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Center Diff Lock Q


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21 replies to this topic

#1 Jibs

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Posted 11 April 2008 - 07:12 PM

Did Subaru ever make an auto tranny with the center diff lock or were they all manuals?

#2 GLCraig

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Posted 11 April 2008 - 08:36 PM

The Automatics do not have a center diff, they have a transfer clutch that engages and disengages the power to the rear wheels, as need. There are a few threads on this board and others, that tell you how to manually control the transfer clutch.

#3 grossgary

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Posted 11 April 2008 - 10:25 PM

what he said - auto's are completely different in every way. there is no center diff.

but there's good news. the rear output shaft (4WD) is controlled via clutches. locking those clutches will perform similarly to a center diff locked manual trans.

i've done it to multiple vehicles.

for newer EJ stuff this makes the automatics better for some types of offroading than manual trans. i'd much rather have my "locked" automatic than an EJ manual for snow, mud, and offroad driving.

there's threads on here about how to do it.

#4 Andyjo

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Posted 13 April 2008 - 11:15 AM

http://www.ultimates...ead.php?t=50264

use at your own risk.... or end up w/ a tranny like mine :rolleyes:

#5 nipper

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Posted 13 April 2008 - 05:10 PM

For a split second i did entertain doing this, a very split second while four wheeling yesterday.

But just putting the car in 1st gear was exactly the same thing, i could feel the AWD shift to a nice 50/50 split as soon as i shifted.

So i really dont see a need for it. Also in reverse its a forced 50/50 split.

When you have a frt engine, frt biased AWD vehical, its sometimes much easier to back up something very steep then drive forwards up it :) (much better traction).

nipper

#6 bulwnkl

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Posted 13 April 2008 - 10:20 PM

But just putting the car in 1st gear was exactly the same thing, i could feel the AWD shift to a nice 50/50 split as soon as i shifted.


Does selecting 1st on the A/T lever not force center 'lock-up' on all the 4EAT trannies? I know it did on the '02 Legacy we had, but maybe that was only for a few years or something?

#7 nipper

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Posted 13 April 2008 - 10:28 PM

Does selecting 1st on the A/T lever not force center 'lock-up' on all the 4EAT trannies? I know it did on the '02 Legacy we had, but maybe that was only for a few years or something?


does it with all the 4eat's

Low
Reverse
and full throttle.

And dont use the word lock-up. Its not a lock up, its a full 50/50 split that still allows for differntial action at the clutch pack.

nipper

#8 Gloyale

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Posted 14 April 2008 - 03:00 AM

For a split second i did entertain doing this, a very split second while four wheeling yesterday.

But just putting the car in 1st gear was exactly the same thing, i could feel the AWD shift to a nice 50/50 split as soon as i shifted.

So i really dont see a need for it. Also in reverse its a forced 50/50 split.


In my mind it's a way to get more life out of worn clutches.

I HAD to use my C-lock switch to get good AWD in my GL. With the switch it worked great. That was until I swapped to a new trans, new clutches(keeping the same TCU)

I have not had to use the switch with the new trans. But if the clutches start slipping I have confidence my switch will be of help again.

And dont use the word lock-up. Its not a lock up, its a full 50/50 split that still allows for differntial action at the clutch pack.


It is a hydraulic clutch pressurized 160% of its intended operating pressures, That's pretty damn locked. Might as well be a solid shaft.

#9 grossgary

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Posted 14 April 2008 - 07:46 AM

Nipper - if you put it in first gear on pavement, does it "hop" and "Jump" like a 4wd "locked" vehicle? i don't think it will.

my XT6 and 97 Impreza Outback Sport (both 4EAT) do not "bind" in 1st gear, but they will with the Duty C switch.

1st gear doesn't seem to do anything in mine or the difference is negligible, it's not even close to the duty C mod in terms of traction.

there have been a few other threads about this...some people say 1st gear does something, others say it doesn't. i don't know why or what the answer is, but at least on some subaru's 1st is not the same as the duty C mod.

#10 johnceggleston

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Posted 14 April 2008 - 09:25 AM

there have been a few other threads about this...some people say 1st gear does something, others say it doesn't. i don't know why or what the answer is, but at least on some subaru's 1st is not the same as the duty C mod.

there is a difference between 'locked' and operating your car in first. when 'locked' the front and rear wheels turn exactly the same number of turns. this is ok for snow, ice gravel dirt etc. not so good on pavement.

in first gear the A/T transfer clutch still allows for a difference in front and rear speeds, similar to an open diff. it also prevents damage to your trans, transfer chutch, drive train and tires. it was designed this way. this is why nipper says not to use the term 'locked' for having the car in first gear.

when operating correctly the transfer clutch doesn't lock any thing, it splits, shares, distributes, sends the power from the engine to the rear wheels. the front wheels are always powerd by the trans just like front wheel drive car with an auto trans.

most of you know this, but some new guys may not.

now that i've stirred the pot, i'm out of here.

#11 bulwnkl

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Posted 15 April 2008 - 03:59 PM

does it with all the 4eat's

Low
Reverse
and full throttle.

And dont use the word lock-up. Its not a lock up, its a full 50/50 split that still allows for differntial action at the clutch pack.

nipper


Thought it was all of them. I used the ' marks around the term lock-up because I was trying to not get overly precise and confuse folks. I agree that because it's a pulsed action to release torque bind, it's not locked in the sense of two steel shafts welded together. However, I'm not comfortable with the term "50/50 split" either because that always makes me think of torque (don't know why), and it's most definitely not a 50/50 torque split. Is this term meant more along the lines of a 50/50 power split? There again, so many folks get confused by a lack of understanding of torque vs. power...

#12 nipper

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Posted 15 April 2008 - 04:11 PM

Thought it was all of them. I used the ' marks around the term lock-up because I was trying to not get overly precise and confuse folks. I agree that because it's a pulsed action to release torque bind, it's not locked in the sense of two steel shafts welded together. However, I'm not comfortable with the term "50/50 split" either because that always makes me think of torque (don't know why), and it's most definitely not a 50/50 torque split. Is this term meant more along the lines of a 50/50 power split? There again, so many folks get confused by a lack of understanding of torque vs. power...


its a 50/50 torque split between the front and rear wheels.

http://www.howstuffw...wheel-drive.htm

nipper

#13 bulwnkl

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Posted 15 April 2008 - 05:57 PM

its a 50/50 torque split between the front and rear wheels.


No, it's absolutely not a 50/50 torque split, but I'm not going to go through this with you again.

#14 Andyjo

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Posted 15 April 2008 - 07:54 PM

This discussion again? :horse:

I'm with gary on this one, in my 97 obs, I find that there is no difference between shifing into '1' or just leaving it in 'D', or even reverse. There is a HUGE difference between '1' and using the switch, noticible. Back when i was beating the snot out of my OBS i did some experiments on the ol' ski hill w/ the 'shifting into 1st', letting the awd take care of it, and the switch.
From those experiments i concluded that at least in my transmission that shifting into 1st, and just leaving it tranny in 'D' is the same, and throwing the switch is the only real way to insure that the traction is where you want it.
Sorry to burst whoever's bubble, but you'll never really know/feel the difference unless you do the mod. As for the shifting into 1st thing, maybe that's how it worked w/ older models, but i'm very sure that in my 97 4eat that there is no signal modification going to the duty C when you shift into 1st.
So...... this discussion/argument about the 4eat is ancient history... the question should be... why haven't i gotten my OBS back on the road again :rolleyes:

#15 nipper

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Posted 15 April 2008 - 08:07 PM

why haven't i gotten my OBS back on the road again :rolleyes:



:popcorn:

#16 nipper

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Posted 15 April 2008 - 08:14 PM

No, it's absolutely not a 50/50 torque split, but I'm not going to go through this with you again.


SAE calls it torque, all the automovie engineering design texts (at college level) call it a torque split.

So i call it torque


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#17 Andyjo

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Posted 15 April 2008 - 08:22 PM

SAE calls it torque, all the automovie engineering design texts (at college level) call it a torque split.

So i call it torque


nipper


I dunno about you, but i consider torque the cross product of a force, and the length of the lever arm it's applied upon :cool: (thank you wikipedia for the pic :grin: )
Posted Image

Why the OBS isn't on the road... well it won't pass inspection... missing that front swaybar, needs new exhaust studs in the block... a few other goodies :cool:

#18 nipper

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Posted 15 April 2008 - 08:25 PM


Why the OBS isn't on the road... well it won't pass inspection... missing that front swaybar, needs new exhaust studs in the block... a few other goodies :cool:



ever fix the tranny (or is that one of the goodies)?

So shes just a planter in the driveway then, or still on all four tires.

One of the few cars i have never seen on cinderblocks, a subaru.

nipper

#19 grossgary

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Posted 15 April 2008 - 08:29 PM

This discussion again? :horse:

I'm with gary on this one, in my 97 obs, I find that there is no difference between shifing into '1' or just leaving it in 'D',

it'd be nice to know why this is always an issue. my impreza and XT6's definitely don't (but i've only owned 20 so maybe i've gotten a bad batch!!).

maybe it's a legacy thing?

#20 nipper

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Posted 15 April 2008 - 08:43 PM

I noticed it out in the woods, so did njdrsubaru...

whatever, argue with subaru.



nipper

#21 nipper

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Posted 15 April 2008 - 08:55 PM

I dunno about you, but i consider torque the cross product of a force, and the length of the lever arm it's applied upon :cool: (thank you wikipedia for the pic :grin: )
Posted Image

Why the OBS isn't on the road... well it won't pass inspection... missing that front swaybar, needs new exhaust studs in the block... a few other goodies :cool:


From the SAE automotive handbook 4th edition pg 384:

"The purpose of the piston, connecting rod, and crankshaft assembly in the reciprocating-piston engine is to trnasform the gas forces generated during combustion within the working cylinder into a piston stroke, which the crankshaft then converts into useful torque at the power-output end of the engine."

And for the more geeky

"The gas force (Fg) which acts on the piston can be subdivided into the side forces (Fn)applied by the piston to the cylinder wall and supported by it, and the connecting rod force (Fs). The connecting rod force, in turn, causes the tangential forces (Ft) to be applied at the crankshaft journal. This force together with the crank radius generates the shaft torque and the radius force (Fr)."

Then it goes into a formula which i have no idea on how to reproduce on a keyboard, but it results in vibration calculations.

and wikipedia is cheatting, and not allways correct.

nipper

#22 bulwnkl

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Posted 15 April 2008 - 08:56 PM

Nipper, if it was a 50/50 torque split, then you could lift the front axle off the ground in gear and use the engine to spin the front wheels freely without particular danger of the rear axle propelling the vehicle over the 2x2 blocks you were chocking the rear wheels with, just like would happen if the center divider was an open differential, which is a 50/50 torque split. That doesn't happen, which is the layman's way to know the torque is being redistributed unequally to the other axle. Another simplified explanation is at the website you posted a couple posts up. I'm sure you can go through the calculations for yourself if you don't prefer the layman's method.




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