Alternator bracket failure

[HJG]

Evening all

A breakdown.....had to happen at some point!
My car has the standard viscous fan and an auxiliary fan on the front of the rad, which is temperature switched. I have noticed it hasn't been coming on so earthed it and the relay clicks but fan doesn't come on. Got 12V to the fan and it spins perfectly. My thinking is there's something in the wiring from the relay to the fan. Anyway, no bother - take it back to where I keep the car and hope temperatures stay where they should. My car normally runs bang on 210degF on the gauge and has been even without this fan. Suddenly I see the dreaded movement of the temperature gauge needle, slowly but relentlessly rising past 210. There is nowhere sensible to stop so it climbs for a little while longer until I can stop the car and the gauge is pretty much maxed out. At this point, and I should have seen it sooner, the ammeter is leaning left in the negative section. Shut if off and open the bonnet. No steam but the expansion has burped out some coolant. This is when I notice the alternator is completely loose and the belt is doing nothing. That explains the ammeter and also fully explains the overheating since the water pump and viscous are no longer turning and my BB has turned into a kettle. Some roadside bodgery got my bracket back together. There is a redundant hole in the bracket, which is where the failure happened. I was able to use this 'half hole' in each section to run a bolt through with some random washers and a locknut on the other side. This has got me 10miles to home without issue

Now to source another bracket. This failed one says "Mr Gasket" on it. Is this a good bracket or not? Are they supposed to be flat or slightly bent? It looks to me as if it wasn't running true and was likely loading it up in the wrong plane. You will see that the bracket has also cracked on the tension adjustment slot, but managed to get away with this one.
Time for new belt also.

Car is '69 427

Cheers all. Unnecessary story perhaps but sets the scene!

 

[sublimemike]

Good you got home... If you ever encounter this again but your heater on hot and full blast to try and dissipate the heat and keep moving if you can... nightmare ...been there

 

[Chuffer]

That was a close call HJG . Good you managed to limp home.

 

[Oneball]

Nothing wrong with Mr Gasket. They’re part of Holley.

You’re missing a belt. There’s a double pulley on water pump as crank. They’re should be a belt that goes round crank and water pump and a second belt for water pump, alternator and crank.

I also think the steady is supposed to attach to the manifold boss but not sure. L88 below so not the same engine but a BBC

 

[Roscobbc]

Harmonics - happens also with stock brackets.

 

[HJG]

Nothing wrong with Mr Gasket. They’re part of Holley.

You’re missing a belt. There’s a double pulley on water pump as crank. They’re should be a belt that goes round crank and water pump and a second belt for water pump, alternator and crank.

I also think the steady is supposed to attach to the manifold boss but not sure. L88 below so not the same engine but a BBC

View attachment 10444

Thanks, good spot on the belt! If I'd had that belt, I would only have lost the alternator and not the fan/waterpump. Another one for the list.

I need to take some time and get all this properly aligned and see if I can improve it. Will have a spare bracket now at all times.

This is what shakedowns are for. Steadily increasing the radius from my house

 

[Daytona Vette]

I have had it before on a 454 even sheared the head of the bolt going into the Cylinder Head (even a high tensile bolt) everything was correct with the brackets and alignment, happened a few times usually failure to the bracket never knew what caused it till Ross mentioned "Harmonics" as he has above - Doesn't happen now as the alternator has different brackets as the pulley system is now serpentine

 

[Daytona Vette]

The auxiliary fan issue may be down to a faulty sender, wire up a separate switch to be able to also control the fan manually when you want to

 

[HJG]

Thanks all for the shared experience. Decided to go full nerd on this one and got the broken bracket on the microscope at work.
You can see that "Side 1" failed first, there is some fatigue evidence and it looks like corrosion has settled in, suggesting the crack was open for some time. "Side 2" eventually gave up completely and is a fast fracture. The hole is the major stress concentration point in this instance. If I have time I will try a modal analysis of the bracket/alternator to check the natural frequencies and to find out the worst RPM at which are likely to be excited by a V8's natural orders - dominant being the 4th order (firing frequency). Meanwhile, new bracket ordered and on the hunt for new belts.
This bracket will be welded as an absolute worst case spare part.

 

[Chuffer]

Wow ! You have a full on metallurgy experiment going here . Very impressive ! takes me back to my Technical Collage days .

 

[Roscobbc]

You'll generally get an early indication of potential failure simply by observing the effects of resonant vibration upon the bracket (brackets) at various rpm's and whether under load. Bottom line is watching the alternator (or whatever accessory) 'wobbling' about. The GM brackets can fail - its a design fault on certain engine/accessory combinations and just taken 40+ years to manifest itself