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175 Black Max needs trim tilt replacment

P

Peter Devil Ears

Regular Contributor
Hi, I have a 1979 Black Max, 175HP. The trim tilt assembly does not work. The relays and motor do work. So it must be the valve body. My local agent could not find a replacement unit. I can get a Mercruiser two pipe assembly that my agent says will work, but it costs alot. Before spending this money, I would like to get some opinions and options if anyone can suggest something. I checked the two hydraulic rams, and the o-rings were replaced, they are good. To be 100% sure that I do not buy a new PTT assembly and waste money, is there a way I can test the assembly without the RAMs to make sure it really is faulty and that the RAMs are not maybe faulty in case I am mistaken? Any suggestions would be greatly appreciated.
 
I never saw a 175 but you have a dc bidirectional motor due to swapping the polarity of the battery voltage applied to the motor. The motor runs the pump that generates the pressure required to activate the cylinders.

I'd remove the motor from the assembly and with it in my hand operate the trim control and see if the motor runs and changes direction as required. If not, break into the power (blue and green on mine) wires to it and with a DVM test to see that you have voltage which you can change polarity when changing the trim button direction. If you don't go chase the relays. If you do, look for a motor.

I don't have a lot of experience here but I understand there are 2 types of motors. One has 3 wires and the other 2. On the two you just swap + and - on each lead. On the 3 wire, you probably will just put the neg battery term on the black lead and whichever blue or green lead you put 12v onto will determine the direction.

Oh, and while you are there at the pump look at the reservoir at the bottom of the pistons for a fill screw. On mine it's about the size of a quarter and white. Full is even with the threads on the bottom of that hole. Fluid is Quicksilver PTT if clear, ATF if red. Add what is used if necessary.

HTH,
Mark
 
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