Flex Plate Failure

[HDRider]

I puled the engine/trans from the 77 coupe Monday. The center of the flex plate had completly broken away. It failed in a circle right at the edge of the spacers. Looks like it cracked and jammed in place for a while and eventually wore the iregularities off of the cracked circle allowing the the crankshaft and the plate to move (or no) independently.

Has any one seen this problem before? I have ordered a new flex plate but if there is some sort of fix to prevent this from happening again I would sure like to hear about it before I put it all back togeather again.

Edward Hamer
Petaluma CA

[Workshop Help]

When you say 'flexplate', do you mean this is for a car with an automatic transmission? In this neck of the woods, cars with standard transmissions use a 'flywheel'.

Mildred Hargis

[HDRider]

Yes, it is a Borge Warner type 65 automatic 3 speed transmission.

A flex plate is similar to a manual transmission flywheel but is much thinner. The torque converter bolts to it and acts as the mass that the flywheel usuually functions as.

Edward Hamer
Petaluma CA

[Cobber]

<font size="2"><font face="Comic Sans MS">Yes I had the same problem with a 71 AMC/Rambler (they were branded Rambler here in Oz) Matador This had The 360 V8 and a Borg-Warner model 12.
The flex plate failed exactly as yours, in a circle around the bolts that fixed the flex plate to the crankshaft.
The odd thing was that it would happily drive at low RPM but start to slip as the revs increased but would drive again if you dropped the revs.
I pulled the trans and didn't notice the broken flex plate because it was hidden behind a small thin plate held by the bolts.

Thinking the trans was buggered, I rebuilt the trans and apart from a bent selector valve in the valve body (I've absolutely no idea how you could bend one of these! ) There seemed nothing much worn and nothing broken.
I reinstalled the trans only to find it still slipping! [:(!]
It was when I ripped the trans back out the I found it!</font id="Comic Sans MS"></font id="size2">


"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.
76' Ford F100

[HDRider]

I am really curious as to why it would fail in such a manner. I bought the car about 6 months ago. The man that I bought it from had the motor rebuilt about 10,000 miles ago so one would think that the flex plate was OK then. Since the rebuild the car has been driven by his wife and then mine, nether of whom seem partucularly hard drivers.

I could understand it if the motor had 300 HP but at 90 HP you won't think that there was enough power to really damage anything.

The only thing that I could think of is that during the reinstallation of the trans they bent the plate. There is some wear on one side of the spigot bushing which seems like more wear than would happen during the short time that the motor ran after the break.

Edward Hamer
Petaluma CA

[Cobber]

<font size="2"><font face="Comic Sans MS">Well in my case I'd had the car for some time and duing that time it worked fine. It broke suddenly without any obvious cause.</font id="Comic Sans MS"></font id="size2">


"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"

80'Triumph TR7, 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
'98 MG-F, 69'Ford F250.
76' Ford F100

[HDRider]

An update.

After some research it appears that the last time someone assembled the motor they swapped the flexplate spacer and the lock ring. They look the same but one is about .020" or so thicker than the other. That would have placed preload into the plate which, while not a lot, could have caused the failure.

Edward Hamer
Petaluma Ca