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Guest Message by DevFuse
 

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Can someone explain "clutch pack?"


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16 replies to this topic

#1 Guest_trinket_*

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Posted 23 December 2001 - 03:13 PM

My '95 Legacy wagon, automatic trans., 150,000 miles, started jerking, like a manual 4-wheel drive, while turning sharply on pavement. Parking lot manuevers is what I'm talking about. The dealer says the clutch pack needs replace, for about $400 total. Has anyone had this work done and can anyone explain the mechanics of the problem? Thanks.

#2 Guest_nuburu2_*

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Posted 23 December 2001 - 03:25 PM

Clutch pack allows some slippage between front and rear differentials , avoiding the "push" one experiences on dry pavement with a 4WD vehicle. Without it the rear wheels push through the front wheel/tire axis when turning, effectively turning the front tires into erasers! Hope that helps. You may want to look at www.howthingswork for more in-depth explanations with pics.

Glenn O

OOPS! Guess I should have finished with; failure means it's no longer allowing the needed slippage, and is either locked up or close to it. Bad news for an AWD vehicle, as well as for the tires and front drive components. You may want to disable the AWD until it's taken care of, by placing the "disable" fuse (I believe) in the under-hood fuse box.

#3 Guest_dscottf_*

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Posted 23 December 2001 - 06:12 PM

Mine started the same thing at about 50,000 miles, because I neglected to do the 30,000 mile service (missed it somehow). Fourtunatly, Subaru replaced it under warenty

Everyone remember to have the fluids changed in both differentials and especially the center diff (clutch pack)

If memory serves, front diff and clutch are done together

#4 Guest_trinket_*

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Posted 24 December 2001 - 08:16 PM

Thanks for the information. Am I to understand the clutch pack is in the front differential or in the transmission? The car has been all syntheticly lubricated since day one. These clutch packs must just wear out or what?

#5 Guest_Commuter_*

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Posted 25 December 2001 - 04:17 PM

The location of the clutch pack was asked by someone about a month or so ago. Unfortunately, we never got a clear answer. I feel quite certain that it is in the transmission and not the front differential (just by the physical layout of the drive train). My "guess" is that it is in the tail end of the transmission, but I have yet to confirm that.

Our cars are essentially front wheel drive cars with the electronic clutch pack in there to transmit torque to the rear wheels as needed. The clutch pack consists of a series of disks (I've heard 4) where half the disks are connected to the input side (coming from the transmission) and the other half are connected to the output side (the drive shaft to the rear).

Under normal driving, the disks are 'loose', just barely touching each other. Since the front and rear wheels/axles are turning the same speed, the disks are as well and there is no relative motion between the disks. There is just enough friction between the disks that one gets the 90/10 torque split. (I know that my 97 OB is 90/10. I'm assuming that your 95 Legacy is too.)

When wheel spin occurs at one axle, a difference in the speed of the 'input' and 'output' shafts at the clutch pack is created. This difference is sensed and the car actuates "stuff" to start to squeeze the clutch plates together. This causes more torque to be transmitted to the rear wheels until one reaches a 50/50 split, which is basically having the clutch pack locked together. The "stuff" I'm not really up on. It will involve sensors, some sort of actuator, etc. I've heard of a "Duty C" solenoid (I think that is the name) that is part of this system that has been known to cause problems. Perhaps someone else can elaborate.

Turning a corner causes a speed difference as well in the clutch pack (simple geometry). However, there is not anywhere near the speed difference as that created by a spinning wheel (or axle). So the action of the clutch pack is minimal (if any really) and it does not create a problem. However, if there are issues with this system, that is when you will notice it (turning). Things will be binding up when they shouldn't be.

There was also discussion on this board a while back about another "flaw" that some of the mid 90's autos have. It had something to do with the extension housing on the transmission. (I don't know if this is where the clutch pack is, or after it. As I understand it, it is the final piece of the transmission where the shaft comes out and connects to the drive shaft.) The problem here (from what I could gather) was the occasional failure (usually high mileage) of some bushing that the output shaft goes through. This allows fluid to get somewhere it shouldn't be and messes things up causing the infamous torque bind. Sorry I can't be more specific here, but it is the exact same symptoms. This might very well be all one and the same thing, I'm not sure. Apparently Subaru changed the bushing design/material in 98.

Dealing with the torque bind issue in a Subaru can get expensive in a hurry. Just make sure that the shop is not doing stuff they don't have to, and that they have got the problem diagnosed correctly in the first place. (That may not be easy.) Do try the fuse for disabling the clutch pack as suggested. This might help narrow things down a bit.

As for wearing out? Hmmm... I'm at 240,000 km (148,000 miles) and so far, so good.

Commuter

#6 Guest_trinket_*

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Posted 25 December 2001 - 05:28 PM

Thanks, Commuter,
That's the best explanation I've had about how the whole system is supposed to work. I looked up "slip differentials" on the web and did found out about the three basic designs for slip differentials and that Subaru's style is of the cheapest and most likely to cause problems.
Merry Christmas.
trinket

#7 Guest_Commuter_*

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Posted 25 December 2001 - 08:56 PM

It's one of the simpler designs, and probably cost effective. I'm not sure if it is 'cheap'. Bear in mind that we are talking of a center differential here, not a front or rear. The center differential transfers power in a straight line typically. A front or rear differential has to transmit power from one shaft to two shafts at right angles. Different ball game.

The manual equipped cars have a viscous coupling for a center differential. (The WRX has thrown a planetary gearset in there as well, but I'm not read up on why.) One might argue that the "smarts" that go along with the clutch pack on the auto are more sophisticated. In general, things seem to be going that way. I was reading the other day about a system from Haldex. The gearheads out there might want to check it out. www.haldex-traction.com Their LSC (Limited Slip Coupling) touts a lot of 'pluses', and is very "electronic". The latest cars from Subaru are moving in this direction too from what I can see. The Outback VDC can split torque beyond 50/50. It normally is 45/55 and it can direct up to 70% (or more?) to the rear during hard acceleration from a stop. Passive systems like a viscous coupling or a Torsen style differential simply do not have all this flexibility. I'm not knocking them mind you (as a Mech Eng, I love the elegant simplicity of the Torsen design), but they can only take you so far.

Best of luck in getting your problem fixed. I'd definitely be taking it to 3 places (dealer and otherwise) for diagnosis. The bit of effort and time to do this might be well rewarded.

Commuter

#8 Guest_trinket_*

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Posted 30 December 2001 - 01:03 AM

Commuter,
I'll let all know what the ultimate repair parts were and costs. It will be very interesting. Thanks for your help on this more than fuzzy subject.
Trinket

#9 Guest_poulinr_*

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Posted 30 December 2001 - 01:36 PM

See this:::: The Subaru Viscous Coupling Variations

www.autospeed.com/A_0920/page1.html

#10 Guest_Commuter_*

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Posted 30 December 2001 - 10:37 PM

Note - This is the center Viscous Coupling and pertains to manual transmission vehicles.

At least it has answered one question. The VC is in the extension housing of the transmission. I would infer from this that the electronic clutch pack is also in the extension housing on the automatics. (Still not a 100% absolute though.)

Commuter

#11 Guest_ccrinc_*

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Posted 30 December 2001 - 11:45 PM

The clutch pack is part of the internal transmission "workings". I've seen these torn apart, and am continually impressed with Rick because he can take them apart, see what's bad, and replace everything exactly right. It's a nightmare in there!
The rear coupling problem is a design flaw where it wears improperly and damages an o-ring, allowing fluid to go where it shouldn't :lol:

Emily
www.ccrengines.com

#12 Guest_trinket_*

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Posted 24 January 2002 - 06:19 PM

For those who followed my questions concerning the "clutch pack" of an auto transmission several weeks ago, I just had it replaced at the nearest dealer, which here in the sticks Idaho, is three hours away. For those new to this subject, feel free to read and learn. My '95 Legacy wagon started binding during tight turning in parking lots, especially on bare pavement (Yes, we do have some pavement here in Idaho). It felt just like a turning a pick-up locked in 4-wheel drive on pavement. Well, that was exactly what the Subie was doing, too. The transfer valve, which tells the 4-wheel drive to disengage during tight corners with no wheel slippage, was non-functional. Thus, the 4-wheel drive was staying engaged all the time. This caused the plates of the clutch pack to stay engaged with the gear reduction drive, which in turn caused the teeth of the clutch plates to start wearing into the gear reduc. drive. So, besides replacing the transfer valve ($83) and the transfer clutch (163), I had to replace the gear reduc. drive ($97). It's fine now. So, the lesson of this story is if you feel you Subie jerking or binding during tight parking lot turns, get it looked at sooner than later. If done all my repairs on the car, but I didn't feel up to this one as I was still kind of fuzzy about how it all worked. Now, I'm an expert. Hopefully, this is the end of this story.
Trinket

#13 Guest_SmashPDX_*

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Posted 24 January 2002 - 09:44 PM

I'm gonna archive this thread-- thanks for the update.

#14 Guest_bobjr94_*

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Posted 26 January 2002 - 04:20 AM

the clutchs that run the rear driveshaft are at the tail end of the transmission..You do not need to pull the tranny to change them..The control valves are also in the tail housing..Pull exhuast,driveline, transmission mounts and crossmember and unbolt the tail end, and unplug one wire as you pull the housing off...You will need a gasket , and new sealing rings are also good, besides clutchs, steel plates, etc..

#15 rainman19154

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Posted 28 October 2009 - 05:43 AM

'found this via a Yahoo search: topic "95 legacy AWD clutch pack". I started on ebay and went to Yahoo, looking for a vendor that sold the 4? disk pack that will be needed to fix TB.

Good read here. Perhaps wordy and maybe not totally accurate but it does cover some bases.


What is the clutch pack called and who is a recommended vendor for ordering it from?

#16 johnceggleston

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Posted 28 October 2009 - 06:46 AM

get pat numbers here: (this is for the 95 legacy you will have to look around for other years)

http://opposedforces...illustration_1/

and here:

http://opposedforces...illustration_2/


then i'd call jamie at www.subarugenuineparts.com .

or

http://www.1stsubaruparts.com/

or

http://www.subarupartsforyou.com/


but until you have taken it a part, you may not know what you need.

#17 mdjdc

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Posted 28 October 2009 - 08:12 AM

Don't order the clutch packs. I have a good set of them here and if we need to we can replace yours with these. At this point, I have not seen a torque bind situation where they need replacing. When they lock up they do not wear. It is only when they are slipping. The real problem is in the solenoid and the drum, both of which we will work on when you get down here.

Mike


'found this via a Yahoo search: topic "95 legacy AWD clutch pack". I started on ebay and went to Yahoo, looking for a vendor that sold the 4? disk pack that will be needed to fix TB.

Good read here. Perhaps wordy and maybe not totally accurate but it does cover some bases.


What is the clutch pack called and who is a recommended vendor for ordering it from?






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