mmb

I have a 1988 Carrera with low mileage and 4 broken alternator belts in the past 400 miles. Belt first broke after some squealing (no surprise, it was old); I had it replaced by independent foreign car garage. Not long after, new belt started squealing again. I thought it was just loose, but it broke and had to be replaced again. About 100 miles later, new belt broke again (just snapped, no squeal), Finally left car with the garage - another belt broke for them on a test drive! They claim to work on a lot of 911s, checked alternator, pulley, shims, etc. and couldn't find problem. They finally called and told me it was the voltage regulator overcharging, causing the alternator to seize up and throw off the belt. Does this sound plausible?? I didn't think the VR feeds back on the alternator.

The problem now is that after getting stranded once too many times, I'm afraid to drive it!! Does it sound like they solved the problem, or should I take it to a Porsche dealer (cringe!) that works on nothing but Porsches to have it checked out? Any other ideas on what it could be, or are they just not putting the belt on properly? I'm desperate!!

Chris57

I think that at this point since the alternator is the only component being turned by the belt I would replace it. What is the history of alternator replacement on this car? They dont last all that long anyway compared to most cars. I have heard that ones from the dealer may be the way to go when you consider quality and price. a porsche independent shop by my shop only installs factory alternators and swares by them. I think the warranty is longer than some aftermarket ones.

autobonrun

Try turning the alternator shaft by hand to see if there is any binding. If so, it could be bearings. If the fan tips were rubbing you could see that so I assume it's rotating freely.

I assume the 86 uses shims behind the alternator nut like my earlier 911. If so, make sure the correct number of shims are used (check yourself and don't depend on the shop to know they are int the right place). How many and where are your shims located behind the nut? The incorrect number or placement of shims could also be the problem.

Other than these items I can't think why the belt would just break.

I've never heard of a VR causing an alternator to freeze up.

ron mcatee

During operation the alternator is seizing up and causing the belt to slip. It doesn't take long for the heat and rubbing to tear it apart. I would go with a new alternator or at least pull it and have it checked. I'd bet that the bearings are gone when it gets hot. Other things inside it may be going bad also.

mmb

Thanks for responding. Actually, when I had it in the shop, they pulled the alternator and said it was fine. I'm sure that if there had been anything wrong at all, those pirates would have tried to sell me a new alternator. I did take it to the Porsche dealer yesterday and they said they couldn't see any problems; the shims were correct, good tension, pulleys lined up. So for now I'm going to take it out close to home when the garages are open and hope nothing else happens. If it's okay for the next several hundred miles, maybe I'll get my confidence back.

You may be right; the alternator may be on the way out, but nobody has found anything wrong with it. If it is going bad, I'm sure it will manifest itself pretty soon. The only other thing I can figure is that after replacing the belt 4 times, those guys at the garage finally figured how to put it on correctly! Thanks.

dvkk

Source a Gates belt. They are the strongest construction I have found so far. What size is it?

scottb

With all due respect, the mechanics at your local Porsche dealer probably don't know the difference between a shim and their backsides! Most dealership service departments are clueless when it comes to the older air-cooled cars.

The safest thing to do is put your own eyes on it. Removing the alternator pulley is not difficult. You should have six shims. If not, then the pulley is too tight and that's likely the reason you're chewing up belts.

It's also not that difficult to pull the alternator. You might consider doing that and taking it to your local foreign alternator/starter rebuilder and asking them to test it. While you have the shroud out, you can polish it and the fan!

theiceman

With all due respect if you can not change your own alternator belt I would not suggest trying to take your alternator out. But I think what you should do is.

1. learn to change your belt and keep a spare in your car ( takes about 10 min to change ) The tools should be in your tool kit.
2. Regardless of how the alternator feels change the bearings. A descent shop should do this fairly cheaply. I pulled my alternator , read the bearing numbers off them, got new ones and took them to a alt shop where they had a press and the guy did it for $30.00. I have a 78 so I am sure my bearings are different.

It is true that an alternator is not designed for 100% duty cycle and a bad regulator could put it at 100% duty cycle but it would boil your battery. The alternator system is under more strain when " charging" as the field effect set up by the regulator is fully active and creates resistance to turning, but holly crap is that ever marginal.

Good luck.