1989 GMC S15 Screaming Transmission

1989 GMC S15
130,000 MILES • 6 CYL • 4WD • AUTOMATIC
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BECKICURTIS
We recently put in a rebuilt transmission and torque converter. Since then, the transmission screams as if it may be trying to engage in 4-wheel drive as we are driving it down the road. This usually happens as we are ascending a grade. Once we reach the top of the grade and the pressure is released, the screaming starts. It stops once the engine has slowed to about 45mph and ends with a thud in the transmission area. It happens more often when there is a load on the truck. Other than this, the truck is running great mechanically and we are not experiencing loss of power. What could this possibly be?
Sep 26, 2008 at 10:15 PM
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SWILLIAMS
  • ✓ASE Certified Mechanic
  • 597 POSTS
  • ASE Certified Mechanic
Could be a vacuum leak to the front axle interlock. That could be causing the interlock to move and the scream is the gear teeth clashing. To test it, disconnect the 4X4 actuator vacuum line and plug it. If the noise goes away the vacuum switch on top of the transfer case is likely sticking open a bit. Not real hard to replace.
Oct 24, 2008 at 3:47 PM
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