A lot has been posted about the gears in the rear, but I still have a few questions for you fellas in the know: What are the advantages/disadvantages of the 2.47 rear? What does the ratio actually mean? Its an '85 150 2WD I6 3sp with overdrive with the 2.47 rear. What can/can't I do (tow, haul, peel out, go highway) with it?
-Thanks!
Steve Jones

 

The 2.47:1 gear ratio means that for every 2.47 turns of the pinion gear (which is connected to the driveshaft) the ring gear (which drives the wheels) will turn once.

You will see high performance cars with gear ratios like 4.11, which gives the car higher acceleration and torque but the engine will be running much faster at 55mph than a car with, for example, 3.56 gears. The advantage of the higher gear ratio (numerically lower) is that you will get better gas milage at the expense of acceleration.

But it also depends a lot on the gear ratios in the transmission. Your 3 speed will drive a little different than my I6 f-150 with the 4 speed overdrive tranny and 3.09 gears. Either way you won't be doing any burnouts. The I6 engine can tow more than any other 6 cyl and some v8's regardless of the gear ratios. Plus it will run forever.

-Jon

 

My owners manual does not reccommend towing anything with your rear end gears.

 

The higher the gears (numerically lower), the harder it is on the engine to tow things, or haul much weight. You will fry your clutch trying to haul any substantial weight with those gears. My I6 F150 has 3.55 gears, which I find work great at all speeds, but my gas mileage suffers. If you do most of your driving on the highway, with little to no load, your gears are perfect, but if you do a lot of stop and go driving, and/or you plan to haul a load often, then you might want to look into getting lower (numerically higher) gears.

 

But if the transmisson is geared lower it would make up for those higher rear end gears. I'm really not sure what kind of ratio the 3 speed runs though.

 

True. Good point. They would have to be pretty damn low to work with 2.47's, though.

 

He's got a TOD tranny with ratios of either 3.01/1.78/1.00/0.79 or 3.25/1.92/1.00/0.78. Either way, they're WAY too high to be of any use with that R&P.

Basically, Ford used the 2.47 as an "economy" rear for the 300 even though the only place it showed any economy gains over a normal rear is in the saled brochure.

If oyu're interested in improving what you have, you have 2 choices: change the rear gears to something around 3.55 or change the tranny. None of the 3+OD trannies are particularly strong so you might want to take a look at that option. Both the NP435 and T18 trannies have very low 1st gears which are non-synchronized. The T19 has a somewhat taller 1st with a synchro. All 3 are much heavier duty boxes than your present tranny.

 

Thanks for all the info!
To change the rear gearing, do I have to get a whole new axle or can I just do the gears?

Strangeranger, what is a "TOD"?

Thanks for the help, it feel good to know what I have.

 

http://www.motivegear.com/tech_info/...nny_guide.html
http://www.4speeds.com/toploader.html

 

Seems silly that they would sell a truck you can't tow anything with!

 

Thanks to all for the helpful info and really great websites!

Kind of like the 4-cylinder import "trucks"?
I just bought the truck from a university entnomology department who bought it new in '85 for driving between two campus buildings. I guess bugs don't weigh a whole lot.
It has been a great daily driver for my girlfriend and a trash hauler on the weekends. With 62,000 original miles, it should be for a while.
-Steven Jones