Cracked Bell Housing

[sapote]

What causes input shaft bearing failure when swapping bell housings?

The input shaft drives a bunch of helical gears which meshed with the output gears. Due to the helical cut, the input shaft is pushed forward when accelerated, and backward when decelerated. Therefore the input shaft bearing is a special 4-point-contact bearing and was shimmed precisely at factory for the pair bell housing and tranny. If swapped with another bell housing, one has to measure and adjust the shim correctly to avoid interference fit that will lead to crushed balls, or too much clearance leading to the input shaft sliding back/forth and hammering the balls. It can die both ways.

This is way I advised people not swap the bell housing when doing the SMG to manual conversion.

[eacmen]

Hmm, if no hands had touched the factory PP then why the bolts are backing out? The proof is pedal went soft and clutch slipping.
Not trying to salvage the bell housing, but install one from other car might cause damaged input shaft bearing, so to avoid the big headache, try to keep the original bell housing.

Interesting. This is the first i’ve heard of swapping bell housing causing issues. What causes input shaft bearing failure when swapping bell housings?

Not disagreeing with you. Genuinely curious.


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[sapote]

Yep it was the original clutch in there AFAIK. 160K miles. The car is "track prepped" so NVH is already terrible...if it has been an ongoing issue that could explain why I didn't hear it. However, the clutch went all at once on the track a few weeks ago, pedal went soft and anything past ~20% throttle and the RPMs would jump. That was the catalyst for replacing the clutch and subsequently finding this mess. I haven't driven it since that happened on track.

Thanks all for the suggestions. I'm proficient in welding steel but don't have any aluminum experience. I'll have my buddy who is experienced with aluminum come by and do it. Good to know it is salvageable!

Hmm, if no hands had touched the factory PP then why the bolts are backing out? The proof is pedal went soft and clutch slipping.
Not trying to salvage the bell housing, but install one from other car might cause damaged input shaft bearing, so to avoid the big headache, try to keep the original bell housing.

[simonnim]

Sorry, read that a little too quickly

[bimmer]

They aren't married to the engine. Tranny replacements happen all the time.

I was talking about bell housing to trans. Not trans. to engine.

[simonnim]

They aren't married to the engine. Tranny replacements happen all the time.

[bimmer]

Yep it was the original clutch in there AFAIK. 160K miles. The car is "track prepped" so NVH is already terrible...if it has been an ongoing issue that could explain why I didn't hear it. However, the clutch went all at once on the track a few weeks ago, pedal went soft and anything past ~20% throttle and the RPMs would jump. That was the catalyst for replacing the clutch and subsequently finding this mess. I haven't driven it since that happened on track.

Thanks all for the suggestions. I'm proficient in welding steel but don't have any aluminum experience. I'll have my buddy who is experienced with aluminum come by and do it. Good to know it is salvageable!

[sapote]

Any suggestions on my options here?

Don’t replace bell housing; weld it.
still has the original clutch?
The root cause is the backing out PP bolts. Not tighten to spec is my guess.

[sapote]

How could driver not hear this hammering noise , especially at neutral.

[sapote]

Not the bell housing fault; either the loosen dowel pins backing out or the PP hit it.

Edit: saw the pin on bottom of BH.

[cobra]

Same thing happened to a buddy of mine, sans bell housing crack. Seems like kind of a sporadic failure that doesn't get mentioned often.

I would also have it welded up and you'll be fine. Typically, welding introduces a lot of residual stresses as the metal cools and can cause warping, but if your welder follows best practices it will be fine, and the bolts will hold it all straight once you install it.

Stop drill the crack before taking it to him. You can also grind a vee in the crack but maybe leave that up to him.

[eacmen]

People swap bell housings when doing manual conversions all the time. I think you can just replace it.


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[FBloggs]

What I would do:
Clean it up with brake cleaner, and take it to a welding shop to have the crack welded.
The bead will probably be on the inside, and/or I could request a weld on both sides.
Then I would use an angle grinder with a cutting wheel, to clean up the protuding beads.
Hopefully the input shaft bearing is ok.

[bimmer]

Went to replace my clutch and after removing the trans I found this mess. Flywheel dowel and a bunch of bell housing shrapnel laying there. There is one crack all the way through the bell housing as well. At first I figured I could just swap the bell housing but then I recalled someone mentioning they are matched to the trans at factory and you should not do that? Any suggestions on my options here?