To regear or not to regear

[TrexMex]

Hi,

My truck has 3.73s on Dana 35 front & a 7.5 Rear axle. I did not notice how poorly the truck performs on low revs since I switched to 31s because I performed the swap last fall and temps weren't so high anymore and my fan clutch and AC where on vacation until this summer..... I can barely hit 55 on a constant hill while on O/D (5th gear on my manual tranny).

So, question is... Regearing to 4.56s on my 7.5 axle would help? I guess I wouldn't lilke to go and do the whole 8.8 swap since I wander off road now and then but nothing really extreme, I just want a good balance between on road and off road performance. I would rather save those extra 200 - 300 bucks... One other thing is that I heard comments before that if I regear on the rear I should regear on the front as well..

Comments/suggestions?

Thanks!

 

[MAKG]

Changing your gears is PRECISELY equivalent to downshifting, except in 1st.

Abandon the idea that you just HAVE to be in 5th gear all the time on the highway, and your truck will work quite a lot better. This is by far the most cost effective route; it's free.

Your 3.0L is going to SUCK at low revs because they just do. So, rev it higher.

My exploder has 31s as well, except the gear ratio is even higher (3.54). I routinely drive this thing in 4th uphill, and ALWAYS at 55 MPH. Sometimes even in 3rd if it's at high altitude or somesuch.

The only time you HAVE to deal with gearing is if you're having troubles in 1st.

If you want to use 4WD, you must regear both differentials. You're going to have a tough time doing this for under $300, even if you pick a gear ratio that you might actually find in a junkyard (no higher than 4.10).

 

[TrexMex]

Thanks for the advice!

What I meant by the extra 200 - 300 was to throw in a 8.8 axle in there since the gears alone would cost actually 200-300 each set (500-600 bucks total for both gear sets?) from what I've been researching. I don't have a lot of trouble on 1st gear and actually I do the downshifting thing a lot on the highway... Usually when driving from Calexico to San Diego which is where I noticed that lack of power. Guess its kind of a tough test too since you climb 4000 feet in less than an hour with 100 degree temps.

I guess It's more a matter of driving style adjustment than anything else then.

Thanks again.

 

[Hahnsb2]

Changing your gears is PRECISELY equivalent to downshifting, except in 1st.

No its not, there's a huge difference between being properly geared and downshifting. You're adding more torque all around with the lower gears to move the bigger tires as well as keeping the original RPM range. Even driving in 4th instead of 5th with my 34s my 2.9 is a pig compared to running 31s in 5th gear yet I'm turning more RPMs in 4th with 34s than 5th with 31s...

 

[fastpakr]

Sorry - if you're turning a higher engine speed in 4th now than you were in 5th at the same road speed, you're very confused about it being a pig. You're geared LOWER at that point.

 

[MAKG]

Keeping the engine in its powerband will also help keep the engine cool. Within the powerband, more of the power consumed goes into the driveshaft than at other RPMs. Off the powerband, a larger fraction of the engine's power consumed goes out the exhaust pipe and -- importantly -- out the radiator.

Ambient temperatures matter only a little for engine power. You'll notice it on a track or a chassis dyno, but very likely not on the road.

HahnsB2, the total "ratio" between flywheel and the road is all that matters to the engine. That's the composite product of transmission, transfer case, and rear end ratios with the tire diameter. If you raise the rear end ratio but lower the transmission ratio in proportion and maintain the same road speed, the engine won't know. The only difference is that the driveshaft spins faster.

You AREN'T keeping the original RPM range. By "adding torque," you make the RPMs spin faster in proportion for a given road speed.

 

[northerncountry]

so with 4.56's what would be the rpms be at say 70 mph with 31's ( can't seem to find a the gear calculator) I have a 5sp manual

 

[Hahnsb2]

2800RPMs, taking into account the tires don't measure a full 31 inches. 4.10s seem like the best ratio for 31s.

MAKG, the further gear reduction in the axle increases torque put to the ground. I don't care what you guys say, there is no substitute for proper gears, drive you explorer with 33s however you like, then switch to 4.56s and you'll see what I'm talking about.

 

[tanbuddy]

They would be about 22% higher than they are now. For ex if your at 2500 rpm now, it would be at 3050 after the gear swap. I just changed my truck from 373 to 410, i bought the rear and front for 100 bucks and did the swap myself.

 

[Evan]

The only reason to regear is if you have to burn the clutch a lot to start out, or you want lower gearing for trail crawling.

Otherwise, you just leave it in a lower gear longer and it's exactly the same as regearing as MAKG said.

With 33s and a 4.0 I was burning the clutch a lot in order to get the torque I needed to start out, so I regeared. I would not necessarily recommend regearing for just 31s, unless you do a lot of wheelin and need a real slow 1st gear low.

 

[Hardwareman]

Just go to 4.56's and be done. That's what I did and it works great!




Allen

 

[Just_Randy]

I have about the same deal as TrexMex.... Only I'm planning on installing lockers, so I'll have it all apart anyway. The problem I'm having is choosing between 4.10 and 4.56.

I figure the 31 inch tires with the 4.10 gear is about the same as the stock 28 inch tire with the 3.73 gear. I've never driven the truck with anything smaller than 31 inch tires, so I don't know how bad it was stock, but I hear it was too tall. So, Im kinda leaning toward the 4.56.

Has anyone had u-joints going out more with the 4.56+??? Back when I had a 4.7 on another truck I was replacing ujoints about once a year. I figured it was because the driveshaft was spinning so fast at highway speeds. I went back to 3.73 and never had another ujoint problem.

 

[4x4junkie]

I have about the same deal as TrexMex.... Only I'm planning on installing lockers, so I'll have it all apart anyway. The problem I'm having is choosing between 4.10 and 4.56.

I figure the 31 inch tires with the 4.10 gear is about the same as the stock 28 inch tire with the 3.73 gear. I've never driven the truck with anything smaller than 31 inch tires, so I don't know how bad it was stock, but I hear it was too tall. So, Im kinda leaning toward the 4.56.

Has anyone had u-joints going out more with the 4.56+??? Back when I had a 4.7 on another truck I was replacing ujoints about once a year. I figured it was because the driveshaft was spinning so fast at highway speeds. I went back to 3.73 and never had another ujoint problem.

What engine do you have?

 

[Just_Randy]

3.0... Same as TrexMex. Everything is the same only his truck is blue n mine's red.

.... n mine's a 97, but other than that.....

 

[Ranger44]

My advice for a 3.0 is just keep it in it's power band. Right around 3,000rpm. Don't be afraid to downshift.

As for regearing, go searching for 4.10's in a J-yard, but if you actually take the time, and money to regear, go 4.56's.

Now as for the future....If you're planning on even bigger tires, etc. An axle swap and even lower ratio would be a wise investment.