blown up again (extension box)
 

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!

What did you find? These threads are more interesting to me than any who done it mystery.

My flanges are not parallel, which is unfortunate because its a lot of work to make it right. The community of high performance boaters is awesome, thanks for all the tech advice everyone!

There is another way besides parallel, if it would save some work. If you can split the angle exactly so the input flange to shaft is equal and opposite the shaft to output, it will work too. Just takes a little more math

Also, you have some range of adjustment vertically in the extension box. They are normally set up on the lowest of three settings. If you needed the box to go up to match the engines, you could do that very easily, and then add spacers if you needed the same propshaft height, or just go faster if you don't. If the engine is already below the input flange, then that's no help.

Double-check your hatch clearances and check the implications on the exhaust before doing anything...

Also, I've wondered about seeing if someone could make up a CV-type shaft to fit the Spicer flanges. That would cure that problem.

T, Moving the box won't help - it will change the total angle but not change the face/face angle. It is possible to make a box with an angle built in to compensate.

Yes the intersecting angles will work almost as good. I have done it by making some flanges with equal length pointers on them then moving things around until they touch at the tips.

I was all set to try a cv back in the 80's ( I had bougt all the pieces) when someone pointed out that Arneson did not have any luck with them and went back to U joints.

Coming back to this guy's......... I may have been confused earlier when I was reading through this. After rereading this it sounds like I can be slightly offset either side to side, or up and down, as long as the two faces are square to eachother. If thats the case I think I am actually still good? I am thinking that I may pull the boxes and put a thin spacer between them and the boat, as under load I may be pushing on the bearings as I had the slip yoke almost..........bottomed out to fit the driveshaft between the two faces.

Also any ideas on were parts can be had for these boxes, or anyone you rebuilds them? Marc do you guy's get into those? Thanks for all the advice so far!!!

Anymore input here, trying to come up with a game plan?

yes it is best if the flange faces are parallel and offset up, down or to the sides a little.

Okay great, any thoughts on parts or who rebuilds them? I have called speedmasters in fl about 4 times no one ever answers, or returned my messages? Does anyone have a # for Marc at Bam, can't seem to find a good number for him?

I remember chatting with my buddy Rob about this a while ago so while greasing my drive shafts yesterday I looked and sure enough its the same setup. Extension box fluid change! LOL it never ends with these boats!

Interested in adding a fluid reservoir to monitor the level. How would I go about that? How much fluid does it hold normally? How do you currently change the fluid? How much fluid would you use if you added a reservoir? Can you overfill it?

The stellings boxes on my last boat just had a grease fitting there.

Thanks!

Spend the $25 each and balance them anyway. I thought the same thing till I went to a drive line shop. You would not believe it until you see it on the balance machine. Remember, they may be spinning up to 5500 RPM

WANTED: Pair of clear merc bravo style drive fluid reservoir bottles and transom brackets. Thanks

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