i need to pull and i have a 4od tranny. (know ive posted about this b4 but i got some new ideas). Would i notice enough difference to pull a heavy load by jus changin my rear end gear? or will i have to change trannys?

 

Rear gears will help greatly, but the m4od is not exactly known for strength. It'll handle some work, but go too big, and you'll be swapping it out soon.......

 

so u would try the rear gear change first?

 

I'd start with determining what rear gear it has now. Ford was very prone to using rather tall gears behind the big 6. If it has tall gearing, it won't matter what trans it has, it won't pull as well as it could.
As an example of tall gearing, it's not unusual to find 3.00:1 rear gears behind a 300 with the OD trans, or gears in the 2.50:1 or 2.75:1 range with a non OD trans.
With an OD trans, you can still get decent MPG with gears as low as 3.50:1 or 4.10:1, but it will pull a heck of a lot better and get better towing MPG.

 

3.55 is a good "mixer" gear for a balance between economy and pulling.

Straight pulling I would shoot for a 3.89 or 4.11. The 300 dont like a ton of RPMs so dont expect to do alot of trips at 75 in a 4.11 geared 300 truck.

 

A good way to go about it is figuring out the gear ratios of your transmission, and then looking at your tire size. Instead of guessing and checking, figure out exactly what each different final drive is going to do in each different gear.

I know the transmission you have isn't the same as mine, but I believe both the early 80's 4 speed/OD transmissions were similar.

1st: 3.25
2nd: 1.79
3rd: 1.00
4th: 0.78

Final Drive = (Engine RPM * Tire Diameter in Inches) / (Speed * Trans Gear Ratio * 336)

Figure out about where you want to be in your RPMs, and what speed you want to do it at for your towing, and what gear you want to be in.
(This is figuring you have 215 75R15 tires, which are 27.7" tires.)

If you figure your best pulling around 2000 RPMs, and only want to be moving around 15mph, and in 1st (to get loads moving).

Final = (2000 * 27.7) / (15 * 3.25 * 336)
Final = 55400 / 16380
Final = 3.38

Closest is a 3.55

If you want more RPMs, or want to be moving slower, adjust from there.

Then do the same thing for your highway speeds, what RPM you want to be at, and in what gear, etc. and figure out which final drive will do best to take care of both.
It may be a bit of math, but gear swaps aren't always cheap, so it's better to actually know what you want, instead of guess and check.

 

Can u buy these gears new? i dont use the highway much at all. bout 55 mph is all i really need

 

Quite a few places sell them new. The gears themselves aren't all that expensive, but installing them is. If all you do is 55 max, you can do some pretty serious and aggressive gearing without limiting your truck. You'll need to find out if your differential is a 9" or an 8.8". Also, do you have 4WD? If so, you'll need to do front and rear.

Precision Gear - Ford 9" Ring and Pinion Gear Sets
1980-96 Ford Truck/bronco - Rear Axle Ford 9" - Ford 9" Ring & Pinions

 

is the front differential the same as the back? mine is 4x4. and my rear end housing has bolts on the gear cover.

 

On the rear, if the gear cover is facing the rear of the vehicle, it's an 8.8". If it's facing the front and is integrated together with the connection to the drive shaft, it's a 9".


The front differential is a Dana 44 stock, so the gears for a Ford 8.8" or 9" will be different. Still as easy to find though.

You will have to do both, or else you'll tear everything up.

 

oops didnt mean to post this one. computers are new around here. lol

 

kk so mines an8.8 is that good? if i put a 4:10 in the rear what should the front b

 

Sounds like a Ford 8.8" if the bolts are on the rear. The 9" has them on the front.

Ford 8.8: http://www.4x4wire.com/jeep/tech/axl...ver_ford88.jpg

Ford 9": http://image.fourwheeler.com/f/28612...+clearance.jpg

The front ratio will be the same, or very similar, to the back.
ie.
Front (Dana 44): 3.54
Rear (Ford 8.8): 3.55


Here's a bunch of Dana 44 gears. If you go with 4.11s in the 8.8, it looks like the Dana 44 will be around a 4.09. Always be sure it's the right Dana 44, since the Ford used a reverse rotation gear setup.
http://www.4x4groupbuy.com/store/dan...40_99_506.html

 

I would recomend a 3.89 unless all you do is tow. The 300 dont like alot of revs so I think this will give you a great mix in a truck used as a hauler.

PS-Dont tow in OD. It is very hard on the tranny.

 

Tire size also plays a big role in determining what gears ratio is the best option. Taller tires require a bit lower (higher number) gearing due to added rolling resistance.