5.38 With 15” Wheels And Warn Od

I’ve just discovered that my 64 CJ5 project jeep has 5.38 axles ratio. Will I be happy with 15” wheels? It does have a Warn (perhaps “worn”) OD. It is powered by F134 that I would like to keep

 

15" wheels are fine. The more important question is, what size tire are you running? 6.00 x 16s and 7.50 x 15s are pretty close in diameter and those are the stock sizes for back then.

My 53 3A has an L head with an OD and the 15" wheels with stock tires drives fine.

 

Thanks for the help. I’ll run the tallest tires I can get. I have a Goodyear Suburbanite on what I assume was the spare and I’d like to find some more. It looks great and has a pretty tall profile.

 

For a F134 Jeep, I would not be too concerned that my tires were not tall enough. Your gearing is not the limiting factor - instead you are limited by the wind resistance versus the power of the engine. Power goes up with engine RPM. If you lower the RPM too much, you won't have enough power to push the air.

 

I'm running a souped up 134L T-90A and D-18 and a ATV 30% OD 5.38's and a P235/75R-15 tire 28.66" tall my rpm at 60mph will be 2665 or there abouts.

 

i think that the engine is really the limiting factor, and if you plan on trying to move somthing heavy, or such things, the 5.38's (stock) are great. these jeeps were made to go about 50 tops (on a good day with a tailwind), and were better suited for agricultural/industrial purposes. if you wanna go fast, it'll take some work.

 

The Overdrive is the clue, it gives you the top speed of a Jeep with 3:73 axels. You should be fine on or off the road.

 

My warn Overdrive didn't gain me any top speed with a worn out f134 with the right steel toe size 11 on the floor I would do 65 In direct and 60 in Overdrive.
I thought it was closer to 4.10 equivalent axles and the military jeeps typically had 4.27 axles and splits the Transmission ratios nicely.

The Overdrive really shines at 50 or 55mph don't expect to hurry with a hurricane.

 

That would make a great T-shirt or valve cover sticker.

"Don't expect to hurry with a Hurricane".

 

Yep, not as tall as 3.73. 5.38 * 0.75 = 4.04 ish. Still taller than the optional 4.27 gears jeep offered with the F134.

30% overdrive sounds like more, but is likely the same thing. 1/1.3 = 0.77, the same within some rounding error. Depends on how you describe the gearing arithmetically.

 

With 5.38’s and 25% OD your final drive ratio is 4.03.
That is the optimum gearing for a strong running F-134.
Simply not enough power to run a faster final drive ratio than that.
I’ve tried running 4.89’s with OD (3.66 FDR) and the Jeep was actually slower.

 

For me an overdrive was not about raising top end speed of the Jeep, it was about bringing the engine RPM down to something I would want to run continuously.
I'm running 29.5" diameter tires with 5.38 axles and Saturn overdrive. I can now cruise 55 mph at about 2600 RPM if I need to pace with traffic, but 50 MPH at 2400ish is more comfortable. Above 55mph with the overdrive the engine really starts to run out of horsepower. So I would not suggest tires taller than mine.

 

4.27 gears were the standard ratio in F134 Jeeps from around late '63 when Kaiser took over and switched to rhe T90C with the lower 1st gear. The 5.38 gears were optional for these T90C Jeeps. 5.38 gears were standard for most all pre-'63 CJs, including the military versions.
An F134 CJ with 5.38 gears equipped with an overdrive gets you the best of both worlds. Low enough for slow off road work, yet a tall enough ratio for cruising the highway (but not interstate speeds!).
-Donny

 

Well once again, I’m pleased with the “behind the barn” find ‘64 I’ve gotten myself into. Lots of work to do on it. But the engine is at the machine shop and the frame is stripped and ready to go to the blaster. Very little rust on the frame, the bumpers have been bent some as well as the transmission cross member. I’ll try to get some pictures into a build thread this weekend. Thanks for all the replies to this thread.

 

I had a '64 CJ5, F134 with 4.27 axles and a T90A. I wonder if this was a transitional model or something got switched around later. It was once owned by a service station so they definitely had the capability to work on it.

 

I'd say the transmission was swapped at some point. The low 1st gear ratio went with the 4.27 axles.
-Donny

 

The Warn overdrive was authorized by Kaiser Jeep Corp in 1964 as “Jeep Approved Special Equipment”.
It was only approved for jeeps with 4.89 and 5.38 ratios. ( I have the original service bulletin )

I ran an overdriven 5.38 F134 3B as my sole and only vehicle till 2000 . I ran it long and hard, always maintaining 60 to 65 on the interstate. At that time I felt I could no longer keep up a good pace. On steep interstate grades it would drop to 55 mph.
As for tire diameter on a stock standard overdriven cj I prefer 6.50 x 16 minimum to 7.50 x 16 maximum.
Or 30” to 32” tall.

 

i need one.

 

That is impressive. I don't think I've ever seen a flat fender on the road here, let alone on the interstate.

 

For me, living in the mountains, and any direction I go means a steep pass, the overdrive is more important for splitting gears. With a 4 speed, 3rd-over is perfect for a 9 percent grade instead of having to go down to 3rd, and 35 mph.