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Transmission mount bushings failure


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Looking for guidance on root cause for repeated failure of Indmar Monsoon 350 transmission mount bushings (Mainly on the port side).

I have a 2009 Wakesetter VLX

Around 30th November 2020 (380hrs) I noticed some fragments of torn soft rubber in the bilge and quickly traced it to mangled lower transmission mount bushings on both sides.

The upper bushings were fine.

This is what the remains of the trashed bushings looked like in situ:

Port: 

https://photos.app.goo.gl/E6WBZjUVtdkpmrp57

Stbd:

https://photos.app.goo.gl/6b2Dg4JhBdsjyeM56

I replaced both bushings with Indmar OEM items on 10th December 2020.

I reinspected the bushings on the 4th Jan 21 at 395 hours and I was surprised to see signs of tearing on the upper part of the port side bushing already (you can still see traces of the green dish-soap used to help press the bushing in) https://photos.app.goo.gl/fxLhR7XMEzbmaBNq5

The Stbd bushing appears to be mostly ok with some minor signs of damage on the upper section 

This weekend past (6-7 March 2021) I noticed that the top section of bushing on the port side has separated completely and when I felt around the bottom edge of the bushing against brass nut and steel washer mate , I can feel tearing there too.

I have tightened the lower nut and washer but I don't have the specific torque settings to confirm so, I have just tightened it until the busing material mushrooms past the washer by approx 1/4"

We surf regularly. I have an Acme 1235 prop, full factory MLS ballast, plus 2 x 550lb rear and 1 x 600lb front, suction-cup surf-gate and a modified hi-lift (downforce) wedge (extra ~300lbs) as per this thread : 

I have watched the bushings when under surf towing power and it seems the port bushing is significantly compressed/deformed (which makes sense due to the loading and torque response corresponding to the direction of prop rotation).

I had a mechanic check the prop shaft and coupling and he was happy that the prop shaft is straight and the coupling aligned without doing a full realignment exercise.

We arrived at one view being, that the additional load was a likely cause of the excessive movement in the mount.

We also discussed potentially changing to a firmer bushing material (e.g. polyurethane) in that specific application (lower port side)

Various other conversations with dealers and distributors have not revealed any new information other than one opinion that even with the additional loads this should not be happening and suggested that something else is wrong or perhaps lower nut/washer may be too loose. (I don't have accurate torque specs for those yet but I tightened them until they mushroomed past the washer by about 1/4")

Main mounts look fine but it it is difficult to see their condition inside.

Has anyone else had similar experience and found a solution or else, have sensible suggestions as to how I may approach this?

Thanks in advance

 

     

 

Edited by tedshred
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5 hours ago, tedshred said:

I had a mechanic check the alignment and he was happy that the prop shaft is straight without doing a full realignment exercise.

The shaft straight and the shaft aligned properly are two different things.  I don't see how the alignment could be correct after a bushing change, let alone after they wear out.

  • Like 2
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Posted (edited)
9 hours ago, justgary said:

The shaft straight and the shaft aligned properly are two different things.  I don't see how the alignment could be correct after a bushing change, let alone after they wear out.

Good feedback. Lack of clarity on my part.

The prop shaft is straight AND alignment was deemed to be Ok. This seems to be confirmed by a general lack of excess vibration at the speeds we often travel (21-32mph). There is some minor play in the Cutlass bearing due to the 440hrs of use but it is "..no cause for concern". 

"..I don't see how the alignment could be correct after a bushing change, let alone after they wear out."

Bear n mind, it is not necessary to interfere with the existing tranny alignment settings in order to press a new lower bushing in.

Edited by tedshred
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49 minutes ago, tedshred said:

Good feedback. Lack of clarity on my part.

The prop shaft is straight AND alignment was deemed to be Ok. This seems to be confirmed by a general lack of excess vibration at the speeds we often travel (21-32mph). There is some minor play in the Cutlass bearing due to the 440hrs of use but it is "..no cause for concern". 

"..I don't see how the alignment could be correct after a bushing change, let alone after they wear out."

Bear n mind, it is not necessary to interfere with the existing tranny alignment settings in order to press a new lower bushing in.

I guess I'm confused.  Your first photo shows the transmission unsupported by the bushing.  Your second photo shows the transmission unsupported by the bushing.  Your third photo clearly shows a flange on the bushing, and it supports the transmission.  I only had to move my engine about 0.030" (0.76 mm) to align it after I changed my strut bushings, but the point is that it was out of alignment before I moved it.

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Posted (edited)
On 3/12/2021 at 11:56 AM, justgary said:

I guess I'm confused.  Your first photo shows the transmission unsupported by the bushing.  Your second photo shows the transmission unsupported by the bushing.  Your third photo clearly shows a flange on the bushing, and it supports the transmission.  I only had to move my engine about 0.030" (0.76 mm) to align it after I changed my strut bushings, but the point is that it was out of alignment before I moved it.

Text fails miserably at conveying nuance...

Maybe I'm missing the point.

I'm not sure what you mean by "unsupported by the bushing"? The images of the failed bushings were captured when the motor is not running. In that scenario, any loading exists due to gravity only and is borne by the main engine mounts and top transmission bushings.  Even if the motor is running, and there is no drive through the transmission,  the load on the lower bushing (as far as I can tell) -for all intents and purposes- will be negligible until the the transmission is generating torque. Furthermore, before I first changed the bushings in November, the port side lower bushing was effectively, non-existent. I have no idea when it failed and hence, how long the problem had been in existence as I wasn't aware of any symptoms.

  1. How and when did you discover that your bushings needed replacing?
  2. By "strut bushings" do you mean lower tranny mount bushings only or both upper and lower? 
  3. Do you know root cause > was your realignment the solution? 
  4. Is the 0.030" that you refer to, at the V-Drive > Prop shaft flange coupling or at the transmission mount?
Edited by tedshred
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4 hours ago, tedshred said:

Text fails miserably at conveying nuance...

...and as luck would have it, it fails both ways!

I have a direct drive, not a vee drive.  The strut bushings (also known as Cutlass Bearings) are below the boat.  My strut was bent when I bought the boat, so I straightened it and changed the bushings.  After I reinstalled the strut as accurately as I could to align it with the shaft, I still had to move the front of the engine 0.030" toward the port side to get the coupler flange parallel within 0.003".  

Obviously, something is allowing motion and tearing the rubber grommets on your mount.  I suspect that you have excessive motion somewhere in your mounts that you need to address.  The engine and transmission have to be supported firmly in order to maintain the alignment with your coupler and shaft.

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I have occasionally found that loose or broken bolts on the mounts that attach to the transmission housing can allow excess play or movement in the drivetrain. 

I would recommend disconnecting the prop shaft coupler from the v-drive, supporting the transmission and v-drive (like with an overhead lift, or something similar), then removing and inspecting the transmission mounts and the fasteners to the transmission and stringers.

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@justgary , Ok. I'm up to speed now! Thanks for taking the time to explain.

I agree that excess movement in the motor/tranny is a major contributor if not, "root cause".

@csleaver A good (and timely) reminder. Thanks

I have read elsewhere on this forum regarding loose/missing mount nuts and bolts.

Maybe 12-18 months back, I found an orphaned brass nyloc nut in the bilge whilst doing an oil change which, for the life of me, I could find no parent. I wonder if this could have been from one of the engine mounts?

I recall engine mount fixings being a stainless bolt/washers and brass nyloc affair?

@both, It also makes sense that main mounts may be a/the culprit as these bear most of the responsibility for engine and tranny support as can be evidenced by their design & construction, with the tranny mounts going "backing vocals" as evidenced by the relatively compliant rubber used in the bushings.

What is also encouraging: It seems that shredded tranny mounts are a relatively uncommon problem in the absence of another issue. I.e. it's not considered "normal" -even in a 2009-vintage VLX carrying 2200lbs plus of additional load. 

I don't have the tools or facilities to lift/support the power plant. Nevertheless, for my own information I'll do what I can to check the mounts including a full visual on the water.

I'll outsource whatever I can't do including ensuring a drivetrain (re)alignment is done also.

Thanks again for the guidance to date and I'll report back when I have more information.

    

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  • 2 weeks later...

When alignment of prop shaft is needed. It can require all four mounts, two engine and two transmission to be adjusted. The only way truly to tell if you need a shaft alignment is to separate the prop shaft coupling at the transmission coupling. Then with bolts removed you put coupling halves back together hand tight or even squeeze together with channel locks or something but leave bolts removed. Insert a feeler gauge between the two halves. You should NOT have any more than .003 of an inch anywhere around the coupling 12 o'clock, 3, 6 and 9. If you have more than the .003 in any of these positions, you have some mis-alignment going on. If you rotate the prop shaft the larger reading will stay where ever it was say at the 3 O'clock position. This may indicate the transmission adjustment may need to be moved to port for example.

hope you get to the bottom of this problem.

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On 3/26/2021 at 2:28 AM, Jason63 said:

When alignment of prop shaft is needed. It can require all four mounts, two engine and two transmission to be adjusted. The only way truly to tell if you need a shaft alignment is to separate the prop shaft coupling at the transmission coupling. Then with bolts removed you put coupling halves back together hand tight or even squeeze together with channel locks or something but leave bolts removed. Insert a feeler gauge between the two halves. You should NOT have any more than .003 of an inch anywhere around the coupling 12 o'clock, 3, 6 and 9. If you have more than the .003 in any of these positions, you have some mis-alignment going on. If you rotate the prop shaft the larger reading will stay where ever it was say at the 3 O'clock position. This may indicate the transmission adjustment may need to be moved to port for example.

hope you get to the bottom of this problem.

Thanks @Jason63 I'll have to get downright methodical on this one and an alignment will be (the final) step in the process. When I'm able, the first thing I'll check will be the integrity of all four mounts. Hopefully this'll give me clarity around root cause. Once I have an update I'll share it here.     

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Well, kudos and points to everyone on this thread and thanks for your input. All of the engine mount fixings (stainless bolts and washers/brass nyloc nuts) were loose. One had lost it's nut and washer altogether (hence the mystery stray I found in the bilge some time ago) and another was on the verge of falling off also. Thanks to years of working on BMC minis and "svelte" limbs,  I was able to reach inside the stringers to hold them whilst a helper tightened them all. Prop shaft alignment hasn't been checked yet. I'll do that next, but a hand-turn of the prop and shaft and a test run seemed to indicate everything was running smoothly with no noticeable vibration.

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12 hours ago, tedshred said:

Prop shaft alignment hasn't been checked yet.

You may or may not notice vibration, but the primary point of alignment is to keep from work hardening the shaft from repeated flexure in a misaligned system.  In an extreme case, you could end up with a broken shaft.  Checking the alignment isn't that hard after you figure it out, so it is probably best to just bite that bullet now and do it.

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21 hours ago, justgary said:

You may or may not notice vibration, but the primary point of alignment is to keep from work hardening the shaft from repeated flexure in a misaligned system.  In an extreme case, you could end up with a broken shaft.  Checking the alignment isn't that hard after you figure it out, so it is probably best to just bite that bullet now and do it.

Thanks for explaining the consequences of a misaligned drivetrain. I figured it would be more serious than just accelerated wear of the cutlass bearing. We're done for this season so I will be adding this to the list of off-season tasks including replacing the damaged tranny bushing.  I know have an service engine code to sort out also... I'll report back here on what I find with the alignment.

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5 minutes ago, tedshred said:

Thanks for explaining the consequences of a misaligned drivetrain. I figured it would be more serious than just accelerated wear of the cutlass bearing. We're done for this season so I will be adding this to the list of off-season tasks including replacing the damaged tranny bushing.  I know have an service engine code to sort out also... I'll report back here on what I find with the alignment.

Excellent, except for the part about your season ending.  I'm sorry to hear that, but it does mean that our season is beginning!

The experts tell us that we should align the drivetrain with the boat in the water so that the hull is in its natural position.  Trailer bunks could deflect the hull and cause erroneous readings when performing the alignment, but I still wonder if this is true.  I suppose it depends largely on the trailer and how well the bunks are adjusted, so I did my alignment at a shallow (and private) ramp with the boat able to float above the bunks.  I still suspect that the hull does deflect while the boat is under way, but we do what we can do I suppose.

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What will happen too if misaligned is premature wear of the prop shaft coupling and keyway. Depending on which one you have, many of the couplings are aluminum (for a reason) the wear happens here and keyway slot will get enlarged and cause play in drive line. In other words--if you rotate the prop left and right, there will be some play where the shaft is rotating but the coupling is not. This will continue to grow until it fails. My engine mounts got loose and happend to me. I caught it before failure but did require a new coupling and to be safe did shaft too.

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7 hours ago, Jason63 said:

What will happen too if misaligned is premature wear of the prop shaft coupling and keyway. Depending on which one you have, many of the couplings are aluminum (for a reason) the wear happens here and keyway slot will get enlarged and cause play in drive line. In other words--if you rotate the prop left and right, there will be some play where the shaft is rotating but the coupling is not. This will continue to grow until it fails. My engine mounts got loose and happend to me. I caught it before failure but did require a new coupling and to be safe did shaft too.

Hi @Jason63 I will be definitely checking the alignment after I replace the chewed port side transmission bushing. Now that the season is effectively over for me here in S.E. Australia, my boat will be off the water for some time while I work my way through the various maintenance tasks preparing for a hassle free next season! 🙏🤞 I will report back here with what I find re. alignments.

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Posted (edited)
On 4/4/2021 at 10:40 PM, justgary said:

Excellent, except for the part about your season ending.  I'm sorry to hear that, but it does mean that our season is beginning!

The experts tell us that we should align the drivetrain with the boat in the water so that the hull is in its natural position.  Trailer bunks could deflect the hull and cause erroneous readings when performing the alignment, but I still wonder if this is true.  I suppose it depends largely on the trailer and how well the bunks are adjusted, so I did my alignment at a shallow (and private) ramp with the boat able to float above the bunks.  I still suspect that the hull does deflect while the boat is under way, but we do what we can do I suppose.

Indeed! as our Season '20 closes, your Season '21 is on it's way!

Re. alignments It feels to me a trailer alignment should be adequate given the amount of movement that would be generated surfing and wakeboarding with 6 adults, an enhanced wedge, a surfwing, 3900lbs of water and 6 adults.  Also, I am not sure any of the workshops I would employ would do it any differently as they don't have the ability to float these boats on-premises.

Edited by tedshred
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