Classic/Antique Car Repair/Modulator valve

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Expert: - 12/17/2007


Question
I bought a 1968 Olds Cutlass convertible. It has a 2 speed transmission that looks rebuilt. It shifts fine but passing gear kicks in and out constantly. I checked for vacuum leaks and then replaced the modulator valve but didn't help.The instructions said the valve was spring loaded but I felt no pressure when I installed it. Is something missing? Could the problem be somewhere else?

Answer
A couple of things to check here. Make sure that there is manifold vacuum at the modulator and that there are no leaks in the line. The down shift (passing gear) is controlled on this transmission by an electrical switch mounted near the carburetor that sends an electrical signal to a down shift solenoid on the left side of the transmission. Make sure that this switch does not engage unless the throttle is wide open. The switch could be defective or the solenoid could be defective. If these check out then the problem is internal. The vacuum modulator only controls the shift points in conjunction with the internal governor.
Brad

Classic/Antique Car Repair

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Brad Sears

Expertise

All automotive including antique and collectible. However if the car has been modified I can only answer in general terms and maybe get you pointed in the right direction.

Experience

Automotive tech instructor. Syndicated auto columnist 1970's though the early 1990's. Syndicated auto radio talk show, Ask Brad About cars, CBS Radio 70's through 90's TV Show "Last Chance Garage" 1980's PBS-TV syndicated. Auto instructor for the following companies: Fram Autolyte Holly Carter AMF Ford Motor University Of Conn Blue Hills Technical School Sugar River Technical Center Grew up in a family garage in Needham Mass and turned wrenches from the age of 14.

Publications
Manchester Union Leader, Nashua Telegraph, Motor Service Magazine, Yankee Magazine, Popular Mechanics (Saturday Mechanic early 80's), Los Angeles Times, New York Times, and lots more.

Education/Credentials
More than I care to remember. Basically Franklin Technical Institute in Boston, Northeastern University, Fitchburg State Teachers College, Tufts University, and a lot of factory schools along the way.

Awards and Honors
Moto Award winner. And much more.

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