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Vibration under load

CobraNewby

New member
Hi all, hoping for some diagnostic help... just got a 1996 Chris Craft Concept 190 open bow with Ford 5.0 FI and SX outdrive. It has 235 documented hours and all service records. It was so clean I bought without on the water test...it idles so smooth 🙄So...took it out today, starts and idles great, however, under load, has a “vibration” until on plane, then smooth as silk. Acceleration on plane is fine too. Also, separate issue (?) When adjusting trim, it seems to suck power from motor and electrical. Anyone out there have any good ideas/suggestions? Thanks!
 
OK.... the SX drive is a gimbal suspension drive, very much Un-Like the AQ series drives that became discontinued at the end of 1996.

In your SX system, you will have a propeller shaft (aka "in-put shaft") that joins the engine's rubber hubbed drive coupler to the upper gear unit.
This shaft will incorporate two (2) bearing crosses (aka U-joints).
The shaft will also be supported by a gimbal bearing just ahead of the two bearing crosses.


Both the Gimbal bearing and the two bearing crosses may need to be replaced!
 
OK.... the SX drive is a gimbal suspension drive, very much Un-Like the AQ series drives that became discontinued at the end of 1996.

In your SX system, you will have a propeller shaft (aka "in-put shaft") that joins the engine's rubber hubbed drive coupler to the upper gear unit.
This shaft will incorporate two (2) bearing crosses (aka U-joints).
The shaft will also be supported by a gimbal bearing just ahead of the two bearing crosses.


Both the Gimbal bearing and the two bearing crosses may need to be replaced!

Hi Ricardo, I appreciate the info from the previous thread. I would have thought so too, but I have paperwork from a reputable shop that says the Ujoints and Bearing were replaced 30 hours ago. I get that it may still be those items, but could it be anything else? Also, any thoughts about the trim issue? Thanks again, Daniel
 
Hi Ricardo, I appreciate the info from the previous thread. I would have thought so too, but I have paperwork from a reputable shop that says the Ujoints and Bearing were replaced 30 hours ago. I get that it may still be those items, but could it be anything else? Also, any thoughts about the trim issue? Thanks again, Daniel

Well, a few things come to mind:

Loose, bad or improperly installed Engine mounts that Capt Bob mentioned.
A bearing cap clip that has become dislodged. (these are external clips on this style bearing cross)
A bearing cap needle bearing that had fallen out during installation.
Something wrong within the gimbal suspension system.
.... bell housing pivot pins for example.
.... gimbal ring upper/lower pivots for example.

A long shot here...... a bad rubber hubbed drive coupler!

Volvo Penta SX  diagram.jpg


As for the trim system...... it may be a bad pump motor.
If so, be careful with the replacement. Volvo made a change to the motor style somewhere within the 90s.
If memory serves me, there are two possibilities for the replacement motor.

NOTE: OMC was no longer in biz after the end of 1993.
Volvo Penta became the owner in 1994 and started producing the Cone Clutch SX and DP-S drives.
Some parts people get confused between the OMC Cobra and the Volvo Penta SX drive.



.
 
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Thank you, turns out it was engin alignment. All good now! Another question though, I have the 1996 Ford 5.0 FI. I need to remove the throttle body to replace the fuel line. I can’t find Pentax throttle body gaskets. Do you know if regular ford automotive throttle body
gaskets will work?
 
https://www.partsgeek.com/gbproducts/MC/5317-07021364.html or
https://www.amazon.com/BBK-1572-70mm-Throttle-Gasket/dp/B000CITD1W
or
images
 
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