The Infamous 1971 - 1976 GM Scissor Top


This page is dedicated to the scissor top convertible top drive assembly used from 1971 through 1976 on GM full size convertible automobiles. This assembly uses an electric motor to drive an attached gearbox which in turn drives two cables. Each cable then drives a larger gear box on each side of the car to operate the convertible top mechanism. It amazes me that this system works as well as it does. The most common failure modes I see for these motors are that they are either rusted solid internally or the direction control windings are completely burned up. I've read on the internet that the most common problem is that the gears strip. Well, after doing a few dozen of these motors, I've yet to see a set of gears that were not in excellent condition.  

Please see the paragraph at the bottom of this page discussing the control relay for this motor. The warranty on this motor will cover defects in material and workmanship only. If your old motor was burned up and you decide not to install a new control relay, I can't help you. Although my motors have all new windings, they're not magically invincible. They'll burn up just like the old one if the control relay is failing. You'll be saving enough money purchasing one of my motors that you can afford to buy a replacement relay.

 

Here's a price breakdown that I got from dealers on the web:

New gears and housing $345

Used gears and housing $275

Drive motor $250

Mounting bracket $35

Control relay $60

Very expensive if you ask me...

  

My charge for rebuilding yours or swapping it with one of mine? $95 + $10 shipping for Method 1. Method 2 would require an additional core charge of $125 which would be refunded when your core arrives at my door.

  

The two photos below show the large gear boxes which are located one on each side of the car by the rear passenger seat back rest. These large gear boxes are connected to the drive motor via drive cables. The arm sticking up connects to the top mechanism.

 

 

I removed these two gearboxes and corner mounting brackets from an old Buick. They were both extremely stiff to operate and would have caused the drive motor to eventually burn up. Please keep this in mind if you're restoring or repairing your car. These gearboxes need attention also. The photos were taken after I worked on them.

 

The most common cause of these motors burning up is the control relay goes bad. If you own one of these cars, I can tell you right now, with all honesty, replace your control relay with a new one. Don't wait until you start having problems because it will be too late. A new $50 relay beats the heck out of a buying a new top motor AND a new relay. I don't sell these relays but I can point you in the right direction. The relays go bad because the OEM design is flawed. The heavy red wire which supplies power to the armature connects to a spade on the relay. This spade is riveted to a contact inside the relay. This rivet was installed by heating it up and then spiking the end to mushroom it. Unfortunately, the heat caused the plastic base to melt inside the relay and eventually the spade and contact lose their connection, preventing power from getting to the armature. Power still gets applied to the direction control windings and they eventually melt.

 

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