Overdrive on a '62 Willys CJ-5 -- is it worth it?

I have been trying to determine if putting an overdrive on my '62 Willys CJ-5 is worth the money. My jeep has the F-head 4-134, with a T-98 tranny and Dana 18 xfer case. What are my expected gains? Now to add more to the mix, the Jeep has been lifted and 10.5-31's X 15's are under it. The tires themselves will make a difference, since they are so much larger than stock. Would the addition of the overdrive cause the engine to not have enough power to really roll this setup, or can the 4-134 handle it, due to the lightness of the vehicle? Since I have yet to get my Jeep to the point where I can drive it, I have no idea what to expect. Any advice would be appreciated. Thanks to all...

 

I run a 55 cj-5 with an f-head , t-90 and a warn overdrive. I also 31" tires. Truthfully , I get maybe 5 to 8 more mph. The trans whines considerably less with OD engaged. Forget about 70 MPH, It wont happen

 

I use mine mainly for splitting gears.....I like it for that... I don't really use it as an "overdrive"

 

The overdrive is on my shopping list for that reason alone. I also want to use it on hills - I can really see myself using a "2nd 1/2" gear in my area. That said, it s at the bottom of the list - I have too many other minor issues to sort out first and it drive OK the way it is.

 

The overdrive is a nice add-on, but it won't turn your F134 Jeep into a highway cruiser. The main problem is not gearing, but power. Wind resistance is a mighty barrier, and increases with the square of velocity (speed). Clearly, the aerodynamics of a CJ are terrible. With the low gears, you run out of RPMs as you approach top speed. With the overdrive, you will run out of power as you approach top speed. But these two top speeds are not very far apart for the F134 CJ.

Same thing happens with taller tires. Tall tires plus an overdrive could actually decrease your top speed by reducing engine speed enough so that you approach the power limit at a lower speed.

 

5.38 axles?

 

I like that Howard... well said.

eti, you may want to check the 4 videos on Utube from jpetrowich testing the overdrive in his CJ2a. Google "Overdrive" or "CJ2a Overdrive test 2"

 

4.27s or 5.38s? With 5.38s I would say definitely. I have 4.27s and 30"ish skinny tires and the od is nice but not necessarily a requirement.

 

here one way i use mine.... i usually only split 3rd and 4th, but i tried the 8 speed just for fun.

https://www.youtube.com/watch?v=6Q9g3bZX_Lo&list=UUlEKC42cNW5o6vk4Miy0MSw

 

My only experience with an early CJ5 is this 1961 I bought last Fall. It's stock and fully restored with the 4-134 F Head.
I push the engine to 50-55 no problem. I cannot imagine wanting to go any faster in a utility vehicle with a suspension, brake system and CG that was not designed to go any faster.
Plus what little gain in economy and or performance is outweighed by the cost of the overdrive unit. $1K buys a lot of gasoline.
And the stock 9" brake drums cannot stop the stock CJ5 adequately at any speed!!

Use the money to upgrade the brakes. At least the stock Gear Ratio provides some engine braking when you take your foot off the gas pedal and try to engage the weak suck stock brakes! These brakes have puckered my sphincter a few times

 

Millenium Falcon....great video....nice diesel jeep. Did you do the work mating the Mercedes diesel engine to it? Wasn't the OM617 a five cylinder? I had that in an 84 300SD....put 325K miles on it before I sold it....great engine!

 

Thanks! Yes it out of an 83 MB 300d. They are good engines but don't have much torque so that's why i needed the Overdrive... So I figured the OP might want to use an overdrive for the same reason... I used to run a 3 speed and it had some huge gaps between gears too.

 

Timgr,

Read you loud and clear. I once had a 280Z that I could run faster in 4th gear with the engine redlined, than I could 5th gear. It would do a respectable 147 mph that way, and that car was a helluva lot more aerodynamic than this Jeep will ever be. A friend of mine dropped a 'vette engine in a 1938 Dodge pickup, a lot of which had been converted to fiberglass. He had it coupled to a 4L60E tranny and the rear end was out of an older Dodge Satellite with really tall gears in it. One night he came up against a 600 Mercedes (don't know the class) and they went for it. He said that the Mercedes was limited to XXX number of miles and when he hit that speed in the Dodge pickup, he figured the front fenders were coming off and flying rearwards. He and the Mercedes owner pulled over and had a good chat. I imagine that the Mercedes dude was a bit surprised...

I will most likely do what Glenn said I should do. When I finally get it on the road, I will drive it and see how it feels. I like the idea that two others had about "gear-splitting" Reminds me of an 1965 Olds 98 that I had. It had the Turbo 400 VP tranny in it. It actually had a variable pitch torque converter in it (hence the "VP"), which would provide a part-throttle downshift by changing the pitch of the vanes in the torque converter. Then if you mashed it, you would get this plus a downshift into a lower gear. Made 6,000 pounds of car move out fairly quickly.

Thanks for the comeback. It is appreciated. Have a good "whatever you are up to". Later...

 

I am not expecting speed out of this vehicle, but I do like the idea of gear-splitting as others have mentioned...

Thanks for the comeback...

 

Thanks, Glenn. I do like the idea of gear-splitting... I will take your advice, however. I may not want to go any faster than stock...

 

jwjeep

5.38 axles on a limited slip...

 

That combination with the OM617 diesel and the OD is interesting. The unturboed 617 reaches it's max torque of ~128 Foot Lbs between 1100 to 2000 rpm.

The 4-134 F Head does not achieve 114 Ft. Lbs until after reaching 2,000 rpm and above. The 617's torque range is perfect for a splitter......but I don't see the cost-benefit of adding an OD to a 4-134 F Head.

Sorry eti engineer......I am not trying to discourage you! But if you do add the OD to the 4-134 rig I would like to hear your feedback.

We had an 88 Vette with the Doug Nash 4+3 overdrive manual trans......now that was fun!!......but that engine had endless hp and torque to push through all of those ratios.

 

my turbo 617 claims 125/180 hp/torque. It doesn't make any power or torque below 2000rpm that is why I needed/love the OD.