5 speed/6 speed swap?

[speedyj]

Can I swap my tired and ready-to-go-any-day-now 5 speed in my '03 3.7 w/ the newer '06+ 6 speed? Are the splines the same? Are they dimensionally roughly the same? (brackets, mounts, etc.) Wiring issues? Am I dreaming?

 

[J-Thompson]

Can I swap my tired and ready-to-go-any-day-now 5 speed in my '03 3.7 w/ the newer '06+ 6 speed? Are the splines the same? Are they dimensionally roughly the same? (brackets, mounts, etc.) Wiring issues? Am I dreaming?

problem is not so much with the transmission fitting
it should bolt up to the bell
the problem is in drive shafts and I think the t-case input or the out put on the trans is different

 

[Powerslave]

If the 6-speed did bolt up, then you would have to machine the shafts... There is a place in Pittsburgh that does them, been in business ever since I could remember... You would need to get the correct output spline on the transmission, dunno how hard that would be, or even if you can swap it. It is doable with money...

 

[speedyj]

problem is not so much with the transmission fitting
it should bolt up to the bell
the problem is in drive shafts and I think the t-case input or the out put on the trans is different

Bellhousings being the same is a no brainer - same motor/casting revision. Drive shafts - the axles/shafts splines are the same that I know of (D30/8.25). I mean a shaft swap is easy but....

 

[speedyj]

If the 6-speed did bolt up, then you would have to machine the shafts... There is a place in Pittsburgh that does them, been in business ever since I could remember... You would need to get the correct output spline on the transmission, dunno how hard that would be, or even if you can swap it. It is doable with money...

Explain what needs to be machined and why. The input shaft on the 231 could be swapped to solve the potential output problem, no?

 

[Atrus]

Stupid question, but why?

From the brief amount that I remember reading, wasn't the 5 speed ratio actually better than the 6 speed?

 

[tjkj2002]

Explain what needs to be machined and why. The input shaft on the 231 could be swapped to solve the potential output problem, no?

The 6-speed KJ's did not come with the 231 t-case.You got other considerations also like clutch actuation,flywheel compatibility,length of trans(driveshafts),trans/t-case mount position,and other small details that will nickel and dime you to death.Plus those 6-speeds are bloody expensive compared to the 5-speeds

 

[speedyj]

Stupid question, but why?

From the brief amount that I remember reading, wasn't the 5 speed ratio actually better than the 6 speed?

Potentially better fuel mileage on the highway (lower revs). Nothing more.

 

[speedyj]

The 6-speed KJ's did not come with the 231 t-case.You got other considerations also like clutch actuation,flywheel compatibility,length of trans(driveshafts),trans/t-case mount position,and other small details that will nickel and dime you to death.Plus those 6-speeds are bloody expensive compared to the 5-speeds

They didn't? That's the first time I've ever heard of a non-231 t-case being under a KJ. Odd. What model is it? Oh I'd certainly do a new clutch/flywheel/master/slave while I was in there but wanted to know what the model of the ****** is and the physical specs of it. I know my 5 speed is the NV3550. I've actually found a few 6 speeds up here in the wreckin' yards under KJ's and Nitro's that have fewer miles on them and are cheaper than the older 5 speeds.

 

[sleeve]

Six Speeds came with the 241... TBJ or JT knows best on this subject.

 

[Atrus]

Potentially better fuel mileage on the highway (lower revs). Nothing more.

Right, but IIRC, the 5 speed had a more favorable gearing in 5th than the 6 speed did in 6th.

I could be wrong, but I'd research that for sure before dropping the cash on a conversion. Anything can be done with enough $$, but the question becomes "is it worth it"

Edit: just checked - I believe the 5 speed has a .73 5th gear while the 6 speed has a .84 6th gear.

 

[J-Thompson]

Oh yeah
the 6 speed KJ did have an NP241
but the 6 speed TJ's did not and IIRC it is the exact same
trans with a different out put to tie into a 231

 

[speedyj]

Well I think at this point I'll just, to keep it simple, stick with a replacement 5 speed. Second question: can I steal one (NV3500) out of an '03-'07 Wrangler 4.0L and will it it work? They are much more common than 5 speed KJ's.