Overdrive Options

My '73 CJ5 with a high torque (modified) 258 engine is great, but with the 33" tires and 4.56 gears in the back it makes my top speed around 60mph... What are my options for adding overdrive to this???? I know that warn and others made overdrive units, but I beleive that they are only for the Dana 18 (mine had a 20). The switch out from D-20 to D-18 involves a new Rear Axle housing if I remember correctly. Has anybody attempted putting a 5 speed in a CJ5???? And if so with what luck?

 

Do you have a tach? What RPM do you have at 60? I calculate 2785 RPM at 60, 3250 at 70 for your setup. That should be ok. Maybe your tires are shorter than you think they are.

You're right about overdrives and the D18. Won't work with a D20.

There are a few 5-speeds that you could consider - the main problem is their length.

 

There's another option for an overdrive here. There is a Ford toploader overdrive transmission called an RUG. It's basically a car 4 speed where 3rd gear is 1:1 ratio, same as any normal 3 or 4 speed, and 4th gear is a 25% overdrive. They are about the same length roughly (don't have actual dimensions on hand) as a T-15 with the T-15 bellhousing when adapted to a Jeep transfer case. Maybe even a little shorter. Being a Ford transmission you can use the T-150 bellhousing from a '76-'79 CJ and it will bolt right up in the front to an AMC motor. These tranny's are the equivalent in strength of a T-150/Ford toploader RAN transmission with a slightly lower first gear. The only other option I see is a T-5 from a later model CJ which is a 5 speed, and not all that strong, and you have to change to a Dana 300 transfer case due to the bolt pattern on the back, and is quite a bit longer than what you have now. An NV 4500 truck 5 speed is WAAAYYYYY too long to fit in a CJ-5. Trust me, I've got one. Nickmil.

 

Nick, do you mean the T170FT shown here? http://www.motivegear.com/tech_info/tranny_guide/tranny_guide.html Will the R&P 4-speed T-TC adapter work with this transmission?

There's a T5WC available aftermarket that would be stronger than a Jeep T5: http://www.5speeds.com/t5/jeep.html Pricey though.

 

I am running at 3100rpm at 60mph....The tires are 33"x12.5". I could still be off on my speedometer calibration though.... I like the Ultimate Jeep T5 you linked to... It has an awsome 1st and OD!!!

 

Sparky the NV3500 might be a good deal as this is the transmission used in the 4x4 Dakota's also, so they shouldn't be rare, so long as they fit.

 

Yup, that's pretty much the one. I've built a couple of these although they were the cast iron car version. The biggest down side to them is the external shifter, but really not a huge deal. The R&P adapter should work but need to make sure of the bearing sizes. Paul at R&P knows the details of that part. I can't remember all the variations on that particular trans. The World Class T-5 is a great trans but VERY expensive to do. The standard T-5 does not hold up very well to stock Jeeps, let alone lifted, etc. You also must change to an Dana 300 transfer case to make one work with right hand front pumpkin and centered rear output. The NV 3550 would be an excellent choice, but I would have to measure one and see if doable in a short wheel base. Again, would have to change transfer cases. Would also have to get the right NV3550 as there are different output spline counts, clocking of the transfer case pattern, etc.
I'm sure it could be done, I just haven't done it yet, although someone else probably has. Might be kind of expensive, I know they are in my area. Nickmil.

 

IF you could find one, use a borg-warner setup from a studebaker(?) to replace the output shaft, seen a few pics of them on flatfenders. Only down side is works in 2wd only.

 

I like all the options... Thanks for all the info. I am not quite sure on Time Frame, but look at keeping the cost around $1500 - 1700. I understand that some fabrication might be required...

 

Other problem is they replaced the output housing and shaft on the transfer case and they are fairly long. Comes down to driveshaft length issues again. Not saying it hasn't been done, cause it has lots of times just like you said, but want to keep the rear drive shaft as long as possible in a short wheel base Jeep. Nickmil.

 

Hurtcs inquired about changing transfer cases from a D-20 to a D-18 and running a Warn OD. Running a D-18 transfer case to a center driven rear axle would create compound angles in the u-joints, would the compound angles cause vibration or excessive wear in the u-joints?

 

Yup, it can. I've heard and talked to people who were able to do that without problems, but most of those were in longer wheel base vehicles like CJ-7's where driveline length and angle is less of an issue. I'd recommend if he goes with the 18 to switch to an offset rear diff. If he can find one out of a '70 or '71 then it would be a flanged 30 spline unit similar to what he has now but offset for the 18 transfer case. The earlier units were a two piece tapered-axle design that was not as strong. They hold up surprisingly well, but the one piece axle is considerable stronger. Nickmil.

 

Do the 18 and 20 still line up correctly on the Front Diff? Offset to the Right or Passenger side? Replacing the Rear Diff May be an option, but I would probably go over what I want to spend, not a problem on doing just means a longer wait.....

 

Yep it will line up with the front fine, they are actually the same transfercase housing just different guts.

 

With some careful shopping, I'm sure you could change the rear axle, convert to a Dana 18 and add an overdrive for your $1500 budget. You'd probably come out at about the same cost as converting to the RUG transmission that Nick suggested. The D18 also has more low-range reduction than the D20 (2.42 to 2.08 or something near that) which would be an added advantage. The D18 will have more gear noise than the D20.

 

Yup, Tim's right. Other advantages are the possibility of running a PTO unit if you ever wanted with the overdrive, better driveline angles with the 18 transfer case, plus the coolness factor. The 20 is a stronger transfer case but has a lousy low range like Tim mentioned 2.03-1 versus the 2.46-1 of the 18. Another advantage is if you ever wanted to you could step up to a truck style 4 speed with granny low and still have the overdrive and lower low range of the 18 transfer case. Down side is the 18 is much noisier than the 20. Nickmil.

 

Looks like a D-18 is a viable option, I will search the web as weel for my next question, but never hurts to ask. Are there any twin stick setups for the 18? I hope to take the transer to at least a 3:1 (if not 4:1) conversion and love the coolness factor of the Twin stick setups.....