AX5 fifth gear and AX15 fifth gear

[eaglescout526]

Here’s an idea. I don't know how many of us have looked at a 5 and a 15 and said I could swap the internals or even conceived the thought. Hell I’ve never seen a 15 in person. I have seen a BA10/5 though. 

 

Well i’m wondering, can the fifth gear of the 15 be swapped and used on a 5?

 

But Eagle, why would you want to do such a thing?

 

Well I would love to cruise at high way speeds without being at 3000 rpm at 65mph on the poor little 2.5L. Now I could go the route of dropping in a 4.56 gear ratio and see if that would help, which it probably would but doing differential work scares the hell out of me. I’m fine with grenading a trans but not a rear diff if I do something wrong on the swap. 

So that being said, I now have an extra AX5 and maybe someone might have an thought on putting the 15’s fifth gear on the 5. 

[mnkyboy]

I doubt any of it would swap, besides  .85 vs .79 isn't much of a difference. 

 

If you did anything, I think you would be much better off just putting an AX15 behind the 2.5l

[eaglescout526]

That thought crossed my mind. I just gotta hunt down the bell housing. Course I did just get AC for the 2.5 so the sky’s the limit on that one. 

[Jeep Driver]

I'm not an LS guy but this should get the point across. 

All you'll do is waste your time, otherwise. 

 

[Pete M]

there's nothing wrong with 3k on the highway.  

[omega_rugal]

i don´t think they swap...

[Jeep Driver]

2 hours ago, eaglescout526 said:

3000 rpm at 65mph

 

2 hours ago, eaglescout526 said:

Now I could go the route of dropping in a 4.56 gear ratio and see if that would help

Going from 4.10 to 4.56...............just guessing...........you'd be at something like 3400rpm. 

 

Just go up a size in tire size. 

[89 MJ]

I would look into getting an 8.8 with 3.73 gears. Then you get better highway gears and a stronger rear end. 

[Eagle]

3 hours ago, eaglescout526 said:

Well I would love to cruise at high way speeds without being at 3000 rpm at 65mph on the poor little 2.5L. Now I could go the route of dropping in a 4.56 gear ratio and see if that would help, which it probably would but doing differential work scares the hell out of me. I’m fine with grenading a trans but not a rear diff if I do something wrong on the swap. 

So that being said, I now have an extra AX5 and maybe someone might have an thought on putting the 15’s fifth gear on the 5. 

 

They won't swap. The AX-15 is a larger, beefier transmission.

 

As has been mentioned, the difference wouldn't be worth the effort anyway. If mnkyboy's ratios are correct, you'd go from 3,000 RPM to 2,788 RPM. But ... you shouldn't be turning 3,000 RPM at 65 MPH. If you're on 225/75-15 tires, at 65 MPH you should be turning 2,756 RPM with 4.10 gears. Even if you're on 205/75-15 tires the RPMs would only be 2,869.

 

As for changing the axle gearing, 4.56 would be going the wrong way. That would increase your RPM. If anything, you should be looking at 3.73 gearing. That would put your RPM at 65 MPH (with 225/75-15 tires) at 2,507 RPM.

 

But don't be intimidated by 3,000 RPM. You have to remember that the 2.5L Jeep engine is derived from the old AMC 199/232/258 cubic inch engine that was first introduced in a Rambler in 1964. I grew up in an AMC family. In those days, overdrive was an expensive option that nobody bought. The standard gearing on the 3-speed AMC cars (and later on the 4-speeds, since they were still 1:1 for top gear -- no overdrive) worked out to 24 MPH per 1,000 RPM. That meant 2,500 RPM was 60 MPH, and 3,000 RPM was 72 MPH. We cruised them at 70 MPH all the time, and the engines lasted forever. My brother's 1972 Gremlin with the 232 was well beyond 300,000 miles when he finally lost touch with it.

[eaglescout526]

2 hours ago, Jeep Driver said:

 

Going from 4.10 to 4.56...............just guessing...........you'd be at something like 3400rpm. 

 

Just go up a size in tire size. 

Probably right about that, wrong direction to go, but ratios were never my thing and I am doing my best to understand them more.

Might do that.

 

3 hours ago, Pete M said:

there's nothing wrong with 3k on the highway.  

 

1 hour ago, Eagle said:

 

They won't swap. The AX-15 is a larger, beefier transmission.

 

As has been mentioned, the difference wouldn't be worth the effort anyway. If mnkyboy's ratios are correct, you'd go from 3,000 RPM to 2,788 RPM. But ... you shouldn't be turning 3,000 RPM at 65 MPH. If you're on 225/75-15 tires, at 65 MPH you should be turning 2,756 RPM with 4.10 gears. Even if you're on 205/75-15 tires the RPMs would only be 2,869.

 

As for changing the axle gearing, 4.56 would be going the wrong way. That would increase your RPM. If anything, you should be looking at 3.73 gearing. That would put your RPM at 65 MPH (with 225/75-15 tires) at 2,507 RPM.

 

But don't be intimidated by 3,000 RPM. You have to remember that the 2.5L Jeep engine is derived from the old AMC 199/232/258 cubic inch engine that was first introduced in a Rambler in 1964. I grew up in an AMC family. In those days, overdrive was an expensive option that nobody bought. The standard gearing on the 3-speed AMC cars (and later on the 4-speeds, since they were still 1:1 for top gear -- no overdrive) worked out to 24 MPH per 1,000 RPM. That meant 2,500 RPM was 60 MPH, and 3,000 RPM was 72 MPH. We cruised them at 70 MPH all the time, and the engines lasted forever. My brother's 1972 Gremlin with the 232 was well beyond 300,000 miles when he finally lost touch with it.

Being only 22 and used to how modern cars are, 3000rpm seems high and foreign for me while cruising. Glad my idea brought more insight on traveling at 3000rpm. I'm currently on 215's and my tach is accurate, 3000 was just a good round number, its some where like 2900.

 

1 hour ago, 89 MJ said:

I would look into getting an 8.8 with 3.73 gears. Then you get better highway gears and a stronger rear end. 

8.8, never happening. Staying stock. I guess I don't do enough freeway driving to really change the gearing.

 

I do appreciate everyone's responses. I had a thought and I have learned that the idea I have won't work.

[omega_rugal]

if you want an on-road only  truck you may regear down to 3.55 as long as you go overboard with the tires... 

[dasbulliwagen]

Any axle gearing higher (lower number) than a 4.10 on a 2.5 will make if feel slower, as there isnt as much torque multiplication at the axle. don't expect too much from the 2.5. Drive it like an old man, and it will last forever, just don't expect it to be a powerhouse and youll be fine. The advice given above is good. 3000 RPM is right in the sweet spot power band for the engine, and it would be happy there all day long!

[eaglescout526]

21 minutes ago, dasbulliwagen said:

Any axle gearing higher (lower number) than a 4.10 on a 2.5 will make if feel slower, as there isnt as much torque multiplication at the axle. don't expect too much from the 2.5. Drive it like an old man, and it will last forever, just don't expect it to be a powerhouse and youll be fine. The advice given above is good. 3000 RPM is right in the sweet spot power band for the engine, and it would be happy there all day long!

Glad to know that! She seems happy to sit there all day. She will even do 70 for me if I ask her. 

 

Again this was just an idea. I had a spare trans laying around now and it turns out the trans is an AX4. Never seen one in person till now.