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Final mounting of 94 amp 12SI alternator

Here are some pictures of my final mounting. I ended up making two version of the upper adapter to work with the stock upper arm. I didn't like the black one as it came out too short to provide a full swing of adjustment for belt tension. Once the lower was spaced and set to align with the crank and water pump pulley I noticed that a 3/16" or so thick flat bar would work perfectly with some tweaking as the extension.

So I made my second upper adapter and shaped it to insure alternator fan clearance as well as full adjustment swing. Once everything was tightened down it is VERY solid! And should be able to use a stock belt. I will double check that later.

Anyway, here goes with some pictures.
 

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Here are some pictures of my final mounting. I ended up making two version of the upper adapter to work with the stock upper arm. I didn't like the black one as it came out too short to provide a full swing of adjustment for belt tension. Once the lower was spaced and set to align with the crank and water pump pulley I noticed that a 3/16" or so thick flat bar would work perfectly with some tweaking as the extension.

So I made my second upper adapter and shaped it to insure alternator fan clearance as well as full adjustment swing. Once everything was tightened down it is VERY solid! And should be able to use a stock belt. I will double check that later.

Anyway, here goes with some pictures.
You better put a large star type lock washer between the brackets because no matter how solid it feels while sitting on your bench it will begin to fold up and loosen the belt when you have vibration from the motor. I have one of those alternators in a box brand new that I never used because I didn't like the way the bracket worked and I went to the trouble to combine an aftermarket bracket with the stock one (welded together) and then had it chromed. It is in the attached picture on the right before I sent it out for chroming. The alternator that I wound up with is 105 amp chrome one and works with the stock bracket.
 

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I planned on finding a star washer to put between them for that reason or tweak the bracket a hair to give it a pivot stop to prevent it from folding if it does. The other option was to go back and fold up another bracket like my first one with the mounting centers farther apart. I will run it and see how it behaves. This wont be on the street, but it would still suck to have it loosen up and lose the water pump rotation in the middle of a autocross course!
 

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Opeler
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You better put a large star type lock washer between the brackets because no matter how solid it feels while sitting on your bench it will begin to fold up and loosen the belt when you have vibration from the motor. I have one of those alternators in a box brand new that I never used because I didn't like the way the bracket worked and I went to the trouble to combine an aftermarket bracket with the stock one (welded together) and then had it chromed. It is in the attached picture on the right before I sent it out for chroming. The alternator that I wound up with is 105 amp chrome one and works with the stock bracket.
Mark is right! What you need is a rigid, slotted three bar mechanism similar to the stock setup. What you have created is a three bar linkage that, with the right amount of vibration and belt tension, will collapse (rotate and/or slide) in the middle and convert into a four bar mechanism.
Not to say that it won't work, but you really have to really lock down all of those pivot points to secure everything.
 

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True, I am and was concerned about buckling/slipping when I set it up. A dowel pin can prevent it hinging easy enough. Or do what my first intent was and make a stouter upper like my first one in the picture, just with the correct center to center spacing on the mounting holes. That may still happen, probably will actually now that I found my flat bar I was looking for in the first place! :pat:
 

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Opel bracket didn't work

Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.

The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:
 

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You could find a rebuilder in your area, maybe they can change the fan for a smaller one. The pulley also looks to be a lot bigger than the Opel alternator has, a smaller pulley would improve charging at idle.
 

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You could find a rebuilder in your area, maybe they can change the fan for a smaller one. The pulley also looks to be a lot bigger than the Opel alternator has, a smaller pulley would improve charging at idle.
The pulley is from the original Opel alternator.
 

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Über Genius
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Discussion Starter · #31 ·
The pulley is from the original Opel alternator.
Do you have the fan from the original Opel alternator?

The F bracket doesn't work because it doesn't have anti vibration mounts.
 

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I've read several of these threads on upgrading the Opel GT alternator. Can someone explain why people are upgrading to higher amperage? Are they adding things to the car that requires more capacity? I have two GTs with original alternators. Both will produce positive current even with everything turned on.

Just asking?
 

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Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.

The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:
There be two different "stock" brackets..
One is aluminum the other aint.
 

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Über Genius
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Discussion Starter · #34 ·
I've read several of these threads on upgrading the Opel GT alternator. Can someone explain why people are upgrading to higher amperage? Are they adding things to the car that requires more capacity? I have two GTs with original alternators. Both will produce positive current even with everything turned on.

Just asking?
With the heater blowing on high, the wipers going and the headlights on, you won't go very long. In this scenario it's a cold wet walk home.

The 35 amps just aren't enough. Not to mention that the Opel alternator is 40 years old and the mechanical voltage regulators are prone to failure.
 
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With the heater blowing on high, the wipers going and the headlights on, you won't go very long. In this scenario it's a cold wet walk home.

The 35 amps just aren't enough. Not to mention that the Opel alternator is 40 years old and the mechanical voltage regulators are prone to failure.
I believe that some Opels came with only 28 amp alternators. They had no problem keeping batteries charged.

If that is happening with your car, you have a bad alternator or voltage regulator.

I ran a test one time where i had everything on, headlights, blower motor, wipers, etc. I shorted across the voltage regulator harness and within seconds the voltage climbed to over 16 volts.

In my opinion it would be better to replace the failed part with a used factory unit or one that is similar from OGTS. BTW, a 45 year old alternator is probably more reliable than the junk being sold today. There is a high rate of failure among alternators and starters right out of the box these days.

Installing large amperage alternators in a GT will require modifications. Wire size issues, amp gage issues, etc. The drive belt and alternator mounting are not designed to handle the mechanical loads that could be produced by a 105 amp alternator charging a dead battery.

Just my opinion.
 

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The stock alt can not handle the extra Mods we add to these cars... electric fuel pump draws approx 7 to 10 amp, electric cooling fan up to 30 amps, electric windows, after market radio. Fog / driving lights. all this drains power from the alternator, when you use up all 35 amps the alternator. Is overworking, low power low voltage. Under powered....That why we use a higher amp alternator to handle extra devices
 

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The stock alt can not handle the extra Mods we add to these cars... electric fuel pump draws approx 7 to 10 amp, electric cooling fan up to 30 amps, electric windows, after market radio. Fog / driving lights. all this drains power from the alternator, when you use up all 35 amps the alternator. Is overworking, low power low voltage. Under powered....That why we use a higher amp alternator to handle extra devices
I can understand if you are using that many options. I am running a redline weber electric fuel pump on my yellow GT. It is rated at 6 amps at full flow. I don't bypass to the tank, so it is pumping very little and consequently using very little amperage.

I haven't had any issues with alternator output with everything on. I'm running the high output lights from OGTS. Very bright lights.

My first car was an Opel Kadett with the 1.1 engine. I don't remember the alternator output, but it was likely quite low. I mounted airplane landing lights on the front. I don't remember the current draw on these but they had to be substantial. I used to drive it for hours at night in Northern Michigan. I never had issues with charging.

My point is that many of these alternator conversions may be unnecessary. We don't need to modify our cars just because we can. If things aren't working, we should first diagnose the cause. Modifications often result in addition issues that then require more modifications.
 

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Opeler
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Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.

The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:
Yep, I tried this last year and ran into the same problem and ended up going back to the "F" bracket too.
 

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In my opinion it would be better to replace the failed part with a used factory unit or one that is similar from OGTS. BTW, a 45 year old alternator is probably more reliable than the junk being sold today. There is a high rate of failure among alternators and starters right out of the box these days.
Yes, buttttt:
We are both cruising around town, and our alternators fail. Yours is original, mine is the GM 105A. Unless you have a spare close by, you are going home on a wrecker. I only have to go a mile down the road to the closest auto parts store, get a replacement, and have it replaced on the road within a few minutes.
The above assumes that you don't continue to drive home under battery power, to not damage it.

Dieter
 

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Just Some Dude in Jersey
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Today I tried adapting the stock aluminum bracket to work with the GM 105 amp alternator that I had. It is from Autozone - a Duralast 1532-6-7 with the 10 o'clock mounting that I've used previously in my GT and Manta with the F bracket. Upon completing the shim swap and some grinding I discovered that the cooling fan on the alternator will not clear the bracket.

The alternator used by the OP is different and does not have the clearance issues that I had. Looks like it's back to the F bracket for me.:sad:

There's something odd about the fan in your pic. It looks as though, in places, it appears to be larger than the housing of the alt. I think I ground the tips of my fan off by eye with an angle grinder on my bench, then to make sure the fan was balanced I held a file or maybe the grinder near the fan blades as it spun with the engine running and got them all evenly balanced.
 
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