5.38 To 4.27 Swap. 64' Cj5 With F134 / 4 Speed

I'm interested in learning ways to increase my cruising top speed and lowering the rpm while cruising around town.

It seems sacreligious because my cj5 is currently set up to be a crawler. Some people might find that appealing. Unfortunately, I don't offroad much anymore and would rather be comfortable cruising around town and not spinning the engine so high. My current top cruising speed is about 45 and the engine is VERY loud at that speed. I don't have a tach so no idea what the revs are. My guess is around 4 billion rpm

I currently have:
Dana 25 front Dana 44 rear. Both with a 5.38 final ratio
4-speed t98 trans
Lockrite locker in Rear

All are unnecessary for my style of driving haha. I've thought about an Overdrive but when I wrote Kaiserwillys about the Saturn OD fitment, they said it wouldn't work for my setup. Maybe something to do with the shift levers getting tangled in reverse? That's the only explanation I could think of.

Oh and the Tires are 215/75/15

Anyway, Is there a way to swap the ratio of my diffs without having to change out the entire axle?

Thanks in advance!

 

Either a Warn or Saturn OD unit “will” work in your Jeep.
I have a 1953 3B with 5.38’s and a factory T98-A (removed from a CJ-5) and it works perfectly fine.
Much cheaper and easier than swapping differential gears.
That said you might also consider swapping Jeeps with one of the many jeepers who would absolutely love to have what you own.
In theory you could upgrade to a nicer condition jeep that way.
And FWIW an OD will increase your road speed a tad more than converting to a 4.27 gear ratio.
So you might consider swapping for a similar Jeep having a 3 speed and the Warn OD unit.

 

LOL I was waiting for that! I know I deserve a roasting for even bringing this topic up hahaha.

I DO love my jeep. It's a show quality rig now, Runs and drives like its really happy and healthy, and I've put almost 200hrs of work into it since December. At this point they'll be prying it from my cold dead hands cause I wouldn't want to give it up.

If it comes to me just embracing the gearing and driving a bit slower, I'm totally fine with it.
That said, If I can make my enjoyment a bit more comfy in a way that's not a MAJOR SURGERY I'm all ears.
The OD would be really cool. That way, I'd effectively have 8 forward gears and 2 reverse. I've also always loved the look of having 4 shift levers. A real conversation starter.
Which OD do you have? Any reason to choose one over the other?

 

If you already have a 4spd transmission and a Hi-Lo transfer case, then you now have 8 forward and 2 reverse ratios. Overdrive gets you 16 forward and 4 reverse.
Warn style Overdrive is most easily adaptable to Dana 18 transfer cases. D20's are rarer and more difficult swaps.

As a Warn OD owner of a 5.38 geared '53 M38a1 and a 4.88 geared '57 Willys stakebed, I wholeheartedly endorse Warn overdrives.
Hermtheoverdriveguy.com is the go to source for OD's, parts and information. But the biz is just him and his son. They are SUPER BUSY with global sales. So communication is slow. Email is often best.

 

X3 on the overdrive

 

I didn't see what transfercase is employed here but assume it is a D18. If that is indeed the case, there isn't a single reason a Warn style OD can not be installed. As other's, the best solution here both dollar and time wise. The gain in top speed with either 134 is usually a bit marginal because the limiting factor is still power. The OD's really shine with a 225.

 

This is a concern with a 4 speed, overdrive, and dual shift tcsse. I just went through this with my 4 speed swap. The clearances between the shift levers is pretty close but it can be done!

 

My f-134 was fastest with 5.38s. In overdrive it ran out of power. I'ld embrace the 5.38s or go to 4.88
you can get an overdrive but I would not commit to 4.27 with a 4cyl. I know the t-90c got 4.27 but it's a big change.

I say that and I have 4.27s stashed away for after a sm465 swap but my 4.3 has more than double the horses and torque than the old f-134 I burned up.

 

As others have said, with a little bending and maybe some custom fab on the OD shift mechanism, you can get all the levers in there and working:

 

Maybe change the tire size to affect drive ratio?
The link below is to a handy tire size chart.

https://www.tacomaworld.com/tirecalc?tires=275-75r15-215-75r15

 

yep i was going to say that. Id go a 31" tire first you can pull that off without a lift thats the size i run. Im not sure if it would gain you as much as gears but its worth a try. Even if you get a used junk set of tires and wheel just to try for a while

 

Just another example of KW not being a reliable source of information. I agree with the suggestions of an OD as opposed to swapping gears in your axles. Less money, and a lot less work.

 

I suspect they don't want people to be disappointed if they expect it to be a kit like the 3 speed.

 

X4 on the overdrive. This would give you a final drive of 4.035. Pretty much bolt in and lower than 3.73. Plus it would be cheaper than changing gears in both axles and be able to split gears depending on the
driving conditions you encounter.

 

I've got the exact setup, f134, T98, single stick dana 18 and running 4.27s in the axle.

My top speed is about 55 mph, comfortably without the engine screaming.

Unfortunately other than an OD there isn't much to be done with the old tractor motor.

I recently bought/drive a 68 with the dauntless and man, I tell you it's opened my eyes to jeeps. The fhead had its time and place, but a racehorse it ain't. Think of it more like a pack mule. It will get you anywhere, reliably, just not quickly.

 

Single stick D18? Such an animal existed?

 

It wasn't ever a tractor motor. It was never actually built for the only "tractor" that ever ended up with it: the Empire. It is a very direct descendant of the 1926 Willys Whippet engine. In a lot of ways, it never graduated from that mid twenty's technology.

And yes, the 225 is/was a night and day difference and I still find if difficult to see why anyone would have purchased the F head after the 225 was available. I had that eye opening experience in 1969 when I bought my CJ5 new. The several years later, the 327 went into the 3B and the eyes opened wider-----

 

All the 225 CJ's got the single stick version.

 

My 1970 with the fhead got one. It was bone stock. So, yes they got single stick.

 

Not for sure...but it seems like the single stick came out when the 225 arrived and was used for both engines.