91 XLT AUTO, Flywheel broke/cracked repeatedly.

[jfirewind]

About 6 months ago, my 4.0/A4LD developed a vibration mostly at idle, this continued for some time until there was a loud metal on metal noise when starter engaged ring gear. maybe a week later, I come out of work at the jiffy lube I was running, and the starter spun and kicked out, but would not turn flywheel. the ring gear was good enough, i removed starter to look at flywheel, and it appeared to have spun on the crankshaft, as if the motor turned but the flywheel/torque converter did not. ther was a crack around alol of the flywheel bolts, and cracks extending outward from the center. the center section was also bowed/bent.
I believe the vibe was due to the fly/torque conv. wobbling causing an out of balance situation. , also not alligned with the startor pinion.
I then pulled the motor because It was due for an overhaul due to cracked heads, leaking valve stems, worn rocker arms/pushrods that sung that "ticking song", even though pulling trans was eisier. was reluctant to pull trans due to the 2 previous builds it's had, didnt want to mess with it.
after re-installation of emgine assy, started 1st try, havent touched since. for the first 1,250 Mi, no shakes, noise, or broken flywheels. after ~1,300 Mi, the subtle vibe at idle returned. it only took 3 days for it to be wobbling so bad the starter almost wouldnt mesh up w/teeth. and also serious vibes at all revs/idle. so I parked it to save the cost of a tow.
I then removed the starter and saw the same damage to the flywheel, it was running when I removed starter, and I observed the flywheel/torque conv. wobbling in, out and side to side. the flywheel-T.C. bolts were tight and I'm stumped.
i rely on this vehicle, today I began to pull the tranny, but simply dont want to repair untill I find an underlying cause.
I need a new flywheel, possibly the fly/crank spacer, too.
the T.C. I reinstalled 1st time was a rebuilt unit installed at the last trans overhaul, 50,000 miles back. trans seems AOK.
trans shop says the fan on the eng. may be out of balance causing the breakage due to harmonics, but I dont believe that (it's mounted on the W/P)
my friend who buids race motors says the harmonic bal. could be bad, but it seems AOK to me.
I believe the Assembly of T.C and flywheel may be out of balance itself causing problems at revs. Make since?
It's possible the flywheel and T.C. were not marked prior to removal. even though a new wheel was installed.
I've been told the crank bolt pattern, or torque conv. bolt pattern are odd, allowing only one possible alignment. is this true?
what are the common generic causes of this problem?
I'm Stuck, please help!
Thanks A million .
J.S.S.

 

[jfirewind]

please help please Jfirewind@peoplepc.com is the contact for this. thax, J

 

[Big E]

I too have had this same problem. I bought a reman engine from Marshall engines. This engine has less than 30K on it. I was wheeling and broke the output shaft on the trans off (alot of R to OD when I was stuck). I rebuilt the trans. I put the trans in. I blew it up again. Realizing this was starting to get kinda heavy on my wallet I opted for a reman trans. I installed the remain trans. I was going to work and about half way there *BOOM* the trans let go and shot all the atf under the truck, I was coasting in a big cloud of smoke. I towed the vehicle to my work. I called the company I got the trans from. They sent me a new reman trans. I went to install the trans and found out at this time the flywheel was cracked in the same matter that you have described. But it was not totalty broken.

I have yet to nail down what has caused this problem. After many hours thinking about it, reading about it, and asking various techs I know, I have yet to find anything that is solid as a rock truth why it let go.

I my mind I look at what changed on my truck from trans to trans. I reused the tc when I rebuilt it. But when I bought the reman trans I used the one they supplied with it. So I would have to say in my case I think I had a bad converter. But, something else I was thinking about too. What if my engine had too much endplay. And as I drove the truck the crank was walking back and forth in the engine. This would put more force on the flywheel. But then I got to thinking. Something would have to stop the tc from moving back and forth. The tc will "float" in the trans a half inch or so. If the crank was walking it would have to move a half inch before it would "flex" the flex plate and cause it to break.

So in your case it seems to me that you kept using the same tc. So inconclusion I would have to say you have a bad torque converter. The holes on the flex plate will line up with any hole on the tc. This is one of Fords good ideas, unlike Chrysler which can only be mated one way. <sigh>. So replace the converter and call me in the morning. I hope this helps. Keep me posted. I am not driveing my X any more. I blew the trans up again and am out of warranty. Plus I have a 302 that is dying yo jump in.

 

[JDraper]

One of the things that causes flywheels or flexplates to detonate is misalignment of the engine and transmission. If one of the mating surfaces is damaged, the bell housing is bent,the bolts aren't tight, or there is something wedged between the tranny and the bell housing, the transmission input shaft may not be aligned properly relative to the centerline of the crankshaft. If this happens the flywheel or flexplate flexes, generates fatigue cracking, and causes a failure. It's very hard to determine if they are properly lined up, and sometimes it just takes swapping components to cure the problem.

Not saying this is what caused either of your problems, but I have seen this before in classic Mustangs.

 

[ALYZ1FLR]

Alignment shims.

Most explorers come with at least one or two shims between the lower transmission mounts and the oil pan. Usually if they are left out it only causes oil leaks on the pan and seals, but it could also fatigue the flywheel. The procedure for checking the alignment is in most haynes or chilton manuals. Were yours replaced after the first rebuild? I would also check to see if all the transmision bolts were tight. Good luck.