I have to replace the flex plate of my 81 300SD.

History:
- car purchased not running
-- engine runs
-- six bolts between flex plate and torque converter sheared off
- previous owner claims transmission recently rebuilt, but has no details
-- transmission looks clean for having 292K miles on odometer
- removed tranny
-- shrapnel in bell housing
-- a few sheared off bolt heads
-- torque converter spins freely on input shaft
-- output shaft spins freely out of park, locks in park
-- fluid is red and free of debris

Questions:
- any tricks to removing and replacing the flex plate?
-- is there a specified tightening sequence or can I tighten every 5th bolt until I've tightened all 12? I have the torque and rotation tightening specs.
-- is there a key or clocking device to be aware of?
- what caused this?
-- bolts overtightened
-- torque converter locked up (looks fine, but what do I know?)
-- none of the bolts backed out intact because there are 6 tips in the torque converter
- anyone got a flex plate for sale?

Thanks,
Sixto
91 300SE
81 300SD

It is very, very easy to fracture the flexplate to torque converter bolts, I;ve done it. I cannot imagine anything else that could shear them off except maybe and starter locking up when the engine was running, in which case the teeth on both flexplate and starter would probably be screwed up.

Please use new flex plate bolts. They are stretch bolts, and cheap enough. No need to repleat this pleasant experience with the flex plate!

Tighten the bolts in a star pattern to the torque spec, then repeat the pattern with the rotation spec. I don't believe there is a key, and on a flex plate it may not matter. The conveter isn't balanaced to the engine, so just put them on.

Starting with the 123/126 chassis, the crank, balancer, and flywheel were balanced separately, before that as a unit. I don't know about the 116 chassis.

I would check with someone in the transmission business about the tranny before I started the engine just in case -- there might be something to shear the bolts off. Check to see if they look pulled apart or ripped -- there should be some distortion on both parts of the bolt if they acually sheared off.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Have you removed the broken pieces from the torque convertor. I ask this as I suspect the wrong bolts were used and bottomed out leaving the flexplate loose to the convertor. This is the only way I have seen the bolts break. Falling out would be a different matter.

The flex plate is only a small triangle of metal on that model. It is not part of the flywheel/ring gear arrangement.

I wouldn't worry about the trans. I guarantee you that if the trans had locked the bolts wouldn't be what gives. There are a number of points internally that would be much weaker. I imagine it was loose and it took a special type of driver to ignore all the noise that occured as it broke one bolt after another.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Does anyone know the tightening torque for flex plate-to-TQ for a 1980 (w116) 300SD? Thanks!