• Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.

Saturn/Warn Overdrive

Make sure you do homework here...especially at this site.
I opted to NOT install the OD and am fully satisfied with my decision.
If you really need the gear reduction for highway running, then fine. Run your numbers!
So what if your engine screams at 3,000 RPM+ for an occasional highway run. This is probably NOT a Daily Driver.

Do you also have suitable occupant restraints? A 4-point system is good.
Do you have an offset steering column to reduce driver injury during a head on collision?
Do you have power brakes to enhance stopping power in emergency maneuvers?

I have most of these mods but still have not invested in OD.
This is where the owner needs to think hard about what they want/need to fulfill their Jeep Dreams.
 
Last edited:
dnb71R2 said:
Make sure you do homework here...especially at this site.
I opted to NOT install the OD and am fully satisfied with my decision.
If you really need the gear reduction for highway running, then fine. Run your numbers!
So what if your engine screams at 3,000 RPM+ for an occasional highway run. This is probably NOT a Daily Driver.

Do you also have suitable occupant restraints? A 4-point system is good.
Do you have an offset steering column to reduce driver injury during a head on collision?
Do you have power brakes to enhance stopping power in emergency maneuvers?

I have most of these mods but still have not invested in OD.
This is where the owner needs to think hard about what they want/need to fulfill their Jeep Dreams.
Click to expand...
Sorry but I'm gonna disagree with this. I use my OD as a gear splitter far more than as an overdrive for highway travel. Having the ability to find that "just right" gear is great for off road use!
If I was starting from scratch with a 100% stock Jeep, the 1st thing I'd change would be brakes. The 2nd would be to add an overdrive.
 
colojeepguy said:
Sorry but I'm gonna disagree with this. I use my OD as a gear splitter far more than as an overdrive for highway travel. Having the ability to find that "just right" gear is great for off road use!
If I was starting from scratch with a 100% stock Jeep, the 1st thing I'd change would be brakes. The 2nd would be to add an overdrive.
Click to expand...
I honor colojeepguys opinion!
I have a Ford T-18 to handle many of the low-end gear requirements (the 6.32:1 granny gear is awesome). It matches typical Wrangler automatics (local club runs), in high range, all day long.
The main point is to consider ALL options before investing righteous bucks in any component! (y)
 
Last edited:
Part of that homework, in addition to whether or not benefits will be derived, includes getting the proper unit for your application. I don't think any CJ 5/6's came with the earlier 2.43:1, 26 tooth drive gear D18 but this is something you should definitely check before procuring an overdrive. A lot can happen in half a century and the earlier cases will interchange with all but the 4" index cases used with the V6. Pop the rear D18 PTO cover and count the input gear teeth. Second, I would look for an original serviceable Warn unit in preference to a new Saturn version.

While it is true you only marginally increase the speed with the F head, the OD's are absolutely wonderful with the 225, most especially so with the 225 and the optional 4.88 gearing.
 
dnb71R2 said:
Ford T-18
Click to expand...
I have a T18 in my CJ as well. Something I find myself using a lot while 4 wheeling is 1st gear overdrive. With the 4 speed, compound low is REALLY low, great for technical situations, but honestly too low for a lot of stuff. Throw it in OD and it's perfect for a lot of average trails.
I do try to keep a light foot on the gas pedal while using it this way, there's a lot of torque going through the overdrive unit.
 
An overdrive on a 4 cylinder is about splitting gears and lowering rpms. Not really adding any highway speed as the motor simply has no more to give. With a granny 4 speed, as mentioned above 1st gear is simply too low to use so over 1st works great. If you have a limited budget, installing a 4 speed and getting rid of the t90 is a far better upgrade then an overdrive though.
 
Last edited:
colojeepguy said:
I have a T18 in my CJ as well. Something I find myself using a lot while 4 wheeling is 1st gear overdrive. With the 4 speed, compound low is REALLY low, great for technical situations, but honestly too low for a lot of stuff. Throw it in OD and it's perfect for a lot of average trails.
I do try to keep a light foot on the gas pedal while using it this way, there's a lot of torque going through the overdrive unit.
Click to expand...
This exactly. The 4 speeds have some wide gaps, and you can find the perfect gear
 
supertrooper said:
Herm is dead to me. F that guy

I got my overdrive from AA and its worked great. I have 4.88 gears and it helps alot on the highway and especially on mountain roads. Its great being able to split gears going up steep hills.
Click to expand...
Herm is still supplying AA with about half of their parts that he sources and imports. Once he stops AA will stop making the Saturn.
 
There isn't much stopping a freelance shop from making functionally equivalent parts.

At what price would people buy steel shift forks?
 
My thoughts on the OD (I currently run one of Herms 30% units)

If you have a less then fresh engine (lower compression) or taller then stock tires (28.5-29") then pushing an OD on anything but pretty much level ground will be difficult. When you combine taller tires and an OD your ending up with your engine running to slow to create the needed HP.

An example

28.5" tire Direct drive 3rd Gear high range 55mph is 3490rpm

28.5" tire 25% OD 3rd gear high range 55mph is 2625rpm

30" tire 25% OD 3rd Gear High range 55mph is 2485rpm with just an inch and a half taller tire you loose 140rpm (remember that 60HP is at 4000rpm)

32" Tire 25% OD 3rd Gear High range 55mph is 2330rpm

My jeep has a 134L Bored .060 over making 140cuin with the compression ratio raised to 7.2-1 A Weber DGV 2bbl carb a Custom built TRI Y design header with 2.25" exhaust a Captive discharge high voltage ignition system with forced fresh air induction It makes about 20 more HP then stock. I run the Herm 30% OD unit

28.5" tall tire 30% OD 3rd gear high range 55mph is 2445rpm (my engine makes its Max Torque at 2400 rpm running this way on mostly level ground I am seeing 17+MPG at 2400rpm my engine is making approx. 37 rear wheel HP

My jeep has 13,100 miles with this setup. If I were to do this again I think I would switch to the 25% OD unit. I'd get a little bit farther up the hills before having to shift down.
 
I removed my AA overdrive when the transfer case intermediate bearings destroyed themselves…and the case, gears, etc, and have not sure I will rebuild it. So far, the 5.38/sm420/buick 231 combo has worked out well. The downside is 50 mph is about as fast as I want to drive, as I’m at just over 3000 rpm. Since this isn’t a daily driver, not sure I will reinstall the OD.
 
I run an ATV 30% overdrive that I got used from a member. The shift linkage was not for my sm420 and it was absolute garbage.. I have a FI GM 4.3, 5.38s and 37’s. I alamos never use it because 60 mph is fast enough and I only hit that occasionally.. I have plenty of power when I do though. My old f134 would not have liked it..
 
You must log in or register to reply here.
Back
Top Bottom