470 grinding gears / speedometer

dn010

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Oct 16, 2010
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Is the drive supposed to grind into gear when placed in forward or reverse? Also, does anyone know where to hook up the air tube running from the speedometer? I can't seem to find anywhere it goes... This is on '78 Mercruiser 470 with 470 drive. Thanks in advance!
 

Bondo

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Re: 470 grinding gears / speedometer

Ayuh,... Alpha drives have to be shifted into gear, Briskly....
Otherwise, you'll grind it into bits...

You need a pitot tube on the transom for a speedometer,...
They weren't added to the drives til 91 or so....
 

dn010

Petty Officer 1st Class
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Oct 16, 2010
Messages
301
Re: 470 grinding gears / speedometer

Mine is pre-alpha which I'm still trying to shift briskly. What should I expect to hear when shifting correctly?

Ayuh,... Alpha drives have to be shifted into gear, Briskly....
Otherwise, you'll grind it into bits...

You need a pitot tube on the transom for a speedometer,...
They weren't added to the drives til 91 or so....
 

Bondo

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Re: 470 grinding gears / speedometer

What should I expect to hear when shifting correctly?

Ayuh,... A single Clunk,....
 

dn010

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Oct 16, 2010
Messages
301
Re: 470 grinding gears / speedometer

Thanks. So it seems as my idle speed and shift cable was at fault for this problem. Took off the cable - moved it by hand and it was difficult to move; sprayed some graphite down it, moved it a few times and it works fine now. Engine was also idling around 1000RPM, lowered it down to 500. The drive now "clunks" into gear as you said.

You need a pitot tube on the transom for a speedometer,...
They weren't added to the drives til 91 or so....

Now for the speedometer - It is the original speedometer in the boat, and there is a line that resembled a vacuum line running from the gauge to the rear of the boat, only the end of it is all burned looking. Can you tell me where on the transom this tube it connects to should be (port/starboard, upper portion or lower?).

Thanks Bond-o for your help! I 'preciate it!
 

Don S

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62,321
Re: 470 grinding gears / speedometer

Thanks. So it seems as my idle speed and shift cable was at fault for this problem. Took off the cable - moved it by hand and it was difficult to move; sprayed some graphite down it, moved it a few times and it works fine now.

It's probably only a temporary fix at best. When cables get like that, replacement is the only sure fix.

As far as your speedometer pitot, it could be anyplace on the transom, you just have to look. no set place for mounting. They look like this.
38659.jpg

For further questions, since the pitot tube and speedometer are not IO engine or drive parts, best to post your questions over in the Boat topics and questions forum.
 
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