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6MT troubleshooting help


Subsandwich
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Need some help trying to troubleshoot something. I have an 07 LGT with an 04 STI trans. Tried to get it dyno tuned the other day, but the front wheels were spinning slower than the rears. I was working with a reputable tuner, and they couldn't get the wheels to spin at the same speed. I have a DCCD wired in, and they tried adjusting it but it didn't work. So the conclusion was that one of three components are messed up: the rear doesn't have the right diff ratio, the center diff is broken, or the DCCD is not functioning.

 

Checking the 07 FSM, the LGT should have a 3.9 rear, which would negate the first thought... I think... That being said, I think something might be going on between the center diff and the DCCD.

 

If the DCC isn't wired properly, then would the center diff just remain open? Would it remain in the 35:65 bias and would that explain the difference of wheel speeds?

 

I'm not too familiar with the AP Suretrac diff in the 04 STI, and I'm not too familiar with Dynos, but anybody have any thoughts?

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After further review of the 2004 STI FSM and 2008 STI FSM:

 

The 04 Center Diff is Open, while the 08 C Diff (any other docs or healthcare providers out there?) has an LSD. The owners manual to both models seem to reaffirm this (the 04 just mentions the DCCD as a method to modulate F/R torque distribution, while the 08 explicitly states the DCCD acts upon an LSD).

 

The AP Suretrac on the 04 STIs refer to the front differential.

 

Based off of that, I am lead to believe that the issue with my car would be a non-functioning DCCD. Since the center diff is open, the torque distribution would remain in the default 35:65 configuration, resulting in a difference in the wheel speeds.

 

Sound about right?

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Inspect the pass through wiring for the DCCD on the transmission (Passenger side just forward of the tail shaft housing. If that's good, then I would move on to checking resistance through the coil for the DCCD via that same wiring. Are you running a DCCDpro or MapDCCD? Yes, if the DCCD isn't wired correctly or if its fried it'll be open. What you can do is go to a parking lot and put in Manual and full lock, turn your steering wheel (left or right full lock) and give it some gas. For "auto" it can be a little more involved with detective work. The car should buck and scuff the tires. If it doesn't its not functioning correctly, more so, the center diff may need to be rebuilt (new clutch pack). Hope this helps.
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