I inherited a Hawthorne Village set that includes Spectrum F7A & B Units. The E-Z Mate couplers on the B Unit are enough lower than the F7A & full dome passenger cars that they frequently uncouple during operation. I replaced the couplers with style number 78005 center shake couplers which match the one on the rear of the F7A, but this didn't fix anything. How can I raise the coupler height to match the rest of the train?
First, make sure that the couplers aren't sagging because they're loose. Tighten the screws that hold the draft gear boxes to the loco frame.
If that doesn't fix the problem, it's possible that the couplers were damaged and got replaced with the wrong style. If you replace the existing couplers with ones with an underset shank, that effectively raises the coupler. Click on the "Products" button on the menu on the left, then select HO Scale/EZ Mate Couplers. You should find what you need. Hope this helps.
Old Timer
Also, as a side note, there is no such thing as Bachmann Spectrum F7As and F7Bs, Bachmann never made HO scale F7A/Bs with the Spectrum name.