Cracked AX-15 bell housing - causes?

I found out that I had a cracked bellhousing about 2 months ago. The crack started at the starter where a starter bolt had broken and carried on up the case. It was about a foot and a half long and when I pushed the clutch in, the housing would spread apart. It was bad. So of course I swapped it out with a good one.

Now, my "new" bellhousing has just cracked. I got back from a wheeling trip and felt the clutch chattering when I would slip the clutch while driving home. Turns out a bolt holding the bellhousing to the engine sheared and it looks like thats where the crack started.

What could be causing this? All I can think of is motor mounts, although visually they look fine. Trans mount is new.

Any help will be greatly appreciated as I do not want to have to drop the transmission a 3rd time if the next housing cracks. Not to mention how hard it is to find an AX-15 external slave bellhousing...

What engine/trans mounts do you have?

Are you torquing the bellhousing bolts to spec? Have you hydrolocked the engine and attempted to start it?

I have a suspicion my cracked bellhousing was precipitated by attempting to start my hydrolocked motor at one point, and I'm sure the fact that I used "gudentight" torque on the bellhousing bolts didn't help either.

So far so good on the replacement, though.

Engine mounts - stock. Look fine visually

Trans - stock autozone replacement. 2 months old.

I used the "Gudentight" method as well. I'll try to find the torque specs for this go round. Any idea where I can find those? I don't think my chiltons manual has those toque specs.

And no, the engine has never been hydro locked.

This thread has a ton of torque specs having to do with yjs but bell housing torque specs should be pretty close.

http://www.jeepforum.com/forum/f12/yj-torque-specifications-587412/

Is the trans input shaft too long for the bell housing? did different years have different length input shafts? I know when I was messing with swapping a t19 into my old willys there was a certain year t19 with the right input shaft to grab from the right make/model ford truck.

replace the motor mounts anyways, even if they "look ok". thats the most likely cause, engine moving too much with the tailend anchored.
what are you using for a rear driveshaft? i broke a tailshaft housing after dropping the rear end down too hard off a ledge and tweaking a leaf spring..

Bump.

Broke another one. Brand new motor mounts, brand new trans mount. Crack started in the same spot, halfway along the bulge for the starter motor, and went up over the bellhousing, just like last time. Not sure how far it's gotten but it's still driveable and I'm replacing it tonight after work.

I have some theories as to why it's happening and how to fix it.

It's NOT the motor/trans mounts... at least not directly. The rear trans mount barely does anything in torsion, you can grab an AX15 mounted to it and twist it probably 15 degrees back and forth by hand. By that point, the motor mounts are maxed out.

I'm pretty sure it's because the 4.0 as installed in the XJ is ass-heavy, since the mounts are further forward than the center of mass of the engine, and obviously the tranny plus mount is front-heavy. So if you drive quickly over rough terrain, every time the vehicle accelerates upward, the center of the drivetrain (roughly around the bellhousing and back of the engine) wants to sag downward, and every time the vehicle accelerates downward, the center of the drivetrain wants to pull upward.

It's also not driveshafts (I have plenty of slip joint left at full stuff and full droop) and I've only been driving on this bellhousing for under two months, mostly highway DDing and some high speed dirt road rally-raid type stuff, though I never hit the bumpstops hard enough to notice.

edit: here is another guy who broke one the same way http://www.wranglerforum.com/f218/bell-housing-broke-in-half-sorta-261352.html

If Chris can race his XJ that weighs twice as much, with more power, over way harsher terrain, including shatter motor mounts and whatnot on a stock bellhousing and not have it break...

then you're doing something wrong :laugh:

In all seriousness, I'm not sure. Something is definitely off though.

Yeah, I dunno wtf. I know a bunch of jeepspeed and KOH guys use AX15s without blowing them up too.

Might just be shitty luck but what the hell, man.

Always have the dowel pins in, I've tried cleaning the BH mating surfaces, leaving them dirty, torquing the bolts, cranking the shit out of them... none of these are a factor.

Does the bell housing still have the two hollow locator "dowels"?

Yup. I'm always very careful to put them in.

I'd expect that to cause pilot bearing, input shaft spline/clutch disc spline, input bearing, and input shaft drive gear issues though, not bellhousing damage.

This particular one:
Bellhousing to engine bolts torqued to spec
Bellhousing to transmission bolts torqued to spec
Both bellhousing to transmission locating dowels installed (I did a full go-through on the tranny and replaced a handful of parts, so I had to pull the bell.)
Both bellhousing to engine locating dowels installed
Bellhousing spacer/blockoff plate (the thin aluminum one between the engine and the bellhousing) installed, after being checked for straightness. Had to straighten a few spots that were slightly bent
Bellhousing front and back mounting surfaces and engine block mounting surfaces cleaned gently with a brass wire wheel

No cracks were present when I installed it on March 17th.

By a week or so prior to April 19th (judging off the sounds it was making - which I thought was a defective TOB, was angry that I was going to have to drop the transmission again to replace it) it had already cracked at least halfway around. With zero offroad usage and only highway DDing of about 140 miles a day. Mass highways are bad, especially this time of year, but they aren't THAT bad :laugh2:

So, this could possibly be a "loose nut" behind the wheel situation.

I seem to recall Dan Turner having this problem in his jeepspeed for a while.

I could be wrong, but i recall hearing it was shockloading causing it and was fixed by changing from 231 to a 249, where the hydraulic coupler dampened the hits.

Send him a PM here, loose_nuts_enterprises.. and ask him.

Very interesting. I'll definitely have to message him.

I still wonder why it hasn't happened to the new bellhousing in my MJ though, because I've treated that thing ten times worse than this jeep.

Jonnie Walker, I'd suspect that but all the rough treatment (a whopping 70 miles on dirt roads, not that big a deal, I only put it in 4x4 once to cross a washed out culvert) was after it started cracking. It was literally 140 miles a day of fairly leisurely (compared to offroad or dirt roads, anyways) highway driving.

cause rally.

Maybe the bolts should be tightened in incremental stages, and try to tighten the bolts from the opposite sides, so that it's not causing any binding on the housing. That's my suggestion.

Have you checked the input shaft length?

What? Dude, it's a stock input shaft and a stock engine and a stock bellhousing, with a stock clutch inspection cover plate. Why the hell would I?

Again, that'd roach the input bearing and pilot bearing and cause weird binding in the clutch and bad shifting far before it'd break a bellhousing, and the bolts would have been difficult to tighten.

Why would you?
Because you have broken three bellhousings. I dunno, at that point I would try anything.

You might try slamming your blankie in the hatch, ive heard that works sometimes