You aren't giving much to go on here, but in all probability you have an MS4 or MS5 model transmission
, so I'll address that.
The most likely ZF candidate for replacing an MS4/5 transmission is the ZF63A. This is a drop center/ down angle hydraulic gear
box that is a fairly close replacement for the VP gear
. Going from memory, the ZF gear has a slightly greater offset between input and output shaft than does the VP gear, so that means the engine
will have to be raised slightly to match the output flange and the prop shaft coupling. Also from memory, I think he ZF gear is slightly shorter, fore and aft, from its mounting flange to the output coupling than the VP gear, so the engine will have to slide aft an inch or so to reach the prop shaft coupling.
The mounting bolt pattern on the front of both gears is a 6 bolt "Borg Warner" pattern (SAE#7), so it will bolt up to the flywheel housing, and both use the 26 tooth involute spline input shaft, so the dampers will match. I would suggest replacing the damper along with the new gear. Both output flanges are standard 5" flanges.
Because the 63A is a hydraulically actuated gear you will have to install a gear cooler and hoses into the seawater cooling
system, but that will be straight forward.
The 63A is available in a variety of reduction ratios, 1.25:1, 1.5:1, 2:1, 2.5:1, and I think 2.9:1. Don't know why you would want to change the ratio that you have, but it's something that should be examined carefully before you make the leap.....it could be helpful or it could be a disaster. The 63A has equal ratios in both forward and reverse, and can be run continuously in either direction so if you have a twin engine boat
there won't be a problem with LH & RH props.
Hope this is helpful. Let me know if you have any questions.