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Author Topic: Overdrive Questions  (Read 3673 times)

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Overdrive Questions
« on: November 09, 2019, 02:41:35 PM »
My new problem is with the overdrive. This is the LH type. It started working intermittently then stopped working so I serviced it following your YouTube videos. I replaced the O-rings in the solenoid, pump and relief valve except for 1 O-ring inside the relief valve which was not available (but the old one looked OK). I also confirmed there is 12 volts at the solenoid only when in 3rd or 4th gears and that the solenoid coil has about 10 ohm resistance. The gearbox oil level is correct. Now driving, the overdrive is still not working and I’m wondering what to do next.

After reading more about the subject, I have 2 specific queries related to your videos.

1: You do not mention the orientation when reinserting the pump. According to the manual, “the flat side of the plunger is towards the rear of the overdrive unit”. I did this (assuming this direction is towards the rear of the car) but without support of the special tool. Is this the potential problem?

2: You do not mention reseating the ball in the Solenoid. According to the manual, “the ball may be reseated by light tapping onto the seat”. I didn’t do this. Is it the potential problem?

I have also seen the warnings about damaging the overdrive by using reverse gear when the overdrive is engaged. What exactly is the potential damage? I wonder if this happened when the problem started.

I would appreciate your help,

Dave Miller


  • AMGBA Club Tech Staff
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  • Posts: 117
    • University Motors
Re: Overdrive Questions
« Reply #1 on: November 09, 2019, 03:04:37 PM »
Double check the power.  Once your test light has illuminated, wiggle the gear lever to see if the power remains HOT.
Remove that filter (again) and watch the action of the oil pump as you rotate the driveshaft.  It should move up and down about 1/4" or about 5 mm.  If the oil pump is not working, there is no hydraulic pressure.  Tap the ball into the oil pressure pump seat -- although that's rarely the problem. 

Drop that solenoid again and ensure the correct position of the ball and piston.  Refer to your manual or a parts catalogue.

If the overdrive is operating and you engage it in reverse, then the Sprague clutch (one-way clutch) jams and can crack the cast ring that surrounds it.  This is one reason for the 3-4 lockout switch.  I've only seen that ring cracked twice in 45 years.  It's not a common problem.  If the overdrive is stuck on and you try to reverse, it feels like you're trying to back over a concrete block -- the car just doesn't want to move farther. 

Sometimes the problem is elusive.  Just drop everything apart again, use carburetor cleaner and compressed air, and reassemble. 

Hope this helps!

John H Twist

John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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