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Old 11 July 2016, 23:05   #1
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Country: USA
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Engine: Yamaha 7.4 Hydradriv
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Hydradrive help

Hi, I'm in the US and I have a 92 7.4 Hydradrive. I am not having too much trouble finding parts but a manual and advice are really hard to come by. I pulled the drive at the end of last season and cleaned the filter while resealing everything I took apart and it has worked great but is now having trouble shifting after high speed runs. I am looking for someone that understands these or can turn me on to a used one that is in good condition. I appreciate any responses and assistance.

Thank you,
Carl
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Old 12 July 2016, 02:32   #2
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You can replace with mercruiser alpha or bravo as they use the same spline and transom drilling pattern
Need to use the yamaha inner transom shield bolted to the mercruiser outer
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Old 12 July 2016, 04:57   #3
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I've found this company helpful ..... Boats.net: Outboard Motors, OEM Marine Parts, Boats for Sale and a good source for parts
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Old 12 July 2016, 11:21   #4
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Country: USA
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Quote:
Originally Posted by beamishken View Post
You can replace with mercruiser alpha or bravo as they use the same spline and transom drilling pattern
Need to use the yamaha inner transom shield bolted to the mercruiser outer
Beamishken;
That is great news on my end. I have found many posts on US forums saying that is not true. Have you done one this way? What else is required? How do you manage the shift linkage? Also, the Yamaha has an external fresh water pump. Do I just bypass that and use the Merc pump? Does it connect the same way? I'm sorry to have so many questions but I would like to have everything ready and do the swap quickly so I can continue my season.

Quote:
Originally Posted by Dirk Diggler View Post
I've found this company helpful ..... Boats.net: Outboard Motors, OEM Marine Parts, Boats for Sale and a good source for parts
I have used them for many of the parts I purchased last year. They are reliable and have about half of the parts available. It has not been difficult to find parts but I'm skeptical of tearing into this thing without a manual. If I can easily swap a Bravo on there, I won't bother rebuilding this one. It will be easier to sell in a few years when I'm ready to upgrade with a merc on it.
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Old 12 July 2016, 11:49   #5
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Originally Posted by vdubr928 View Post
Beamishken;
That is great news on my end. I have found many posts on US forums saying that is not true. Have you done one this way? What else is required? How do you manage the shift linkage? Also, the Yamaha has an external fresh water pump. Do I just bypass that and use the Merc pump? Does it connect the same way? I'm sorry to have so many questions but I would like to have everything ready and do the swap quickly so I can continue my season.
You can't fit a Bravo Drive to a Yamaha Transom. I suspect the suggestion was to replace your current drive and transom with a Merc one, using the Yamaha inner transom plate to hook it all up.

You'd also need a Merc raw water pump and a shift bracket to make it all work.
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Old 12 July 2016, 12:47   #6
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Quote:
Originally Posted by Dirk Diggler View Post
You can't fit a Bravo Drive to a Yamaha Transom. I suspect the suggestion was to replace your current drive and transom with a Merc one, using the Yamaha inner transom plate to hook it all up.

You'd also need a Merc raw water pump and a shift bracket to make it all work.
What I mean to say is that in the US most people say the hole isn't the same and the inner transom won't work. I'm wondering if anyone has done a writeup on this. I have heard enough people say it will work that I am seriously considering buying a bravo (and transom assembly) but it would be nice to have some confirmation from someone who has done this. I have suspected that much of the advice I've seen posted in the US forums is from mechanics who really just want you to repower. They also say parts are not available and I have had no trouble finding parts.

I have a couple of more questions.
1: Doesn't the mercruiser have a raw water pump in the lower drive? Do I just remove the impeller and run an external raw water pump?

2: How do I know what gear ratio to purchase? I do not know the current ratio or how to find it but I know mine is a 300hp 7.4 and was turning a 16x16.
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Old 12 July 2016, 15:32   #7
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Country: UK - England
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Hydradrive helkp

Are you running the hydra drive on a petrol ? The ratio on the petrol version are 1.50:1
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Old 12 July 2016, 16:49   #8
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You will need drive and shield the drilling pattern in the transom is the same. if you use a bravo drive there is no pump so you need an engine mounted pump.if you use an alpha it has a built in pump.
Bravo is stronger drive but more expensive alpha is said to be good for 450hp petrol but needs carefull use of throttle with the big blocks but will be cheaper. for gearshift you just use the merc shift plate with merc adapter kit to your 33c cables from the helm
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Old 12 July 2016, 17:01   #9
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Mercruiser drives come in a variety of ratios 1.5:1 being prety common so easy to swap like for like ratio wise but it wouldn't be hard to run a prop calculation through mercruisers website for your boat and engine combo the engine will be the same as a merc engine of the same era so prety simple to do prop calcs for your boat with the merc drive
You could also consider a bravo 3 but would need to reduce the ratio to 2.2 or 2.0
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Old 13 July 2016, 00:34   #10
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Or simple enough get 7.4 bell housing of merc same block . The only thing maybe a problem is the trim sender as May mess up the Yems an retard the ignition .
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