4EAT torque bind advice needed

[SubaruFred]

A few months back I bought a 93 Legacy LS wagon with 170k miles on it. The transmission works fine except for intermittent torque bind. With the FWD fuse installed, TB is minimized but still appears randomly. It appears to me that the duty C is failing or that other wear is allowing line pressure to develop on the transfer clutch pack.

 

So far I've added 8 oz of GM LSD additive - no change

Drained and re-filled 5 qts of ATF - no change

Added 15 oz of Trans-X to possibly free-up the duty C - no change

 

Given the high mileage I suspect that this is not a case where subsequent ATF changing will help but I could be wrong. The old ATF looked and smelled great with no discoloration or burnt smell. I'd like to fix the TB as economically as possible but would rather spend more to do it once than risk an unknown used MPT assembly from a bone yard.

 

I'm considering the following options but am wide open to suggestions:

 

1) R&R transmission with a lower mileage used unit

2) R&R MPT assy with a trusted used or rebuilt unit

3) Re-build MPT assy with new duty C, clutches and repair sleeve the case

4) Keep changing ATF and hope that it helps

5) ???

 

I was going to re-wire the FWD circuit to a switch as others suggested but now that the TB is appearing intermittently even in FWD mode, I've shelved that idea.

 

So what do you guys recommend? I'm especially interested in buying a known-good used or rebuilt MPT assy, suggestions on where to buy a rebuild kit or parts and any info on installing a repair sleeve into this old style housing. Will a later model MPT assy work? I'm a bit concerned about the condition of my clutch hub having seen many photos of badly grooved hubs as a result of TB. I'd hate to have a rebuild kit in hand only to open it up and find that I also need a new hub assy. TIA.

Edited March 12, 2011 by SubaruFred

[idosubaru]

Sounds like you're on top of this and replacing the Duty C is the only option.

 

I'd replace the Duty C with new, I believe they're around $75-$125 if you don't want to go back in again.

 

The intermittent nature suggests to me the clutches are fine and with the Duty C new, fresh fluid, and proper tire rotation I would not expect those to fail. So while replacing the clutches and hub isn't a bad idea, I wouldn't hesitate to reuse them either and would prefer those being "used" over the solenoid.

 

I'd post on here in the parts wanted forum. I had a known good trans with a bad front diff and sold the entire rear housing to someone in your shoes - clutches, hub, duty C. Someone might have a bad trans for parts that they know is good. If you found something like that maybe used would be more attractive.

 

You could call around yards and ask if they have any bad trans to sell parts off of, but a gamble that will be. Though usually they're wrecks or blown motors so you can guess the trans to be good.

 

And I'm sure you know you don't have to pull the transmission to do this job.

[Jack Foulard]

I had similar problems in my 04 H6 outback and they replaced the duty C and the purge valve and that solved my problem. I was at 16K and now am at 50K and have not had the problem since.

[SubaruFred]

Sounds like you're on top of this and replacing the Duty C is the only option.

 

I'd replace the Duty C with new, I believe they're around $75-$125 if you don't want to go back in again.

 

The intermittent nature suggests to me the clutches are fine and with the Duty C new, fresh fluid, and proper tire rotation I would not expect those to fail. So while replacing the clutches and hub isn't a bad idea, I wouldn't hesitate to reuse them either and would prefer those being "used" over the solenoid.

 

I'd post on here in the parts wanted forum. I had a known good trans with a bad front diff and sold the entire rear housing to someone in your shoes - clutches, hub, duty C. Someone might have a bad trans for parts that they know is good. If you found something like that maybe used would be more attractive.

 

You could call around yards and ask if they have any bad trans to sell parts off of, but a gamble that will be. Though usually they're wrecks or blown motors so you can guess the trans to be good.

 

And I'm sure you know you don't have to pull the transmission to do this job.

 

 

Thanks yet again Grossgary, you continue to provide very useful insight and advice. I was thinking along similar lines but with very little soob experience or even high-mileage auto experience, it really helps to hear opinions from someone with more experience. At this point with the weather getting better and my bad-weather/dump-run car needed less and less I suppose I can afford to remove the MPT assy and ascertain it's condition first-hand. I know I need a new duty C but if I end up needing more I could have the car down for a few weeks while I acquire parts. Replacing only what I really need to makes good sense at this point. It might be a few weeks but I'll post back with my findings and photos after disassembling the MPT assy.

 

 

I had similar problems in my 04 H6 outback and they replaced the duty C and the purge valve and that solved my problem. I was at 16K and now am at 50K and have not had the problem since.

 

Thanks Jack. I'm pretty sure that my duty C is failing but what is the purge valve you mention?

 

To all: I've read that early 4EATs had a design flaw that contributes to torque bind. This flaw being an un-sleeved shaft support in the MPT housing that requires a steel repair sleeve after so many miles. One source even stated that this flaw was the cause of most early model torque bind by allowing hydraulic pressure to develop on the MPT clutch pack after bleeding through the worn case shaft support area. Any truth to this?

[idosubaru]

i've never heard of the design flaw speculation. post links to your sources and we'll check it out.

 

if it says "the early 4EAT's", then it's wrong already because the first generation of 4EAT's do not have any torque bind issues ever - the late 80's/early 90's stuff on XT6's and some EA vehicles just don't have torque bind.

[SubaruFred]

i've never heard of the design flaw speculation. post links to your sources and we'll check it out.

 

if it says "the early 4EAT's", then it's wrong already because the first generation of 4EAT's do not have any torque bind issues ever - the late 80's/early 90's stuff on XT6's and some EA vehicles just don't have torque bind.

 

I've read other mentions of this case wear problem at Legacy Central but this is my primary source:

 

http://www.legacycentral.org/library/torquebind.htm

 

I've also noted that Rock Auto sells a "extension housing repair sleeve" for 93 Legacys.

 

I readily admit that I'm finding a lot of this random www info to be confusing. The author states that pre-95 soobs are not affected by this case wear issue but also that the case wasn't sleeved until 97+. So does this issue only affect 95-96 AWD 4EATs and if so, why are 92-94 4EATs without sleeved cases immune? Thanks for your help.

[idosubaru]

if your symptoms are indicative of a particular failure that's a good indicator of what your issue is. check into the symptoms that it causes and let us know if that's what you have.

 

it's interesting, but we do know that this issue you speak of is far less likely to cause torque bind than fluid, solenoid, and clutches. to my knowledge every single case of torque bind i've seen personally and on this board has been fixed by fluid, solenoid, or clutches.

[SubaruFred]

if your symptoms are indicative of a particular failure that's a good indicator of what your issue is. check into the symptoms that it causes and let us know if that's what you have.

 

it's interesting, but we do know that this issue you speak of is far less likely to cause torque bind than fluid, solenoid, and clutches. to my knowledge every single case of torque bind i've seen personally and on this board has been fixed by fluid, solenoid, or clutches.

 

I'm so used to having only one car that I often spend a lot of time speculating on needed parts prior to attempting any repair. I have to remind myself that I now have 2 cars and a motorcycle and can afford to have the Soob down for a week or more if necessary.

 

At this point it's time to order a duty c, remove the MPT housing and see if it needs anything more. Thanks again for sharing your experience and knowledge.

[idosubaru]

good luck with it. thanks for posting that link.

 

there's some parts and stuff that typically "fall out" of place when you pull it off, kind of disturbing when you first do it, wondering where/how they go. not sure if anyone has posted details on that before or maybe an FSM picture would help.

[SubaruFred]

good luck with it. thanks for posting that link.

 

there's some parts and stuff that typically "fall out" of place when you pull it off, kind of disturbing when you first do it, wondering where/how they go. not sure if anyone has posted details on that before or maybe an FSM picture would help.

 

I've seen photos of the MPT housing disassembled but no DIY guide and the only reference I have is a worthless Haynes repair manual. Anything would be appreciated.

 

The more I think about the random, intermittent nature of my TB problem the more I am convinced that the primary culprit has to be the duty C. Any of the other possible causes would result in more consistent TB issue. Thanks again.

[SubaruFred]

I still haven't replaced my suspect duty C solenoid but recently my alternator failed. Since replacing the alternator the duty C has been working fine with no more TCU failure codes in almost 2 weeks now. Makes me wonder if the duty C might have been failing under low voltage conditions and once the TCU sees it fail, it defaults to 50/50 torque split mode. FWIW I heard and felt the duty C fail numerous times previously under low-voltage conditions. I knew the alt was weak due to dim lights that grew brighter with rpm but I never thought that the charging system could cause a transmission problem.

 

I'll report back if and when the torque bind re-appears.

[idosubaru]

that's got to be a good feeling that it disappeared? you don't get much luckier than that, but that's great if so.

 

low voltage would affect that solenoid and nothing else. wonder why that is?

 

got that old alt still - reinstall it and see if the TB comes back?!

[SubaruFred]

It sounds pretty far-fetched, doesn't it? I won't be at all surprised if the TB re-appears but at least for now it's gone. The only info I can add at this time is that I've felt and heard the duty C fail numerous times and it was always at idle speed when the alt wasn't charging. Perhaps the failure wasn't the duty C but the TCU. Perhaps the weak alt was only one contributing factor in the TB, perhaps not even that. Time will tell.

[SubaruFred]

Okay, 2 months later and I feel pretty confident in saying that the failing alternator was a contributing factor but not the root cause of my Suby's torque bind. The binding is back, just not as often. Although for whatever reason it has been more prevalent recently. A failig duty C, dirty ATF, 175k miles of wear all play a part, IMO.