Different gears

Some one please school mean on gears?
I have a rear Dana 44 with 3.73 gear ratio. I see that there was an optional 4.88 gear ratio. What would be the difference in the two. The lower the gear ratio, the bigger the tires you can run or vise versa?

Thank you

 

I was taught Bigger number = lower gearing. Here is a place to read up om gearing. http://www.fourwheeler.com/how-to/1211or-why-change-gear-ratios/

 

On a CJ the 3.73 and 3.54 final drive ratio (FDR ) are generally optimum for onroad use.
The 4.89 and 5.38 are generally optimum for offroad use and or big tires.
Other in between ratios, 4.09 , 4.27 and 4.54 are generally compromise gears for a CJ.
The optimum FDR for your CJ is fully dependent upon intended use and the engines power.

 

Thank you for your response. My CJ is stock and just used as a ride
for the weekends. I was just curious about the optional gears mentioned in my service manual.

 

In my experience (IME) back in the day the 4.88s were considered a little too deep for daily driver use. As Ken mentioned, the 4.88s will give you a boost on the trail with more power and better control at lower speeds, but I think you'd be wishing for a Warn overdrive on the street unless you have really tall tires. The 3.73s are very deep gears compared to most passenger cars, and should serve you well for tooling around and general Jeepin'. Use your transfer case low range, and you'll be ready for nearly all the trails you can find.

 

I have 4;10 gears and the granny low t18 4 speed and no overdrive with the 225 v6. I like the combo both on and off the trail as a compromise.
Peter

 

3.73's here with a T86AA and 33" tires. Great on the highway (Dana 20 so no overdrive) and good enough for me on the trail in 4 low, but also have an SM420/D20 already adapted for future upgrade.

 

Just my opinion here..........

If your jeep is running a D18 then O.D. becomes a huge plus.
With low final drive ratios (FDR's) the O.D. unit becomes nearly mandatory for Highway use.
For D18 I would highly suggest a 25% O.D. unit with 5.38 or 4.89 up to 4.54 FDR.
My favorite D18 setup is 4.89 FDR / 25% O.D. unit / Wide Ratio T18 / either standard 2.46 or 3.15 Tera Flex Low reduction.

If your jeep is running a D20 that obviously implies no O.D. option.
For D20 I would highly suggest 3.54 or 3.73 FDR with 410 or 4.27 being the lowest for any kind of Highway use.
With Dana 20 the 3.15 Tera flex gears and or a 4 speed transmission becomes a huge bonus.
My favorite D20 setup is 373 FDR / 3.15 Tera Flex Low / Wide Ratio T18.

 

IMO the 4.27 gears are the best choice for an early CJ that is street driven. That is assuming you stay 31 inch or smaller tires, which to me is really all you would ever need on the street and if we are honest in almost all off road situations as well.

If you think you will be driving 60 mph plus then the 4.27 gears plus the OD is pretty much the perfect combo. But, it is worth keeping in mind just staying with the 3.73 ratio and no OD is just 400 RPM more at 70 mph and that might be useful if you live in hill country.

You really do need to think about how you want to drive your Jeep and pay attention to the other people drive theirs when taking advice from them. For example, you will hear people say their Jeep is their daily driver but the truth is you will find almost no one that is the true in the sense most people mean. For example when most people say daily driver, they mean they would use the car/Jeep to drive 30+ miles to work and back, at 65+ mph each day of the week and on top of that drive around town to pick things up and run errands. If you apply those criteria then I am not sure you will find anyone who uses their vintage CJ as a daily driver.

With that in mind, you then thinking what would I really do with my Jeep? For me, I realized I would certainly drive my Jeep anywhere in town, I would pull trailers with it, I would occasionally drive on the highway and that is pretty much it. When I realized that I also realized that the fhead engine is fine for now, and all I really swapped was the brakes to 11 inch drums (only because of the trailer) and the steering will be swapped (only because it is completely worn out, might as well upgrade if I am doing the work anyway)

One day I will pick up an OD most likely because right now I can only drive 60 mph. But, it can wait for sure.

Just wanted to reveal a thought process I went through because it is easy to get caught up reading stuff on the internet and thinking of your vintage Jeep in terms of a "daily driver" slash off-road vehicle and truth is that is going to be rare, if it exist at all.

 

My 69 is my true daily driver and has been for the past few years, though it's not strictly "vintage". It has power steering, power brakes, hanging pedals, aluminum radiator, electric fan, etc... I also take it off road but I obviously can't afford to break things so I stick to milder stuff...I mostly just like to get out in the desert or mountains...no real rock crawling for me. The 3.73's fit my usage very well.

 

The "perfect combo" is fully dependant on the particular engine.
I must ask. Have you ever tried Hurricane 134 with 4.27 FDR and O.D. ?

I run a well tuned Hurricane with 5.38 FDR and 25% OD.
I'm positive that it is absolutely the optimum gearing for the Hurricane engines.
Yes I have driven some 4.27 FDR CJ's with a Hurricane. 4.27 is certainly a compromise ratio.
4.27 FDR was designated as the CJ standard in September of 1962.
I suppose that change was a marketing effort by Willys Motors to try and keep pace in the burgeoning muscle car era.
The Warn 25% O.D. unit was officially approved as Jeep Special Equipment in September f 1964.
It was only designated for use with 5.38 and 4.88 FDR's.
It was never approved for 4.27 nor higher FDR's.
The Hurricane with 4.88 FDR and O.D. is actually slower than 5.38 with 25% O.D.
I tried Hurricane 4.88 with 25% OD and switched it right back to 5.38 with O.D unit.
Hurricane with 5.38 plus 25% O.D. at Wide Open Throttle (W.O.T.) will barely maintain 55 MPH on the steeper interstate grades that we have in the Missouri Ozarks.

When I state "one and only daily driver" I mean to imply that I drive no other vehicle period.

In the mid 70's I drove a 304 CJ-5.
In the late 70's and early 80"s I only ran the Go-Devil engines.
That was during the days of the 55 MPH national speed limit.
By the mid 80's I went to exclusively to the Hurricane engines only.
Excepting a 300 Ford pickup that I no longer have I have been running Hurricane engines exclusively since 1983.
I get 80, 000 miles from are re-built Hurricane as I run them hard.
I have 1 remaining pristine, flawless, new condition Hurricane in my possession that I hope to never put but few miles on it.
I am currently driving a "stock optional" Hurricane powered 3B.
I began to install Dauntless engines back in the late 80's but the Hurricane was still meeting my needs at that time.
Because of my current needs all my present and future builds are going to be Dauntless projects.
The Dauntless will readily handle the more fuel efficient higher FDR's.
Higher FDR's will decrease engine crankshaft velocity and thereby increase the service life.

The jeep should always be envisioned as a complete synchronous system of complimentary components.

 

I have a hurricane with 4.27s, OD, and 7.00-15 (30") tires. The OD is nice for the gearing options but doesn't improve my top speed unless going down a large hill. That said I am fairly satisfied with the gearing (and I'm sure it would work even better with a more powerful engine). I do daily drive my Jeep, however I don't have too far to go on a daily basis, usually between 10-25 miles a day.

 

Yeah for sure you can make them into a daily driver if you want. I would love to do it with mine. Do you more or less drive the distances and speeds I mentioned? Just curious since it has crossed my mind to use mine that way also

 

Yes. I drive my Fhead Jeep with 4.27 gears now and I have driven it with OD. For my use it was perfect - about a 1000x times better than when it had 5.38s and a little better than a friends who has 4.88's

And I completely disagree with it being a compromised gearing. It is far from being "certain" that is a compromise. I believe that the engineers who actually designed the Jeep experimented with it for years and came up with that gear ratio as being perfect for that engine. So they officially swapped, for use with that engine and never went back until they swapped to even higher gears for other engines. IMO there is a reason for that.

Great thing about forums we don't need to agree on everything.

You would have to prove that for me to believe it. I know several people that bought Jeeps brand new with the OD and 4.27 gears - mine came that way from the dealer and it was covered under warranty - which, I don't believe it would have been if it was not officially approved.

I have no idea where you get the idea a Jeep with 4.88s + OD is slower than one with 5.38s +OD. For starters, if we assume the Jeep has tires smaller than 31 inches, like say the common 235/75/15s then the Jeep with 4.88s+OD would have no problem hitting and running at 75 MPH where as the Jeep with 5.38s+OD would struggle to run at that speed because of the high RPM's. No way it could do it long. That is the exact reason I stopped running the 5.38s

I can run for hours, not at WOT in my Jeep, at over 55 mph and I DON'T have the OD installed right now. My Jeep can easily accelerate over 65 mph with just the stock engine, in stock configuration and the 4.27 gears. The only reason I drive it 60 mph and below is because of the RPM's, the engine could easily pull it faster.


With the OD I have driven my Jeep over 85 mpg, the only reason I slowed down was the Jeep became unsafe at that speed. Talking purely stock Fhead engine, 4.27 gears and the normal WARN style OD. One thing I did note when driving that fast was that all the drive train components were very loud. I seriously doubt any of them could hold speeds like that long without over heating. The engine though? Easy, did not even go up in temperature.

 

So, Bob-the-CJ,
What type of inclines, (I.e. mountains) do you have in your area that you have experimented the different gear ratios with?
I had a Warn Overdrive with 5.38-1 fdr, and 29"- 30" tires in my '59 CJ-5 and on a long or any steep hill there is NO WAY it would do more than about 50 mph uphill, with overdrive disengaged. There simply was not the torque and hp to run faster. Typically much less. On the flats, yes, no problem, or down hill. And this is at basically 500' above sea level with a good condition, good running and well tuned F-Head.
Just because a dealer took it upon themselves to install something does not mean the factory considered it "authorized" or "approved"
Back then dealers were installing all kinds if cool things (thankfully) that were not "approved" by the factory.

 

It's a good and civil discussion for certain, but I have neither experience with these jeeps at those gears and engines, but it reminds me of the old days... I have a 225, soon to have 4sp and 4.88s and a Warn OD... Looking forward to it and the opinions I get to form with it...

While travelling in my 4L 4wd ranger...
a vw beetle shot past me on the flats going about 80. On the hill, say of a decent incline or so and lengthy! I passed it. I was doing about 60 and the beetle about 40. Topped out, and I kept at 60, and fawooom, beetle shot past again...

Let's just say we played this cat and mouse game give or take for several hundred miles along US 97 between Weed, Ca and the Biggs, Or, sort of a reasonable paced race to the gorge (in my mind). Discounting the little places then (when Bend was a small town) and such similar little speed traps along the way.

difference in horsepower and gearing... Pure and simple..

 

I don't usually do above 60 on the freeway--I can when I need to--but I don't like to. I've found that there are actually quite a few drivers who are happy to drive in the 55-60mph range on the freeway and I just kinda blend in with them. I drive it everywhere under all the normal conditions and distances you would drive your everyday car--to work, running errands, shopping, etc. But--my Jeep as my daily driver isn't entirely by choice. I'm in construction and, when the recession hit Las Vegas, I was really worried about the work situation. I sold my 2007 Dodge Ram because I had a loan on it. I guess I got spooked because, in hindsight, I would've been fine. And, honestly, I do look forward to the day when I can get another late-model, fuel-injected, quiet, air-conditioned vehicle. But I'm not sure when that will be (I'm a single dad with my son starting college). I know Ken also uses his Jeep exclusively, but my impression is that he does so completely by choice. I guess what I'm saying is, an early CJ as a true daily driver isn't for everyone. Overall, I love it, but it's not without its drawbacks and it can get tiresome.

 

Yes I agree that the 4.27 gears without an O.D. are much better for road use than the lower FDR's without O.D.
But Hurricane engine with 25% O.D absolutely performs its best with 5.38 FDR and no higher.
5.38 x 25% O.D. = compound FDR of 4.03 which performs very well from my experience.
4.88 x 25% O.D. = 3.66 compounded FDR and that is too high from my experience.
4.27 x 25% O.D. = compound FDR of 3.20 which is way too high from my experience.

Jeep NEVER installed 3.73 FDR into any production Hurricane powered jeeps.
So how could a compounded 3.66 or 3.20 FDR possibly be desire able ?
I have extensively tested the Hurricane in real world situations and it does it's best with a compounded FDR no higher than 4.03.

If you look way back into Willys past you can more clearly understand the progression of changes that occurred.
The first military LRV's used 4.88 FDR simply because 4.88 is absolute optimum FDR for the Go-Devil engine.
The first production CJ's used the lower 5.38 FDR because the Jeep was introduced into the civilian market as a "UNIVERSAL" in 1945.
The then new universal status included "AGRI" jeep useage thereby requiring the exceptional low FDR.
The lesser powerful Go-Devil engine became obsolete for use in the CJ's in 1953.
The CJ's FDR was never increased at that time because it was still being used as an "AGRI" jeep.
By 1953 It was also promoted for "INDUSTRIAL" useage.
By 1960 it became clear to Willys that the industrial market was also very limited.
The main market for the "Universal CJ" was still the typical civilian.
The Hurricane powered CJ needed a speed increase to help keep up in the early 1960's during the muscle car era.
In 1962 the Warn unit was not yet available.
Willys needed a quick fix for the CJ's cruising speed.
The Willys engine had already been updated once yet they had never increased the CJ's viable cruise speed by increasing the FDR.
Willys decided upon 4.27 as being the optimum FDR for the Hurricane engine.

When I state that 4.27 is a compromise gearing I mean that in lieu of the post 1964 gearing options.
4.27 is perfect for the Hurricane CJ's but only if you can't afford an O.D. unit.

I have in my possession the September 1964 Willys Special Equipment Bulliten stating exactly that.

4.88 with O.D. is slower in real world useage because of changing terrain.
I certainly don't mean to imply slower downhill travel speed.
The acceleration is notably slower and fuel consumption is sacrificed.

Yes I have very often driven mine sustained at 65 MPH.
As I get older I hopefully get smarter.
I don't like to run the engines that hard anymore and I really want better MPG so I am finally (long overdue)switching my daily driver to a more powereful engine with a higher FDR.
I love the simplicity of the Willys engines but they are becoming increasingly impracticle as my daily driver.
In many ways the Dauntless engine is nearly as simple and it fits near perfect into the CJ engine bay.

I have had my 100% stock optional CJ-3B up to 81 MPH on perfectly flat ground.
That is all it can do with 4.03 compounded FDR because the stock engine cannot turn faster than 4000 RPM crankshaft velocity.