Changing gear ratios

[86jpcj7]

I have 33 inch tires with an AMC20 in the rear and Dana 30 up front with 3.54 gears but I am thinking about changing to 4.10 gears. Would this help my fuel economy or power? What's the ups and downs? If I tear into this what else should I modify or change?
Thanks.

Sent from my Z665C using Tapatalk

 

[IOPort51]

If your mileage gets better it won't be by enough to justify the cost of the R&P change. you will have more "power", an increase in mechanical advantage does that. you may try 31 inch tires and see if the mileage improves, this will simulate a drop in ratio, not as much as the gear change you are thinking about, but a bit.

 

[hole]

More torque/power yes, but it will limit the top end. I dont think 4:10's will help in the economy department though. If it were me I'd look into lockers of some sort at this time too.

 

[Torxhead]

If you have 3.54s it would have had to be an add on since they came with 3.31s as an option, and the standard gear was around a 2.73. If you spend a lot of time driving flatland I think what you have would be fine.

 

[86jpcj7]

I will be doing some wheeling but this is a father and son project and it'll be my first vehicle so I don't want to be drownded in bad fuel mileage so it's Goina take some thought. Thanks for your responses.

Sent from my Z665C using Tapatalk

 

[86jpcj7]

Do you guys think 3.54s will do a little mild off tossing, like just some small mud and little rock trails?

Sent from my Z665C using Tapatalk

 

[86jpcj7]

Offroading not tossing

Sent from my Z665C using Tapatalk

 

[IOPort51]

I have 3.54s and have no major complaints so far. you should be ok. If you wanted fuel mileage, you got the wrong ride.

 

[hole]

Do you guys think 3.54s will do a little mild off tossing, like just some small mud and little rock trails?

Sent from my Z665C using Tapatalk

3:54's will be just fine for most off road situations. I have 2:73's still and they work just fine for the most part. I like the high gears for the highway, so I picked up the LoMax 4-1 gears for my Transfer Case to give me a little better crawling speed in rocky situations.

 

[oss]

I've got 4.10s and gas mileage is about the same, 3.73s are a little closer on the chart for 33s. There's a chart on most vender web sites for tire size vs. gear ratio. I kind of like the lower ratio (just my opinion), but if your going to open the axles up it's better to only do it once. I'd just start by collecting the parts I know I'm going to need like bearings and seals first. Then make the decisions about lockers and gears after I've gotten the needed parts out of the way. sorry for being wordy

 

[Old Dog]

I like 4:10 with 33's but I'm not a highway driver, 45-50 on the backroads is what mine sees.
What Transmission do you have, that could make a difference in our answers.

 

[86jpcj7]

Thanks guys I'll check the the Transmission later and get back to ya

Sent from my Z665C using Tapatalk

 

[Saddle Tramp]

We seem to have been talking about this lately in several threads. A lot has to do with what you want to do with the jeep and I don’t think there is a right or wrong answer, just a personal one. I don’t see what Transmission 86jpc07 has in his jeep. If a T 5 it has Overdrive , if a T-176 it’s not, and if it’s a transplant who knows, all of which will affect what gears in the pumpkins would be best. Don’t forget with a Dana 300 it’s possible to lower the crawl ratio way down while keeping tall axle gears using a Teralow or Lomax kit.

 

[Lumpy Grits]

I run 4:88s with a 5 speed and 33 BFG/ATs.
Love it.
If you going to keep that dang model 20 rear end. Get a set of Moser 1 piece axles.
If you run a 4 speed-Go with 4:10.
LG

 

[billyballer]

As has been said an automatic Transmission vs a 4 speed vs a 5 speed make a lot of difference. You can get away with taller gears with most automatic transmissions, and a 5 speed will let you run lower.

All that said, I started planning a gear swap for my '86 when I was a lot younger and had plans to do a lot more wheeling. I couldn't wait to ditch the 2.73s. Well I gathered the parts to do a 4.10 swap with rear Ox locker and front Truetrac Limited slip, and now have installed them. Now part of me is wishing I had gone with a 3.55 or 3.73. I do a lot of highway driving because I live in the city and to get to trails need to hit the interstate. Even with a 5 speed the 4.10's and 31" tires leave me stuck in the slow lane. I'm planning to step up to 33" tires and that will drop rpms a little. If you have the opportunity try to find some local jeepers with different combinations and see if you can get a ride or at least get feedback.

As for what else to change, do one piece axles in the back, new ball joints in the front, maybe new hubs (the stock ones are weak), and upgrade the yolks on the differentials and Transfer Case to the u-bolt style (the stock strap style are failure prone). If you really want to dig in, it is a good time to do springs as well.

 

[86jpcj7]

I like 4:10 with 33's but I'm not a highway driver, 45-50 on the backroads is what mine sees.
What Transmission do you have, that could make a difference in our answers.

My jeeps an AMC 258 i6 / 4.2l AMC 258 i6 / 4.2l automatic so I'm thinking it has the TF999 does this sound right?

Sent from my Z665C using Tapatalk

 

[Posi]

Yes, if it's original.

 

[Lumpy Grits]

TF999 has the same 1:1 top gear ratio as a 3 or 4 speed manual does.
Keep that in mind as autos do not do well be'n 'lugged' down(heat)with 'tall' gears.
LG

 

[86jpcj7]

Is the TF999 geared low

Sent from my Z665C using Tapatalk

 

[Posi]

2.47:1