My son has a 2001 Forester that’s engine will from time to time suddenly rev up while driving on the highway as if the clutch was suddenly disengaged. The clutch only has about 20,000 miles on it and there is no burned clutch smell. What else could this be?
So it only happens in high gear, and when the throttle is applied?
The engine rpm’s go up but the vehicle speed doesn’t change? About the only thing that could cause that – beyond catastrophic driveline problems, which you’d likely already know about – is the clutch is slipping or the tires are slipping on the pavement. My guess is oil or some kind of contaminant has found its way to the clutch surface. If so, there could well be no burning smell b/c nothing is burning since it is so well lubed. An engine rear crankshaft seal failing could offer an explanation. Often that seal will be replaced when replacing a clutch. Was it?
I’m not sure if the rear crankshaft seal was replaced or not. I believe it only happenes in 5th gear. The car has never done it while I was driving. Could it have something to do with the all wheel drive?
williamclang
I believe it only happenes in 5th gear. The car has never done it while I was driving.
Someone with mechanical knowledge needs to drive this car.
Could it have something to do with the all wheel drive?
Unlikely.
Subarus have been known to have guide sleeves (they hold the throwout bearing) bind on the nose of the transmission input shaft housing. The steel of the sleeve can dig into the comparatively soft aluminum of the snout and cause premature clutch wear along with intermittent operation in which the pressure plate never full releases at times.
This is an area that should be addressed during a clutch job and there is even a repair sleeve made of stainless steel that can be fitted over the transmission snout to cure this problem.
Whether this was considered during the clutch job I have no idea.
Second point. Instead of a potential slippage issue could this be due to the transmission jumping out of 5th gear into a neutral position? Just verifying the complaint as it makes a difference.
No. It stays in gear. It happenes momentarily. Like it is on an icy road but the road is dry.
+1 @ok4450. Take it in with a printout of his suggestion and have it looked at.