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1971 Mark III Transmission Issues

Hi Bill,

I come from Berlin / Germany and have a Continental Mark 3 Coupe from 1971 and a problem with the gearbox and the vacuum system for controlling the gearbox, which I have not been able to solve for over 1 year. Myself and my workshop don’t know what to do next. 1st + 2nd gear work normally In 3rd gear it only drives in 1st gear and does not shift into 2nd or 3rd gear. We did step by step: – Vacuum modulator on the gearbox exchanged, – Step by step 7-8 found and repaired vacuum leaks in the whole vacuum system – Spark plugs and ignition cables exchanged, after that it also ran much better with more power – Another 2-3 leaks in the vacuum system were found and repaired with a fog printing machine – Entire vacuum systems disconnected to rule out further problems and leaks And after EACH of these repair steps (10-12 steps total) the gearbox has worked for 5-10 miles. After that, no more, regardless of whether the car was warm or started cold again the next day. I checked and adjusted everything in the periphery of the transmission – shift linkage, kick-down and everything else that can be adjusted from the outside. We are faced with a mystery, mainly because the car works after individual repair steps and then after a few miles (regardless of whether it is cold or warm) it no longer works. I also need a vacuum diagram, but at Lincoln Land I can only find a wiring diagram for Mark 3 1971 and the vacuum diagram is only for heating and air conditioning. Is there no vacuum diagram for the Mark 3 for the whole system? I would be very happy if you have any advice or advice for me!

Thanks a lot.


Greetings Marcus –

Assuming that you are using the correct Fo Mo Co maintenance manuals and performing the adjustments correctly a transmission that is in good shape internally and maintained properly should work just fine. If you suspect a transmission vacuum problem you could “T” in a vacuum gauge and then road test to observe for a vacuum change at the 5 -10 mile failure speed. Anyone checking out the transmission now needs to know if possible the maintenance history regarding any previous internal repairs and transmission fluid changes. At this point in time however, your transmission should be road tested by a transmission expert who has FORD C6 experience preferably.

If Lincoln Land cannot supply you with the correct wiring vacuum diagrams, they can be found available On Line from the USA via a Google search. We cannot recommend any particular supplier of manuals. Good luck to you with the diagnosis.



Hello Bill,

Thank you for your quick answer!

I will follow your advice and hope to find a solution.

nice greetings from Germany


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