Busted 3/8 bolt from trans bellhousing to engine. Fix or forget it?

71monacomoparmechanic

71monacomoparmechanic

Member
Joined
Feb 25, 2019
Messages
131
Reaction score
58
Location
Detroit
I pulled the trans off my 71 monaco to install a 2500 rpm stall converter on a 727 tranny. Found one one of the six mount bolts missing. Upon further diag. The diver side middle bolt was missing and busted off. I intend on replacing this engine from 383 to 440 eventually. should I bother attempting to extract the broke bolt as it could cost several hours of time or forget it. By the way thats what happens when you have someone else work on your car.
 
71monacomoparmechanic said:
I pulled the trans off my 71 monaco to install a 2500 rpm stall converter on a 727 tranny. Found one one of the six mount bolts missing. Upon further diag. The diver side middle bolt was missing and busted off. I intend on replacing this engine from 383 to 440 eventually. should I bother attempting to extract the broke bolt as it could cost several hours of time or forget it. By the way thats what happens when you have someone else work on your car.
Click to expand...

The missing/broken bolt puts extra strain the the others and the bell housing for the transmission. If you 383 engine is built and you need the 2.5k convertor for a big cam, I would replace the bolt. PIA, I know, but why take the chance. If this is a Sunday cruiser that does not get jumped on, then it is probably ok as is.

Dave
 
Yea that's what I figured. Better take care of it while the trans is out. Cross my fingers and hope it extracts without too much drilling and heli coil work. I know better but was hoping someone would say otherwise. Six bolts is already not many.
 
I've never done it, but old timers always say to melt wax into it and let that work on the threads.
 
Took the teans back off.. no broken bolt. Chased the thread with tap. But found an uneven mating surface on the block which is a reman 71 block based off a 66 383. I'll probably just put in the 440 after this fun revelation.

20200904_234202.jpg


20200904_234152.jpg


20200904_234144.jpg


20200904_234139.jpg


20200904_234116.jpg


20200904_234104.jpg


20200904_234056.jpg
 
Somebody at the machine shop must have been thinking about what they were going to do to their wife after dinner. That error should have caused some major alignment issues, has the car been eating transmissions?

Dave
 
I have seen that before. It’s really not a big deal. The torque on that bolt is 28 Ft Lbs From the 1970 Plymouth manual. Not the 80 ft lbs that most people put on them.


EDIT, I didn’t print the book, just read what it said. LOL

A9C1FD12-896F-417B-9F8A-76C19B420F49.jpeg
 
Last edited:
413 said:
I have seen that before. It’s really not a big deal. The torque on that bolt is 28 Ft Lbs From the 1970 Plymouth manual. Not the 80 ft lbs that most people put on them.
Click to expand...
^This^ Although it's 30 ft/lbs per the FSM (looked it up in my '70 Chrysler FSM to be sure), and I'll admit to never using a torque wrench to tighten those bolts.

The car has been running down the highway just fine missing that bolt... Correct? It'll be fine with a bolt in that hole. There's enough meat around it to pull the bellhousing to the block without any issue.
 
I really wouldn't be that worried about one bolt missing. Whole torque of the engine is transmitted to transmission via four smaller bolts in significantly smaller diameter. I doubt that the bellhousing connection to the block is the weakest link. Of course it will induce some uneven strain there but unless drag racing with slicks, I wouldn't loose my sleep with it.
 
You could cut a washer to match to provide support around the hole itself
 
I got it all together. Turned out that hole wasn't lined up right. The strange part was the mating surface on the engine has that dip next to that bolt hole. We will see how it works.
 
The car doesn't eat transmissions but had a bit of a vibration. We'll see how it does with the new flex plate and tc. Thanks for all input
 
The alignment dowels are a must exact tolerance than the bolt holes. Put the five bolts, if you twist off the dowels or break the bell housing you have bigger problems. The broken bolt is either bottomed out or cross threaded.
 
You must log in or register to reply here.
Back
Top