What Goes Wrong With A VISCOUS Coupler.

[suba1]

.... Before I bought my 2000 Outback Limited Wagon 2.5L 5 speed manual. Subaru was in the process of recovering from being flat on their back, sales were way way off and the AWD concept was pulling them out of the hole. When I first read about the VISCOUS coupler it sounded like a very simple unit with very little that could go wrong. A device that has two moving parts, front and aft, with silicone fluid filled. As the front half of the sealed unit spins it causes the silicone to harden up between the sets of fixed veins (on both halves of the unit internal) and become a solid causing the unit to turn as one. Now that sounds pretty simple and maybe I have over simplified this a bit? Now, this car is nine years old, absolutly nothing wrong with it except VC. If all goes as scheduled, this will be the third VC in this transmission. The first one went out soon after I bought the car, as I recall, and was replaced with a second one which did last a little longer than the first, but with clump, clump, clump from time to time in a sharp turn either side but NOT consistantly up until now it has become a regular thing. The point I am trying to make here is apparently it does NOT matter how new or old this unit is it can go out anytime. Why do I have such a hard time understanding something so simple and foolproof supposedly. As of yet I have not had one of these units opened they all go back to Subaru? Apparently there's no way of fixing them?

 

.... Is there anyone here that can be informative.

 

.... Thanks in advance

:-\

[bheinen74]

my guess is mismatched tires. this in not a normal item to go out 3 times. If you aren't aware, if you have to replace a SINGLE tire, then you have to replace them ALL, with same make brand etc ALL at the identical time. My assumption is that the tires are not matched. My assumptions can be wrong tho. It could be improper maintenance upkeep on tire pressures, which will do the same as mismatched tires.

[NorthWet]

It is not so much a mechanical issue as a chemical/physics issue. The silicone fluid is a non-Newtonian fluid, something whose viscosity increases when exposed to shear forces. When movement is slow (shear force is minimal), the long chains of the molecules can slip past each other; when movement is faster and the shear force is higher, the molecules snag on each other and remain entangled making them seem more "solid".

 

My understanding (subject to me being wrong ) of the issue in the VC is that slippage/shear forces cause the silicone fluid to heap up, and starts to chemically alter the fluid permanently. (My guess is that the silicone molecules polymerize with each other, forming a big cross-linked mess.)

 

My guess with your situation is that you have something going on that causes excessive slippage between the front and rear outputs of the VC, causing it to heat excessively. Mismatched tires are the most obvious culprit, but also the one that you are likely to have already checked and ruled out. Any form of towing with 2-wheels on the ground (again, pretty obvious). Final drives could be mismatched, but improbable if you have owned the car since new.

[bheinen74]

could very well be mismatched drive ratio of the tranny vs the rear diff.......

 

3 times is very excessive, but mileage on the car not stated. 3 times in 300,000 maybe. 3 times in 150,00 not normalcy

[suba1]

.... Thanks again for everyone's input. Tires have been checked, three times for consistency 6' 10'' on the last set all four. New set just purchased for circumference more than anything else. Don't know what the tolerance is exactly but as I understand they are one of the consistently roundest tires you can buy. Air pressure is always checked every 3000 miles if not sooner. I keep a log book on this car. Outside of gas and what the dealer did everything is accounted for within reason.

 

bheinen74

 

.... I couldn't agree with you more, the car now has 135,000 miles on it. I also just replaced the clutch which started slipping at 113,000 miles and I believe there is a direct relationship between VC and the fast wear of this clutch.

I have another car that I put 476,000 miles on and it still has the original engine, transmission, clutch, and muffler. Now, it has a little blow-by and it leaks around the mains but it will still run. The point in mentioning this is I don't think anyone can accuse me of abusing the clutch on the Subaru when I can show evidence like this.

.... I never gave any thought, since the car was bought new, to the fact that there could be a mismatch in drive ratios. The question now is: How do I prove that, and if it is so, would Subaru correct the problem as this should be their responsibility?

 

could very well be mismatched drive ratio of the tranny vs the rear diff.......

 

3 times is very excessive, but mileage on the car not stated. 3 times in 300,000 maybe. 3 times in 150,00 not normalcy

Edited June 13, 2009 by suba1

[idosubaru]

something is causing this indeed, this isn't just 3 failed VC's - that is a symptom not a cause.

 

only thing i can recommend to verify ratios is to get the entire car off the ground and rotate a tire by hand - the opposite side/end tire should also spin i think. if you spin the drivers side rear, the passengers side front should spin.

 

count 10 - 20 or 50 revolutions of one and make sure the other does the exact same number of revolutions. hard to imagine the manual being off, but you need to check something because something is defintely wrong. essentially subaru offered 3 different common EJ final drives 3.9, 4.11. 4.44. spin the tires enough times to make those differences stand out.

 

you can also count number of driveshaft rotations verses wheel rotations for the rear to get a final drive ratio in the rear diff. then do the same with the front - rotating it via the engine with the car in gear. compare those two numbers.

 

is your gas mileage good?

[suba1]

.... Thanks for your input. I too felt you might have had a good, valid point since the ratios hadn't been a consideration up until now. Today I put the car up on the lift and used two 34 1/2" pedestals, one under the driver's side front left and the other one under passenger's side rear right and let the lift down very gently to lock both these tires from moving. Then, I chalk marked dead bottom on the passenger side front right and the driver side left rear. I then proceeded to rotate the Left rear 10 times as my wife counted off each rotation. The same thing for 20 rotations, 30 and finally 50. The results were: where the chalk mark started is exactly were it ended. So apparently there is NO Ratio mismatch. I personally felt, like you, this might show something but was just one more item to be ruled out.

 

.... As far as mileage goes: I do my calculations with every fill-up. I have all the gas tickets. I would say my average is 24+mpg, once in a while I'll hit 25+ and very rarely 26+, and very, very rarely I'll come up with 23+ [(+) meaning that fraction part of]. I also have a bad O2 sensor under the driver's seat which I have been purposely procrastinating in replacing because I was told that my gas mileage would drop off if not replaced. So far, to my surprise, I have NOT noticed any drop in mileage or performance but I will be replacing the unit in the near future.

 

.... But I feel you are right. This is NOT just two bad VISCOUS Couplers with a third on the way but a symptom of what is causing it? This transmission has been problematic (and expensive at that) ever since I bought the car new . How this whole thing got started was just after I bought the car, FIRST gear started jumping out of gear. The dealer mechanic told me that the nut on the tail stock hadn't been torqued at the factory and there had been some digs in the casing on the inside so they replaced the Aluminum housing as well. And that took care of the problem until the first VISCOUS coupler went out which doesn't seem like it was very long after that as I recall. So unless the job wasn't done correctly or something wasn't completed the VISCOUS coupler is suspect.

 

 

something is causing this indeed, this isn't just 3 failed VC's - that is a symptom not a cause.

 

only thing i can recommend to verify ratios is to get the entire car off the ground and rotate a tire by hand - the opposite side/end tire should also spin i think. if you spin the drivers side rear, the passengers side front should spin.

 

count 10 - 20 or 50 revolutions of one and make sure the other does the exact same number of revolutions. hard to imagine the manual being off, but you need to check something because something is defintely wrong. essentially subaru offered 3 different common EJ final drives 3.9, 4.11. 4.44. spin the tires enough times to make those differences stand out.

 

you can also count number of driveshaft rotations verses wheel rotations for the rear to get a final drive ratio in the rear diff. then do the same with the front - rotating it via the engine with the car in gear. compare those two numbers.

 

is your gas mileage good?

Edited June 14, 2009 by suba1

[kiwi subbie]

as I recall, and was replaced with a second one which did last a little longer than the first

 

Was that a new one or a 2nd hand unit?

[suba1]

Hi and thanks for the question. As far as I know it was a NEW unit install during the warranty period by the dealer. :-\

 

 

Was that a new one or a 2nd hand unit?

[GeneralDisorder]

Something isn't right with your tranmission. If it were me I would probably just replace the thing on principle. There are TONS of 5 speed AWD's out there that have never had a single issue. I have 170,000 on my '91 Turbo (similar HP and greater torque than your 2000). It hasn't had any issues other than the 2nd gear syncro grinds a bit.

 

I'm not even particular about the tires I run. Within 1/8" tread wear is all the closer I look at them.

 

Something is fishy about the warantee issue and the subsequent multiple VC failures. I would say your dealer doesn't know what they are doing inside that tranny or something was incorrectly assembled when they fixed that shifter issue.

 

My opinion - dump the tranny and get a used one that hasn't been messed with half a dozen times.

 

GD

[suba1]

Something isn't right with your tranmission. If it were me I would probably just replace the thing on principle. There are TONS of 5 speed AWD's out there that have never had a single issue. I have 170,000 on my '91 Turbo (similar HP and greater torque than your 2000). It hasn't had any issues other than the 2nd gear syncro grinds a bit.

 

I'm not even particular about the tires I run. Within 1/8" tread wear is all the closer I look at them.

 

Something is fishy about the warantee issue and the subsequent multiple VC failures. I would say your dealer doesn't know what they are doing inside that tranny or something was incorrectly assembled when they fixed that shifter issue.

 

My opinion - dump the tranny and get a used one that hasn't been messed with half a dozen times.

 

GD

 

.... My sentiments are very close to yours. This morning when we went to church you would never know that there was a problem with the car. About six miles away some tight turns not a bit of trouble. The trouble starts when the transmission comes up to operating tempature then it starts with the clump,clump,clump in the tight and not so tight turns by the time we got back to the house.

.... This is some additional information: Within the past five or six weeks or so, just after the new clutch was installed, I detected a very low audible very slight rumble going down a moderate hill on very smooth asphalt with my foot off the gas pedal at about 25 mph coming from the transmission. Didn't know quite what to think of it at first. Checked the transmission fluid level and that was OK. Then I started hearing it on very smooth road at faster speeds when I would let my foot off the gas. If I pushed the clutch in, it stopped in all circumstances. So I added a can 24 ozs. of "Lucas transmission fix", didn't notice much change. Read the container again and it suggested up to two cans, which I did. That took out 85 - 90 % of the noise. My thinking is that the VISCOUS coupler, over time, has stressed the gear box side of this modular transmission somehow causing the low audible rumble now. It has been suggested that this is just backlash wear but I am not so sure because it started pretty much suddenly? :-\

Edited June 15, 2009 by suba1

[GeneralDisorder]

Sounds like an input shaft bearing. The diffs in Subaru transaxles are tough - failures are simply unheard of in that department. I have heard of some input shaft bearing failures, but there's also stub shaft bearings and several other's inside the unit. Frankly it could be anything - you are probably correct about it being stressed due to the VC failures. I would say the tranny probably has seen better days all around.

 

GD

[suba1]

Sounds like an input shaft bearing. The diffs in Subaru transaxles are tough - failures are simply unheard of in that department. I have heard of some input shaft bearing failures, but there's also stub shaft bearings and several other's inside the unit. Frankly it could be anything - you are probably correct about it being stressed due to the VC failures. I would say the tranny probably has seen better days all around.

 

GD

 

 

…. You know this modular transmission (5 speed manual) was made this way for a reason. A transmission that is cast as one unit is, I would think, a better, more stable unit than one that is divided up into sections or pieces and bolted together, especially when it is not only modular but divided in half down the middle and also bolted together. Now it may be in Subaru’s defense that the machining operations on a production scale is the lesser of the evils here, that part I don’t know and they may NOT want you to know? I would think that there is far more chance of NOT being able to HOLD all the tolerances with everything bolted up the way the transmission is presently put together. Apparently, this approach on AVERAGE has worked out well for Subaru. Any problems that they do have with those few transmissions that are problematic are so few and far between that it is insignificant as far as Subaru is concerned. I find it odd and concerning that it is quite convenient that for them that last modular unit on the end of this transmission has been engineered and built this way, containing the VISCOUS coupler; making it very convenient to change out when it goes BAD. Suggesting, of course, that these units (VISCOUS couplers) aren’t as reliable as all the hoopla in advertising would have you to believe or as is suggested. The other point here is, the customer that has a bad VISCOUS coupler is charged for its replacement. But after its replacement by way of the rear module, if it is found later that there is something else that is wrong, there is a second and more significant charge for removing the whole transmission for a second time for evaluation. Where as if the complete transmission had been removed the first time and inspected or evaluated there would have been only one charge not two disassembles and assemblies, and yes a little bit more charge but NOT the combination of both???

:-\

[Yo'J]

On principal I have to make mention of the similarities in materials between wood, a cutting board and possibly, your transmission.

 

Wood is a great thing, but it moves alot when it changes its level of humidity or water saturation. Minute differences can be measured. A solid wood, one piece cutting board will only last the rigorous torments of family life if the grain is in perfect order. If you have, twisted or knotty grain, grain that is grown on unstable or un-level ground, the wood will have tensions in it enough to break on its own. Most cutting boards today are made of many little strips. You might think thats the size of the trees they are cutting down, looking at the quality of the wood in your local stores selection. True it is, unfortunately. Wood with mass internal tensions, the tree had a hard time growing up. But the strips are to diffuse all the tensions by giving them a purpose to fight with each other, straightening each other out. (Buy the one with breadboarded ends if they are splined, dadoed or dovetailed especially.)

 

I don't know a lot about metal working, but I do know that it shares a lot of the same characteristics when it changes from heat. Your transmission might have a casting flaw.

Edited June 20, 2009 by Yo'J

[Zefy]

do you spin the tires a lot on ice or anything?

 

i've seen them blow up if the driver is revving the poop out of it when there is no traction to be had.

 

for instance i've seen a woman with bald tires try to make it out of her driveway when there was no grip on the back wheels. she would roll a bit with the AWD but once she was on full ice it would slide back down and she would try it again. now this woman figured the correct solution is to push the pedal down harder. the VC overheated and got wrecked.

 

any of this sounds familiar? probably not, but i figured it might be important.

 

any young drivers that like to slide around in the family wagon perhaps? i know i did that...

[Gloyale]

…. You know this modular transmission (5 speed manual) was made this way for a reason. A transmission that is cast as one unit is, I would think, a better, more stable unit than one that is divided up into sections or pieces and bolted together, especially when it is not only modular but divided in half down the middle and also bolted together. Now it may be in Subaru’s defense that the machining operations on a production scale is the lesser of the evils here, that part I don’t know and they may NOT want you to know? I would think that there is far more chance of NOT being able to HOLD all the tolerances with everything bolted up the way the transmission is presently put together. Apparently, this approach on AVERAGE has worked out well for Subaru. Any problems that they do have with those few transmissions that are problematic are so few and far between that it is insignificant as far as Subaru is concerned. I find it odd and concerning that it is quite convenient that for them that last modular unit on the end of this transmission has been engineered and built this way, containing the VISCOUS coupler; making it very convenient to change out when it goes BAD. Suggesting, of course, that these units (VISCOUS couplers) aren’t as reliable as all the hoopla in advertising would have you to believe or as is suggested. The other point here is, the customer that has a bad VISCOUS coupler is charged for its replacement. But after its replacement by way of the rear module, if it is found later that there is something else that is wrong, there is a second and more significant charge for removing the whole transmission for a second time for evaluation. Where as if the complete transmission had been removed the first time and inspected or evaluated there would have been only one charge not two disassembles and assemblies, and yes a little bit more charge but NOT the combination of both???

:-\

 

You are just burned over having to spend money.

 

 

None of this is relavant to how Subaru Engineers there cars. EVERY transmission has parts bolted toghether.

 

I suspect one of your rear axles, also a rare failure, but more likely than 3 bad VC in less than 100k

[MtTech]

+1 for GD's answers...

I think you might have a thrust or alignment issue after the 1st gear/case halves were fixed. Get another tranny.

 

MT

Edited June 24, 2009 by MtTech

[rguyver]

not to bad mouth any shop but out of all the shops i know of i would only trust two that i would let touch the inside of a subaru tranny , me and a local rally shop , almost everyone i have heard of messing with them some how screw it up all it takes is a missing shim or over torquing the case and they have problems.

 

i would go with a good use one next time it gives you problems

[suba1]

not to bad mouth any shop but out of all the shops i know of i would only trust two that i would let touch the inside of a subaru tranny , me and a local rally shop , almost everyone i have heard of messing with them some how screw it up all it takes is a missing shim or over torquing the case and they have problems.

 

i would go with a good use one next time it gives you problems

 

…. Yes, I couldn’t agree with you more. And what you have said is in essence exactly what I said to the Subaru Rep. The manuals I have, point out exactly just that. Matter of fact, I have two manual which, to my surprise, don’t even show a cut-a-way view of the guts of this transmission, not even the gear section. And both of these manuals suggest or imply that the manual transmission is somewhat critical and should be treated just like an automatic by a professional and or have hands on, up-to-date experience? My feeling is now; if I had known all of this when I bought the car, I would have most likely gotten the automatic instead of the manual. As I recall, in purchasing this car with the manual transmission there was a definite delay with the purchase, I think because of the manual transmission. Most people prefer the automatic over the manual and that should have been a clue that I either missed or didn’t consider at that time. Subaru’s efforts and attention, I think, were concentrated on what they sell the most of, not the least?

:-\

[suba1]

You are just burned over having to spend money.

 

 

None of this is relavant to how Subaru Engineers there cars. EVERY transmission has parts bolted toghether.

 

I suspect one of your rear axles, also a rare failure, but more likely than 3 bad VC in less than 100k

 

 

…. From your perspective, you are probably right. When I bought this car, admittedly I spent more than I should have. After I bought it, I understand that Subaru gave back a $2000.00 refund to the dealers that they could use either to keep themselves or pass it along as an incentive to the customer for each sale. Needless to say, I saw none of that. In buying this car, I spent the extra money because I thought I was buying something TOUGH as the advertisements suggested. I don’t want to sound naive here but I didn’t feel it would be that misleading! What I wanted was a car that I wouldn’t have to worry about as far as the engine, transmission, and rear, from a reasonable point of view. And at that time, I felt Subaru could deliver on that. Well, to date, the car has delivered on EVERYTHING satisfactorily with some minor exceptions during the warranty period - EXCEPT for the TRANSMISSION. It has been PROBLEMATIC right from the beginning.

:-\

[suba1]

+1 for GD's answers...

I think you might have a thrust or alignment issue after the 1st gear/case halves were fixed. Get another tranny.

 

MT

 

 

…. Thanks for responding. I feel now your diagnosis; sorry to say, along with the VISCOUS coupler is in the right neighborhood. It’s a shame I was NOT more aware of the symptoms of the VISCOUS coupler as they progress over time until they developed into the present condition. And now, stressing other parts in the transmission and I firmly believe that the VISCOUS coupler is also responsible for the FAST WEAR of the clutch and replacement compared to all of my other cars with manual transmissions.

:-\

Edited June 27, 2009 by suba1