Going on 3rd Flexplate Any Upgrades?

....besides a 5 speed. (not being rude here)

First one totally cracked around crank bolts. 2nd one, (Omix-Ada 16913.10) hard to see with a inspection mirror and flash light, but see some cracking. .....and the same noise is there.

Before I get another brand to test it out, is there a company that knows about this problem and has corrected it?

Why do they crack?

Are you using the other piece that goes on that you bolt through? It looks like a section of a flexplate has been cut out to be used like a large complex washer?

Yup, and installed correctly, flexplate, flexplate backing plate, and bolts torqued to 105 ft lbs.

Sounds like maybe the torque converter is not square causing a flex each revolution.

From all of the post I've been reading, this is an all to common problem with 4.0's in the 90's. Heck a search on here throws up many pages worth on the subject. With 35 years of wrenching, this is the only ones I've replaced.

Now that I'm thinking of it, maybe the bell housing bolts came loose/lost and is causing the flex. When I replaced the flexplate last time, there was only 3 bolts left, the 2 star head ones and 1 other. I replaced all the old with new grade 8 hardware and lock washers. I'd be stumped if they backed out.

If the TC was not square to the flexplate, that would cause enough vibes to back the bolts out.
Honestly after seeing how thin the flexplate is, I am suprised more folks don't have problems.

If the bolts are backing out you probably had enough of a difference between the trans input shaft + torque converter centerline and the crankshaft centerline to flex the flexplate slightly on every rotation... if that "slightly" is past the limit of elastic deformation (I'm not a materials scientist, so this might not be strictly correct) then the flexplate will metal fatigue slightly at the weakest point every rotation, and eventually will crack.

I never managed to kill a flexplate, and reused several in various jeeps, and I killed two AW4s... I suspect the bolts are where your issue lies, either that or something else is causing excessive flexure during operation. Have you checked to make sure the torque converter snout is not bent slightly? Observed the flexplate+torque converter while it's idling to see if it has any wobble to it or anything?

I figured with thousands of us having the same problem, the aftermarket would have picked this up and come to our rescue. I have yet to find a definitive answer why this happens to so many 4.0 in XJ/YJ/ZJ, heck all Jeep 4.0.

I replaced mine last year, it was cracked 3/4 of the way around. The torque converter bolts had loosened up at one point but i think the real issue was most of the bellhousing bolts had backed out, which is scary but i can see how that could do it (Use locktite on ALL the bolts when you reassembly it!) I looked everywhere for a heavier duty one but found nothing. I got one from Jeep for like $100, seems like very good quality. No issues as of yet.

ALL of this information is from a tech bulletin from ATP-INC.COM and a copy of the link.


http://www.atp-inc.com/Portals/0/tech/10-10.html


When replacing an automatic transmission flywheel (flex-plate) because it was either cracked or completely broken at the center, indicates a problem exists somewhere within the vehicle's power train assembly.
The illustration below is a standard setup of a flex-plate mounted to an engine assembly. Let us pay close attention to these critical areas that may possibly cause failure to the flex-plates.
If a transmission assembly has been removed from the engine assembly, re-installing the transmission plays a critical row on how the bellhousing is mated to the engine. If the dowel pins are worn or the transmission case is damaged, it will not allow the transmission to mate and bolt up correctly to the engine causing excessive movement between the both units. Ultimately, this will allow more than the recommended flexing of the flex-plate. The fix would be repairing the transmission's case and/or replacing the worn dowel pins.
When installing the flex-plate to the crankshaft area, measuring the engine crankshaft endplay is also a critical area that may affect the flex-plate. More than allowable movement of the crankshaft due to a worn thrust bearing will allow the crankshaft to walk fore and aft causing stress on the center of the plate. High mileage vehicles are prone to this condition. The fix would be installing flywheel shims to reduce stress on the flex-plate's center.
Here are other possible causes the will also contribute to flex-plate failure:

• Worn or broken engine and/or transmission mounts.
  
  The Fix: Replace mounts
• A rebuilt torque converter and/or front pump was installed on the transmission during a transmission rebuilt. Rebuilding the torque converter and/or front pump removes metal and increases clearance at the flywheel.
  
  The Fix: Install flywheel shims
• Out-of-balance engine, harmonic balancer or torque converter.
  
  The Fix: Balance engine or replace the harmonic balancer or torque converter
• Worn front pump bushing will cause excessive movement of the torque converter.
  
  The Fix: Replace the front pump bushing
• Failure to install the flex-plate perpendicular to the crankshaft recess area and/or over-tightening of the flex-plate bolts, tightening the bolts in the in-correct sequence.
  
  The Fix: Install the flex-plate correctly to the crankshaft flange. Tighten the flywheel bolts to manufacturer specifications and in a star pattern sequence.
• Sudden shock to driveline-"neutral drops" (high engine r.p.m. in neutral and then dropping into drive), racing etc.

The most common applications that experience these types of flex-plate failures are high-mileage trucks (pick-ups, 4 X 4s, and vans).
Replacing the flex-plate is an expensive, time-consuming job and we all want the job done right the first time.
Remember! A broken or cracked out center of the original flywheel is a big warning flag that a problem exists and if the problem is not fixed, failure to the replacement flywheel will more than likely follow shortly.
Visit our website at www.atp-inc.com for updated product information and Tech Direct® Bulletins.

My motor mounts were really beat up. I replaced them last week with Energy Suspension ones.

http://www.naxja.org/forum/showthread.php?t=1081504

Locked98GC said:

I figured with thousands of us having the same problem, the aftermarket would have picked this up and come to our rescue. I have yet to find a definitive answer why this happens to so many 4.0 in XJ/YJ/ZJ, heck all Jeep 4.0.

Click to expand...

Is it really that common?
Between me and my buddies we have 5 xj's all 4.0 Autosand have never been aware of this or had an issue.

Hopefully i can remain in the dark on this one ..

I know of 3 XJ's in my local club , including mine, that have had them go bad. There a bunch of threads on JeepForum about this too. Not common but it does happen, I'm sure lots of wheeling doesn't help. Bad motor and trans mounts were probably contributing factors as well. My motor mounts had 180k on them and had shrunk a good 1" or so. I went with Brown Dogs.

thanks for the info I'm actuallly already doing my motor / trans mounts.

I think I'm going to recommend to my buddies they do the same.

hopefully that will help us not join the flexplate replacement club.

Yeah pulling the trans really blows, it's heavy as f**k and even worse getting it to bolt back up again. That's not to mention the reverse torx bolts they totally suck!

robsjeepxj said:

Yeah pulling the trans really blows, it's heavy as f**k and even worse getting it to bolt back up again. That's not to mention the reverse torx bolts they totally suck!

Click to expand...

I don't think I'll ever use the E12 socket again, but it's in the roll away, somewhere.

Going to order another flexplate today and see what happens and pay attention to the little details.

After my last experience with E12s I only use it to take them out. I put in a washer, lockwasher, and 2" grade 8 3/8 bolt to replace em every time... that stackup ends up about 1/8" longer than the stock bolt and fits fine.

So got around to replacing the flexplate yesterday. Everything was still torqued/tight. 2 areas of concern, 1 the motor mounts and some really hard crud buildup on the tranny case mounting surface. I have to assume this formed when the tranny came loose the first time. It looked like oil but upon further inspection it was really hard and I scraped it off. 1/32" of uneven surface would have caused an unsquare surface. Here are pictures of the 2nd flex plate. There is nothing wrong with the OmixAda brand, just installation problems I did not address.

Because it was wobbling out of round, the CPS was hitting the flexplate in this area. CPS still good.

That much debris/corrosion on the bellhousing mounting surface could definitely cause an issue over time. I think you've probably solved the problem at this point... guess you'll know in a few months.

It's November and haven't had a problem.