Ok folks I asked this before about changing gear ratios but here I go again. I was told if I change the gear ratio on my truck from a 3.50 to a 3.00 that it is to much of a change and the truck will have to power at all at speeds around 60 to 65 mph anybody have anything on this. Btw I don't want to chance the tranny at all just want to change the gearing in the pumpkins, suggestions would b welcomed tks Yooperuno

 

Shouldn't be an issue. Setting up a differential can be a bit of an art, though, so make sure you a) really know what you're doing or b) pay someone who does to do the job.

With standard size tyres and a 3.00 rear you will top out somewhere north of 100mph if you have the power to get there.

Cheers - boingk

 

I had a c6 tranny behind a 302 mild build and had plenty of power with 300 gear ratio in rear end , I had no problems , but I transferred the whole rear end which is easier than changing the pumpkin

 

What some people use for advice.

 

[QUOTE=YooperUno;17499094]Ok folks I asked this before about changing gear ratios but here I go again.

What kind of answers did you get? And what didn't you like about them that made you want to ask again?
Was it here on this forum? Got a link to the old discussion? Just wondering why you didn't continue on from the earlier thread for us new guys to come up to speed.

[QUOTE=YooperUno;17499094]I was told...that it is to much of a change and the truck will have to power at all at speeds around 60 to 65 mph

Not sure what you mean by "will have to power" (have no power?) or "all speeds around 60 to 65" either?
It is a big change, but depending on the rest of your setup and what you want to end up with, it's not necessarily "too big" of a change.
With 30" tires for example (pretty small by 4wd standards) and your transmission, you should be cruising at about 2600 rpm at 65. That would go down to nearer 2200 rpm with 3.00 gears.
Still within the reasonable power range of a good running, strong 351M. But still pushing lots of wind with a truck at 65, so not sure if 2200 rpm is the sweet spot or not. But we definitely want to hear how it feels to you.

What is it you're trying to achieve in the first place?
What size tires?

And with a Ford 9" being relatively easy, and less expensive to have someone do it too, if you pull the center section (or "chunk" or "hogshead" or I forget the other common old name) for them. That way all they have to do is put it on their bench and do the work.
What I always suggest when there is any doubt is to do just the rear first. Even if that means that you can't use 4wd until you do the front, at least you can live with it for a time before you decide to do both diffs.

Good luck.

Paul

 

In the case of a truck, gearing is going to greatly change what the truck will be capable of handling or, handling well.

Low ratio gears (high numerically) are good for quick acceleration when the truck isn't loaded or pulling a load --as in getting up to speed when merging onto the freeway or when passing someone. They are also good for getting the truck into motion when it is loaded. The downside is when the truck isn't loaded or pulling a load the engine RPMs will be high at highway speeds. This will also mean greater gas consumption.

High ratio gears (low numerically) are good for highway cruising , lowered engine RPMs and lower gas consumption. The downside to that is the truck is less responsive to quick acceleration and it'll struggle more to maintain speed when hauling/pulling heavy loads.

To take advantage in having the best of both worlds, it would be best to have an overdrive transmission. You keep your lower rear end gearing for acceleration, hauling/pulling capabilities and when not doing these things, you have an overdrive to greatly reduce the engine RPMs and gas consumption at highway speeds.

If you currently have 3.50:1 rear end gears and your (non-overdriven) transmission is 1:1 in high gear, then your final drive equivalent is 3.50:1.

Most overdriven transmissions are 2/3rds overdriven. If you had an overdrive with a .68:1 overdrive ratio (for example) with 3.50 rear end gears, your final drive equivalent would be 2.38:1. To the engine, when in overdrive, it would perceive the rear end ratio as being 2.38:1 (.68:1 x 3.50:1 = 2.38:1). This would be a much higher gear ratio than the 3.00:1 ratio you're contemplating swapping to but, you would have the greater flexibility to use the truck as a truck or, cruise it down the highway without the engine screaming.

An overdrive will allow you to do both and to keep your lower rear end gear ratio.

 

It depends on the engine you have in front and tire diameter... and as many have mentioned the use of the truck. I think the chart posted above is great.

Personally I like to be able to haul a load or trailer and have good acceleration when empty. I also don't mind if the engine spins a little on the highway... low 3000 RPM range is fine. I run my 4.10 equipped truck with 31" tires at 70.

With three speeds to work with and 1.00 final drive in the transmission I would not want less than a 3.5 in any PU... but that is just me perhaps.

 

With 4.10 rear end gears and a .68:1 overdrive ratio, your final drive equivalent would be 2.79:1 (.68 x 4.10 = 2.788:1).

 

before you swap out the rear gears, are there 3.00 gears available for your front axle?????
in the correct rotation?

 

Early eighties Fords had 3.00 front axles, but it has been a long time since I have seen a Dana 44 3.00 ring and pinion set for sale. Hit the pick n pulls with an axle code chart and see what you can find, that's what I'm doing. I want to hear how your plans work out, better fuel mileage is always a good thing. I have a small block ZF5 I found at the pick n pull and hope to install it someday.

 

I thought the TTB ring-&-pinion gears were different from the solid-axle versions. And though both reverse cut, not compatible with each other.
The only gear ratios I see that are the same for both are the 3.07 ratio. Only the TTB had a 3.00 available. At least as far as my old charts go. I'm sure they're not the complete be-all and end-all of information.
So even though they have different part numbers, are they in fact compatible? You can put a TTB 44 r&p gear set into a '79 and older high-pinion solid axle?

Paul

 

There are a lot of opinions on this but I tend to agree with yours. 3.50 is just a good all around ratio. 3.00 can be too tall in a heavier truck, IN MY OPINION
A lot is going to depend on tire diameter and cam so the engine runs where it's happy (sweet spot), as mentioned.

And to be a bit of a different opinion than Ultra, I think you'll find most overdrives to be more in the .75 to one range.A ZF will be .76-.77.
Swap gears or swap trannys, I'd probably go with the tranny swap if there was a good overdrive that is going to bolt up.
Gear swaps aren't difficult but best left to a person capable of setting one up. The 9 inch is a little easier than the Dana because you don't have to use shims on the sides. On the Dana, it is best to have a set of sacrificial side bearings with the centers enough oversized to slide on without being pressed because the proper puller (which you
will need) tends to destroy the shim pack pulling the bearing off. I did my first time using an old Motors Manual which had illustrations of the contact pattern and what to correct. You are also going to need more savvy on bearing preload than most other things on a vehicle require.

 

There are a lot of opinions on this but I tend to agree with yours. 3.50 is just a good all around ratio. 3.00 can be too tall in a heavier truck, IN MY OPINION
A lot is going to depend on tire diameter and cam so the engine runs where it's happy (sweet spot), as mentioned.

And to be a bit of a different opinion than Ultra, I think you'll find most overdrives to be more in the .75 to one range.A ZF will be .76-.77.
Swap gears or swap trannys, I'd probably go with the tranny swap if there was a good overdrive that is going to bolt up.
Gear swaps are difficult but best left to a person capable of setting one up. The 9 inch is a little easier than the Dana because you don't have to use shims on the sides. On the Dana, it is best to have a set of sacrificial side bearings with the centers enough oversized to slide on without being pressed because the proper puller (which you will need) tends to destroy the shim pack pulling the bearing off. I did my first time using an old Motors Manual which had illustrations of the contact pattern and what to correct. You are also going to need more savvy on bearing preload than most other things on a vehicle require.

 

I've never used or swapped in one of the more modern truck overdrive transmissions. As such, I'm not familiar with their specific ratios.

I made reference to the .68:1 overdrive ratio because that's fairly common in Mustang T-5 and AOD/AODE overdrive transmissions --something I am very familiar with. A 4R70W transmission has an overdrive ratio of .70:1. I also stated that the .68:1 overdrive ratio was just an "example" for reference to illustrate the point in the advantages of having an overdrive and not giving up your lower rear end gear ratio.

I also explained the math of how a person would determine what their final drive equivalent would be, if a person knows what their specific overdrive ratio is and if they know what their rear end gear ratio is. You simply multiply the overdrive ratio by the rear end ratio to come up with the final drive equivalent.

My truck has 3.50:1 rear end gears. I don't plan to give up this ratio to make the highway RPMs lower. I intend to install a Ford 4R70W transmission with a .70:1 overdrive ratio. At highway speeds, and in overdrive, my final drive equivalent will be 2.45:1 (.70 x 3.50 = 2.45:1).

 

I think the Mustang T5s even had a .63 overdrive for a year or two!

And I can vouch for the gears numerically lower than 3.50:1 being too tall, especially with a three speed. Mine is supposed to have 3.00:1s but I think they might be the 2.75:1, as my truck seems to have been built from someone's parts collection. I would love to find a 3.50:1 rearend, or even just the pumpkin.
However, I gave thought to this before, and even did some calculating, and found that I could put my extra T5 in my truck, and put 4.11s in the rear, and still turn a lower highway RPM than I run now.