Swapping 4.10's for 2.72's

[007]

I'm thinking of going to 2.72's in my Dana 30 and AMC20 . I have 4.10's now and I'm tired of running almost 3000RPM's at a mere 55mph.

Using the GrimmJeeper gear ratio calculator, with my low range I'll be fine with 2.72's off-road and 31" tires.

Is there any special equipment or process I'll need to do this swap? I'm buying a nice used 2.72 carriers and ring-pinion sets for each differential - is that all I'll need?

I'm having a good trusted mechanic help me, he works on contstruction equipment by day.

 

[tarry99]

I'm thinking of going to 2.72's in my Dana 30 and AMC20 . I have 4.10's now and I'm tired of running almost 3000RPM's at a mere 55mph.

Using the GrimmJeeper gear ratio calculator, with my low range I'll be fine with 2.72's off-road and 31" tires.

Is there any special equipment or process I'll need to do this swap? I'm buying a nice used 2.72 carriers and ring-pinion sets for each differential - is that all I'll need?

I'm having a good trusted mechanic help me, he works on contstruction equipment by day.

Gear ratio's are personal to the guy who own's the Jeep..........If all you do is freeway it then by all means go the 2.72.......if it's a Combo Jeep I might suggest looking at putting a taller Tire on it.........best of both worlds!

 

[007]

I had hoped that too, but I can't get tall enough without a 4" lift and I have no desire for that.

Go to Grimm Jeeper and go to the gear ratio page. Use a GM Turbo 400 and a Borg-Warner 1345 with 29" tires (235x75x15).

You have to remember this has the low-range so that saves me on trails...

 

[tarry99]

I had hoped that too, but I can't get tall enough without a 4" lift and I have no desire for that.

Go to Grimm Jeeper and go to the gear ratio page. Use a GM Turbo 400 and a Borg-Warner 1345 with 29" tires (235x75x15).

You have to remember this has the low-range so that saves me on trails...

Cool.........Yep that should work OK.

On your R/R of the used gear sets, make sure you pay close attention to all the shims that are stacked up that set the clearance to the Ring gear Carrier to the case and also the Pinion gear..........some may even be damaged as you take them apart.

They both should have Pinion crush collars that need replacement and I would also replace the Pinion nut's, Be a good time also to change / inspect the bearings............and replace pinion seals and inner axle seals while your in there.

Also measure the two case's to see if there is any difference's between the two.......even a .001 difference will make a change to your new gear mesh setup and should be addressed.......

 

[007]

Good info... Thank you!

 

[1986cj7]

I'm thinking of going to 2.72's in my Dana 30 and AMC20 . I have 4.10's now and I'm tired of running almost 3000RPM's at a mere 55mph.

Using the GrimmJeeper gear ratio calculator, with my low range I'll be fine with 2.72's off-road and 31" tires.

Is there any special equipment or process I'll need to do this swap? I'm buying a nice used 2.72 carriers and ring-pinion sets for each differential - is that all I'll need?

I'm having a good trusted mechanic help me, he works on contstruction equipment by day.

I've a set of 2.73 AMC20 carrier and ring and pinion. Unfortunately I use the spider gears to make gear shifter knobs for me and a Friend but have the ring and pinion gear and carrier, you can have if you pay shipping. PM me if interested.

 

[007]

I've a set of 2.73 AMC20 carrier and ring and pinion. Unfortunately I use the spider gears to make gear shifter knobs for me and a Friend but have the ring and pinion gear and carrier, you can have if you pay shipping. PM me if interested.

I can't use my 4.10 carrier, so how about we swap carriers WITH spiders?

 

[Old Dog]

Cool.........Yep that should work OK.

On your R/R of the used gear sets, make sure you pay close attention to all the shims that are stacked up that set the clearance to the Ring gear Carrier to the case and also the Pinion gear..........some may even be damaged as you take them apart.

They both should have Pinion crush collars that need replacement and I would also replace the Pinion nut's, Be a good time also to change / inspect the bearings............and replace pinion seals and inner axle seals while your in there.

Also measure the two case's to see if there is any difference's between the two.......even a .001 difference will make a change to your new gear mesh setup and should be addressed.......

^^ what Tarry99 said.^^
I also have a set of 2:73 gears with open carriers that I would trade with you.

 

[007]

^^ what Tarry99 said.^^
I also have a set of 2:73 gears with open carriers that I would trade with you.

Are these for the Dana 30 or AMC20 or both?

 

[Old Dog]

Are these for the Dana 30 or AMC20 or both?

Yes.

 

[007]

Yes.

Yes to which...both?

 

[CJ]

Barter, swap, sell or place wanted items via PM or the classifieds.

Thanks,

 

[Old Dog]

Sorry bossman. I should have know better.

 

[CJ]

Don't worry about it, it is easy to get carried away.

 

[IOPort51]

darned right you should have!!^^^

anyway, I don't want to get in the way of commerce or anything but the 2.72 is a pretty drastic change, I am wondering if you may be happier with something like a 3.54/1 ratio.

I have 3.54 in my CJ5 and it works pretty well on and off road, with 31 or 33" tires and a 2.5 inch spring/1" body lift.

the combo puts me pretty close to the power curve peek ( 2000-2500 rpm) at 55/60mph.

 

[007]

darned right you should have!!^^^

anyway, I don't want to get in the way of commerce or anything but the 2.72 is a pretty drastic change, I am wondering if you may be happier with something like a 3.54/1 ratio.

I have 3.54 in my CJ5 and it works pretty well on and off road, with 31 or 33" tires and a 2.5 inch spring/1" body lift.

the combo puts me pretty close to the power curve peek ( 2000-2500 rpm) at 55/60mph.

Hey there IO (I'm the guy you met in Ouray by pure coincidence). Going from 4.10's to 2.72's is indeed a big swing - but I've gotta be realistic about what's going to happen with this Jeep. I want to be able to hop in this thing and drive literally "anywhere" on the Interstate or whatever (and not get my doors blown off OR run the motor at 3500rpm for a day straight), then be able to put it in 1st or 2nd in low range and be able to go do Black Bear. I also (as per your recommendation) I don't want to go over 31" tires with a 1"-2" body lift. I've spent alot of time on GrimJeeper's gear page and I can't find a better scenario. That doesn't mean there isn't a better option, but I can't think of one.

I guess what I'm wanting is perhaps a little different than most. I know I'm going to give up my 4.10 low-range stump pulling power, but I still think (based on the math) that I can do about every trail in Ouray with 2.72's and low range keeping the automatic in 1st or 2nd.

I'm open to thoughts on this, as well as mechanical tips/tricks spare parts I might need while doing the swap, etc.

And CJ - my apologies - point taken...

 

[tinhorn]

Going from 4.10's to 2.72's is indeed a big swing - but I've gotta be realistic about what's going to happen with this Jeep.

I envy you. Since I don't own a modern 1977 model, the best swap I can make is 4.27 to 3.73. Good luck on your project. (Isn't it fun knowing we can sell our rock-crawler parts for more than it cost us for our street gears?)