Scary failure

[ronniejoe]

I recently experienced a scary failure. While towing my travel trailer, the flexplate that couples the crankshaft to the torque converter failed, leaving me stranded. Here is a picture of the flexplate:

http://www.thedieselpageforums.com/photopost/data/500/medium/IM001981.jpg

As you can see, there are several cracks that emanate from the center out into the large holes. This flexplate had over 262,000 miles on it when it broke.

After installing a new one, I immdiately noticed a strange noise. After a day or two of searching, I finally found what it was. Here's a picture:

http://www.thedieselpageforums.com/photopost/data/500/medium/IM001983.jpg

Yes, that is a completely separated torsional damper. The small piece in the middle is all that was left of the rubber. I found it lying on the floor under the truck.

This happened on April 1 and I had it running again by the following weekend. So far, I don't think there was any internal damage to the engine.

Keep an eye on those flexplates!

[Shikaroka]

Wow!
Yeh, scary is right! That could certainly have gotten dangerous and expensive, real quick.

[Mark Rinker]

I broke a flexplate last year on an older 350 gasser engine. Was sure that it had grenaded internally from the racket...what a relief to find an external cause!

Ever wonder why they call them 'flex' plates??? Do we really want them to flex???

[ronniejoe]

The main purpose of the flexplate for an automatic configuration is to take up angular misalignment between the engine crank centerline and the transmission centerline. This misalignment comes from normal manufacturing tolerances and must be handled in some fashion. The total angle is probably on the order of 1 or 2 minutes. So, yes, we want them to flex, or internal hard parts will suffer.

This is just something that I have never looked at as a maintenance or replacement item (unless the ring gear teeth were stripped). I've learned a lesson from this.

[Robyn]

One of the things that I have seen over the years is that converter rebuilders dont always do a fantastic job of realigning the hubs and pilots on converters when they weld them back together.
I pulled one out of the little diesel Blazer I had because the rig vibrated badly.
The converter pilot was out of alignment with the hub that goes into the tranny by .020" YESSS I wrote that right 20 thousands out.

I have seen many of these in the past as converter rebuilders were trying to get their rebuilding skills up to speed.

Most of the top name rebuilders do a great job on their products but I fear there may still be a few out there that are turning out trash.

This sort of things ruins flex plates and will really rip up the front pump and bushing in the tranny.

The vibrations can be from subtle to enough to shake the mirrors under medium RPM.

I have seen these not only ruin pumps and plates but actually cause catastrophic failures of the input shaft on the tranny as well as the stator support.

Ron was your converter a rebuilt any time that you know of??

The only way to tell if the things are bad is to stick the converter in a lathe with a known good chuck and indicate the pilot and the mounting pads. Any variations in the thing should not exceed .002" especially the hub and pilot alignment.

Been many a good tranny trashed this way.

I have seen whole converters run out radially, wobble axialy and as I mentioned the crank pilot and hub be misaligned too and many combinations of the above.

Years ago I had to yank a tranny back out after a rebuild to replace the converter. Cutomer was not amused at all. This was my first taste of many to come. Learned fast on who to not buy from!! :eek:


Might be a good idea though to pull off the flywheel cover and take a peek at the converter with the engine running and see if it wobbles any at all.

If you can see any wiggle at all I surely would investigate.

Hate to spread doubt but I have seen far too many of these issues and my shop was just a little small town hole in the wall.

Having any extra vibration or stress on a 6.5 is certainly something to make one nervous.

I am not sure of the incidence of flex plate failures in the 6.5 but I personally have not seen one and the plates are fairly tough.

Good luck and glad you are back up and running.

Robyn

[billschall]

Would a cracked flex plate produce a knocking sound? I had posted my issue over in the drivetrain section, but haven't received much response. Odd thing is that it only makes the noise after the transmission is warmed up (i.e.- after driving five miles) I can let the engine warm up at idle and no knock.

[ronniejoe]

Yes, I put a rebuilt converter in it in 2004 at 213,000 miles. There were no noticeable vibration changes when I installed it. However, I am still chasing a vibration since this incident. I have considered a new torque converter and another new flexplate.

[ronniejoe]

Would a cracked flex plate produce a knocking sound?

Certainly. But I don't know how to reconcile the warm up issue just yet.

[Robyn]

Just another little tid bit.

Speaking of the flex plate flexing!!! Under heavy usage such as towing and or 4X4 activity the aluminum bell housing on many auto trannies will flex and give as the torque is applied.

This is the very reason GM went to using all the steel struts from the engine to the lower flywheel cover and on some models the long steel bar that connected the T case to the bell housing on the right side.

I have seen a few T400's that have actually split the bell housing radially .

What Ron was talking about in terms of misalignment from manufacturing tollerances is very close to the mark.
The issue is more related to movement during operation.

You have a fairly long span between the engine and the T case on a 4X4 and a lot of weight in between to bounce around.
The addition of the heavy flywheel cover to all the 4X4s from the late 70's on was to stiffen the bell housing and make it harder for things to move.

Always give me a laugh when I see a newer rig that someone has removed the stabilizer bars and or replaced the heavy cover with a little sheet metal one.

So for all you folks out there that have the liitle tie bars laying in the bottom of your rollaway and or the heavy cover hanging on a nail somewhere get the stuff back on the truck, its just good business.

Be sure to install all the bolts and if the threads are bad use a helicoil.

Engineers went to a load of trouble to figure this stuff out, only because it was needed certainly not because it was cheap.

Robyn

[billschall]

Certainly. But I don't know how to reconcile the warm up issue just yet.

Would it help if I recorded the sound then posted it somehow?

[Robyn]

Ron
I would definately be checking the converter.
Was/ is there any wierd operations as far as the tranny goes ??
If the converter is moving axially it wont be as bad or possibly not noticeable as compared to radial runout where the pilot and the snout(hub) are misaligned.

A quick check can be made by unbolting the converter and allowing everyting to float free.
The converter mounting lugs should all touch evenly without the bolts pulling them in.
If they dont best be finding out why.

I have also seen shops replace mounting lugs when some get the threads stripped or bolts broken off and they dont get them aligned so they are all in the same plane with each other.
This will allow the plate to be tweeked out of shape and then the stresses applied are anybodies guess at that point.

If you detect any oddities in the way the tranny is working I would be giving things a really good look over.

[Robyn]

Ron
Did the demise of the ballancer cause issue with the rubber mounted serp pulley??

Have you run the thing with the serp belt off to eliminate that end of the world??

[ronniejoe]

The pulley showed no signs of any damage. I looked it over very well when I had it off.

[Robyn]

I know its very hard to describe noises or vibrations on a text forum but can you give me a little hint as to where it is and or during what RPM range its most prevalent.

In gear and running only or just reving the engine?? Front, back,

Any strange associated noises??

Robyn

[Robyn]

Ron
I am not sure on the 6.5 if its possible but if your vibrogremlin keeps avoiding capture try unbolting the converter and running the engine.
If the converter will spin free by shoving it back into the gear box you should be fine.


I have never done it on one of these rigs so I am not sure if the converter lugs will clear the ballance weight on the flex plate.

Good luck
Robyn

[ronniejoe]

It can be done on these. That is one test I plan to do soon. Currently, I have my dad's 95 K1500 5.7 gas in the shop. Four teeth off the pinion...

[Robyn]

That sounds ugly.

Rear gears I assume.

Well good luck and keep us posted.

Robyn

[john8662]

Another killer of flexplates is how the plate is torqued onto the crankshaft.

Special care should be taken during the install to torque the fasteners on evenly and to the specified torque in the book.

The only reason I mention that is because of flexplates that are installed with an impact wrench, that tend to be over torqued and will fail prematurely as a result.

Since these engines are externally balanced, another replacement flexplate of nearly the same balance should be used as a replacement.

I have often worried about getting a replacement flexplate to match an engine that I've had professionally balanced using the flexplate that the engine would ultimatly use. The worry comes in with the replacement. During a balance of a 6.2 it took two flexplates to get one that was good enough to use.

I ended up using a Pioneer plate, it was very close the GM. I can't recall the brand of the one that was way out of balance (according to the man that operated the balancing machine).

As for the harmonic balancer, they're mainly close, except the fluiddampner.

Perhaps the vibration you're getting is mount related? Engine or the newly disturbed transmission/transfer case mount.

J

[billschall]

I know its very hard to describe noises or vibrations on a text forum but can you give me a little hint as to where it is and or during what RPM range its most prevalent.

In gear and running only or just reving the engine?? Front, back,

Any strange associated noises??

Robyn

In order to prevent confusion in this thread with Ron's issue, I'll redirect to the thread I started.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=27271

[grape]

damn, that sucks now you have to have the engine re-balanced.

[john8662]

damn, that sucks now you have to have the engine re-balanced.

nope, the flexplates are supposed to be very close. It's just some are better than others, that's all.

If one were super picky, another crank could be selected and matched with a known good flexplate (balanced) and compare the difference to the new flexplate to be installed on the crank balancing machine or other method.

But for troubleshooting the vibration (if all else fails), another could be swapped in for comparison.

A flexplate bolt (just one of them) not tightening down and not bottoming down into the TC due to bad thread can cause a vibration, faught this for years on my 6.2. More like a "groaning" in certain RPM's.

[gmctd]

If the vibe remains in Park\Neutral, index the TC one bolt-hole at a time, noting any change in vibes at each positon - can remove the serp belt to prevent mixed signals.

Should also monitor Cylinder Balance to verify equal injection events.

[grape]

i have 5 flexplates, none of which have weights that are the same lol........

[DA BIG ONE]

Changing out the flex plate at first tranny rebuild is a good idea after seeing what happened to yours................