"Hot" smell on Subaru -- AWD hardware?

[rationull]

My dad's visiting this weekend and drove up tonight (3 hr drive on the freeway) in his 1997 (I think) Subraru Legacy with the 2.2 engine and 4AT. He had previously been talking about a smell from the car after longer drives, and thought it was oil burning on the exhaust pipe due to leaky cam seals. When he got here tonight and I went outside, I could smell something too and it smelled more like hot brake pad or clutch than oil to me.

I'm curious -- does anyone know how the AWD system works on automatic trans legacies from this generation? Is there a variable center diff that uses a friction clutch or a fluid coupling that could be heating up and smelling for some reason?

 

[ron917]

Check the passenger side inner CV joint boot - you can see it from above in the engine compartment. It is very near to the exhaust, so the heat causes it to fail earlier than the other boots. When it splits, CV joint grease gets splattered all over, including on the exhaust. It smells awful!

The AWD system in an automatic Subie uses a hydraulically controlled clutch pack at the back of the transmission to send power to the rear wheels. The transmission controller varies the power sent to the rear wheels by adjusting the pressure on the clutch pack. It varies from 90/10 split front/rear to 50/50 depending on conditions (wheel slip, throttle position, etc). It is inside the trans, bathed in ATF, and its sealed in there with the rest of the transmission parts. You wouldn't smell it if it were slipping, and it slips pretty much all the time by design.

 

[Eddie]

+1 as I had a boot split and the smell is hot or burning grease. The AWD system requires that ALL tires be the same circumference to within 1/4 inch. If you are running tire of two different sizes it could cause problems to.

 

[edhackett]

It was also common on the 2.2 for the oil seals at the oil pump to leak and drip oil onto the exhaust system.

Ed

 

[Kitto]

Check the oil seals. Mine used to have that problem too. 1996 Subaru Legacy 2.2L 5MT.

 

[Thermo1223]

Originally Posted By: Eddie
+1 as I had a boot split and the smell is hot or burning grease. The AWD system requires that ALL tires be the same circumference to within 1/4 inch. If you are running tire of two different sizes it could cause problems to.


Last I heard that only affected odler Volvo's, Subies don't care as long as the tires are the same size. You will however get unpredictable handling and traction if one tire is worse off than the others.

 

[ron917]

Originally Posted By: Thermo1223
Originally Posted By: Eddie
+1 as I had a boot split and the smell is hot or burning grease. The AWD system requires that ALL tires be the same circumference to within 1/4 inch. If you are running tire of two different sizes it could cause problems to.


Last I heard that only affected odler Volvo's, Subies don't care as long as the tires are the same size. You will however get unpredictable handling and traction if one tire is worse off than the others.


Check your owner's manul, you will find the requirement that all tires match within 1/4 inch circumference. Note that tire with the same size designation but different brands/models will not match in circumference. And of course, identical tires that are worn differently will not match.

1/4 inch circumference translates to just over 1/32 inch tread depth, assuming identical brank/model/size. That is a very small difference, you will easily hit that with normal wear differences between front and rear tires. Frequent tire rotation and proper alignment will keep the wear even on all four tires.

There is a lot of discussion on various forums about this, and whether it is a reasonable requirement. But that is Subaru's official position on the subject.

 

[rationull]

Thanks for the info on the AWD system, sounds like it's not an issue. I'm pretty sure the CV boots on this car are fine. We checked out the brake calipers and none appeared to be sticking. I think it was just leaking oil burning off on the exhaust after all..

 

[Thermo1223]

Originally Posted By: ron917

Check your owner's manul, you will find the requirement that all tires match within 1/4 inch circumference. Note that tire with the same size designation but different brands/models will not match in circumference. And of course, identical tires that are worn differently will not match.

1/4 inch circumference translates to just over 1/32 inch tread depth, assuming identical brank/model/size. That is a very small difference, you will easily hit that with normal wear differences between front and rear tires. Frequent tire rotation and proper alignment will keep the wear even on all four tires.

There is a lot of discussion on various forums about this, and whether it is a reasonable requirement. But that is Subaru's official position on the subject.


I checked my manual and just FYI it makes no mention on anything other than the standard commonsense warnings.

Don't drive on differing brands/sizes/traction tires. It does not say anywhere as it being a requirement to be within a certain tread depth on all four. So my original statement stands that Subaru's are not picky about this whereas other manufacturers are.

 

[OVERKILL]

I think you need a loyalty badge. Will fix you right up

 

[dk1604]

The 1/4 inch requirement has been discussed on various Subaru forums.

To see where the 1/4 inch circumference difference (basically about 1mm in tread depth) came from and whether it really matters:

http://www.subaruforester.org/vbulletin/f72/clarification-tire-diameter-awd-system-66931/

Consensus on that particular forum seems to be that it was drafted by Subaru's legal department and that it will take much more than 1/4 inch to do harm to the system.