I Keep Breaking U Joints And Destroying Transom Units
 

I have a 98 baja with a 540 blower motor with a imco extreme drive. I broke three U joints last year and everytime it breaks it destroys the transom unit and the input shaft in the drive. I had a 540 blower motor in it in the past and never had a problem with it then I blew it up so I put a whole new motor in it last year same size but all new stuff. I put it in the water to test it everything was smooth no vibes no nothing. Cruising along and the U joint broke. I replaced the transom unit and fixed the drive. put it back in the water it was good for about two weeks and then it broke another U joint so a replaced the transom unit, fixed the drive, changed the bell housing and put a new coupler in. Everything was fine for about a month then out of the blue it broke again. So I was done for the season. Im trying to figure out what can be causing it to keep breaking. Any ideas ????

I think the alignment of the shaft is in correct. The only way you break a u-joint is by stressing it with too much of an angle.

Re check your alignment and heights to make sure they are all correct.

i agree with smitty :ernaehrung004:

alignment
 

The second and third time I fixed it i checked it and had two other people from different marinas check it with alignment shafts and everything was lined up.

with your drive bolted on have some body big jump up and down on the cavitation plate while you look at the transom at the bottom of the boat and transom assembly.
My bet is there is not enough glass or there is rot down by the drain plug and when you hammer it the whole transom assembly is flexing in on the bottom and stressing your u-joints.

one more for the alignment

Check for rear engine mount sag.
If the rear mounts sag you can still get the alignment tool to show proper alignment by lowering the front mounts. BUT the engine is NOT aligned and will blow couplers and U joints.

how are thestringers? sounds like it might align but things are moving underway.

Had the drive coupler replaced on my Powerquest when I still had it a few years ago. The marina never tightened the motor mount adjustment locking nuts. Idiots! Point is, make sure the engine isn't moving around if you are saying everything else is in check.

When you checked alignment, did you rotate the motor over 180* and check it again. I had a coupler with a warped donut and it would move the engine 2-3" from side to side when I did the 180* thing. I borrowed a good coupler, lined up the motor and ran it for another 6-8yrs without a problem.
Your not forgetting the extended lock washers on top of the rear mounts are you? The go on top of the mount and under the bellhousing mount.. Or in between the two.
Can you watch the engine, transom while coming up on plane, that should reveal if there is any flex going on?? I would think.
What input shaft are you using, with or without grease fittings?
Which coupler did you use, the long snout or short snout, does the coupler side yoke have three orings or two? Or is that all new also?
There is something wrong, they should not be breaking that easy. Keep at it, there is something not right.

Dick

I would bet that either the mounts or transom are flexing under the torque. You need offshore engine mounts if you don't have them. Transom could be wet and flexing as well.

[QUOTE= I borrowed a good coupler, lined up the motor and ran it for another 6-8yrs without a problem.


[/QUOTE]

Dick, remind me not to loan you anything I might want back.:eek::drink:

Not to overlook the obvious but do the drive rams have the correct stops in them and trim limit switch adjusted to prevent u-joints from binding? This was part of a swap from Bravo to Bravo XR.

+1 If the transom isn't thick enough (2"+ something) the driveshaft would bottom out in the crankshaft and put a huge stress on the u-joint.

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everytime I fixed it I put a new coupler in just to be on the safe side because I didnt know what was causing it to break. I just checked the stringers and the transom both are solid and didnt see any flex in either of them. Both motor mounts are solid and no movement. Everytime it broke I was just cruising along about 60 or so but not under any torque or anything. What do you think the possibility of maybe the flywheel having a defect with either the coupler mounting holes or just the casting of the flywheel itself ????? I am running the Dart Big M block now compared to the GM block I was running in the old set up. Does that block have different specs or need to use different parts ?????

If you can put the alignment tool in and out with 2 fingers, alignment is ok. When you say you replaced the whole motor, is the flywheel housing new. The new rear mounts don't require the lock washer type spacer on top of the mounts like the old ones did. If they put the new engine in without knowing this you would have an alignment problem. But alignment problems usually are compensated for by the rubber coupler, which should fail before the u joints. Also are you replacing the entire u joint shaft and yoke complete or just replacing the joints. I would replace the entire assembly, not cheap but these are not like the old joints that you could smack in with a hammer.

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Each time it has been new from mercury shaft, u joints, ect.

http://www.offshoreonly.com/forums/g...p-coupler.html what about something like this causing your problem???

fixx
 

you replaced several gimbal's,couplers and ujoints..the aleignment is spot on,, my next strp would be to start looking into the drive.their may either be a bearing starting to go bad then locks up after a few hours of use or mabe a broken tooth off of one of the gears getting jammed wher its not soppose to be and locking up then shering the ujoint..i had a volvo do this years ago and it turned out to be the drive..

If the alignment is right, then the hull as it is is junk, stringers and or transom flexing under power killing the parts....just like anything else when that boat was built they never intended it to handle that amount of power...not much extra built in...no different than sticking a big H/P engine in a street car and wonder why the rear expired...you may run without hatch, and have someone watch the engine for movement under power..transome flex going to be tuff to see. good luck, Rob

Payton,
I guess I left a little of the story out.. after I aligned the motor, I pulled it back out and put my old coupler back in.. then ran it for 6-8yrs.. and Yes I did return the borrowed coupler. :)!
Bowtie, I did not realize that they eleminated the spring washers on the new mounts.. That is a cause for confusion. My bellhousing and transom plate are from my old 88 checkmate. Good point to remember when mixing and matching.
Twin Spins, thanks for that thread. I was talking to Goebel about things and he told me of his problem with the coupler/inputshaft. I have heard of other engine failures due to that issue..
I would suspect that if the drive was causing a problem it would have self destructed by now.. Besides if he put a whole new input shaft in, the drive would be opened up and you would see something. Not that something can't be binding up while cruising, but I think the drive would show signs of self destruction.
I know of one boat that had Stellings boxes and the bearings inside were not aligned properly.. they snapped the splines off the coupler yoke, on both drives.
This is a tough one.. Just a thought, maybe you could fasten a rod to the engine, say on the valve cover bolts?? At the end of the rod tape a magic marker on it, just touching the transom. If it moves you would see a mark. If the distance got closer, it would push the marker on the rod.. Kind of crude, but it may tell you something. If there is flex in the transom, I would think the highest stress would be from getting on plane? What does every one think?
Dick

could he have trim cylinder leaking down,,and letting the drive bounce around while he running,,,that could put it into somekind of bind,,,,i thought i read someone else had a problem like that????

You don't start the thing with the drive trimmed all the way up do you? Do you boat in shallow areas where you have to trim the drive way up while idling around?
I know a guy who beached his boat a bunch & he always trimmed it up to the trailer position & he broke stuff like you are.

Yeah, I found that out the hard way rigging a new bravo engin package in a SeaRay last year... Had me scratching my head for a few minutes.... :drink:

I found out the hard way also, installed new mounts into a flywheel housing and didn't read the little piece of paper that came with them. I don't know how many rear motor mounts I have pressed in over the years so why do I need to read directions on doing that? Now I find myself reading those little notes.

You say you replaced the input shaft to the drive, but did you replace the input shaft to the drive? That would be the one that gets the pinion gear mounted to it. If the yoke is tweaked you would have serious stress issues on the cross upon assembly and then much worse in operation. I highly doubt a transom or stringer issue as you would need 15*+ flex to approach failure. The boat would be on the bottom long ago.

I think he said they replaced the whole shaft. If it is the new style, then he shouldn't have to worry about binding the ujoints, because of missing spacers in the trim cylinders. I am not sure, but I think that is only needed for the old style XR/XZ ujoints. I have seen them crack a yoke if trimmed up too far. Shouldnt be an issue with the new style. But then again, you shouldnt run them in the way up position.. as Jason said.
This is a tough one, any pics of the damage?

I like the something binding in the drive theory.