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Old 09-13-2017, 12:19 PM   #26 (permalink)
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Originally Posted by sdmuleman View Post
Do you have a reference for this? My understanding has always been that the inter axle differential/power divider is a standard differential type system (ie, side bevel gears on a common carrier connected to input power driving 2 side bevel gears connected to the outputs) except that the side gears are attached to the input yoke via a carrier instead of a ring gear and there is a mechanical locking coller which sides to lock the carrier to one output bevel gear when the lock is engaged. What parts and service manuals I've looked at seem to support this, but I can't claim to be an expert. This also makes sense to me - why would you need a complex limitted slip/power divider system when a regular open system would be cheaper and simpler?

I also am somewhat confused by the claim that most semis have locking axles. Again, not an expert, but the 4 TA tractors I have been around (all different history/specs) where open axles with a lock for the inter axle diff.

I'll take a pic of my Kenworth when I get home tonight, if it's still light out. The front axle is not powered unless switched "on" for a lack of better words, simple air switch on the dash, all it does, is engage "4wd" essentially, meaning all 4 set's of duals can receive power, vs only the rear axle.

OTR trucks are rare to have lockers, log trucks, dump trucks, heavy haul etc, very common to see a single/dual locker option on them, again, an air operated on/off (same concept as an ARB, but works TOTALLY different) My current KW does not have a locker. But my single drive axle Freightliner toter home does though.
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Old 09-13-2017, 01:49 PM   #27 (permalink)
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Couple point's of misunderstanding in here.

a power divider: a tandem axle semi, in normal dry condition road driving, is only powered by the rear axle, while every part in the front is spinning, it is disengaged inside the power divider, The big goofy thing on the front of the front diff. Imagine it like a vacuum disconnect on a Dana30. everything spins, it's just not locked in. It's usually labeled on the dash as "inter axle lock" which is totally different from a locker, as a majority of semi's have air locking diffs, (think ARB) some have just one in the rear, some have them in both.
for fucks sake, NO!! thats not at all how it works..

It amazes me how many people spread this shit around the internet, just stop..
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Old 09-13-2017, 01:52 PM   #28 (permalink)
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I'll take a pic of my Kenworth when I get home tonight, if it's still light out. The front axle is not powered unless switched "on" for a lack of better words, simple air switch on the dash, all it does, is engage "4wd" essentially, meaning all 4 set's of duals can receive power, vs only the rear axle.
I got a better idea when you get home, put a bottle jack under the left front drive tires, start it up, put it in gear, and gently let the clutch out.. Then post up what happens.. and then try it again with the power divider locked.
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Old 09-13-2017, 01:58 PM   #29 (permalink)
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for fucks sake, NO!! thats not at all how it works..

It amazes me how many people spread this shit around the internet, just stop..

Aaaah... OK, so. you're saying that with adding a little brake pressure to add trailer resistance on wet pavement, that with it unlocked, the front tires would spin as well as the rears? Hmmm...
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Old 09-13-2017, 04:47 PM   #30 (permalink)
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With the power divider disengaged, as little as one wheel will (or could) receive power. That's why spin-outs with tandems can be so destructive - one wheel can be rotating up to 4x the gear speed of the power divider is not in.

The power divider locked-in simply send equal power to the front and rear axles.
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Old 09-13-2017, 05:58 PM   #31 (permalink)
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Originally Posted by Tfab View Post
a power divider: a tandem axle semi, in normal dry condition road driving, is only powered by the rear axle, while every part in the front is spinning, it is disengaged inside the power divider, The big goofy thing on the front of the front diff. Imagine it like a vacuum disconnect on a Dana30. everything spins, it's just not locked in. It's usually labeled on the dash as "inter axle lock" which is totally different from a locker, as a majority of semi's have air locking diffs, (think ARB) some have just one in the rear, some have them in both.
how the fuck's a three speed rear sposed to work with it doing that?
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Old 09-13-2017, 08:54 PM   #32 (permalink)
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Quote:
Originally Posted by Tfab View Post
Couple point's of misunderstanding in here.

a power divider: a tandem axle semi, in normal dry condition road driving, is only powered by the rear axle, while every part in the front is spinning, it is disengaged inside the power divider, The big goofy thing on the front of the front diff. Imagine it like a vacuum disconnect on a Dana30. everything spins, it's just not locked in. It's usually labeled on the dash as "inter axle lock" which is totally different from a locker, as a majority of semi's have air locking diffs, (think ARB) some have just one in the rear, some have them in both.
No

Quote:
Originally Posted by sdmuleman View Post
Do you have a reference for this? My understanding has always been that the inter axle differential/power divider is a standard differential type system (ie, side bevel gears on a common carrier connected to input power driving 2 side bevel gears connected to the outputs) except that the side gears are attached to the input yoke via a carrier instead of a ring gear and there is a mechanical locking coller which sides to lock the carrier to one output bevel gear when the lock is engaged. What parts and service manuals I've looked at seem to support this, but I can't claim to be an expert. This also makes sense to me - why would you need a complex limitted slip/power divider system when a regular open system would be cheaper and simpler?
Yes

Start on page 72

http://www.roadranger.com/ecm/idcplg...ILE&dID=297625

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Old 09-14-2017, 09:10 AM   #33 (permalink)
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Originally Posted by sdmuleman View Post
What exactly wears out? As I understand the system, it's a mechanical lock on a differential - only difference would be load on the locking member vs the differential bevel gears.

What I have found on google seems to boil down to 3 common failure modes, none of which seems to apply here:
-Locking with a tire spinning (shock load breaking things)
-Spinning a rear tire for a long time without it locked (IAD is lubed by front axle rotation, so this deprives IAD of lube and burns it up)
-Drivability issues from locking it on road (locked IAD causes drivetrain wind up, same as driving on the highway with 4wd in)

I agree that the right way to do this would be to use a air lift axle - not going to do that for cost and other reasons. Super singles is also out due to cost and the fact that I have 8 like new tires already on there.

Honestly probably not going to do anything with it, but still seemed like an interesting idea to explore.

I would need full TA load capacity down the road but don't right now.
Sure, technically just having the inter-axle locked without any bind shouldn't hurt things. But, driving with the front axle lifted and powered, you will undoubtedly run into situations where the tires contact the ground and induce bind. Not to mention the severe operating angle of the driveshafts from the front axle being lifted imparting loads on the bearings of the through shaft etc that are not normally there. It is a horrible idea, but you guys are free to do whatever with your own trucks.
Travis..
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Old 09-14-2017, 12:16 PM   #34 (permalink)
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OTR trucks are rare to have lockers, log trucks, dump trucks, heavy haul etc, very common to see a single/dual locker option on them, again, an air operated on/off (same concept as an ARB, but works TOTALLY different) My current KW does not have a locker. But my single drive axle Freightliner toter home does though.
We had tractors similar to this (but green) in the navy that had Detroit's in the rear, that was the biggest vehicle I've ever spun doughnuts in.
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