7.4 volvo penta I/O vibration help!

thanasi

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Jul 5, 2010
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I have a 99 chris craft 7.4 I/O AND PICKED UP A HEAVY THUMBING vibration yesterday, it even does it in neutral but more in drive and even more when the unit is all the way up. It is comming behind the motor, between the engine and outdrive. Engine still runs excellent I was still able to accelerate and bring the boat in, vibration/thumbing almost goes away at top speed. Can anyone tell me what would cause that and if it an easy fix. Is something loose or is there a bearing in there that goes bad. Thanks
 

Bondo

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Re: 7.4 volvo penta I/O vibration help!

Ayuh,... The U-joints, and/ or the Gimbel bearing....
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

Thank you, Do the u joints make the thumbing even in neutral? Is it an easy fix can i do it myself. I am a car mechanic. never worked on a boat.
 

Bondo

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Re: 7.4 volvo penta I/O vibration help!

Do the u joints make the thumbing even in neutral? Is it an easy fix can i do it myself. I am a car mechanic.

Ayuh,... It ain't too bad,... The U-joints turn With the motor...
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

Thanks AGAIN, what do i need to remove to get to them.
 

Bondo

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Re: 7.4 volvo penta I/O vibration help!

Ayuh,... The Drive...
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

Ayuh,... The Drive...


Can i do it or are there special tools required. I have every automotive tool required for vehicles. I there a link somewhere or service manual. we also have alldatapro in the shop ,however there is nothing about boats.
 

KJSmitty

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Re: 7.4 volvo penta I/O vibration help!

As stated above,

The u-joints/drive-shaft turn when ever the engine is running (whether in neutral or not). With the drive/tilt in the full up position the u-joints are articulating at their max - more so than when fully turning, thus the reason you get more noise in that position etc.

Have you ever had the drive removed and/or bellows replaced?

Which VP drive do you have (SX or Dual Prop)?

Just remove the prop (for weight and or ease of handling the drive), disconnect the shift cable, trim cylinders, and remove the 6 nuts and the drive and shaft should just pull straight back and off. Make sure to have a lift or small stand to place it on etc.

Cheers
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

Thank you all so much, I do have the DPduoprop. Anything else I need to know?


OH! one more thing anything else i should replace while I am ion there?
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

One more thing! Should i also replace the gimbal bearing or upper steering bearing while I have it apart or is that not necessary.
 

KJSmitty

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Re: 7.4 volvo penta I/O vibration help!

OH! one more thing anything else i should replace while I am ion there?

Well, you wont know until you're in there...

If it's making quite a ruckus then you will most likely need new u-joints and a gimbal bearing. The gimbal bearing is easy to R&R if you have the appropriate puller. The u-joints can be replaced just like vehicle drive shaft u-joint yet if they are bad enough and the shaft is all rusted you may consider just replacing the shaft/u-joints all together.

If you have never or don't know if the bellows were ever replaced do that now as well. Most likely a cracked/leaking bellow is what caused the rest to go bad. You may have two bellows, one for the shaft and one for the exhaust. Some however (like my DP), only have the one for the shaft/u-joints. A single kit will cost you about $85, both will be near $150. Both are easy to replace with the drive off - and you don't need to remove the pivot housing either.

Thus - start with:

Bellows kit
U-joints and gimbal bearing
2 O-rings for the drive shaft
O-ring for the water passage between drive and pivot housing


Cheers
 

thanasi

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Re: 7.4 volvo penta I/O vibration help!

Thank you very much, where do i buy those parts?
 

KJSmitty

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