Engine/Transmission (1998.5 - 2002) Ever Break a Flexplate?

[GatorRam]

Was driving on I-75 today, about to get on the off-ramp and started to feel a rumble and then a burst of noise. Engine was still running but there was a clanking sound and NO power transfer. I had enough momentum to coast to the first gas station and the truck quit. When I tried to crank it back up you could hear the starter spinning along with a clanking sound and the engine would not turn over. After a quick phone call (thanks John) and closer inspection it was revealed that my flexplate was trashed. After talking to a few people it was thought that when I was getting something fixed recently that it was possible that the TC was not bolted up properly. There was also concern that a heavy billet TC cover could be to blame. The power that I make is definately not the highest in the world and I know there are a ton of people making more than me and not breaking it and they are on the stocker. So what gives. Is there someone\thing to blame besides me? I mean, I accept responsibility because I bombed my truck but I don't sled pull or drag race and was driving towards an off-ramp with the box on 1X5! Why would it break then and not on a higher level? Well... either way I'm stuck now having to pay for the transmission to be jerked so I can put a new flexplate it and then I have to drive it up to where they did my transmission for them to pull it out again and figure out why a four-month old performance transmission is blowing through third gear (previous problem). This isn't fun anymore. If anyone has any input on this it would be much apprecieated.



Sorry to vent,



Adam

 

[Rob Thomas]

I have heard of several broken flex-plates, and at least one was caused because one of the two dowels between the trans and the block were missing (due to an installation error, since they can't simlpy fall out after they are bolted together).



Good luck, Rob

 

[Ray Torresdal]

broken flex plates

Not uncommon - I saw several on my last visit to Goerand Bros.



Ray

 

[Huff N Puff]

The most common reason a flex plate breaks

is misalignment of: bellhousing to block,converter mounting pads to flex plate,front pump bearing problems. Or have it dynoed to make sure you're not making toooo much torque. Only fix there is to back of pressure of right foot against the throttle Merv

 

[ntillm01]

I'll go with Rob and Huff on the misalignment of the trans and engine being the reason for any flexplate breakage. They are incredibly strong in the twisty direction, but misalignment in the flat direction causes stress, fatigue and cracking of the metal. Too much torque from the engine would shear off crank bolts before the flex plate, I think.

Check (or have them check) the dowel pins for sure. I've seen them still in their hole, but pushed in too far. It happens when the trans gets "drawn in" with the bellhousing bolts and the dowels are not lined up. Good luck.

 

[DavidTD]

Very Common with these trucks when additional power is added.



Just read this old thread from Nowell.



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=75709



I have seen flexplates break in many trucks. Most of them are raced and shift either with very firm fluid coupling or in lockup and are usually 450hp and up.



Looks like your truck should be putting out a good amount of power. Add the performance flex plate and it will be a perfect match to your billet input shaft.



Good Luck.

 

[DavidTD]

Originally posted by ntillm01

I'll go with Rob and Huff on the misalignment of the trans and engine being the reason for any flexplate breakage. They are incredibly strong in the twisty direction, but misalignment in the flat direction causes stress, fatigue and cracking of the metal. Too much torque from the engine would shear off crank bolts before the flex plate, I think.

Check (or have them check) the dowel pins for sure. I've seen them still in their hole, but pushed in too far. It happens when the trans gets "drawn in" with the bellhousing bolts and the dowels are not lined up. Good luck.

I disagree. I have seen trannys pulled when they were installed correctly and before the new or rebuilt unit was installed the flex plate is inpected. What is found are hairline cracks near the center of the flexplate. When they break this is where they break. These stock flexplates are going from enduring 460 lb. ft. of flywheel torque to over 1000 lb. ft. at the wheels. They are enduring going from a stock soft mushy shift to a firm crisp one. Just too much torque IMO.

 

[ntillm01]

I stand corrected. Thanks for the information David. I'll add that to my mental list of "things to remember" when figuring out why something broke.

In this case, it must have been pretty much almost gone, and the last decel coming up to the on-ramp was the last it could take.

 

[Stefan Kondolay]

As we have a lot of high hp trucks i can tell you that these guys are not breaking flexplates,I know Doug Smith did break one but we discovered when he came to our shop that he was missing a dowel pin. Needless to say, that shop never touched another transmission of ours after that. Mis=alignment of transmission to engine and the weight of the billet covers are what we see breaking these flexplates. If you ever have to deal with a broken flex plate make sure you replace your oem factory dowel pins with a set of new dowel pins, chrysler part # 4429678, you will need 2 of these. They are about $5 each.



I checked with Bill on this and he said most consumers are not aware of this small fact. The converter in the Dodge Cummins Diesel is centered by the flexplate not the crankshaft. The pilot of the converter whether you buy brand A,B or C doesnt matter is 1. 8 inches. The center of the flexplate is approx. 1. 8 but the actual center of the crankshaft is 1. 945, think of it like this, if you had a standard transmission and your input shaft bearing was not centered would you have problems shifting your truck. In other words everything has to be centered properly to make things work properly and last. Guys seem to understand that the pilot bearing is critical to the standards but dont seem to realize the centering of the TC in the automatic is just as critical.



So do not let shops try and convince you that its hp and torque that is breaking these flex plates.



Things to check for when you have a broken flexplate,



Dowel Pins, either kinked damaged or missing dowel pins.

You can check to see if you have a missing dowel pin without removing the transmission, remove the 3rd bell housing bolt from the bottom of the transmission( dont worry the transmission is held in by a lot more than 2 bolts, and insert a magnet, the magnet should grab on to the dowel pin. Since the transmission case and the adapter is made out of aluminum the magnet will not grab onto either one of those pieces.



When the transmission is out , since you have to take it out any way to fix the broken flexplate , the pilot of the TC must be checked for any damages, ie) nics , burrs, or damage to the hub of the TC or the pilot of the TC. If there is any damage , you cannot sand away the burrs, you must replace the pilot of the TC. Trying to sand or file actually makes the odds increase of having a second broken flexplate.



Check your flexplate ID, it shoud measure 1. 8 , since all manufacturers have a plus or minus in tolerances verify the measurement.



More rotating mass is more likely to break an oem factory flexplate . HP and torque have very little to do with it.



Bill has made this very clear when training , the torque converter is only turning the pump, whether you have a 200hp truck or

700 hp truck, it is still only turning the pump.



As for tighter fluid coupling causing broken flex plates





I am sure you were joking but some guys might actually believe you .



transmission guys know the shock of a tighter fluid coupling is felt from the turbine back not forwards. Since the turbine is free floating in oil inside the TC and not physically attached in any way shape or

form to the flexplate it would take one heck of a load to even come close to even nicking the flexplate. And i know the Dodge trucks we are discussing are not equipped with transbrakes.

 

[MCummings]

Originally posted by Stefan Kondolay

If you ever have to deal with a broken flex plate make sure you replace your oem factory dowel pins with a set of new dowel pins, chrysler part # 4429678, you will need 2 of these. They are about $5 each.



Bill has made this very clear when training , the torque converter is only turning the pump, whether you have a 200hp truck or

700 hp truck, it is still only turning the pump.

That's pretty deep for me. But,, the load on the flexplate and input shaft is going through the flexplate?



What part of the TC does the Input shaft slide into? Stator?



So, locking, and unlocking works the flexplate much harder becuase the power is transferred directly from the flex plate to the input shaft, technicly (sp?) bypassing the TC?



Merrick

 

[Stefan Kondolay]

Thanks a lot Merrick, i showed Bill your post and he said it was a good question and that the answer is in the books. Which i might add he threw at me and told me to find the answer and come and see him.



This is what i found from the Chrysler service manual, the input shaft is splined directly to the turbine in the Torque Converter. The only time the turbine comes in contact with the flexplate and the TC cover is in lockup. The stator does not come in contact with the flexplate or the rest of the torque converter itself as it is splined directly to the transmission pump assembly. So according to the dodge manual the stator does not make contact with the flexplate at all.



Even when the turbine is in contact with the front cover of the torque converter it is being held there by hydraulic pressure. The flexplate is protected by a series of damper springs so the actual input shaft when it is splined on to the turbine is actually free floating, not only in oil but seperated from the TC clutch piston by a set of springs. The odds of fluid coupling or high hp causing broken flexplates are so small you wouldnt even be able to calculate it. Like i said earlier, if you had a transbrake that would be a different story.

 

[Floor It]

I want to know what adam finds when they replace the flex plate,I feel that its not from too much HP as stefan has said. I still feel that some sort of installation error has happened.



John