in the coming months we will be purchasing a TT that will be just a hair under 9,000 lbs. loaded. My Excursion has 3.73 gears, which I'm told are not ideal for the V-10's power band. Is it worth making the switch to 4.30s, or how much of a hindrance will it really be? I've noticed that the tow ratings seem the same no matter what the ratio for some reason. Also, it's a 2wd so it would only be one gearset to change.

Why not try it before changing anything. Then you can decide. Its not like it won't pull it at all.

Not worth the investment. You will not have any problems.

Gear box ratios are torque multipliers and generally are about 10% differencebetween ratios offered Your 3.73's multiply the drive shaft torque by 3.73...4.3's will multiply andprovide about 15% more torqueSo if the drive shaft has 100 ft/lbs of torque, the 3.73's will send approx(there will be losses) 373 ft/lbs to the axles. 4.3's will send approx 430 ft/lbsto the axlesMTWR's is very dependent on axle ratios...just check any brochure or specificationsheet from any OEMAbsolutism this is NOT, as the axle ratio is just one of the components of this...meaning to just talk about a 3.73 vs 4.3 is out of context of the whole system. There are many other factors. Diesel, big block, small block, forced fed, cam profile, etc, etcThe tranny gear ratio(s) and the ICE's torque curve must also be factored in...as would the tire OD...best to use their rev's per mile...that is more accurate"Torque band" is the HP/Torque curve and choosing the tranny gear ratioand axle ratio vs whatever you wish as your priorityIf MPG is high on the 'have to have' list, then the lower numeric diffratio.If towing is high on the 'have to have' list, then the higher numericdiff ratio.BUT...you can't have the best of both worlds...there will be compromises...

Coming from someone who has a V-10 X originally with 3.73`s I can tell you the 3.73`s will not be enough for a 9klb trailer! my trailer is 9200lbs loaded. I towed one season with 3.73`s and switched to 4.30`s for the next season. You will notice how much better it tows. you will be much happier when you get to an incline and the X pulls right up. you will get about .5 mpg better towing. It will also stop hunting for gears because he engine and trans will not be working as hard. When I had 3.73's with my trailer I couldn't hold O/D at 65 because the RPM's were to low in O/D. And too high in 3rd. With the 3.73's it would stay in O/D with no issues. It's all about how efficient the powertrain is, and with 3.73's and a heavy trailer it will not be efficient with higher gears. The lower gears (numerically higher) will always tow better!Add in a 5star tuner and it will pull with the diesel guys all day long! I would even say 4.56`s wouldn't be out of the question even with stock size tires!Yes it is well worth it!

Just for comparison sake, class A motorhomes with the V-10 use the 6.17 rear end to move a max of 30,000 pounds.

Worth the switch to 4.30s? | Good Sam Community

44 Replies

Westcoasting
Explorer
Aug 13, 2016
Hemling wrote:
in the coming months we will be purchasing a TT that will be just a hair under 9,000 lbs. loaded. My Excursion has 3.73 gears, which I'm told are not ideal for the V-10's power band. Is it worth making the switch to 4.30s, or how much of a hindrance will it really be? I've noticed that the tow ratings seem the same no matter what the ratio for some reason. Also, it's a 2wd so it would only be one gearset to change.

I have not owned and Ex but i can guarantee at that towing weight that an upgrade will do wonders for you. It will give you better power off the get go and at highway speeds will hold gears better instead of hunting for them. You will get better gas mileage towing too, a lot of people think higher rpms will mean less mileage but it makes it easier to tow and mileage improves. I have done it a number of times and never once have i been disappointed.
SoCalDesertRid1
Explorer II
Aug 13, 2016
A lower axle ratio increases torque multiplication in EVERY gear of the transmission.

400 lb-ft motor with 3.73 gears = 1492 lb-ft
400 lb-ft motor with 4.30 gears = 1720 lb-ft

That's a difference of 228 lb-ft in direct gear.

So for about $750 per axle, you can give your engine over a 200 lb-ft increase in effective torque output. That's a pretty cheap upgrade with a very big bang!
dodge_guy
Explorer II
Aug 13, 2016
With the switch from 3.73 to 4.30 a few hundred rom change makes a big difference. Don't try to think your way out of doing it! You'll never fully understand till you've physically done the change.
Huntindog
Explorer
Aug 13, 2016
Hemling wrote:
So, not to resurrect this topic, but I have one final question. With my 3.73 ratio, dropping it into 3rd puts me at 2500 rpms at 65 mph. I understand that a 4.30 would help getting things going as I accelerate, but if a 3.73 in 3rd is essentially the same as a 4.30 in OD for highway cruising, what is the benefit of switching gears? If 2500 rpm is the sweet spot for towing, I can accomplish that with what I have now and use OD for everyday driving (or lighter loads) and have a lower cruise RPM on the highway.
If the only thing you are concerned about is the cruising engine RPM, then you are correct.
But where the gear multiplication happens matters in the overall towing performance. A lower axle ratio will make things easier on the everything in the drive train. From the motor to the tranny to the u joints, they will all benefit. Engine braking will be improved as well letting the brakes take less abuse.
If you really want your TV to tow the best it can.... There is no substitute for lower axle gears.
carringb
Explorer
Aug 13, 2016
Hemling wrote:
So, not to resurrect this topic, but I have one final question. With my 3.73 ratio, dropping it into 3rd puts me at 2500 rpms at 65 mph. I understand that a 4.30 would help getting things going as I accelerate, but if a 3.73 in 3rd is essentially the same as a 4.30 in OD for highway cruising, what is the benefit of switching gears? If 2500 rpm is the sweet spot for towing, I can accomplish that with what I have now and use OD for everyday driving (or lighter loads) and have a lower cruise RPM on the highway.

If you never tow in the mountains, they sure.... You can keep doing what you're doing. When you get out west, and your 3.73 gears leave you stuck in 1st gear holding up traffic on major mountain passes, you'll wish you had lower gears. Ditto if you ever need to back up a steep road or driveway.

PS - I had 3.73 gears originally.... I'm not just talking theoretical. I've been there.

My first trip through the gorge with a headwind (~40 MPH that day, gusts over 65) left me in 2nd gear THE WHOLE TIME. Towing with 3.73 gears is the worst gas mileage I've ever seen.
Hemling
Explorer
Aug 13, 2016
Right, I understand the mechanical advantage of lower gears for accelerating, but once you're up to speed the engine doesn't care how cruise rpm is maintained, 2500 rpm is 2500 rpm whether it's accomplished through OD and 4.30s or Drive and 3.73s. The trans is essentially doing nothing in D and lockup so there is relatively no heat buildup in the trans. I just don't see the logic of dropping hundreds or thousands on a gear change. It would be different if it had 3.08s or some horrible highway gears, but 3.73s are not stressing the engine or trans on acceleration at all.
Chuck_thehammer
Explorer
Aug 13, 2016
its about mechanical leverage.. same reason going from stock wheels/tires and going to 35 or 37 inch wheel/tires.

turning a rusty bolt with a 6 inch wrench and a 12 inch wrench.. being axle and wheel/tire.

extra load on gear teeth, transmission Heat, engine bearing load.
Hemling
Explorer
Aug 13, 2016
So, not to resurrect this topic, but I have one final question. With my 3.73 ratio, dropping it into 3rd puts me at 2500 rpms at 65 mph. I understand that a 4.30 would help getting things going as I accelerate, but if a 3.73 in 3rd is essentially the same as a 4.30 in OD for highway cruising, what is the benefit of switching gears? If 2500 rpm is the sweet spot for towing, I can accomplish that with what I have now and use OD for everyday driving (or lighter loads) and have a lower cruise RPM on the highway.
dodge_guy
Explorer II
Aug 02, 2016
Hemling wrote:
I always thought that towing in OD was discouraged because the converter would unlock but the trans. would stay in OD, causing a great deal of heat as opposed to running in 1:1 ratio, where the input/output shaft would be going the same speed so even if the converter unlocked it wouldn't fry the trans. Or is that not a thing anymore? Should I just shut up and put in in OD?

That was the thinking years ago when O/D came out. since then they are much stronger and can withstand the use of being used while towing.

My 97 Mercury Grand Marquis goes into lock up in 2nd gear. I hate it because it pulls the RPM`s down to early. I have a tuner from 5star for it with a custom tune and it is night and day better.
WE3ZS
Explorer II
Aug 02, 2016
Hemling wrote:
I always thought that towing in OD was discouraged because the converter would unlock but the trans. would stay in OD, causing a great deal of heat as opposed to running in 1:1 ratio, where the input/output shaft would be going the same speed so even if the converter unlocked it wouldn't fry the trans. Or is that not a thing anymore? Should I just shut up and put in in OD?

Your 4R100 transmission was designed to be in OD while towing, it will downshift when it needs to. The only time you need to be concerned about which gear to be in is if the load and terrain conspire to make the trans frequently bounce between OD and 3rd, known as hunting, in that situation it's best to lock OD out to prevent unwanted heat buildup from the constant hunting. Once the terrain flattens back out tap the shifter's end button again and pop it back in OD.