Hello everybody-

My '65 F100 has a stock 300, and close-to-stock tires.
It also has a Mustang T5 transmission (overdrive!)
and a 3.00 axle (from a v8 donor truck)

the 3.00 gears are too tall- the motor can't push them.
i'm looking for recommendations.

I have *no need* to go over 65mph in this thing, so interstate speed/mileage is not a concern.

 

What is your tire diameter?

With the tall OD in that trans, I am thinking you could go as far as 4.10s.

 

4th gear is 1.00:1 just like a 4 speed transmission. Just use it for your top gear and don't shift into 5th OD.

 

I'm with 85e150six4mtod on this one. With the T5's OD and your 9" diff I would go with something in the 3.89-4.10 range.

 

Anything in the drivetrain, and questions about it, are relative. The OD is nice, but if its not going over 65 and the mileage isnt a concern, then why not use a bulletproof 4 speed? T19s came with lower gears, all syncho'd, and can be bought and installed pretty cheap. If you're running a t5, world class or not...like the other fellas mentioned...why not just stick with direct drive and not upshift?
Certainly not trying to step on your toes here. Just trying to get an idea what exactly you are trying to achieve. If you want more punch down low, getting off the line, your running gear is only part of the equation. Tire size, power band, weight, trans gearing, shift points, the list goes on.
What specific results are you looking for, from your truck? What do you use it for mostly? Any other future plans for it to consider? Just trying to narrow the scope of the discussion.

 

No worries, you're not stepping on my toes- this is exactly the kind of conversation i was hoping to have.

tire: 255/70 R15, so the diameter is 29.1"

you bring up a good point- if i'm not going over 65, did i even need OD?

my problem at the moment: i have to *baby* this thing to get it moving, and the OD gear is completely useless. the truck is used for light duty. no towing or heavy hauling.

i don't mind 1st gear being short, but i don't want it to be so short as to be unusable.

 

4.10s will bring a miraculous transformation.

 

If your truck has the T5 already in it, then why swap transmissions? That gets into changing around a whole lot of stuff. You are talking changing bell housing, flywheel, clutch, clutch linkage set up, shifter, driveshaft, etc.

If your truck has the stock 9" rear. You can just pick up a different center section/pumpkin with the gears you want. Make sure to get correct one for axle splines ( 28 or 31, etc. ) . A steeper gear will help you with your issues. If you do a lot of highway driving a 3.70 gear would work out good. Otherwise like I said something in the 3.89-4.10/4.11 range would be the way to go. Those gears will make it a whole lot livelier to drive and will make the OD usable for highway driving.

Another benefit to picking up another center section is you can find one with a limited slip carrier.

Swapping the 9" center section is cheaper and easier then swapping to a different kind of transmission. Especially since you don't want a grany low 1st gear.

 

Not to mention a whole lot of smiles per mile!

 

Do you know which T5 you have?

From what I'm seeing, there are two 1st gears available. One is a 2.95 and the other is a 3.35 (roughly).

If you have the 2.95, I can see why it'd be a dog. I have a 3.00 rear end in my Bronco, but I have a 3.34:1 starting gear with the NP435. It's good enough to get my 32" tires moving, but I have a lot more power than stock, and I would definitely not want to go any lower.

Remember, your gear ratios are really more about your (final drive * transmission gear) and not just the final drive.

For example, my NP-435

3.00 * 3.34 = 10.02:1

If you have the 2.95

3.00 * 2.95 = 8.85:1

So, even though we both have a 3.00, my gearing is 13% more aggressive. (It'd be like you swapping in a 3.40 final drive in yours.)

I've found a 10:1 to be a minimum final gearing for a good starting gear to get a heavy truck moving, but I think 11:1 or 12:1 would be much more ideal.

If your transmission does have the 2.95 1st, 11:1 would be a 3.73 final drive and a 12:1 would be 4.10.

If you kept the T5, you'd also still technically have overdrive too, which would be nice for overall drivability.

Hopefully that all makes sense.

 

First I have to say a T19 is a truck trany and is a slow shifting trany unlike the T5.


You are thinking on the right path with the ratios.
If the OP knew what trany the truck had before the T5 swap and drove it he would then have something to go by in picking gear ratios.


Little math: trany gear ratio x rear gear ratio = final gear ratio
ie: first gear T5 2.95 x 3.00 = 8.85
Do this for both tranys so you know the ratios in all gears to see how they compare, it's fun


You can also find on line for what speed & ratios gives you said RPM.
https://www.ford-trucks.com/calculators/mph-rpm/#MPH
With that and knowing the working RPM range of your 300 six motor you should be able to pick a rear axle gear that will work for you.


IIRC the 2.95 first gear T5 is a WC T5, read stronger trany, and with the right rear gear is not bad when taking off from a stand still.
Now the motor may not like to pull good when in 5th gear (OD) so depending how you drive the truck you can gear the rear axle for that.


BTW I did a WC T5 swap in to a 70 AMC Javelin with an AMC 360 that had a T10 4sp and 3.54 rear axle gearing.
The T10 first gear was to tall and had to slip the clutch to much to get going, an issue with all AMC cars using that T10.
Also with 4th being 1:1 and the 3.54 rear gear the motor would be screaming going down the high way at 70 MPH.


The fix for me, WC T5 with the 2.95 first gear and with the OD and 3.54 rear worked out great on the high way (on paper) for my v8.
I say on paper as I have not driven it so cant say how OD is but moving it in/out of garage the 2.95/3.54 is great.
Dave ----

 

Kind of apples to oranges, my '66 has a 240, three spd, 3.54 rear. On faster roads, 50-55, I wish I had OD or numerically lower gears. I don't haul heavy loads but do have a small contractors shell on it to haul my tools. If I hauled heavier loads on a regular basis than
I would want something in the 3.7-4.1 range

 

for what it's worth, the T5 swap involved:
transmission spacer ($100) from Modern Driveline
T5 off Craigslist ($400)
new driveshaft ($400) - i went to a one-piece and eliminated the carrier bearing. you may be able to save $$ here by just shortening the stock piece.
new crossmember - (free?) it's just a piece of angle iron with some risers


thank you everyone for the info- i'm going to pull an axle to count the splines, and then order a 4.10 ring & pinion.

 

I'm pretty sure your axles should be 28 spline. But it's always better to check and confirm.