I’m the owner of a 2002 Subaru WRX with about 285,000 miles. I’ve owned it since it was new and recently I had an issue with the car stuttering when making tight turns at slow speeds.
A local shop diagnosed it as a bad differential and recommended a used transmission with 42000 miles on it. After they installed it, they informed me that there was a shimmy at 55-60 MPH and recommended replacing the drive shaft.
With the drive shaft and transmission replaced, I picked the car up today. After driving on the highway for about 5 minutes at 60 MPH, I noticed a RPM drop and what felt like a transmission slip. Almost immediately after that, I lost control of the car. It swerved left, then right. I was able to safely get it on the side of the road.
I had a flatbed tow it back to the shop, and later in the day, they called me saying they couldn’t reproduce the issue.
It was very lightly raining this morning, but given that I was traveling at a constant speed in a straight line, I don’t think that led to the loss of control.
Is there a failure mode for a transmission that could cause this behavior? Also, they didn’t change the clutch when performing the transmission swap. When I asked why, they said it looked OK so they left it as is.
Any suggestions would be much appreciated.
-Vance
Sounds like possible failure in the AWD system, like it detected a little wheel slip and reacted badly.
The shop didn't replace the clutch in a 22-year-old car with 285K miles while replacing the transmission? It's one of the most obvious things to do while in there especially when dealing with an old high-mileage car.
I was wondering if that was a possibility since the road was dry when they tested it later in the day. It really was dumb luck that I didn’t hit anything this morning so I very much want to run down the root cause before trusting it on the highway.
If it was just the clutch slipping you'd see RPMs climbing without a corresponding increase in road speed but it wouldn't make the car swerve all over the road.
Any suggestions if the shop insists it’s OK? Is there anything I can do to diagnose the issue (other than waiting for the next rain storm)?
I'm not real familiar with those and don't know how much of the AWD system is controlled mechanically (like old school limited slip differentials) or electronically with features like traction control and stability control. If the latter, data from the system would probably need to be recorded and analyzed using a dealer-level scan tool.
Chuck, thanks for the quick replies. I had someone suggest it could be the speed sensor in the transmission or that the alignment was off I’d they had to remove the struts during the replacement.
Hopefully it's something simple like that!
The shop also mentioned there was a bit of oil around the rear differential. I wonder if the RPM drop I saw right before loosing control were the rear wheels locking. There might have also been a stuttering noise but my attention was focused on keeping the car on the road at that point.
Took a ride with the mechanic this morning following the same route and I was able to reproduce. The issue is the rear differential locking up (luckily on a dry road this time).
OK, so it is an issue with part of the AWD drivetrain. Is the diff electronically controlled or mechanical limited-slip?