1974 Cj6 Axle Questions

I plan to start a build on a 1974 CJ6 and have a couple axle option questions. I have a D30 Power-lok LS I could install in the front axle, but was considering a Spartan locker instead. Which of these two options would be better? The rear has a Trak-Lok already. I have read about it's inherent weakness, but was thinking to run it to failure. Plus most of the Jeep's use is in Minnesota with muddy terrain, not so much hard rock traction. I would say 70% road, 30% off-road use. The other question is about gear ratio's. I will be running 33" MT's, AX15 dana 300, and have a set of axles 4.27 ratio. But was considering 4.56 ratio. The RPM calculation looks pretty close, but 4.56 calculates a little bit better....in theory. I mildly 4-wheel a CJ2A w/dauntless, but want to step up my off-road game a bit with this CJ6. So give me some opinions please.

 

Aussie or go full carrier...

For 70% on road and the overdrive keep the 4.27

 

What are you powering this with? How much Horsepower?.........................You say 70% on road and 30% Off , but you want to step up the off road portion?

Living where you do.........with the possibility of Ice and Snow on the roads..........I would re-think those lockers both front and rear.

The AX-15 has a 3:83 low gear , which is not much when it comes to low gear ratios as well as the Dana 300 has a 2:62 ratio when in low gear...........couple that all together and the 4:27 Axle gets you a 42:1 crawl ratio while the 4:56 gets you a 46:1 CR when in Low range............neither being anything to write home about in crawl ratio's...............couple that with the 33" in tires and you loose additional mechanical advantage..........

Again depending on the Motor Horsepower it may also be doubtful that your Motor / Jeep would be happy in 5th gear with a .079 Over drive............If it was me and I was looking to improve the off road capabilities I would be looking at lower gears in the back perhaps even 4:88's as on the highway you can always use the Overdrive to mask the low gears in the back.

 

I have a 1973 jeep 304 V8 from a donnor rig. Haven't inspected it internally yet, but believe it is still stock. Came with headers and non-stock block paint, so who knows. Intend to keep it stock. The front locker option I've read has some quirky actions in ice/snow. But I store my rig in the winter (too much road salt around here). Would the longer wheel base of the CJ6 reduce this "quirky" behavior of the front locking up? In muddy situations do you loose your steering ability when it locks?

 

If it's locked it's locked..........the extra 20" is nice for keeping it pointed straight down the boulevard , but with any locked axle the steering will become harder.........same thing for mud if it's locked plowing through the mud will also require more steering effort.............hope you have power steering.

On your gear ratios I would spend some time with a gear ratio calculator ............one that you can plug in the tire size , gear ratios and see the MPH speed and RPM of the motor...........no guessing then.

 

If you have free hub on the front and you don't drive in 4 wheel drive on the road a spartan locket is a good candidate. I have one in my cj5 (front) and it work pretty good on the trail, but you need free lock on the road.

 

Another possibility is to go with an automatic instead of the AX-15. With the 4.27s and 33s that would be about 3000 rpm at 70, which is fine for a 304. I would expect the automatic to be better in mud and snow, and you can source a TH400 from a Wagoneer easily. It easily fits in the CJ-6, and is pretty much abuse-proof. The only downside would be the low efficiency of the TH400, affecting fuel consumption. Then go with a selectable locker in the front (for safety on ice), and your choice of LSDs (Powerlock?) or lockers in the rear. I wonder if you really want to drive the TracLock to failure - when mine failed, a piece of the spider gear exited the cover and I lost most of the oil. They also fail by breaking the case in two, which I expect would immobilize the Jeep.

Sometimes the TracLock is mentioned as an option for the front axle. It's said that its good manners are well suited to that use, giving you loose surface traction and not affecting steering too much.

Regarding the locker in the front, as I understand it, you'll have problems steering and the Jeep will tend not to go the direction you point it. The locker will add steering forces at the wheels that you will have to overcome with the steering wheel. I expect that's not too bad at slow speeds, where you have time to counter-steer against the locked wheel with traction. This effect is said to be worst on icy roads, where directional control suddenly goes away with a locked axle. This can be unsafe in the snow on the pavement, at street or highway speeds. An open differential is much more predictable in this situation.

You could also go with the AW4, which has an overdrive gear. That's not as easy for a V8 since there's no flex plate... pretty sure you'd have to have a 4.0L flex plate balanced to your V8. There's also the TF999 which was used in the CJ-7 with the 304, and the A727 used in Wagoneers from 1980 on (though you may have driveshaft interference with passenger drop).

I think your crawl ratio would be fine with an automatic - it's a different style of driving, with one foot on the brake and the other on the gas. You get quite a lot of torque multiplication with an automatic, and you can slow down your progress with the brake.

 

Don't forget that a th400 you will loose some hp vs an manual transmission.

 

That's true - it goes along with the lower efficiency of the "early" automatic. But the TH400 is durable and strong - really strong - and it shifts nice, and can be set up to have a sportier shift feel than it had originally, if you prefer. In stock form, it will run forever behind a 304 in a Jeep. Since it was used in millions of GM and other cars, parts are cheap and widely available. And if you were worried about power, you'd take the 360 from the same Wagoneer and get a significant and cost-effective increase in HP.

 

Yes, got my cousin who run a boggy with 500hp and he has a stock th400, hold up pretty well.

I have one from a 1973 commando i bought for 50$ with the dana 20 hook to hit, it wait in my storage the day i will get my 5 to a 6

 

I will have power steering and lock-out hubs. So what would perform better when one tire is lifted off the ground in the front, the Powr-Lok LSD or the Sparten locker? Which one do your think would last longer? About the transmission, I have three AX15's and prefer a manual, although an automatic makes backing up with a trailer easier IMO. I am going to rethink the Trac-Lok for the rear. Some day I would like to trailer to the Black Hills of S.D. so if the crawl ratio becomes an issue, maybe look into modifying the D300 xfer case?

 

LSD never see someone happy with it along my friend, they need to apply some brake to make it lock. You can drive it 4 wheel drive on the road.

Spartan is a full locking device, you cant drive in 4 wheel drive on the road.

 

Some thoughts...

Your original question was regarding the Powerloc in the front so I'll address that first. The Powerloc is a great unit. There aren't a lot of negatives to them.
They are a clutch driven limited slip; strong, as positive as you want them to be, and rebuildable. I have ran them in both the front and rear for decades.
One of the nice things about using them in the front is that you can adjust the order of the clutch plates to make the action of the clutches either more or less positive. Think of it as being able to adjust the clutch packs for the amount of grip you want. Depending on your intended use ( like the front for example) you could arrange the clutch packs so that only 3 of the 5 are grabbing, making for slightly less "grip" which some find more desirable in the front.
If maximum performance is desired you can set the clutches so that all 5 grab. This is documented in the instructions from Dana Spicer.
A Powerloc in the front will cause changes in steering and handling, particularly on pavement. Be prepared for an understeer condition, even on the trail.
And, contrary to what was mentioned earlier, a Powerloc does not require braking action for engagement; it's always there and you can feel it in the steering. That is one thing I always liked about them; you know they're there. Also, remember that you only experience their characteristics when your hubs are locked in.
I commented earlier that you can tweak them to be as positive as you want them to be. I have installed them in the front of Jeeps before that were used primarily for trail use, and in that environment I shimmed the clutch packs with pinion shims to make them tighter. You can actually shim them so tight that they wind up being a spool; i.e. the clutches are so tight that they don't slip anymore! Forget trying to turn the wheels when they're that tight- don't ask how I know. Another trick is to put 2 Bellevue clutch disks on either side. They are a concave shaped disc that provides resistance in the clutch packs. Seeing the documentation shows it better than I can explain it. You should be able to google the docs, or they're probably floating around on the forum here somewhere.

To summarize, they're a great unit with a lot of good features. I would not recommend a lunchbox locker in the front if you're use is going to be 70% pavement.

Your second question was regarding gear ratios. You mentioned your AX15 and 33's. Tarry said it all in his post. He did the calculations for you regarding crawl ratio and spoke about the 4.88's. I agree completely with his recommendation. While we use 1st gear, the low range of the transfer case and axle ratio to compute crawl ratio, we use overdrive ratio and axle gear to determine "final drive ratio". We know that the AX15 overdrive is 0.79.
With 4.27's that will give you a 3.337 final drive ratio- too high geared for 33's. That's roughly 2200-2300 RPM at 65. 4.56's would yield a FDR of 3.60, with around 2450 RPM. 4.88's seem to be approaching the sweet spot for 33's, producing a FDR of 3.85- somewhere between 3.73's and 4.10's and putting you right around 2600 RPM, right about where a 304 likes to go down the road.

Hope this helps; keep us posted on how it turns out.

Mike

 

I almost forgot...
You mentioned using a Dana 300. I can tell you from experience that using a Dana 300 in an intermediate or early 5 (or in your case a 6) will require clocking the Dana 300 up, closer to level. The 300 was designed around the later 5 floorboard that had more of a hump in it to provide more room underneath. The intermediates and early 5's don't have that, as their floor is flat, so in order to run a 300 you either have to drop your crossmember down or clock the transfer case to provide enough clearance.

Mike

 

Thanks for the response Mike, wasn't aware about the body interference's either.