Gearing help

[tylertrebilcock]

Im looking into re gearing my truck to accommodate 35s, I’m kind of stuck between 3:73 or just going with 4:10. Is anyone running these setups and how does it do. Also is there an equation to calculate final ratio with the bigger tires? My MPG is like 12 it town and 15 on highway with the quad. I think gearing should fix my problem. 

[AH64ID]

It might help some, but it likely won't cover the cost of the upgrade. 

 

What trans do you have?

 

Personally I'd go 4.10's, especially if you have an auto. 

[tylertrebilcock]

4 minutes ago, AH64ID said:

It might help some, but it likely won't cover the cost of the upgrade. 

 

What trans do you have?

 

Personally I'd go 4.10's, especially if you have an auto. 

I have a 47re rebuilt about 30k ago. I can find gears on eBay for around 300 bucks front and rear plus an install shim kit. I did a calculation and I need around a 3.94 ratio for 35s so I feel like I could go with either or. Just wondering how 4:10s would do on the highway. 

[AH64ID]

 

With the tall OD ratio of the 47RE the 4.10's will do better on the highway, especially if you ever tow. 

 

I wouldn't go with cheap gears, you have a high torque motor and big tires. 

 

Have you ever installed gears before?

 

I would look into Yukon gears. They are decently priced and strong. 

 

 

Edited July 6, 2018 by AH64ID

[Mopar1973Man]

45 minutes ago, AH64ID said:

With the tall OD ratio of the 47RE the 4.10's will do better on the highway, especially if you ever tow. 

 

@AH64ID is right the 47RE is a 0.68 ratio in 4th. Compared to the manuals at 0.73 and 0.75 ratio. 

 

45 minutes ago, AH64ID said:

I wouldn't go with cheap gears, you have a high torque motor and big tires. 

 

Exactly. You quickly find out the weakest link. Tall tires tend to trap torque in the driveline where the gear ratio is in hopes of releasing that torque to the tires but if the gears are of poor quality it might go SNAP!

[trreed]

Rock Auto also has genuine Spicer gears for around $200 for the ring and pinion.  Timkin bearings are another $200.  Shim kit is separate for some reason. 

There is also a carrier break somewhere around the 4.10 area for Dana axles.  I've seen accounts that the break is at 3.73 / 4.10 and also that the break is at 4.10 / 4.56.  But I'm almost certain that it's at 3.73 / 4.10, so you'd need a 4.10 carrier.  Something to research before buying gears.

 

Edit: Do you have a D70 or a D80?  If you have the D80, it looks like rock auto offers Spicer gears with a thick ring gear to use your current carrier.  D70 does not have this option looks like

Edited July 6, 2018 by trreed

[AH64ID]

As a SRW with an auto it should be a D70U. IIRC it will need the 4.10 carrier. 

[tylertrebilcock]

If I have to change the carrier it seems like it’s not worth the money. The reason there so cheap is because there used, the ad says it’s out of a Dana 60 so I’d imagine genuine spicer. I’ve never done a gear change myself, my dad will be helping me who has done several on jeeps. 

[Scottfunk]

Every single search result I've ever seen on the topic says the Dana 70 carrier break is between 4.10 and 4.56. I just picked up a set of 4.10's this morning from the junkyard and I'll be doing the install tomorrow so I'll let you know (changing from 3.55). I've only got 33's on my truck and I never even considered 3.73. I guess the final drive ratio of my Allison being so much higher (.61) probably helps. I'll let ya know how everything goes in the morning @tylertrebilcock

[Scottfunk]

The marks on my gears indicate that they're a matched set ton tre same run. The part that I'm curious about and I'm hoping someone can help with this is the "5.375" engraved into the nose of the pinion. And no, it's not a 5.375 gear set as indicated by the "10/41" stamp on both parts. @Mopar1973Man ? Any insight?

[Mopar1973Man]

6 minutes ago, Scottfunk said:

@Mopar1973Man ? Any insight?

[trreed]

I believe it is the thickness of the shim pack to get you started.  Dana parts usually have a +/- # to indicate how many shims to add or remove to get to the correct pinion depth.  Obviously, you'll have to set up the gears and that number may change.

Edited July 29, 2018 by trreed

[IBMobile]

Could be the pinon depth setting which would be the distance from the pinon face to the ring gear centerline.  

[Scottfunk]

Well I never did figure out what 5.735 means but I got the gears in. I may actually be getting pretty good at this. I even got a carrier bearing shim from the donor vehicle so I ended up with some carrier preload which I didn't have before. Next time I'll have dummy bearings for sure, what a pita! The ring gear in a 4.10 is a beast compared to the ring gear in the 3.55. I'm anxiously counting the hours until the rtv is cured and I can test drive her! 

[trreed]

How did the pattern turn out?.  If you took the carrier out easily, that means the original preload was gone.  My D80, the carrier fell out of the housing, and when I put it back in, it was so tight that I had to kick it in lol.

[Scottfunk]

The pattern looked good and will also not be suffering from diaper rash. I beat the carrier in with a rubber mallet but it took like 5 tries cuz the damn carrier shim kept spitting out. Saw this guy in a video with this little ratchet deal to test the pinion preload instead of a nut. I will definitely be figuring that one out. That and dummy bearings everywhere. All in all I think it went well and it's tons better than it was when I took it apart the first time. I had almost a quarter inch play in the pinion and there were no shims in there. I am seriously dying to test drive!

[trreed]

I waited an hour for the rtv on the cover to set.  And it hasn't leaked yet. I had a lot of pinion play before I filled mine and drove it.  Afterwards, almost no play at all. 

 

Edited July 30, 2018 by trreed

[Mopar1973Man]

I should get you two @trreed and @Scottfunk build a differential article showing how to do this. (Hint!)

[tylertrebilcock]

On 7/28/2018 at 6:36 PM, Scottfunk said:

The marks on my gears indicate that they're a matched set ton tre same run. The part that I'm curious about and I'm hoping someone can help with this is the "5.375" engraved into the nose of the pinion. And no, it's not a 5.375 gear set as indicated by the "10/41" stamp on both parts. @Mopar1973Man ? Any insight?

That is your pinion depth. If you don’t have the tool to set this you will have to change the shim thickness until you get the right pattern