Drive-line length
 

I am considering putting extension boxes on an existing side by side, plug-in speedmaster setup and was wonder if anyone has any creative short drive-line options. I don't really want to move my motors forward, this year anyway. What is the shortest traditional drive shaft length I can go with considering two flanges, two u-joints and some sort of slip yoke? Is there any sort of coupler out there that can accomplish the same thing in a shorter length?

Thanks
Jim

Not sure exactly what you're asking. Guessing your looking at the standard Merc drive shaft lengths.
If a short drive line is all you need, try Rex or JC. They make custom length drive shafs for V drive applications.
Gary

Hey Gary,
Thanks for the reply. The main thing I am looking for is with a drive shaft or some form of coupler, what is the minimum length I can have between the flange of the extension box and the flange on the tranny. How much length do I need to make a drive shaft work. My guess is I will not be able to fit a "normal" 2-flange, 2-u joint, and slip joint configuration shaft in my application without moving the motors forward. This being said, I was wondered if anyone had any other ideas of any other coupling devises out there that could be used in a tight configuration.

Jim

I'm assuming the extension box has a short shaft in it that you'll be connecting to.
I have seen setups where the boxes internals were removed and the drive was rigged with a flange (staggered setup).
The engine was coupled with a shaft to the drive directly.
-or-
If you can have a little machining done, have a look at:
http://www.mcmaster.com/
"Flexible shaft couplings"

Gary,
Thanks!!! What a great idea. I never thought about working outside of std components. For that matter why couldn't you make a drive shaft off the cv of the drive and have the splined plug in shaft fabricated on the other end and keep the plug in trannies? Come to think of it, doesn't IMCO make a long plug in shaft that works with their standoff boxes for Bravos? Might be a b_tch getting the longer shaft into the tranny but I could bolt a "ramp" off the mid-carrier mount to provide support for the shaft during installation. I have a pretty good drive shaft shop close. I'll run it by them and see if I am missing something.

Thanks again.
Jim

I think a long shaft like the Imco will need a carrier bearing (like a bravos transom assembly). But that might work. I doubt the tailstock alone could keep a long shaft aligned.
Good luck.

So, if I came off the cv with an imco style shaft(more like an HD axle shaft than a traditional diameter drive shaft) running to the plug-in tail stock of the tranny and replaced the Merc plug-in style bearing carrier in the extension box with a shaft bearing to support the new custom shaft mid span, that might work? Additional question, when the drive trims up and down does the spline portion of the shaft in a plug-in style configuration slide in and out? Or does the CV just tip? Thanks for the thought generating ideas.

Jim

That might work. As you pointed out, there are aftermarket products that do the same thing.
And yes, the spline shaft does slide in and out when the drive changes angle. Not much, but it needs that capability.
On a staggered setup, the drive also uses a female splined shaft/yoke. This rides on male splined shaft/flange that mounts where your tranny "wing" mounts are bolted to the transom assembly now.
You could modify that setup to mount in the box. Then use a short driveshaft to connect that flange to the new tailstock flange on your tranny. That's the setup I've seen before.
Of course that would require a new tailstock, rear motor plate (if you dont have one now) machining your bell housing, and a driveshaft.

Gary,
The staggered configuration you described is similar in concept to the existing box set-up just moved to the inner transom plate. The problem with that for me is I am trying to not move the motors or change to a drive-line tranny(this year anyway). I currently have double plate mounts for the motor set-up. My plan was to lose the stock Merc inner transom plates and use the billet plates that came with the ext-boxes. I'm leaning toward the longer "custom" plug in shaft with a mid-span bearing support after the cv joint, mounted to the original extension box carrier attachment points. I think I can fab up a single bearing, two seal carrier and then tee off the drive vent to keep the bearing cavity filled with lube. An inner transom mounted overflow can will provide expansion room for both the drive and the bearing. The mid-span bearing support would also act as a guide during installation.

Jim

I dont see why it wouldn't work. Just make sure the alignment of the carrier bearing and the plugin tailstock is dead on. I know how dfifficult it is to get a standard SSM drive shaft in.
I think all the parts for that should be available at any custom axle shop.
A splined yoke, Axel with splined to match. Then just have them cut it and spline to match your tranny. You're going to have to figure out the carrier (axle) bearing mount, but that doesn't sound too difficult.
BTW, the mod I was descrbing was to use the staggered drive parts and move the flange from the inner transom plate, back into the box.
Gary

Fringe,
Have you thought about the X dimension? Any need to change?

Gary,
Yup I was trying to figure out a way to align that bearing. I can make an alignment tool, but I have no way to then tighten the carrier mounting once it is aligned, without pulling the tool and snaking my hand through the bellows. I thought about a side access port(again looking at some of the Imco boxes for bravos). I guess if I did that I could leave the bearing carrier loose and put the drive on(I would be able to guide the shaft into place throught the port too) and then tighten the carrier down. Is that the way the bravo boxes work?
Ben,
The boat was originally set-up with a 2" spacer with 3 blade props. I'm switching to 4 blades so I went to a 1" spacer. The Merc boxes in the center mounting hole raises the drive 1" over the std gimbal mounting. That will be my starting point. I can go up a max of another 2" between taking out the spacer completely and moving the box to the highest mounting location.

Jim

The Stelling boxes have an access port on the side. That would be the way to go. Not sure how to get in there with a shaft in place to get it aligned correctly.
You might consider mounting it, shimming to get it strait as possible, then aligning the engine and trans to the shaft.
Gary

One thought I had was having an adjustment bolt/bolts on the top of the bearing carrier so I could slowly adjust the bearing carrier up(maintaining it's height location) with the mounting bolts hand tight and re-inserting the alignment shaft until I got the carrier adjusted before doing the final torque on the carrier. This would be an iterative process of adjust, reinsert to check, remove, readjust, but it would require the minimum modification in the engine bay. I just talked to Moser Engineering in Indiana and they feel they can make the shaft. They were thinking a Dana 60 axle shaft would work. I have to mic the intermediate shaft off the std merc bearing carrier. If I have the mid-span bearing surface on the new shaft ground for that inner diameter, I should be able to use the std bearing and 50% of the original carrier.

Jim