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FWD Fuse...vibration


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19 replies to this topic

#1 captainehh

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Posted 09 November 2003 - 01:07 AM

I've got a 97 OBW with 67K. It shudders when I make sharp turns at slow speeds. A seat of the pants vibration. Gone when I straighten her out. The vibration also leaves when I insert the FWD fuse which disengages the AWD. Any insight into the prob? And also, is it bad to drive with the FWD in place for extended periods of time? Thanks guys!

#2 calebz

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Posted 09 November 2003 - 03:14 AM

Sounds like you might be experiencing a little torque bind. Most common problem is different sized tires. either altogether different sizes, or same size, but different brand. uneven tread wear can cause this as well.. on an AWD system its very important that you have 4 matching tires that are rotated regularly to prevent uneven tread wear

#3 captainehh

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Posted 09 November 2003 - 03:34 AM

What's the easiest way to determine if my tires aren't all the same size? Do tire shops have a reliable means to figure this out?

#4 captainehh

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Posted 09 November 2003 - 03:36 AM

They were all the same size when new, which wasn't all that long ago. Maybe 10,000 miles ago.

#5 mrtoyou7747

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Posted 09 November 2003 - 10:02 AM

I underatand that as little as 1/4 inch variation in the diameter can be a problem.

Jack up the car measure the circumference (around the outside) of each tire number. Should not vary more than about 3/4 inch (C=3.14 x D)

Replace front and rear diff fluid with synthetic diff fluid (Mobile) worked for me.

Also try and rotate the exsisitng tires it may help but will be only temporary.

#6 frag

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Posted 09 November 2003 - 11:02 AM

The tolerance is 1/4 inch in CIRCUMFERENCE not diameter.
Here's what i did to check.
Go to an empty (or almost) parking lot and measure the width of one parking space. Get a rough estimate of your tires circumference (around 76 inches for a 14 inch whee) and compute how many parking spaces you have to drive thru to have your wheel go thru at least 20 revs.
Put a mark on front and back tires at point of contact with the ground.
Drive thru the appropriate number of parking spaces in a straight line (13 was enoug in my case)
If front and back tires are more than 1/4 inch apart in circumference, the marks on the tires will be at least 5 inches apart at the end of the experiment.
Much simpler to do than to explain. Alsok, if you can have the help of someone, have this someone count the wheels revs from the outside instead of using the parking spaces method.
In my case, I discovered not more than one inch of discrepancy between front and back, the equivalent of 1/20 of an inch in circumference.
One extra advantage of this method is that you're getting real life measurements of the rolling circumference of your tires taking into account every variables like pressure for example.

#7 captainehh

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Posted 09 November 2003 - 12:52 PM

Good, i'll give this a try. Thanks.

#8 calebz

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Posted 10 November 2003 - 12:37 AM

Originally posted by captainehh
They were all the same size when new, which wasn't all that long ago. Maybe 10,000 miles ago.



Have th etires been rotated every 6k or so? if not, you could very easily have uneven treadwear causing problems

#9 captainehh

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Posted 10 November 2003 - 02:55 AM

I'll have to check this out. The car is new to me, i'll have to dig up the paperwork to find out. Otherwise, what mechanical fault could cause the shudder that is eliminated when the rear wheels are eliminated from the equation?

#10 alias20035

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Posted 10 November 2003 - 05:10 AM

Originally posted by frag
The tolerance is 1/4 inch in CIRCUMFERENCE not diameter.



It is virtually impossible to measure the circumference of the tires within 1/4 inch margin of error. I'll bet that if you measure perfecty identical tires, you could never get within 1/4 inch on all four. In fact I doubt the manufacturing tolerences are within 1/4 inch in circumference.... Remember that we are talking circurference and not diameter (diameter * pi (3.14) = circumference).

Within 1 or 1.5 inches in circumference is PERFECTLY OK....

From another of my recent replies:

I was told by a Subaru Canada technical rep that a 1 or 2 inch circumference difference will not harm the AWD system. In terms of percentages, the Outback tire diameter is about 27 inches (0.394inches/cm*(2*(22.5cm*60%))+16 inches = 26.638 inches in diameter. 26.64*3.14 = 83.65 inches in circumference. So a 1 inch circumference difference is only a 1.2% size difference. Subaru's AWD system does very little work until the axle speeds differ by 10% or even 20%. But keep in mind that a 1.2% difference between tires on one axle is divided by 2 (because of the differential) and then multiplied by the axle ratio (4.11), so 1.2% becomes 2.47% to the VTD clutch or viscous coupling.

Think of it another way:

How much smaller in diameter (which directly relates to circuference) are your rear tires when you load up with the 880 pounds of cargo and passengers that the Outback is designed to handle? A tire spinning at high speed will expand, but the front tires will still be less compressed and larger. A 1/2 inch diameter decrease equals a 1.6 inch (pi/2) circumference decrease. 1/2 inch is not a lot! 4 PSI less pressure in one tire will easily equal a 1/2 inch or more of sidewall flex. Virtually all Subaru's have at least one tire 5 or more PSI below recommended, this is because virtually no one takes the time to check tire pressure anymore.

For measuring a wheel:

1. tires should be cold (not driven in 3 or more hours).
2. set tire pressures at recommended (see driver's door B pillar plate).
3. raise wheel off ground
4. using a flexible fabric ruler (at least 8 feet long), wrap around the center of the tire to measure circumference.
5. repeat steps 1-4 for all tires.

The above is the official Subaru technical method.

If the circumferences are within a 1 inch range, all is OK. 1.5 inches borders on requiring action, and 2 inches is bordering on risk of damage.

If tires are uneven and within a 2 inch range you can rotate the tires so that the average circumference on the front and rear axles are within 1 inch, and if the vehicle has a rear viscous LSD, keep the two rear tires within 1 inch as well.

If you are not able to rotate to correct, new tires are required.

AWD failures are mainly caused by:

1. torque transfer solenoid fails, these solenoids often fail, and when they do the rear axle becomes locked to the front axle.

2. bad design on pre 1999 transmission (or is it 1998?). The seals on the transfer clutch go bad causing hydraulic fluid pressure to drop. A replacement kit with a hardened steel insert corrects this problem (about $1,000 to fix). The new transmission is a new design that does not have this problem.

3. not changing the ATF fluid and filter at the recommended intervals. The ATF does double duty in Subarus, working both the transmission and AWD system, and the front differential is also in the transmission case, which means that the transmission runs hot, which is enemy number one for the fluid.

4. owner abuse, like driving with one tire at 15 PSI and others at 30. Or installing different tires front and rear. The marked tire size will give a rough estimate of diameter, but different tire constructions could mean as much as a 1" difference between models. Or driving more than 30 miles on the donut spare, or doing more than 45 MPH with it. The max on the donut spare is 45MPH for a maximum of 30 miles, at which point the donut spare tire must be allowed time to cool down.

Subaru dealers often sight tires as the cause, but this should be taken with a grain of salt. It is easier to blame a customer, than to admit that Subaru did not properly design the earlier transmissions.

Virtually all high mileage Subaru's with the uncorrected older transmission will have a leaking torque transfer clutch. Minor leaks are inconsequential, since the pump pressure will exceed the pressure loss.

Since your issue occured at only 67K I would assume that a torque transfer solenoid has gone bad, and the internal seal is most likely ok (or not bad enough to be the issue).

The steps to diagnose this problem are:

1. rule out AT fluid level and condition (smell fluid to see if burnt)
2. rule out tires (size, damage, all the same, etc)
3. rule out wheel bearings (distinctive whine or rumble)
4. rule out axle shafts (torn boots, clacking, rumble, etc)
5. rule out driveshaft (can vibrate severly if the center hanger bearing or U joints are damaged or worn, and this is somewhat common!!) Driveshaft vibration sometimes disappears when the FWD fuse is inserted as well. Driveshaft sometimes only vibrates when stressed, such as when turning.
6. rule out differential fluid level and condition
7. rule out AWD solenoids (requires replacement solenoids unless TCS indicates a specific failure code)
8. rule out internal tranmission AWD tailshaft problem (always requires replacement/rebuild)

You always check the transmission last, because you may locate the real problem first, or locate a problem that led to the torque transfer clutch problem.

As I recall the FWD fuse is for temporary use only and has a 30MPH and 30 mile limit!!!

The FWD fuse powers up an electical pump at full power to disengage the rear axle.

#11 alias20035

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Posted 10 November 2003 - 06:52 AM

Found a link on torque bind.

http://www.legacycen.../torquebind.htm

According to this web page the redesigned tailshaft assembly was put in place in mid 1997, not sure whether that means late 1997 model year vehicles, or whether they started to install them in mid 1997 on 1998 model year vehicles.

#12 frag

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Posted 10 November 2003 - 09:10 AM

I was told by a Subaru Canada technical rep that a 1 or 2 inch circumference difference will not harm the AWD system.


Alias,
(1) I wish you are right cause a tolerance of 1/4 inch in circumference seems to me to be too thin a margin bo be realistic, but, this !/4 inch max tol. in circumference is what I've benn told by every one i spoke to including a Subaru tech. And I've also read this everywhere including here on numerous posts. But we could be all wrong. I would very much like this to be cleared up once and for all

It is virtually impossible to measure the circumference of the tires within 1/4 inch margin of error. I'll bet that if you measure perfecty identical tires, you could never get within 1/4 inch on all four. In fact I doubt the manufacturing tolerences are within 1/4 inch in circumference.....


(2) I take exception to your statement that it's impossible to measure the tires within 1/4 inch margin of error. If your reread my post attentively you'll see that my simple method is exactly aimed at doing just this and my result show that even 3 year old tires can be within 1/20 inch in circumference of each other (of real world rolling circumference to be more exact).
In the light of that experiment one might even think that a 1/4 inch max tolerance in circumference is not that exagerated after all.
(3) What you say about tire pressure and load is exact. But it only shows that trire pressure checking and correcting acoording to load is even more important on an AWD than on any other car. Moreover, if all those factors can vary the rolling radius of a tire, it's even then more important to have tires of equal circumference at the start. An important difference in pressure or load could have a more serious effect on the center diff if it's added to an already existing difference in circumference.

#13 alias20035

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Posted 10 November 2003 - 02:34 PM

I will state it again and stick to it. The 1/4 inch tolerence is too small. My measurements on both my summer and tires only fall within about a 1/2 inch range. I rotate and check tire pressures religiously, and have about 30,000 km on each set of tires.

Remember that I am talking about the range of all four tires, not a single tire. example: all four tires should be between 84 and 85 inches.

Subaru always blames tires for their torque bind problems, but the tires are usually not the issue. Subaru's are designed to allow a 20% axle speed difference for cornering, and only the VTD/VDC models have circuitry to detect steering wheel inputs and the VTD uses a planetary gear system which can not suffer from torque bind in the way the multi-plate clutch pack does in the regular 4EAT.

The plain 4EAT has two internal axle speed sensors. The 4EAT by default sends 50% torque to the rear axle, unless the solenoids activate the hydraulic system to remove rear wheel power. When something goes wrong with the hydraulics, you get torque bind. When you wear out the clutch pack (ex. from different tires) the clutch pack will slip (like a worn 5mt clutch) and fail to provide rear wheel traction.

The 4EAT's logic is as follows:

While engine is running reduce rear axle power (or if FWD fuse in place)
Send power rear when accelerating (uses throttle position sensor to detect movements, and vehicle speed sensor to evaluate cars response to throttle inputs)
Reduce rear power when braking
Send power rear if front wheel spin is detected (but only if speed difference is greater than say 20%) Wheel spin is technically occuring during tight turns in parking lots where axle speed differences can be as high as 20%, but the system is set up to ignore this.

On some models, the ABS system can disengage the rear wheel drive, since locking the axles together confuses it. ABS detects wheel lock up by comparing wheel speed against the fastest spinning rear tire. If the axles are locked together you are more likely to lock up the rear tires.

And face the truth here, the ABS system on all wheel drive vehicles is not good in snow and other very low traction surfaces when compared to simple front wheel drive cars. While you may have good steering control, the braking distances are horribly long. Audi's with the gleason/torsen differentials are much better in terms of ABS since the torsen diff does not respond to braking forces.

Most of the time the logic to send power rear when accelerating will prevent wheel spin in the first place, but logic is there to control slip if detected, but the torque transfer is quite slow to respond (about 1 second).

Among my group of friends and co-workers there are more than 30 Subaru's (34 if I counted correctly), and none of them have had torque bind as a result of tire size problems, even though some of them run different tires front and rear, and others don't ever check tire pressure. Some have even run on the donut spare at highway speeds for months.

All of the torque bind problems due to clutch pack failures that I have seen (and I have seen many) all show up at around 180,000 to 250,000 km. Problems earlier than this that I have seen have all been solenoid, wiring or computer failures. So it would seem that the soft aluminum case has a wear limit of about 200,000km. I have yet to see a 4EAT pass 300,000km without this problem, and among my friends there are at least 10 Subaru's beyond 300,000 km (4 of them over 500,000), each of the automatics has had its tailshaft replaced.

Yes, torque bind can be the result of tire size differences, but they have to be substantial and for a prolonged period of time.

Have you seen any torque bind on low mileage vehicles? Well under 200,000km?

or on the redesigned transmission with the hardened steel sleeve(1998-current)?

Subaru loves to blame the customer for its own shortcomings, and they have been doing it for years, first with tire size issues, and now by claiming that head gasket failures are an rare problem (outright lie), and that piston slap is perfectly normal (only partially true).

As for adding pressure to the rear tires for heavy loads Subaru doesn't recommend this anymore. My old Subaru Legacy was 30/29 PSI, and 32/35 when loaded. My new Subaru Outback is 30PSI all around, all the time. There is no second tire pressure recommendation anymore.

As for my Subaru's

1985 GL dual range 4WD wagon, retired in 1996 with 727,000km on the odometer, it still ran good but had severe corrosion.
1993 Legacy AWD wagon, bought in 1995 and destroyed in a collision in 2000 with 466,00km on the odometer
2000 Outback wagon, bought new in 2000, now with 59,000 km

I haven't had torque bind myself, since all three are manual transmission vehicles. No failures of the viscous couplings yet, although a drive shaft was replaced on my Outback (severe vibration).

#14 captainehh

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Posted 11 November 2003 - 10:25 PM

Thank you all for the extremely thorough replies. Grad school keeps me way busier than i'd like so i'm not sure how soon i'll be able to attack the problem. I picked up the 97 OBW for a great price due to a wreck in its past. Does a wreck make any of these probs more likely than another? The tires are very new and have proper air. The tranny was rebuilt at 50K. This strikes me as strange. Something tells me the accident messed with the drivetrain. The car was smashed in the front and rear and sat for three years before being repaired.

#15 duane b

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Posted 12 November 2003 - 07:53 PM

Originally posted by alias20035
Found a link on torque bind.

http://www.legacycen.../torquebind.htm


I read the website you mentioned. If the guy is talking about the clutch-pack assembly, I was quoted twice the amount he mentioned. There should also be a some sort of Tech Bulletin form Subaru about tire wear and how it affects clutch pack wear in the owners manual because if I knew the repair bill would be $1400 I never would've bought the car I did. It had one low tire (15psi) for how long before I bought it no one knows. Now the clutch pack assembly will need replacing according to Subaru Service. The $1400 was their quote. I told them I will drive the car into it's grave before I give them $1400! The funny thing is the car drives great, no problems with the tranny. My AT OIL TEMP light flashes a code (27 i think), but it acts fine as far as I'm concerned. It's a 96 L AWD wagon with 90K. Bought it only 4 months ago. Just my story.

#16 DooMeSuuby

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Posted 11 March 2005 - 05:57 PM

1997 Legacy GT 2.5 - 150,000 miles.
Just had the HEAD GASKET replaced (Rrraaarrr!) and I am out of money....

Three days ago, I replaced the two rear tires with two tires from a different manufacturer.
Soon, the car exhibited the Satanic Torque Bind.
(shuddering, feels like the axel will drop)
I drove on freeways for approx. 150 miles like that. Problem got worse and worse.

Today, I replaced the two tires, so now have ALL 4 identical manufacturer/size/pressure (35 psi)

The TB symptom has quieted down when starting from stop and going in a straight line. HOWEVER, if I slowly TURN left or right, the symptom is still there, strongly.

Thank YOU for the time and solutions! ~~ ~~
PLEASE HELP because my back is against a wall here...



QUESTIONS:
1) Have I ruined my clutch packs? - How can I tell?

2) Given that there is still SHUDDERING after making the tires identical, can I reasonbly expect that I will find a solution to this issue, outside of opening up the transmission, replacing the housing liner, or something worse?

3) Are there any LIMITS to driving the car with the FWD fuse inserted for FWD only driving?

4) The mechanic says the tran.fluid is fine.. but others on this list have posted that changing the ATF can be part of the solution.

5) Any other potential solutions?

THANK YOU SO MUCH ! Subby's rock! (until they don't..)
David
dasani25@hotmail.com

#17 mrtoyou7747

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Posted 12 March 2005 - 09:11 AM

See if the binding goes away with the AWD fuse in place. If it does it probably means you have problem with the clutch pack.

Replace the diff fluid in both the front and the rear diffs with synthetic. Worked for me for about 2 years.

They can now replace the clutch pack without removing the tranny - should cost about $800


1997 Legacy GT 2.5 - 150,000 miles.
Just had the HEAD GASKET replaced (Rrraaarrr!) and I am out of money....

Three days ago, I replaced the two rear tires with two tires from a different manufacturer.
Soon, the car exhibited the Satanic Torque Bind.
(shuddering, feels like the axel will drop)
I drove on freeways for approx. 150 miles like that. Problem got worse and worse.

Today, I replaced the two tires, so now have ALL 4 identical manufacturer/size/pressure (35 psi)

The TB symptom has quieted down when starting from stop and going in a straight line. HOWEVER, if I slowly TURN left or right, the symptom is still there, strongly.

Thank YOU for the time and solutions! ~~ ~~
PLEASE HELP because my back is against a wall here...



QUESTIONS:
1) Have I ruined my clutch packs? - How can I tell?

2) Given that there is still SHUDDERING after making the tires identical, can I reasonbly expect that I will find a solution to this issue, outside of opening up the transmission, replacing the housing liner, or something worse?

3) Are there any LIMITS to driving the car with the FWD fuse inserted for FWD only driving?

4) The mechanic says the tran.fluid is fine.. but others on this list have posted that changing the ATF can be part of the solution.

5) Any other potential solutions?

THANK YOU SO MUCH ! Subby's rock! (until they don't..)
David
dasani25@hotmail.com



#18 rude

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Posted 14 March 2005 - 12:59 PM

Many thanks in advance to alias20035! He seems to be the expert on the TB question. I believe he’s correct because a shop told me the same thing. Tomorrow my 95 legacy goes into that independent shop who specializes in subbie drivetrains. At first I thought the guy might be ripping me off (stating I should be ready for a total cost of $500, because the dealer kit alone is $300). Now I think it sounds too good to be true.


Just wish I knew if I ruined my clutch packs, done a mile here and there in AWD over the past few years. Had the fuse in for the other 20,000 miles.


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#19 rude

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Posted 15 March 2005 - 08:30 PM

Nice guy, got to see the wear on the old housing! Strange that the teflon seal seemed fine but Al housing was worn bad. He believed my AT OIL TEMP 16 blinks were due to a valve assembly on that housing so we replaced it too.

My damage:
Torque diff kit $278
Valve assembly $83
Pipe (from valve) $12
Exhaust bolts $20
5 Qt ATF fluid $10
Labor $200
Tax $36

Over $400 in parts was more than I expected, perhaps $200 would have been a little too good to be true, but seems to have fixed it!

He also said the clutch packs looked good and since it's not a 2.5 with Dual Cam we shouldn't see each other for a long while. Early Forester wheel bearings and replacing a short block on a 2002 Subaru have kept him busy lately.

Many thanks again,
Rude

#20 mrtoyou7747

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Posted 16 March 2005 - 09:38 AM

When I had the seal replaced we noticed that the shaft was covered with burnt fluid. Don't know why but we checked the cooler lines and found them to be almost clogged. You might weant to check the cooler lines.



Nice guy, got to see the wear on the old housing! Strange that the teflon seal seemed fine but Al housing was worn bad. He believed my AT OIL TEMP 16 blinks were due to a valve assembly on that housing so we replaced it too.

My damage:
Torque diff kit $278
Valve assembly $83
Pipe (from valve) $12
Exhaust bolts $20
5 Qt ATF fluid $10
Labor $200
Tax $36

Over $400 in parts was more than I expected, perhaps $200 would have been a little too good to be true, but seems to have fixed it!

He also said the clutch packs looked good and since it's not a 2.5 with Dual Cam we shouldn't see each other for a long while. Early Forester wheel bearings and replacing a short block on a 2002 Subaru have kept him busy lately.

Many thanks again,
Rude






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