I just put in a Powermaster 200 amp and the rear black "bar" brace that fixes the alternator to the exhaust manifold stud does not fit. I can make one but the alternator seems to be quite rigidly fixed with the two front bolts. Is the rear bar really required?

According to the instructions, it's a grounding bar. My alternator has solid metal brackets to the block so I assume the ground is way good. But I could add a ground strap as a safety.

Just wanted to see if that rear bracket is structural.

Update: checked ground resistance from alternator housing to battery and it was 0.1 ohms. Voltage drop at high electrical load across the same points was 0.081v. I have a very good connection.

 

It's structural, but seems to be unimportant. Mine doesn't fit with headers. etc. Hasn't been an issue for me. I believe they are optional or not included with the official GM serp belt conversion kit, etc. Something like that.

GD

 

Thanks. I checked the manual, they call it a brace. Seems pretty stout without it. Good to know it hasn't been an issue. Makes it 33% easier to R&R the alternator, Lol.

 

Oh yes it is an issue, leave it off and you will have a broken aluminum bracket.
I will break the small ear off sooner or later. Don't ask how I know that.
Find a way to fasten it.

 

Harmonics, metal fatigue, and time. It won't break until you are in the least convenient location, at the least convenient time, when it can do the most collateral damage. Murphy's Law.

 

Trust GM:

They spent an extra, what, $1.37 PER CAR to put that bracket on there. Over a however many year production run of cars using that bracket, that means it cost them $$$MILLIONS$$$. We all know how steeeeeeewwwwwpid GM is, and how their engineers can't design a car, and everything sucks and we can do it better out here in the back 40 under the shade tree by the crick, and on and on; but I can GUARANDAMNTEE you if they thought they could get by without it, it wouldn't have been there in the first place.

Install it.

 

Lol. Love this board. OK, bracket going in. I can see how the tension of the belt torques the bracket and stresses it. I agree with GD in that it probably would be fine for my application but hey, I am running out of "project" right now.

 

sofakingdom is correct, it's there for a reason. The design target for that brace is usually set so that the natural frequency of the system is above either the redline of the engine or at least the above the WOT shift points. So as you're designing the modified brace, keep in mind that the vibration in the alternator (and other accessories) will be primarily driven by the firing frequency of the engine. V8=4 per rev x rev/sec. For your V8, that's probably 300-400hz. The brace is intended to keep the system stiff enough to resist that.
As an example of this, I once had a new boat with a stern drive by a major manufacturer. In a model year redesign, they simplified the bracket system and removed the rear attachment. Someone must have thought they were saving money. At about 3500 RPM it would go through resonance and spit off the V belt. If you reefed on it hard to tension the belt, the belt would stay on the pulley, but the adjusting bracket would fracture about once a year. After a couple of years I found that they had designed a new bracket as a service part to put the rear attachment back in place. Without the rear support, if you hit the alternator with a rubber mallet (gently), you could watch the alternator vibrate. With a rear support or brace, it was very solid.

 

Done. Took a little blacksmithing but modified (well, mangled) the factory bracket.

 

That looks great, I expect it should do the job.

 

Thanks. Your previous post is very interesting!

 

Well, after 40 years working in various vehicle and powertrain engineering jobs, you learn a lot of interesting bits of information.

 

I actually have a similar problem. I recently purchased a high amp alternator from G2 Dynamics. But it only has the two holes to mount it from the front. But nothing behind it to mount it with the bracket. I contacted G2 and they told me that bracket isn’t necessary. So what do you all think?


Nothing to mount here.

 

Yeah my car didn't come with a motor, so looks like I'm going to have to fab one up lol!

 

Dang those are very expensive! Hand built/special order. Yikes. Not sure. If resonance is the issue then the weight of the alternator has a lot to do with the resonant frequency. I would guess that if it was the same weight as the stock one, then yes. If it is significantly heavier, your resonant frequency would probably be lower (RPM) and the bracket would be required. If it is lighter, then I would guess that the bracket MIGHT not be required. The fact that we have had people here have the front bracket break when the rear is not used concerns me. That's my 2¢. It's probably worth less than that!

 

And that’s what I’m worried about. I would be very upset if my alternator bracket breaks. Just something extra to deal with. I’ll have to weigh both of them and compare which is heavier. So others actually have broken the front brackets without using the rear bracket?

 

Also they don’t offer returns or refunds. And it was very expensive. So I definitely need to find some way to mount this up.

 

Looks like the back cover comes off and that might allow you to mount a tab to the housing in the correct area to pick up the factory brace.

 

Yeah, that’s not a bad idea. Maybe I can even have some threads welded to it or something.

 

With that style of alt, if you mount it with both of those through-holes, it'll be fine. That's all they had on the cars & trucks they came on. Won't bolt up to the stock brackets on a 3rd gen.

Totally different situation from a 10SI such as Tootie's or any other that came in these cars.

 

Ok, I’ll give it a go!