vibration when turning on alpha I

[wruebs]

I have a 96 tompson fisherman with twin 4.3's. Last year I started to get a vibration when turning (and only when turning) under power. The vibration is there whether I'm going slow or fast. It seems to be on the right drive. So I pulled the drive hoping that it was a simple case of bad uni's. But they are good/ no slop. The gimbal is smooth with no rough spots. I had an alignment check two years ago and drive came off with no problem. I also pulled the left drive for a comparison feel. The only difference I can come up with is that the propshaft seems to have more backlash on the top gear (right side).

Now I read a related post awhile back that mentioned preload. I don't understand preload. Does it have to do with the mating distance of the propshaft gear/top gear? Is this controlled with shims? Can I do this or are special tools needed?

Could anyone explain preload, and could it be causing my vibration? Thanks for all replies

 

[Don S]

Re: vibration when turning on alpha I

Bad ujoints is the normal cause.
When was the last time you pulled the drive and greased or checked them?

The ujoints normally go bad because there is water in the bellows. have you checked?

 

[Coors]

Re: vibration when turning on alpha I

I think Don has a sticky somewhere- the u-joints can't be inspected by feel.
You can feel no slop because the needle bearings are resting tight in the grooves they made.
Take them apart.

 

[Bt Doctur]

Re: vibration when turning on alpha I

hoping soon to post a pic of the new style with flat rollers , smooth as silk
but only mild vibration.Good till the blow up.
Never guess on a u joiont. Replacing them is the best option.

 

[Bondo]

Re: vibration when turning on alpha I

So I pulled the drive hoping that it was a simple case of bad uni's. But they are good/ no slop.

Ayuh,.....

I bet if you pull them appart,.... They'll be Beat, with ridges carved into them.....

 

[Haut Medoc]

Re: vibration when turning on alpha I

Another vote for worn u joints......​

 

[wruebs]

Re: vibration when turning on alpha I

Well, I guess I should look at the u-joints. I've had plenty of experience with worn uni's throughout my farming/trucking days and never had bad uni's without feeling some sort of slop. But since I have the drives off right now, I'll take one apart. BTW everything looks like new, and there is no water in the bellows.

Does anyone think I should look into the preload? I am still hoping someone explains preload. I'll see if I can find that thread I mentioned about preload and bump it up.

 

[Bondo]

Re: vibration when turning on alpha I

Does anyone think I should look into the preload?

Ayuh,...... Preload on What,..??

 

[bomar76]

Re: vibration when turning on alpha I

Ayuh,...... Preload on What,..??

Kneudsen Valve.

He is never gonna be satisfied with the fact it's the ujoints, so let him repair and replace the Kneudsen Valve.

 

[Bondo]

Re: vibration when turning on alpha I

Ayuh,...... I just Hate changing the darn Kneudsen Valve....

I think that's even Worst than doing the Bellows,+ Trim Senders,......

I'd probably just hire it out.....

 

[Coors]

Re: vibration when turning on alpha I

This is the one time owning an old OMC is good-no Kneudsen valves.

 

[wruebs]

Re: vibration when turning on alpha I

Ayuh,...... Preload on What,..??

The propshaft/universal assembly is attached to the short yoke and drive gear which engages the driven gear on the drive shaft in the upper gear case. From what I have learned on another site is that there is certain amount of pressure (or distance) in the engagement of these gears. This is set up with shims and torque on the bearing retainer. This is what I interpret as preload.

I guess what I'm asking now is has anyone experienced vibration due to inappropriate preload? According to a iboat member from Australia, faulty preload can lead to said vibration.

I will inspect the bearing pins/cups and crosses this weekend and post back. I'll give you guys the benefit of doubt, but I just don't think the uni's are bad.

 

[Don S]

Re: vibration when turning on alpha I

IF you had a vibration after a rebuild, and a preload had a lot of slop instead of any preload, yea it might cause a vibration. But out of normal wear, preload WILL NOT be your problem.
Get some new ujoints and replace them. Make sure the yokes and center section all go back in the same orientation. Cause when you pull the ujoints out, you will not be able to put them back together in the same wear pattern.
You WILL find grooves in the cross piece of one of the ujoint crosses. I have replaced hundreds of ujoints, and many times could not feel a defect in them, but could see the problem when they were dissassembled.

 

[96lt4c4]

Re: vibration when turning on alpha I

After reading this I feel like I need some new U joints. I had a vibration with the lower unit trimmed all the way down and at cruising speed with the unit trimmed up. In between was fine. I just put the freakin thing back together too.

 

[bomar76]

Re: vibration when turning on alpha I

No big deal, 6 nuts and an e clip, plus a gasket set.

 

[wruebs]

Re: vibration when turning on alpha I

Well I pressed out three cups and the crosses are like brand new, no wear whatsoever. I was going to post a picture but the file was to big. Against my better judgement, I pressed out a cup near the retainer nut and wound up breaking a tab. So now I need to replace that. I'll probably put it back together after I replace the ret. nut and wait for some warm weather to access it further on the muffs. I may have to surrender it to the mechanic and wait the mandatory two months to get it back, fixed or not.

BTW, last fall I checked the run out on my propeller shaft and had .009" Funny thing was I had .013" on the left side. I also have SS props so I don't think those would be out of balance. No hits either. I do have some play in the steering linkage between the drives but no more than before.

Anyways, thanks for all the replies

 

[wruebs]

Re: vibration when turning on alpha I

Don S. I re-read your post. Are you saying that you could have wear on one of the joints but not elsewhere on that same cross? I pressed out one cup on the cross near the short yoke and two on the other. Also, could I swap drives from right to left and see if the vibration transfers? Thanks...

 

[Don S]

Re: vibration when turning on alpha I

IF you didn't break off more that just the tab itself and the threads are still in tact, you don't need to replace it.

Yes, you could change drives, as long as they both run the same direction. If one is a counter rotating then you can't do it.

Yes, I have seen one ujoint bad, of the two in each drive, and yes, just one arm of a cross could be bad.