Switch One or Both Axles

[cpmont]

I am in the process of doing a SAS on a 1997 Mountaineer. I have in hand a DANA 30 from a Cherokee that has 3.55 ratio, I also have the rear axle but it has drum brakes. Should I change the gearing in the front to match the D4 3.73LS axle currently in the Mountaineer (has disc brakes), or put disc brakes on the Jeep rear axle. I plan to go to at least 35" tires and this vehicle will get enough miles to be considered a daily driver. I am also open to changing the gear ratio on both axles the Dana and D4 as lockers are in the future plan.

 

[traveler]

If you're open to changing both ratios, and you are planning on going with 35" tires, I'd put at least 4.10s in both front and rear. I have 32" tires and went from 3.73 to 4.10s and haven't regretted it.

 

[colintrax]

Change gears in both, 3:73 is too tall for a 35. And keep your stock rear end. Its the strongest axle made for midsize/compact trucks.

 

[traveler]

.....And keep your stock rear end. Its the strongest axle made for midsize/compact trucks.

X2 There are Jeep guys out there snapping up Explorer 8.8 rear axles left and right because they are both stronger than the Jeep axles and they already have Disc Brakes

 

[DirtJunky]

Id agree on keeping that 8.8
But would say do 4.56 gearing in front and rear

 

[SWIGIN]

I would complete the SAS and just run it in 2wd and see if you like the 3.73s. If it's too high then go lower on both rears.

If you have a V8 it might not be too bad depending where and how you drive. If it's a V6 then I'd probably just go lower right off the bat.

 

[Spudhut]

If you decide to keep the 3.73's in the rear - you will need the Dana Spicer kit 706930-5X kit if you have D30 Hi Po Axle. Only company that makes this ratio for them.

https://www.summitracing.com/parts/sdh-706930-5x

Summit has the best price, you can get the Ring gear set with shims and new Diff bearings cheaper than the same single kit from any Jeep site.

I verified part number from axle specialist at 4wheel parts

 

[Jeff213]

With 35 inch tires you won't be happy with 3.73s

I went to 33" tires and I am unhappy with 3.73s, planning on going to 4.56 with the 33 inch tires.

The truck feels so sluggish going from 29" tires to 33" tires still with the stock gearing, and this is on a V8.

 

[DirtJunky]

With 35 inch tires you won't be happy with 3.73s

I went to 33" tires and I am unhappy with 3.73s, planning on going to 4.56 with the 33 inch tires.

The truck feels so sluggish going from 29" tires to 33" tires still with the stock gearing, and this is on a V8.

If your mind isn't already made, look into 4.10/4.11.
Since i drove at higher speeds, when i had 33s i thought 4.10s were perfect.

 

[Jeff213]

The truck isnt going to be a daily driver, going to be my towing/ camping/ offroad rig. I wont be going over 65 with it.

 

[MAS Tequila]

going to be my towing/ camping/ offroad rig.

You answered you own question.

I have 33's with the stock 3.73 gears.

The only time it's really happy is on the highway in excess of 75 mph.

Towing, forget it.

I'm going 4.56 soon, and this IS a daily driver.

The required gear to have the same rpm's would be a 4.29/4.30, you can't find it.

By using the chart it shows with a 28" tire (that's what my stockers were) I should be turning 2909 rpm's.

With 33's a 4.10 will be @ 2720 or 211rpm's less where a 4.56 will be @ 3018 or 109 more.

If you're going to be doing ANY towing, run the 4.56, 100 rpm's will do little to hurt you economy, where 200 will hurt your ability to turn torque into motion, especially with 35's.

I don't have a clue what speed this chart uses for a baseline, but the result is the same.

differential gear chart - Yahoo Image Search Results

 

[Spudhut]

Great info @MAS Tequila ... Thanks!

 

[Jeff213]

Lol, i was arguing for the 4.56s, and against the 3.73s.

 

[MAS Tequila]

Lol, i was arguing for the 4.56s, and against the 3.73s.

Then you had your argument corroborated.

 

[cpmont]

I found a calculator that says to get same performance as stock I need to run 4.56 or there about so I am changing both. Thanks for all the advise.

 

[93XploderMS]

I would go 4.88. I have 5.13 and worn 37’s, 55 mph is about 2100. Anytime you go up a tire size and regear it’s best to make it one lower then stock.

 

[DirtJunky]

I would go 4.88. I have 5.13 and worn 37’s, 55 mph is about 2100. Anytime you go up a tire size and regear it’s best to make it one lower then stock.

Personally I saw almost no difference when I went from 4.56 to 4.88 on 35s. But 5.13 on 37s made a huge difference