jwbeck17

Looking for your mechanical expertise and suggestions here. I'm pretty sure my voltage regulator is shot on my '89 928 S4, as I get voltage spikes over 15v and had to replace the battery this summer due to a battery leak. By the looks of it and the service records, I believe the alternator and voltage regulator are original.

While I could just replace the voltage regulator as the problems are usually related to that element, would it make sense to replace the alternator as well, or is that overkill?

Alan

It is impossible to say without testing it - if you have an 'old world' alternator store nearby that can properly test these you can get a good answer. It is likely rebuildable there too and while it may need new rectifiers, bearings etc and a new regulator, this can be much cheaper than a new alternator.

If all you have nearby is an Auto Zone, O'Reilly, Pep Boys etc.. then you have few options but to either try a new regulator alone because its a cheap initial option OR (and later?) consider a full replacement.

Alan

jwbeck17

Thanks for the feedback, Alan. Since it is a lot easier to take of the voltage regulator when the alternator is removed, I wasn't sure if an alternator change would be recommended at this age as a "while you are at it" repair.

I'll do some research on how to remove the alternator, and maybe see if someone can test it while Helga (the 928) is on jack stands.

While a have a few projects for her, the spring can't come soon enough so I can get her on the road and track again!

jwbeck17

Well I guess I found the removal and install instructions!

https://rennlist.com/forums/928-foru...-88-928s4.html

outbackgeorgia

I still have the original alternator in my 87. Three new regulators/brushes over the years. Bearings once. The later Bosch alternators are pretty reliable, no reason to replace if it can be checked out by a reliable Bosch shop. Look for a tractor/truck Bosch repair shop.
Dave

Avar928

Tip: Don't pull the long 17mm all the way out, just enough so that the alternator clears. It'll be shallow but it should be able to rest on the shroud and the power steering bracket. Threading it back in with that lower radiator hose in the way is a major pain.

You could also drain the radiator (blue screw underneath the radiator) and remove the bottom lower radiator hose connection for clearance. Threading the 17mm bolt while simultaneously lining up the alternator is a challenge so having that bolt at least in a position to just be pushed in is a plus to do and will get you 75% of the way there if you can at least get it into the first slot of the alternator. The rest is just minor adjustments to get it to go through the back. and threaded.

dr bob

FWIW, I'd replace the whole alternator as one. I replaced mine with ~90k of gentle driving, and while not worn out, there were pretty decent grooves on the slip rings. If your slip rings are OK, a new set of bearings should go in while you have it out of the car. New brushes come with the new regulator, so you would be good to go. Of course, you get to clean everythin while it's easy and apart. You can use common detergent and hot water on everything, provided you are replacing the bearings. Put the rotor and housing in the toaster oven overnight at 175º or so, to bake out any moisture that remains in the windings.

On replacement, tap the sliding rear sleeve gently with a plastic-faced mallette (small hammer) to pick up some installation clearance. Tightening the through-bolt then draws the sleeve tight again.

New engine ground strap and battery ground cables while you have stuff disconnected. Trust me, it will help with a lot of seemingly unrelated symptoms like the apparent voltage spikes and poor charging. The factory engine ground is available inexpensively from the usual suspects, and the uprated 2ga battery ground strap from most.

supercedar

I had the 15v spikes and just replaced the reg. I still had the 15v spikes so then replaced the whole damn alternator. I wish I would of done it right the first time. My old school alt. shop found no issues with the old one, and did not want me telling him it was faulty
Thomas

PC-85-928S

It seems like genuine Bosch parts are coming with a check QR label on them now.