Warn Overdrive

Hello,

Could you guys please give me a quick run-down on the Warn overdrive? My 1970 CJ5 has this unit installed on my T-case (D18 I'm assuming).

Does the overdrive have oil of its own, or is it using the oil from the T-case?

How do you shift the overdrive? While moving, stopped, etc?

Can you use the overdrive low range in combo with 4wd Hi and LO?

Sorry if these questions have been answered before - just a newb here looking for some instruction!

Thanks!

 

I have a Warn behind a D18.

Oil is shared with the t-case and transmission
I shift it as it were another gear, on the move or stopped (mostly moving). Actually seldom shift out of OD. My axles are 4.88.
It should work regardless of how you have the 4WD engaged. I don't off-road so maybe someone else can advise as to the wisdom of using the overdrive in 4WD.

Also check out Herm's website.

Herm The Overdrive Guy | Shift into High Gear!

Here is a bit more information on the D18 and PTO

The Novak Guide to the Dana Spicer Model 18 Transfer Case

 

Thank you guys, that makes sense and really helps. Much appreciated!

 

so ,my top speed is 57 or so with the f134 and t90.. what kind of gain would you get with the OD?

 

The OD is between the tranny and transfercase which is what allows the OD to work in all gears in both ranges. I have been told using it like a splitter each time you run through the gears can be hard on the units.

 

What units ?
Do you even have an overdrive ?
Not true at all. The unit is designed to be used.

 

"Between" is correct in a sense, but it actually is on the back side of the transfer case. The Warn overdrive is an auxiliary planetary transmission that replaces the output gear of the transmission. It has two ratios, 1:1 and 1:0.75 (IIRC). It also is synchromesh, having a brass blocking ring just like your transmission gears. This means that you can split all your gears between the two ratios as you wish - though I don't know about whether routinely splitting all the gears is good for it or not. I imagine the blocking ring would wear out faster if you do a lot of shifting, but whether that's significant or not I don't know.

 

When I shift from overdrive to direct, I always put the trans in neutral first. This makes less spinning mass for the synchronizer to have to change speeds. This way, the OD shifts easier and there is less wear.

 

Very important to keep the oil in the transfer case topped off. Most problems with them start with low oil. Some of the later Warn units had very poor surface hardening and can be problematic. Warn's quality control was not very good at times throughout the almost 30 years that they produced the units. Advanced Adapters bought the rights to the unit and have been building them for many years now. As with just about anything on an old Jeep if you take care of it it they really help. If you beat on it, it won't last long. And yes I have had a couple dozen Jeeps with an overdrive so I am not just repeating Internet lore.

 

Yes I do have a 30% OD from Herm the OD guy who is the onecthat told me most the ODs he has to rebuild is due to people super trucking them splitting every gear as they go.

 

This mirrors my experience. The Warn unit in my Jeep was worn (warn was worn haha) where the bearings ride on the planetary hub. A friend of my dad's gave me a box with three disassembled overdrive units in it, and they all three had wear in the same location. One had obviously been running low on oil, but the other two were just plain worn out. Then, I bought a used one and guess what? It was the same way! I ended up buying a new planetary hub from advance adapters to get my Jeep put back together.

 

One tip that I read online (I think it was here) was to raise the passenger side of the Jeep slightly when filling the transfercase. This allows you to get a little extra oil in there.

 

Just drive the right side up on a 2x4. Works great.

 

Howdy, noob here, but my m38a1 has been one of my pet projects since the 80s. When I got it it had been hacked up bad so I did a resto mod. T He latest version is a Kubota turbo diesel, a SM465 trans, d18 tc with a warn overdrive. The shift pattern is start off 2nd direct, 2nd overdrive and leave it in overdrive through the rest of the gears. The axle gears are 4.11 incedently. This works best for this set up because it closes the gap from 2nd and 3rd.

 

I have found that when shifting the OD to let the engine "rev down" before shifting. I will occasionally get grinding if the engine RPM's are too high when shifting.
On the Rubicon trip last year we were heading off the trail and the others that had OD's said they are fine to use in 4wd. I hadn't until this past weekend and it worked fine.

 

I went down to the hardware store. Bought a 90 degree elbow. Screwed into t case and used plug on as cap. Now t case oil level is approx 1/2 in higher. Works great for me.

 

re:termin8ed
The unit is always turning but when it is in direct the planet carrier is locked to the shell by the synchro so the carrier turns with the shell without turning the planets. Kinda makes the whole mess into one long gear. A good plan to have if one of your planet pins break