Loud Bang, something broke, then bad vibration in park or driving

[R8rPhan]

I had vehicle problems on the way home from a customer's house today...

Was going up the steep incline passing lane into the mountain town I live in, and stepped on the gas to pass a semi, and all of a sudden 'bang' something broke in the drive train...

Then the engine was vibrating really badly... Like something in the rotating power train was 'wobbling' or way out of balance...

But I can find no holes in the engine block or pan, so I don't think it's 'inside' the engine.. and after pulling over and then starting the truck, it started right back up, but vibrated badly even at park... Auto transmission still seems solid, not slipping at all, and shifts..

Don't see anything leaking anywhere... Anyway, I was able to drive it the last 12 miles home with my emergency flashers on, going about 20mph..

I'm 'hoping' that a couple of the bolts snapped on the flex plate to torque converter connection, which would cause it all to wobble right there...

But someone suggested to me that it could be the motor mount broke... It makes sense... Man, that would be good news! Way easier fix than the flex plate thing... or replacing the engine or trans (not to mention exponentially cheaper)

How do I check the motor mounts? Would that cause a bad vibration like that whether driving or sitting still?

I put a crow bar between the cast iron exhaust manifold and the frame and lifted, and it seems similar on both sides... Could a broken tranny mount do the same thing? How would I check that?

What am I looking for? What are the methods to test this?

 

[eskimomann209]

**** take a picture of the motor mount. Usually when those go the engine will sag to one side. And the bolts are a little obvious. Look at the engine while it’s running. It’ll almost look like it’s jumping. If not obvious pull nn the throttle a bit. See if it jerks.
If that all checks out look at the trans mount. Maybe the casing of the bellhousing, Those can break. don’t go under while it’s running tho... anything under the truck should be a visual inspection to make sure it doesn’t toss something at your head.

Patience. You’ll find the issue.

 

[Vbb199]

U joint




Wait Nvm you said vibrating at park.

Torque converter?

 

[PrairieDrifter]

There can be nasty carnage internally even if it didn't window the block or pan. Seen it many times, every time a rod is thrown doesn't mean it has to put holes in stuff.

 

[Turbo4whl]

Had a similar incident years ago on my '74 K5. Loud bang, rough running engine. Turned out one blade of the factory aluminum flex fan broke and flew off.

The broken blade took a small chunk of the shroud and then sliced the steel brake line that runs across the top of the frame. The unbalanced fan made the engine shake. I would find it hard to believe your truck would still have the original flex fan as many failed back in the day. But something to check.

 

[R8rPhan]

There can be nasty carnage internally even if it didn't window the block or pan. Seen it many times, every time a rod is thrown doesn't mean it has to put holes in stuff.

I worry about that too... But the 'bang' sounded like it was outside the engine, sounded 'under' the truck... but hard to tell... Engine starts and revs fine.. Actually sounds pretty good... Just vibrates bad... Worse at lower RPMs, but of course, the higher the RPMs, the closer the vibrations are together, so that would naturally smooth things out some...


Engine doesn't seem to 'jump' when I rev it....

 

[R8rPhan]

Had a similar incident years ago on my '74 K5. Loud bang, rough running engine. Turned out one blade of the factory aluminum flex fan broke and flew off.

The broken blade took a small chunk of the shroud and then sliced the steel brake line that runs across the top of the frame. The unbalanced fan made the engine shake. I would find it hard to believe your truck would still have the original flex fan as many failed back in the day. But something to check.

Hmmm... I didn't notice evidence of any shrapnel flying in there.. But it is the stock style fan, and old one...

Another thing on the list to check... Man that would be sweet if that was the problem..

 

[1987 GMC Jimmy]

An improperly affixed engine is hard to miss. More so in a FWD in my experience, but if that was it, it should still be obvious. I would inspect the harmonic balancer (both hub and outer ring) and the flexplate very closely. I agree on not ruling out the internals, but if it otherwise runs well and revs normally, you should be alright there.

 

[R8rPhan]

Had a similar incident years ago on my '74 K5. Loud bang, rough running engine. Turned out one blade of the factory aluminum flex fan broke and flew off.

The broken blade took a small chunk of the shroud and then sliced the steel brake line that runs across the top of the frame. The unbalanced fan made the engine shake. I would find it hard to believe your truck would still have the original flex fan as many failed back in the day. But something to check.

DUDE!

Just went out there and looked... Immediately noticed the shroud was damaged, and lo and behold, one of the fan blades is gone!

Yippeee! Fix don't get much easier that that!

Thank 'YOU'

 

[CorvairGeek]

We had a Big 10 do that when it was fairly new at my family's business. Left a big dent upward in the hood!

 

[eskimomann209]

Had a similar incident years ago on my '74 K5. Loud bang, rough running engine. Turned out one blade of the factory aluminum flex fan broke and flew off.

The broken blade took a small chunk of the shroud and then sliced the steel brake line that runs across the top of the frame. The unbalanced fan made the engine shake. I would find it hard to believe your truck would still have the original flex fan as many failed back in the day. But something to check.

FTW

 

[R8rPhan]

FTW

I had the whole fan come off on my 2001 chevy express 1500..

Had to replace the fan, clutch, shroud, and radiator... That one made a hell of a noise....

 

[R8rPhan]

I'm having a hard time finding an OEM fan...

AFtermarket lightweight flex fans and shroud are gonna cost over $100

Thinking maybe I should look at a dual electric setup as a possible option... Seen a couple on eBay for about $120, that have dual 12" fans and an aluminum shroud..

Any thoughts on this? If I were to go that route, how many CFM do I need? Any suggestions/experiences to share?

 

[Catbox]

My son found a set of Flex-A-Light fans and the controler in the junk yard not long ago.
He installed them and they work like champs.

I have no idea what CFM they are, but when they come on you can feel they are moving a ton of air.
Enough so that the big block in my truck does not have any issue with cooling itself.

I have a set of fans out of a Windstar that was going to go in it as others have had good luck running them on their trucks.

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[Bextreme04]

I would definitely say junk yard it... you should be able to get either a factory fan or electric fans, wiring harness and relays for well under $100