Hey everyone,

I figured I would add to the flexplate knowledge database here on the forum after... you guessed it... my flexplate grenade-ed itself. I talked to people on Facebook, I read through the forums, and I spoke to Toyota techs. One thing we know is, we don't have a conclusion for how they break.

If you have not heard about a flexplate, it is in our automatic transmissions and is attached to the crankshaft and torque converter in the bell housing of the transmission. The flexplate could be referred to the drive plate or even a flywheel (though not politically correct since a flywheel is what is in a manual transmission). Should you ever replace or install a flexplate, buy OEM only. If you read the article below, someone learned this out the hard way so we don't have to.


Flexplate Replacement PSA

Also, if you don't know what a bad flex plate looks or sounds like, check out this YouTube video:

Engine knocking? Could be a bad flexplate

Back story with my 02 4Runner SR5 4x4... I started noticing a quite and infrequent metallic rattle from the engine area but resonating under the vehicle. This started over a month prior to date of failure. I brushed it off because sometimes the exhaust may rattle but it also would go away for some time or I just wouldn't hear it since I would jump in the car and drive. The rattle is only really heard when you get outing the vehicle and then engine is still running. Fast forward to last week and i was hearing it clear as day when i had the vehicle idling. Something was wrong and it wasn't from the cold weather. I diagnosed it as the flexplate and said I'd take the inspection cover off on Sunday before leaving for a drive from Wisconsin to Toronto, Canada today (Wednesday). Well on Friday, it failed and I rolled to the side of the road.

When the flexplate fails, your motor will run while it is on, but it doesn't sound good because you have broken metal in the bell housing. Pro tip, shut that sucker off. You also will not be able to start it back up and when you try, it will also sound nasty, real real nasty.

In my case, the flexplate separated in two parts. One part was bolted to the crankshaft and the other was bolted to the torque converter. This is a pain to remove like this - FYI. When the bell housing was removed, I found DIRT in there. This might have aided the flexplate failing by maybe adding something that shouldn't be in the mix to a moving part. Do yourself a favor if your flexplate is good, CHECK YOUR INSPECTION PLATE and consider adding some gasket maker to it so it helps seal crap out! I believe this may have helped it go, and that was a consensus by some. I didn't best to remove most of the dirt that I could so hopefully it's good. But adding a lot of engine torque may also aid to this. Like being stuck in mud or deep water and being hard on the motor because your stuck (been there)....

Anyways, here was my flexplate that came out of my transmission. The new one is in and I just drove ~800 miles before writing this before falling asleep.

Attached Images

 

Also, if you have questions about the replacement process of your flexplate, watch these two YouTube videos that explain how to remove the transmission.

Transmission removal - Part 1
Transmission removal - Part 2

You can leave the transfer case on, but it's easier to remove it for more room. If your flexplate breaks like mine, you can pull the transmission before unbolting it from the torque converter since the wheel will spin freely from the crank. Otherwise have a friend hold the crank while you unbolt all 6 bolts from the torque converter.

Also, some of the steps of the removal video can differ for just sliding the transmission back. But you want to disconnect the trans cooler lines from the radiator and all electrical connections from the trans/transfer case including the wiring loom that is bolted on. This way nothing is snagged. Also the dip stick tube.

Ill make a bold statement and say bad egine and transmission mounts, yes the bell housing is bolted to the engine but the bell housing is only bolted on the top portion of the housing. there is a large enough moment introduced into that input shaft of the transmission which causes the TC to apply a force that isn't directly centered through the flexplate.

And you can see the main mode of failure is straight shear. Which honestly is probably caused by fatigue. The flexplate can only withstand so many cycles with a new force introduced that isn't through the center of the flexplate. Ie, fatigue , there is a finite number of cycles it can take at a center level of stress before it ruptures.

You also have to think too, the TC is way thicker than the flexplate so the TC has way more leverage on the flexplate than the flexplate has on the TC.

Keeping the transmission and Engine mounted on good mounted would be the only reason I can think of failing like that. Or maybe the bolts on the flexplate are coming lose but the locktite that so chances are slim.

Good thread though. Sorry that happened glad to hear it's back in the road

Sent from my Pixel 3 XL using Tapatalk

I can't fathom how a little amount of dirt is going to cause a flex plate to shear like that.

I'd venture to guess it was cracking and then eventually sheared in half.

Like STI said, “excessive run out”(Not good alignment of engine shaft and tyranny shaft) caused that. Either through flex of the engine/transmission alignment, or worn torque converter or transmission input bearings, or........,

Hopefully in the act of replacing the flex plate the root cause of its demise was resolved.

My '02 has had a ticking noise at the front of the bellhousing since I purchased it (verified by automotive stethoscope) that is loudest after starting the vehicle, particularly after driving ie restart after getting gas. The noise is somewhat inconsistent mainly making 1 tick per revolution of varying volume, but it may skip 1 or more ticks at any given time, and it gets much quieter (though still always present if you listen hard enough) after running for a couple minutes. My presumption is that my flex plate it cracked, however the symptoms have only progressed very slightly in 25k miles.

So I need some advise- Should I wait for failure before pulling the trans? Yes, at some point it will presumably crap out and I'll be stuck wherever I am at that time. The other wrinkle in this is that my trans has an occasional harsh shift in traffic that I've kinda been waiting for to get worse so I have an excuse to overhaul the trans while I've got it pulled.


Thoughts anyone?

Personally, I always lean on the side of doing it before it grenades on the side of the road. Depending on where you are, having it towed could get expensive (have AAA?).

Rebuilding a trans is something I've been considering just as a fun DYI project (would that be considered fun?). I've seen many Youtube videos of the auto trans (A340E/F or AW4) tear down and rebuild and it seems somewhat doable for a DYI'r like myself.

There's this too, but it hasn't gone much of anywhere as of yet: DIY garage auto trans rebuild

I've got 100 mile towing with AAA, so not too worried about that side of things, but I do go wheeling and I really don't want to be on a tough trail and have it pick that moment to crap out on me.

Any trans work is going to be farmed out, I don't want anything to do with that.

I won't be wheeling in the winter months, so maybe I'll just see if I can kill it with the new supercharger

IMO, get it fixed now otherwise it could take out other items with it when it goes. Not worth the hassle if it does. In my case, nothing else was broken. We inspected the starter and TC just in case. But you may not be so lucky so best to be on the safe side.

Good thoughts. The trans mount looks great, but I didn't inspect the engine mount. Might be worth a look when I bring it to my shop to have them replace a rear driveshaft u-joint for me in a couple of weeks.

Some believe a bad starter can cause the failure as well. From a visual and hand inspection, both the starter and torque converter look good. They are also OEM and not aftermarket - just like the new flexplate since aftermarket flexplate don't play nice from what I've read on the forums.

I can't either, but you never know. Plus, there could have been more in there that what dumped out. Which was a fair bit. I don't think it is the main cause, but it certainly could have been aiding the failure.

Why would dirt cause anything to crack and shear in half? Dirt is going to cause things to grind down if anything. Vibrations from something is more likely the root cause or manufacturing defects (unlikely).

I'm going to disagree with your bold statement. Engine and transmission mounts by their design are meant to give the drivetrain some movement and insulate the vehicle cabin from the vibrations of the drivetrain.

Once the transmission and engine are bolted together, there is no true independent movement between the two. There are 6 very large bolts bolting the transmission to the engine and there's no way the transmission is flexing without movement also from the engine.

The only thing that makes sense to me that causes these failures is excessive play in the crankshaft output bearing or maybe there's excessive play in the transmission input shaft bearing. Something is obviously causing excessive forces for the metal to fatigue and fail but I don't think it's due to bad engine or transmission mounts.