I have merc extension boxes (drive line style) for my #5 drives. Prior to purchasing these boxes the previous owner blew the carrier bearing up in each box and had them rebuilt. I have put about 12 hours on this set up, and just blew up the starboard side burning rubber smell lot's of smoke and then a loud claddering sound. You can now Grab the drive shaft and move it up and down about 2 inches at the carrier bearing flange. These carrier bearing housings have a vent at the top of the case, and the previous owner had also drilled and tapped 1/4 lines into the housings so that you can add fluid to them. They where checked and full of fluid at time of install 12 hours ago. Can anyone please...... chime in on why these may be blowing up

The drive shafts have u-joints...correct? What is the driveshaft angle? You can measure with a digital angle finder. You can run more angle, but 2% +/- is safe=long life.

I would have to measure to be exact, but yes they have u joints and a slip yoke, they only measure about 8.5 inches in length. Would these little drive shafts have to be balanced, is that even possible on such a short setup? Thank you, any help is much appreciated!!!

I have Stellings/bravo boxes.

I had my driveshafts checked this spring, and they
did have to add weight to both of them to make
them right.

They hold very little oil. I never liked the fact that they were hard to check buried in the box so I put clear resevoir bottles on mine. I just needed to open the hatch and look back.

Saved my butt more than once when the seal at the back end went out.

I had 15 deg driveshaft angles at one point which was hard on U joints but the carrier was never a problem. It is important that the 2 ujoint flanges are parallel. The merc gimbal is designed for a 13 deg transom which few boats have. This means the engine has to be installed at an angle to match.

I agree that balancing is not likely the issue; however, DynoTech is where we have our driveshafts rebuilt and balanced in Detroit. Marc is right on. Once the X-dimension is set, re-align the engines to get the targeted driveshft angle. This is a good winter project!

DynoTech
800 633 5559
www.dynotechengineering.com

I also ran the clear 1/4 line to my clear drive reservoirs with a small needle valve. I was afraid of them overfilling due to the reservoirs being higher than the carrier housing and just have fluid keep pumping out of the vent. This way i can open the valve making sure the housings are full but then closing the valve so they would not over fill. Did you Run a valve on yours Marc, or was overfilling not a problem? I figured being a double ujoint set up that the flanges not being perfectly parallel was not a huge deal, but maybe I was wrong?

+1 drive flange parallelism is important. You could take the shaft out, and use a pair of squares, or even mill a piece of something nice and square to the right length. Even if the flanges are offset, vertically or horizontally (I have same Merc SSM V boxes with engines offset down and outboard, giving about 5 degrees total angle), the flanges must remain square to give smooth operation.

The other thing I would check is whether you came up hard against the end of the slip-yokes. I would think any significant thrust on those bearings would eat them up quickly.

Rob, I attached the bottle to the vent fitting, the support was sealed. I would fill the bottle then pull the plug until oil came out, then put plug in.

Yes - parallel flanges are very important. And slip yokes as tcelano pointed out.

Thanks for all the input guys, I think I have the answers to my problem. I really appreciate the advice!