What would the difference be between a 3.73 in 5th gear and a 4.30 in 6th?Wouldn't the power be fairly close?

 

everything you want to know in this link https://www.ford-trucks.com/forums/1...xle-ratio.html

If you look at the chart its only @ 300 rpm

 

When thinking about 3.73 and 4.30 you have to think about torque multiplication not rpm. If you take the two identical trucks with the same size tires but one with 3.73 and one with 4.30 it will take less torque to turn the drive shaft on the 4.30 geared truck it's just that simple. A 4.30 geared truck will put more torque at the ground were so it counts so it can tow more with less stress on the rest of the running gear.

Denny

 

yes at low speeds, but....

what happens to the total torque delivered from the engine when the 3.73 is going down the road at 65 mph in 5th (1st overdrive) and the 4.30 is running in 6th (2nd overdrive)?

 

Also remember the pinion size it gets scary went you look at the 4:30's you would swear you strip all 5 of those gears right off, diesel and trailer weight I get the chills thinking about it, while I never had a 4:30 fail it looks like its built to fail.

 

Unless your going up a grade you don't need total torque at 65 mph, mine just coasts along at 2K rpm in 6th. If I'm pulling on flat ground with little wind I just lock it into 6th and it will and it will go over overpasses in CC and lose very little speed. When you consider the amount of time you need full torque when pulling it's a very small percentage but when you need it you will get more of it with lower gears at the pavement with less stress on the running gear, you also get into the power band faster with lower gears.

Denny

 

The way gears are ground there is only one tooth fully engaged at one time with the ones on either side starting to engage or disengaging, you can't run a pinion from a 4.30 on a 3.73 because because the tooth spacing is different they have to be matched. Every transmission I've every managed to destroy in my youth I always took one tooth first and the rest if I didn't stop, I've never been able to tear the gears out of a rear end in all the trucks I have owned but I've never dumped clutches or dragged raced one just pulled them hard, I have taken the bearings out but never the gears.

Denny

 

What Denny said. And ATP thanks for posting my link, hope it helps someone!

Flat ground on the highway the engine "sees" about the same load whether 6th in 4.30 or 5th in 3.73. The difference is that when it gets into the hills with the 4.30 you have 5 gears available vs 4, giving you more chances to find the right gear for the engine powerband.

I can see this with my 4R100 - I could use two more gears. OD is too tall for some hills but 3rd is a big jump in RPM ... and I could replace 2nd with two gears spaced evenly between 1st and 3rd. There are places on some tows where the engine either struggles to hold the hill and gets into lugging, or the tranny drops a gear and makes the engine wind out.

Another way I think about it is a single gear bicycle. It may take me the same effort to pedal it along flat ground as a multiple gear bike, but when the hills start I reach for the shifters!

These are more extreme analogies as we're just talking 1 gear diff between 6th locked out in the 3.73 or using 6th in the 4.30 but they hopefully illustrate the case.

At the end of the day there are people who successfully tow heavy with 3.73 and those who really like the fact they have their 4.30. You have to consider your intended usage and go from there ... and the fact that all that I've seen on lots are 3.73 and 4.30 has been a special order (someone correct me if I'm wrong).

 

... and the fact that all that I've seen on lots are 3.73 and 4.30 has been a special order (someone correct me if I'm wrong).[/QUOTE]

Correct 3.73 seems to be the default "stock" ratio and if you mistakenly order a 4.30 Limited Slip you end up with a Dually, Ask me I know

Regards

 

You only see 3.73 gas on the lot because the people ordering them will order the highest gears available for mileage empty they have no idea what they are doing or talking about when they are trying to sell you one, most only want to sell diesel. What's really funny is some of the people we rv with had a hard time finding a diesel off the lot with the right gears for pulling because the dealers want to sell trucks that get the best milage possible running empty they could care less about us that want to use them for what they are built for.

Denny

 

Correct 3.73 seems to be the default "stock" ratio and if you mistakenly order a 4.30 Limited Slip you end up with a Dually, Ask me I know

Regards[/QUOTE]

3.73s is the standard gearing for the gas powered F-250s and F-350 SRWs. 4.30s is the optional gearing. In my opinion, it should be the other way around. Back when I ordered my truck, 4.10s was the lowest gears that you could get in a DRW gasser.

 

Correct 3.73 seems to be the default "stock" ratio and if you mistakenly order a 4.30 Limited Slip you end up with a Dually, Ask me I know

Regards[/QUOTE]

I special ordered my 2014 F250 with 4.30. I knew that a lift was being installed with much larger tires (37s now, 39s next summer). Bigger gears (4.88) made a huge difference on my 150 with 35s.

 

3.73 in 5th will be stronger, I believe, by about 7-8%.
Gman

 

Because of the added mechanical advantage 4.30 gears will be stronger in all the gears when compared to 3.73.

Denny

 

6R140 gear ratios are:
5th - .85
6th - .67

About 21% difference. 3.73 to 4.30 is about 15%.

Based on that, 5th gear with 3.73 gears will be about 6% stronger than 4.30 gears in 6th.

Is this not the case? Or is it just 6% higher rpm?

Either way, my current 4.30 6.2 does not pull as well in 6th as my 2011 6.2 in 5th with 3.73's. 6th gear is pretty much useless for towing with either ratio on anything other than flat (no headwind) or downgrades.

Gman