Why do LP axles exist?

[duke000088]

For instance, why are there both low pinion and high pinion versions of the Dana30 axle? I understand the obvious clearance advantage of a high pinion D30... but are there any ADVANTAGES to a low pinion D30 from, say, a drive-ability perspective? In other words, what would compel designers to swtich from the HP D30 in the 1999 XJ to the LP D30 in subsequent years? Cost?

[blacksheep01]

To make us mad!

[Johnnie Walker]

Well, the LP has been in the Wrangler for quite some time.. they just decided to use it in the end of the cherokee years, probably due to not having to make a seperate axle housing any more?

[Boatwrench]

Cost?

Yes.

[Starboard M]

Header downpipe clearance as well as cost of having two axle assemblies rather than just one.

[MoparManiac]

LP in a front axle application is stronger when in reverse, since now the pinion is driving the DRIVE side of the ring gear teeth, rather than the COAST side.

For instance, say you are going downhill and need to back up over a ledge, LP would be stronger than HP.

As far as switching to LP in 2000, x2 with what Starboard said.

[asp]

also, it was to get the driveshaft lower than the body in very old cars. some old cars had the driveshaft running through the interior of the rear seat. i don't remember what make/model, but i've seen pictures.

but as far as jeep switching in yr 2000, yeah it was all about cost. the xj would have been the only vehicle they made that had a HP fr axle, at that point. and it's the exact same other than the pumpkin. less parts = cheaper.

[DrMoab]

LP in a front axle application is stronger when in reverse, since now the pinion is driving the DRIVE side of the ring gear teeth, rather than the COAST side.

Having busted a front R&P on a HP axle trying to tug someone out of a hole backward... I can attest to this.

[kastein]

LP in a front axle application is stronger when in reverse, since now the pinion is driving the DRIVE side of the ring gear teeth, rather than the COAST side.

For instance, say you are going downhill and need to back up over a ledge, LP would be stronger than HP.

As far as switching to LP in 2000, x2 with what Starboard said.
So you're saying French military vehicles and the UN peacekeeping forces should use low pinion axles in the front?

:conceited:

[GoSlowGetStuck]

So you're saying French military vehicles and the UN peacekeeping forces should use low pinion axles in the front?

:conceited:

Hah! "Did you mean French Military Defeats?"

So LP is stronger in reverse, which I hardly ever use. So that still sounds like an argument in favor of HP, where it's using the drive side of the R&P when I'm going forward.

It is interesting that they chose to make XJs HP all those years while still having other vehicles be LP. I would guess that clearance is less of a problem on a Wrangler than an XJ, but I could be wrong.

[bjoehandley]

So you're saying French military vehicles and the UN peacekeeping forces should use low pinion axles in the front?

:conceited:

HAHA:roflmao:

Hah! "Did you mean French Military Defeats?"

So LP is stronger in reverse, which I hardly ever use. So that still sounds like an argument in favor of HP, where it's using the drive side of the R&P when I'm going forward.

It is interesting that they chose to make XJs HP all those years while still having other vehicles be LP. I would guess that clearance is less of a problem on a Wrangler than an XJ, but I could be wrong.


Yea same thoughts here, seems like it would be a better arguement to have put the HP's on the TJ's at the factory than LP's on the last 2 or 3 years of XJ's but hey, what do I know:dunno:

[5-90]

Cost and logistics, primarily.

LP fronts can use the same gearsets as HP rears - even tho they drive on the 'coast' side of the gearteeth (which isn't as strong as the 'drive' side - this is why HP fronts with a reverse spiral came about.)

However, using HP axles means you have to keep track of an additional train of gears - while this would be a problem if you have a line that, say, uses D44 fore and aft (just as an example) since you'd have to keep track of which gears are which, if you have an axle that is a dedicated front (like the D30 in Jeep,) it should not be a problem. Jeep hasn't used a D30 rear since the early 1970's, in the Jeepster (as I recall.)

Cost to manufacture RS gearing and HP housings should be similar, so I don't see that being a significant problem. Yes, there could be clearance issues in running HP/LP housings (given that the difference in the pinion exit/driveline entry is about a vertical three to three-and-a-half inches,) but that should be something that can be worked around, no?

[Phil]

Cost and logistics, primarily.

LP fronts can use the same gearsets as HP rears - even tho they drive on the 'coast' side of the gearteeth (which isn't as strong as the 'drive' side - this is why HP fronts with a reverse spiral came about.)



Huh?

HP is HP, LP is LP. Front or rear doesn't matter.

[5-90]

Huh?

HP is HP, LP is LP. Front or rear doesn't matter.

Oh, damn. CRS acting up again on the details...

So all HP sets would be RS? Aren't pretty much all rears HP entry? If they are, why aren't there RS gearsets used in the rears? Or am I missing something else?

[srmitchell]

The fact that they switched all cherokee front axles to LP in 2000 was a good indicator that the model was coming to an end.

[tbburg]

So all HP sets would be RS? Aren't pretty much all rears HP entry? If they are, why aren't there RS gearsets used in the rears? Or am I missing something else?What? All factory rear axles are low pinion, and standard rotation.
The fact that they switched all cherokee front axles to LP in 2000 was a good indicator that the model was coming to an end.I read they switched that to clear the split exhaust manifold and dual pre-cats.

High-pinion, reverse rotation, and reverse spiral all mean the same thing.

The existence of the low pinion FRONT axles comes from back in the mists of time when they started making 4WD vehicles. They just took a rear axle, added knuckles, and put it under the front.

Hi-pinion REAR axles are all custom, made for ground clearance over strength.

[GoSlowGetStuck]

The fact that they switched all cherokee front axles to LP in 2000 was a good indicator that the model was coming to an end.

That's probably true. When they started WJs in 99 they were LP as well. Fun to see people complain about that now that WJs are old enough to wheel. :D

[Starboard M]

Oh, damn. CRS acting up again on the details...

So all HP sets would be RS? Aren't pretty much all rears HP entry? If they are, why aren't there RS gearsets used in the rears? Or am I missing something else?
What the heck is CRS, RS, CS and all these other random abbreviations you are using?

High pinion gears go in high pinion housings, low pinion gears go in low pinion housings.

There were no factory high pinion housings used in the rear of any vehicle. They were all low pinion as they are stronger in a rear application.

The fact that they switched all cherokee front axles to LP in 2000 was a good indicator that the model was coming to an end.
Possibly, but more than likely it was cost. Why make two different axle housings when you can make one that bolts into all Jeeps?

[kastein]

RS is reverse spiral, CS and CRS I'm not sure.

[Phil]

CRS is cold rolled steel. Not sure what it has to do with anything else.

[5-90]

Depends on context, Phil. CRS = Can't Remember S***.

The advanced stage of CRS is CRAFT = Can't Remember A F****** Thing.

Sometimes my wires get crossed. I hate having memory dysfunction - especially when I can remember it working so well before...

[srmitchell]

The lp housing just sucks.

I have a hp in my garage, and it's so much beefier. The bracing on the backside is much more substantial.

I just need to find an income to get that hp under the jeep!!

[egon]

Low pinions exist because before there was 4WD there was only rear wheel drive with very few exceptions. The differentials used/use where developed way before the XJ/YJ/TJ/ZJ what have you was even though of. Most axles used by Jeep were first designed in the 40's and 60's. Since the low pinion was the only game in town when the first 4x4s appeared they just took a rear axle and spun it around and put it up front. It wasn't until Ford put in a request to Dana for a Reverse Spiral (the proper name) version of the 44 for 1965. Jeep uses low pinion axles on many vehicles because they are cheaper and due to clearance issues. A RS30 would never fit well on a stock height ZJ and they had to notch a section of the XJ crossover pipe so the diff wouldn't hit it under full stuff of the driver side tire. The cost factor, reverse spiral differentials cost more to engineer and build because of oiling issues. Because of the oiling issue, a reverse spiral diff is not the best for a rear application. Not only because it is weaker run in a rear application, but due to not keeping the pinion bearings bathed in oil.

--Matt