[Mark Fellows]

..and ask a question. Since getting my wife's XV we have towed our 1180 pound(dry) little guy trailer about 3 times for about 50 miles since about 1200 miles new.

The car has pulled the trailer like a champ, and there have been no complaints. However, this weekend, I felt something that I thought was odd.

I felt a low frequency vibration while pulling the trailer up the hill after turning out of the driveway. The car had been ran about an hour before we left(wife took it to the store). Then I let it run for a few minutes while hooking it up and then shut it off, and then started and let it run for about 30 seconds minutes after that, and left.

Everything was fine, but then I decided to give it more accelerator going up hill, and all though it pulled fine, I felt a vibration.

Not floored or anything, just about 50% more throttle than normal.

After thinking about it, I can kick myself, because I think what may have happened is I put enough torque on the drivetrain, while towing the trailer to defeat the viscocity/thickness of the oil film, and had the steel cvt belt touch the pulley.

I really feel like an idiot, but whatever was done was done, and the car drives fine with and without the trailer, but I can't help but think it doesn't run quite as smooth as it did. It could be just my imagination in thinking of little micro divits in the variators, but does anyone else have experience with this?

This is the first time I ever joined a car forum....

Here is my towing review below...

ATTENTION PLEASE. I HAVE EDITED SOME OF MY FOLLOWING POSTS BECAUSE I WAS ON A STUPID, WRONG TRAIN OF THOUGHT.. I DON'T WANT TO MISLEAD ANYONE WITH MY PREVIOUS FOOLISH IDEAS... Thank you for your patience! I came to the right conclusion by my last post on page two I think...

 

[ScoobyXV-L]

I've towed heaps on my XV and have never had what u described
I would get it checked out at least

 

[Mark Fellows]

Thanks for the reply, with your experience! I am not sure at this point what I would have them check out... It didn't do it since, and I am pretty sure it was a result of me giving the car too much throttle while towing. I guess if I wanted to haul the trailer over there, I could reproduce it, although I am not sure I would want to. I also remember seeing a warning in the manual "that subaru is not liable for damage while towing" or something like that. I guess it just makes me a little leary, and I will be more careful. However, with my Mazda, that is not supposed to be used for towing, I can floor it if I want to in any gear with no issues. Manual transmission I know, but it had 172000 miles on it! Thanks again! I guess I am just rambling... I guess really what I wanted is for someone to say "yeah, I've felt that a few times. Don't worry about it, it will go away..."

 

[Subi]

I personally would never tow with a CVT, but if Subaru says it's OK then I say do until it breaks and let them pay to fix it.

 

[Mark Fellows]

Subi,

I like your attitude! That is how I felt. I told people i was leary about towing with a CVT, but if Subaru listed the towing capacity at 1500 pounds who was I to argue?

I should just take your advice and not worry about it, and just do it until it breaks...

 

[soakes]

Um, maybe a stupid question, but why the heck would towing with a CVT be any harder/worse/stressful than towing with any other sort of transmission?

 

[dRider800]

Not sure if you did this already, but my dealer told me to disable traction control (the button left hand side dash) while towing.
Maybe your auto-brakes were engaging trying to stabilize the sway of the trailer?

 

[Subi]

Um, maybe a stupid question, but why the heck would towing with a CVT be any harder/worse/stressful than towing with any other sort of transmission?

My limited knowledge of CVT transmissions comes from the problematic Subaru Justy days. The "gear" ratio is determined by a combination of acceleration position and load on the vehicle. It seems towing would cause the CVT chain to adjust either more often or to an area that may not be ideal for longevity. The bottom line is with a CVT you have no choice what "gear" you are in like you do with a manual transmission.

I have no experience with the Crosstrek CVT so things may be different now so take my advice with a grain of salt.

 

[soakes]

The bottom line is with a CVT you have no choice what "gear" you are in like you do with a manual transmission.

Well, basically you would be using a higher engine speed than normal. This is the same as for a geared transmission. In fact, the CVT would tend to even out the use on a particular "spot" in the transmission. I guess there must have been some sort of problem with early CVTs because a lot of people say "don't tow with CVT" but they don't seem to be able to explain why.

 

[Mark Fellows]

Um, maybe a stupid question, but why the heck would towing with a CVT be any harder/worse/stressful than towing with any other sort of transmission?

EDITS BY AUTHOR.

The reason it could be potentially bad despite any experience, is there are really no gears with teeth that are used to drive the car. The transmission relys only on the friction coefficient at each point on either side of the steel belt, through a film of oil, to the Variators, or pulleys. UPDATE: THE BOND ACTUALLY DISPLACES THE OIL FILM UPON LOCK UP, AND IS MADE THROUGH THE ADDITIVES IN THE OIL. ONE MATERIAL THAT CAN BE ADDED IS ZINC. ON THE MOLECULAR LEVEL, ZINC MAKES LITTLE PADS THAT COAT THE VARIATORS IN AN ATTEMPT TO KEEP THE BELTS FROM CHEWING ON THE MATERIAL OF THE PULLEYS.

If either the oil is too thin, or the load is too high, there is a chance to one break down the oil film(while switching positions on the variators), and two to have the belt slide on the variators causing damage to them. Think about ruts or valleys in the pulleys left by passage of the steel chain cutting into them.

Now the question is, how much tension do you need in order to break that bond?

In this particular scenario, I was going up hill just fine, and for a stupid reason I don't wish to mention, I gave it about 50% more throttle than I normal would.

In my manual transmission that is no big deal. The gears won't slip, and are hardened. So with such a light load as my tear drop trailer it isn't a problem. Certainly in the short run. It is harder on the tranmission for sure, but to get the gears to slip on that tranmission, you would have to break teeth off of the gears. Unlikely with such a small load. Other parts of the car would break before that.

I knew going into the deal that yes, CVTs are weaker than other tranmissions, but like I said, if Subaru said it could tow 1500 lbs, who was I to question? I assume they had testing, but more likely they just had calculations.

In my case, I am 90% possitive the belt didn't slip, but am also 70% possitive there was enough tension on the drive line, and enough force provided by the engine to overcome the thickness of the oil, and the steel belt touched the Variator, or pulley as the belt traveled around the circular variator(hence the vibration). UPDATE: THE PREVIOUS SENTENCE IS APPARENTLY WRONG... I NOW THINK WHAT HAPPENED WAS WHAT IS CALLED A "STICK SLIP" PATTERN, OR WHAT MOST PEOPLE REFER TO AS A "SHUDDER" WHICH IS LITTLE MICRO SLIPS, IN SUCCESSION. THE SLIP/STICK CAUSES A LOW FREQUENCY VIBRATION TO BE FELT.

Now I have no idea how much of that the variators can take. Did it mar the variators? I don't know. I am not so worried about the steel belt touching the variators once or twice, as long as that action didn't leave divits in the material of the pulleys.

At any rate, the trailer is parked until spring, and the car runs fine.

I am considering if there is a better CVT oil that is slightly thicker(a little less mpg), but harder for the belt to overcome the viscoscity/thickness of the oil....UPDATE: YOU WANT THE OIL THICK ENOUGH THAT THE STEEL BELT DOESN'T TOUCH DOWN ON THE VARIATOR WHILE SWITCHING POSITION, BUT LOCKS SOLID ONCE IT STARTS TO PULL THE CAR. THIS IS DONE WITH ADDITIVES TO THE CVT FLUID APPARANTLY.

I posted this because I wanted to see if other people had this issue? Although I haven't done much mechanical work in that last 22 years, I have lots of former experience, and a great imagination, so it could just be me picking up things that some might miss, and me getting high strung about it. So, it may have happened to other people, and they just didn't notice.

The steel belt is rough, and if it touches down, you will get a low frequency, rough vibration as you are pulling.

 

[Mark Fellows]

Well, basically you would be using a higher engine speed than normal. This is the same as for a geared transmission. In fact, the CVT would tend to even out the use on a particular "spot" in the transmission. I guess there must have been some sort of problem with early CVTs because a lot of people say "don't tow with CVT" but they don't seem to be able to explain why.

EDITS BY AUTHOR

As I think you are saying, as far as gear ratio it is BETTER than any other tranmission as long as the bonds between the steel belt, and variator don't sheer.

The CVT can better pick a gear ratio that doesn't allow as much force on the transmission and car. It is like having an ULTRA low first gear when you take off, and then having an infinite gear ratio to select as you pick up speed. It is just better in that respect. The car will take off better, and as has been said, the car will provide the most torque, with the least strain on the car engine.

That is as long as the oil film doesn't break down, and the steel belt doesn't slip. EDIT: THIS SHOULD REALLY SAY AS LONG AS THE CVT FLUID DOESN'T BREAK DOWN ALLOWING THE BELT TO TOUCH THE VARIATORS DURING RATIO CHANGES, AND THAT THE ADDITIVES DON'T DISINTEGRATE ALLOWING SLIP..

One thing I forgot to mention is that THIS car in particular fit my 4'9" wife perfectly, so that is really the main reason we got it.

It can tow. It is automatic, and although my wife can drive a stick, and auto matic is better for her. If the car that fit her best also could come with a standard automatic, we would have gotten that, and I would have put a large cooler on it.

It just worked for her, and Subaru said it could tow... That was really the sum of why we got it.

Yes, I do believe subaru is the absolute BEST in the snow, but that is besides the point.

We needed a car she could tow with that gave her the most comfort level doing so, and her feet would touch the car floor, and had high visibility.

Mark

 

[tommi]

I'd imagine if what you said happened it would be pretty loud. Also, how much weight was in the car? Can't imagine you hurt anything, how do you drive your car without trailer? Aggressively, lot of rpms etc. Mellow, don't exceed 3500 rpms etc.

 

[Mark Fellows]

I'd imagine if what you said happened it would be pretty loud. Also, how much weight was in the car? Can't imagine you hurt anything, how do you drive your car without trailer? Aggressively, lot of rpms etc. Mellow, don't exceed 3500 rpms etc.

I would say my wife drives it like a sissy, and I try to drive it much easier than my own in normal cases.

I beat the crap out of my Mazda, and it currenlty has 172000 miles on it. I would say I have towed the trailer about 4000 miles with that car.

As for the towing in this situation, there I would say there was 50-100 pounds of cargo, myself(180lbs), my wife(95-100lbs), and maybe 1300lbs tops in the trailer. The trailer dry is 1180 pounds. I had the water tank full(I think 5 gallons). I believe there is 8 pounds per gallon, which would be 8 x 5=40lbs, Plus maybe 20 pounds of clothes, a 20 pound tent, and two sleeping bags(10-20lbs)

 

[fouigee]

There is a CVT high temperature light in the dash. Did you notice if this light came on when you sensed the vibration ?

Sent from AutoGuide.com Free App

 

[Mark Fellows]

There is a CVT high temperature light in the dash. Did you notice if this light came on when you sensed the vibration ?

Sent from AutoGuide.com Free App

It was only for maybe10 seconds I felt this vibration, and I am sure the light didn't come on. I would have noticed.

I think maybe also this happened because I had started the car up maybe 30 seconds before this. Although the car was warm because it had been taken for a drive 30 minutes before hand, and running for a minute or two about 5 before this, I really should have waited longer to pull out of the drive way.

Or taken it easy until 10 minutes or so after taking off.

 

[dRider800]

Reading your post about the CVT a few ago doesn't sit well with me. Isn't the oil there to allow slip when moving through the pulley points and not to keep the chain off the variator? If the chain was separated from the variator then you would defiantly get slip which would result in no power to wheels and possibly marring along with a sudden burst in engine speed... in some cases high friction is a very good thing just like tires! Rutting would probably only happen if you used manual mode for an extended time. The purpose of the CVT is to pick the point that's best matched for requested acceleration, granted this is tuned for better mpg than performance. And just because the chain is jagged and not smooth like a belt doesn't mean it's going to cause a shutter because there are many, many other points of contact while going around the pulley.

While it may be that the CVT did a miss or allow a small skip, there are many other factors I would look at first that could have caused shutter like bad fuel, bad injection mapping (too lean or rich vs airflow when you "stomped" on it), stability control engaging, active AWD shifting power, or even tire slip.

 

[Mark Fellows]

Well, you could be right. Thank you for your clarification and support!


Of course you don't want the belt touching the variator while it's switching gears. Are you sure there is enough pressure to break through the film of oil when it is locked up?

I had to watch a course on Fluid Dynamics to try and understand. Sure that makes perfect sense, but i read a little about this model. One thing I read, is that the oil film is there to keep the belt from "ever touching the variators"

Then I watched the link I will provide, and I was fastenated. This transmission is basically the same as what was in my 81 arctic cat. No more complex. That is until you think about the steel belt. On the snow mobile, it was the friction between the rubber belt, and the variator.

I seriously doubt it was traction control. I didn't punch it though. Although your explanation would be much nicer.

 

[Mark Fellows]

One more thing, to try and further understand, I was reading somewhere else where a person was talking about Sheer force at right angles of the flow of oil. THIS PERSON DIDN'T KNOW WHAT THEY WERE TALKING ABOUT. THEY WERE JUST TRYING TO SOUND SMART. IT IS NON SENSE.

What led me to look into this was the "oil is there to make sure that the steel belt never touches the variator directly" It didn't say when the variators are moving in or out, and the chain is changing positions. THIS LINE I READ ON BOTH WIKIPEDIA(AND THE RESEARCH PAPER THAT WAS PLAGIARIZED TO MAKE THE WIKIPEDIA PAGE) SHOULD HAVE SAID, "the oil is the there to make sure the steel belt never touches the variator directly WHILE THE STEEL BELT IS MOVING UP OR DOWN THE VARIATOR VERTICALLY.

YOU CAN SAY THAT ABOUT THE CVT FLUID, BUT NOT JUST SAY THE "OIL" IS THERE FOR THAT PURPOSE. Just saying the Oil is misleading..

The following line is what really threw me off "A film of lubricant is applied to the pulleys. It needs to be thick enough so that the pulley and the belt never touch and it must be thin in order not to waste power when each element dives into the lubrication film."

So I watched the course on fluid dynamics, and then my over active imagination took over!

So if the steel belt does touch down and lock up, which is easier to understand and makes more sense, then perhaps I was feeling some miniscule slipping... Baring it wasn't all the things you said...

 

[Mark Fellows]

I found this as well.

"In addition, surface analysis techniques were utilized to gain a novel insight into the chemical composites and morphology of the tribofilms. As a result, it is vital for greater torque capacity to give higher boundary friction coefficient between the metal contacting interfaces, and the process of boundary lubricant film "

Reading further it says "the films generated by Zinc dithiophosphate (ZnDTP) additives in the contact regions are known to contribute to achieve a higher metal-metal friction coefficient "

Tribological Properties of Metal V-Belt Type CVT Lubricant

 

[Mark Fellows]

Reading your post about the CVT a few ago doesn't sit well with me. Isn't the oil there to allow slip when moving through the pulley points and not to keep the chain off the variator? If the chain was separated from the variator then you would defiantly get slip which would result in no power to wheels and possibly marring along with a sudden burst in engine speed... in some cases high friction is a very good thing just like tires! Rutting would probably only happen if you used manual mode for an extended time. The purpose of the CVT is to pick the point that's best matched for requested acceleration, granted this is tuned for better mpg than performance. And just because the chain is jagged and not smooth like a belt doesn't mean it's going to cause a shutter because there are many, many other points of contact while going around the pulley.

While it may be that the CVT did a miss or allow a small skip, there are many other factors I would look at first that could have caused shutter like bad fuel, bad injection mapping (too lean or rich vs airflow when you "stomped" on it), stability control engaging, active AWD shifting power, or even tire slip.

Eureka!!! I found what I was looking for. People I am not trying to spam this post, but using it as a place for my learnings. At the same time, I thought others might benifit from it..

Baring what Rider800 said, I think I might have found the culprit I think what I experienced were little microslips. that is what I originally thought. BEFORE I WENT OFF ON THIS CRAZY, STUPID THOUGH PATTERN OF THE PREVIOUS THREADS THAT IS.

These aren't what people would call "belt slipping", but little tiny microslips, that then stick. There is a cycle microslip,stick,microslip,stick...

This phenomenon is aparantly pretty common and called "stick/slip" behavior. Or some people call it "shudder".

I think this is what I experienced.

I think the load of the trailer, along with my ambitios throttle foot caused this phenomenon.

I also found conclusively that there really is no "oil film" perse in between the belt, and the variators when they lock up to drive the car.

However, manufacturers put additives into the oil, to help the belts lock up to the variators. This is commonly zinc additives and others.

So, it is becoming more and more apparant that the type of fluid you use, and the "health" of that fluid is more and more critical.

As I said, the tranmission it's self isn't that interesting, but the properties of the fluid, and what it does under different temperatures is truly very fastinating. Fluid dynamics come into play, as well as the general properties of how the fluid behaves, as well as what additives are being used, and for what purpose. This is endlessly fastinating, and there are many technical papers, and masters thesises written on this.

The following lead me to the conclusive info on this "This phenomenon is commonly called “stick-slip” or “dynamic frictional vibration” and manifests itself as “shudder” or low speed vibration in the vehicle"

Patente US6660695 - Power transmission fluids of improved anti-shudder properties - Google Patentes

Thank you all for helping me through this, by allowing me to explore this with your helpful input!

Mark