Broken Flexplate - again?

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Originally Posted by Scouse

I've never heard of a flex plate failure afterwards. I'm not saying that it can't be the cause,

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I know of at least one other bloke that had a new flex plate fitted and the new one failed in short order - just like mine.

I'll check the records and see how long they lasted on mine - certainly less than 30,000km each, maybe 20K or less.

Ron

The engine is out of the P38A. Tomorrow I strip it to take the heads and inlet manifold to Bruce Davis for working over.

The flex plate is shattered. I'm surprised the car drove at all.

Pics will be taken tomorrow.

Ron

have you done a bit of a ring around to different dealerships to see if they have found an actual cause
or a remedy for this problem.......?


its seems to be common enough.......




it could be something out of alignment.....or out of balance causing it.......
or maybe even the material used.......
there may even be a superseded flex plate available......

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Originally Posted by discowhite

if it were that out of ballance you would feel it through the whole car!
the flex plate shoud only be there for the starter motor. its the torque convertor that joins/drives the lot together.
if the flexplate is cracking ide put it down to incorrect fitment, ie to much play in the bolt holes maybe a bent flexplate, a bur on the mating faces??
something like that??

cheers phil

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Phil, the flexplate transmits drive to the torque converter, not just there to start the engine !

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Originally Posted by discowhite

the flex plate shoud only be there for the starter motor. its the torque convertor that joins/drives the lot together.

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No. The flywheel with starter ring (called the drive plate in LR parlance) is solidly fixed to the engine.

The flex plate is a thin sheet of steel that bolts to the flywheel at the inner circumference and the torque converter at the outer edge.

The starter motor doesn't apply any starting torque to the flex plate.

The photos I'll put up later will explain it all.

Ron

Surely it has either a flywheel or a flex (drive) plate it can't have both

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Originally Posted by p38arover

No. The flywheel with starter ring (called the drive palte in LR parlance) is solidly fixed to the engine.

The flex plate is a thin sheet of steel that bolts to the flywheel at the inner circumference and the torque converter at the outer edge.

The starter motor doesn't apply any starting torque to the flex plate.

The photos I'll put up later will explain it all.

Ron

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Keh??????

you have a flex plate OR a flywheel...

all of the starting torque from the starter motor is applied to the ring gear which is firmly attached to the flywheel if you have a manual OR the flexplate if you have an auto. The flexplate (or flywheel) is in turn bolted to the crank.

What kills flexplates..... lots of things.

1. Over powering the engine and prolonged stall tests.
2. If the torque convertor cavitates it vibrates and will stress the plate (but youve got bigger more expensive worries if this happens)
3. incorrect tensioning of the ring gear or the torque converter to the flex plate
4. any misalignment between the gearbox and engine that causes the TC and flexplate to be misaligned
5. wear of the TC support bearings that allow the TC to sag (again if this happens you have bigger things to be worried about)
6. Age
7. poor machining and deburing
8. poor balancing of the plate and ring
9. Murphy.

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Originally Posted by Blknight.aus

Keh??????

you have a flex plate OR a flywheel...

all of the starting torque from the starter motor is applied to the ring gear which is firmly attached to the flywheel if you have a manual OR the flexplate if you have an auto. The flexplate (or flywheel) is in turn bolted to the crank.

What kills flexplates..... lots of things.

1. Over powering the engine and prolonged stall tests.
2. If the torque convertor cavitates it vibrates and will stress the plate (but youve got bigger more expensive worries if this happens)
3. incorrect tensioning of the ring gear or the torque converter to the flex plate
4. any misalignment between the gearbox and engine that causes the TC and flexplate to be misaligned
5. wear of the TC support bearings that allow the TC to sag (again if this happens you have bigger things to be worried about)
6. Age
7. poor machining and deburing
8. poor balancing of the plate and ring
9. Murphy.

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I've never worked on a P38a, but assuming its the same as in a classic, you have a flex plate with ringgear attached, then a machined boss, then and adaptor plate, the thin bit he's talking off, which the convertor bolts to, as in it bolts narrowly to the plate through the boss, then outwards to the converotr to give it some purchase on the torqued area

I.e the convertor doesn't bolt directly to the flex plate, there is an adaptor between the flex plate and the convertor, the convertor b

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Originally Posted by rovercare

I've never worked on a P38a, but assuming its the same as in a classic, you have a flex plate with ringgear attached, then a machined boss, then and adaptor plate, the thin bit he's talking off, which the convertor bolts to, as in it bolts narrowly to the plate through the boss, then outwards to the converotr to give it some purchase on the torqued area

I.e the convertor doesn't bolt directly to the flex plate, there is an adaptor between the flex plate and the convertor, the convertor b

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yep but you still dont have a Flywheel (as the type used in a manual) and a flex plate...

In the case that your desribing (IF I follow you correctly) you have 2 plates 1. the starter plate thar mounts the ring gear then running off the same boss as the starter plate the flex plate that hooks up to the torque convertor. in which case all the afor mentioned things still apply to the plate that holds the TC.

If you only have the one plate but you have an adaptor ring inserted to assist in distribution of torsional forces the same things apply, but you have an additional chunk of metal that has to be bolted up balanced and aligned correctly.

and with the second setup here any problems from misalignement would be amplified whenever the startermotor was doing its thing.

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Originally Posted by 51jay

Surely it has either a flywheel or a flex (drive) plate it can't have both

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It can and it does.

Flex plate (broken). Inner holes bolt to engine/flywheel. Outer holes to the torque converter. The torque convertor has a spigot which fits into the end of the crankshaft boss - like a pilot bearing.

https://www.aulro.com/afvb/images/im...007/09/164.jpg

Below: Driveplate (Flywheel), engine side. The spikes are the part of the reluctor ring used by the crank angle position sensor to determine engine rotation asnd timing (missing tooth is 30 deg from TDC).

https://www.aulro.com/afvb/images/im...007/09/165.jpg

Drive plate (flywheel from flex plate/torque converter side. Note the wear from the flex late.

https://www.aulro.com/afvb/images/im...007/09/166.jpg