carb but better think twice if the gearbox won't stand up to the increased power. 85e150six4mtod mentioned that no one likes the 3-speed overdive anyway, I'll have to ask him why?

 

I'm a little un-clear here everyone hates which trans the SMOD or SROD trans or both are no good and if so why are they hated? Thanks.

 

Inline 6,
Crawl up under your truck with a screw driver or pocket knife and a wire brush and look at your rear end. You will see several studs that are holding the pumpkin in the rear end housing. On the driver's side of the truck there should be a little metal tag on one of those studs. It will be about an 1" by maybe 3". There will be 2 rows of numbers and letters on this tag. Scrape off all the dirt and grime, and post the bottom row of numbers. You gear ratio will be the first 3 numbers closest to the stud on the bottom.
Doc

 

Sorry, couldn't find any such tag. Thanks Richard

 

The T-85 tranny with the R-11 overdrive was an option in Ford PUs thru the '72 model year. They also used the lighter version tranny with the smaller R-10 with the 6s and small V-8s for a few years. Believe me the T-85/R-11 combo will take the torque of a 390 quite readily and won't even "breathe hard" behind a 300 six. Being a SB truck with a one piece driveshaft, finding an OD tranny is much easier as it is the same unit used in the big block Ford cars up thru '66. As a matter of fact, these T-85/R-11s were used exclusively in the New York State Thruway "interceptor" cars up thru '66. Those used in the '65/'66 trooper cars had extra thick gears in the tranny but the already rugged 4 pinion Overdrive unit remained unchanged. I ran one of the "light duty" overdrives from a '56 Ford car in my '75 Ford SB P.U. for 75,000 miles without any problems and I don't even know how many miles were on it before that. The toploader 4 speed overdrive was used in PUs for a few years beginning around '76 or '78 and these units will work fine behind a six or 302 if treated decently. They are much easier to install since there is no electrical system involved. However, they do require a floor shifter.

 

Both the T-85/R-11s and toploader overdrives show up on e-bay pretty regularly. Of course finding one within a proximity of you may be a problem; I saw a late model T-85/R-11 go real cheap a few months ago but it was in FL and the shipping to NY made it impractical for me to bid on it. If you were close to NY State, I would sell you the complete 3 speed w/OD out of my '75 SB Ford P.U. for $450 including all the wiring and electrical componets. It hasn't been registered for a few years but we could take it for a short ride so you could see how it works. This tranny is in excellent shape and originally came out of a 289 powered Fairlane.