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Discussion Starter · #1 ·
Pulled the automatic transmission out of my son's 2002 325ci. Discovered the triangle flex plate had broke in two sections where it bolts to the flywheel. What would cause this?
 

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2002 BMW 540Ti, 2004 BMW 330i ZHP, 2001 325Ci
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I bought a 2003 wagon RWD ZF tranny with the same thing, also broken TC nose/support to crank. I don t know which happened first. I found a good used tranny at the junkyard.
 

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Not sure if loose hardware, or just metal fatigue is to blame. I haven't seen this on an E46 personally, but have seen flex plates break in the center on other vehicles. As broke completely away from the rest of the flex plate right around the bolts on the crankshaft. One of them was just spinning the outer parts when you engaged the starter and was making an awful sound. The other actually spun and wedged itself back together and still started and drove. The flex was hitting something as it rotated, though, which clued us in to the issue.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Not sure if loose hardware, or just metal fatigue is to blame. I haven't seen this on an E46 personally, but have seen flex plates break in the center on other vehicles. As broke completely away from the rest of the flex plate right around the bolts on the crankshaft. One of them was just spinning the outer parts when you engaged the starter and was making an awful sound. The other actually spun and wedged itself back together and still started and drove. The flex was hitting something as it rotated, though, which clued us in to the issue.
LOL, I saw that 30 years ago on a Chevy. Funny s#!t.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Interesting failure and NOT one we've seen before on a BMW. Most usually we see a fracture/stress crack emanating from one of the center mounting bolts. My best guess is that two of the torque converter to flex plate bolts were ever so slightly loose. Over time movement was allowed between the two and a failure ensued?
 

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Discussion Starter · #10 ·
The transmission was leaking fluid below where the converter is. We purchased a used auto trans and rebuilt it, so we hope all issues will be resolved.
 

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My best guess is that two of the torque converter to flex plate bolts were ever so slightly loose.
+++1

The pic shows the plate mounting holes were sheared off at the turning direction. This would also kill the torque converter as the plate remaining "arm" pulling the TC off center and placed a big acentric load on the bush bearing. Some lazy mechanic didn't torque the 3 bolts down properly.
 

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E46 320d touring 2002
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Check this.


 

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2003 330cic, 2003 325iT
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What should the torque be on those 3 bolts?
Automatic flex disc/flywheel to crankshaft - 121Nm (88 ft-lbs)
Torque convertor to flex plate - M10 8.8 45Nm (33 ft-lbs)
 

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Torque convertor to flex plate - M10 8.8 45Nm (33 ft-lbs)
Do you know how much clearance of the bolts to the flex plate holes? With no dowel pins between them and only 3 bolts at 33 ft-lbs, I would add Loctite on the bolts threads. The plate has 8 bolts around the center at 88 ft lbs each, and its outer only has 3 bolts with 33 ft lbs each, and the load torque is the same at the crank and the TC, so each of those 3 outer bolts carries a lot of load.
 

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bit off-topic, was there any logic on using only 3 bolts to secure the tc to flexplate?
Since the heavy TC could move fore/aft as the car accelerate or braking, and so the flex plate needs to be flexible. This probably dictates why it is a triangle/3bolts instead of a disk / many bolts, or square/ 4 bolts.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Do you know how much clearance of the bolts to the flex plate holes? With no dowel pins between them and only 3 bolts at 33 ft-lbs, I would add Loctite on the bolts threads. The plate has 8 bolts around the center at 88 ft lbs each, and its outer only has 3 bolts with 33 ft lbs each, and the load torque is the same at the crank and the TC, so each of those 3 outer bolts carries a lot of load.
If you look at them, they have the heavy micro-encapsulated Loctite on them. Definitely re apply!
 
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