Mercury INSTALLATION MANUAL D7.3L D-TRONIC - Manual (Page 4)

D7.3L D-TRONIC DIESEL ENGINES - BRAVO MODELS
Page 4 of 90
Multiple Sterndrive Steering Tie Bar Arrangements
With multiple sterndrives it is important to consider which of several possible steering sys-
tems should be selected.
CAUTION
Failure to observe the recommended Tie Bar Arrangements as presented in this
section could result in serious damage to the steering and/or trim system compo-
nents. This damage could adversely affect control of the boat.
INTERNAL TIE BAR ONLY
At the lower end of the performance spectrum (boats not capable of speeds in excess of
60 MPH) the basic internal tie bar is recommended. It connects the slave sterndrive to the
sterndrive that is directly connected to the factory power steering output. This internal tie
bar is available in a variety of lengths from the sterndrive manufacturer.
INTERNAL AND EXTERNAL TIE BAR
As a boat moves into a moderate performance range (60-70 MPH) or for a reduction in steer-
ing backlash, an external tie bar should be added. External tie bars are usually designed
to attach at the aft power trim cylinder bosses which is an excellent location because of its
proximity to the propeller. HOWEVER, because of the potential overstress that can occur
if one drive is trimmed much differently than the other, a dual trim control kit (Part Number
90362A3) should be installed so as to limit this potential tilt differential to about 20 ° .
EXTERNAL POWER STEERING
When boat speeds move past 70 MPH or if additional steering backlash reduction is desired,
external power steering is recommended. This normally will include an external tie bar
mounted at the same general location of the power steering cylinders which are generally
attached at the top of the sterndrive’s drive shaft housing. With this steering system, no inter-
nal tie bar should be used. These steering cylinders can be attached either inboard (be-
tween) or outboard of the sterndrives.
EXTERNAL POWER STEERING WITH LOW EXTERNAL TIE BAR
For the fastest boats (over 80 MPH) or for the ultimate in steering backlash reduction, use
external power steering, BUT (where mechanically possible) with the external tie bar
mounted at the trim cylinder boss location (as previously described in “Internal and External
Tie Bar” statements). Again this system does not use an internal tie bar.
Mercury Marine does not recommend the use of an external tie bar ONLY (no internal tie
bar) when using the internal power steering system. This can cause excessive loads on the
steering components on the drive connected to the internal power steering system. These
increased loads can damage the steering components, resulting in increased play in the
steering of the boat.