I have never seen a regulator that gunked up, probably what's jamming the brushes. Soak (overnight) the whole thing in Potassium Hydroxide (Zep Indusrial purple , Purple power, Grease lightning etc), rinse in hot water, then put a tooth brush to it and it should become spotless. See if that restores the spring tension. Dry before install. The brushes can be replaced. They are welded in (soldering iron won't melt it) so drill it out and solder new brushes in. New brushes can be bought from alternator rebuild shops.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Ive got Simple Green and its been soaking for about an hour and already some of the spring tension is restored. Soaking and getting it wet wont do any damage to it?

By the picture in one of the earlier posts on this thread the new Bosch V.R. seems to have a good centimeter or more sticking out of it. I Imagine this would compress in as you install it though.

Is the car rendered incapacitated now without the regulator? Im not going to try and start it while its taken out, but what would happen if I did?

Regulator elec components are hermetically sealed so no worry getting it wet. after drying, spray some penetrating fluid in the brushes and work them up/down to get more of the gunk out. If the brushes have sufficient springyness and length, install in the alternator and see if it charges.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

With all due respect, why put that voltage regulator back in when you are just going to have to replace it soon. At about $30, a cheap and easy replacement.

__________________
"Life is tough...it's even tougher if you're stupid." John Wayne


Dave
Pawleys Island, SC

'79 300CD

Just to see if the regulator was the culprit and whether it was a brush contact problem. If the brush length is under spec, then I would replace just the brushes ($4 or so)

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

If I go to the trouble of removing one, I just install a new one and keep the old one as a spare.

You need a new volatge regulator. i wont even keep that as a spare.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

But if you do not install the old one, you will not know if you have a good spare!

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Funola, I would respectfully say that I think you are making more of this issue than necessary. Throw that old piece of junk regulator in the trash and put in a new one. You won't need a spare for a long time.

__________________
"Life is tough...it's even tougher if you're stupid." John Wayne


Dave
Pawleys Island, SC

'79 300CD

I am trying to save him some work. Some would say "put in a new alternator" and be done with it but that is a much bigger job. If he has a new regulator, I would say put it in. But he does not, so for diagnostic purposes, I suggested putting the old one in to see if it charges. If it does charge, it was the brushes not making contact. The electroinic components in the regulator do not wear out like the brushes. Putting the old regulator in takes minutes.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

In my case, I replaced the VR and it did not solve the problem. My problem turned out to be a corroded wiring connection at the alternator. I assume the the VR I removed would still work in an emergency (road-side repair), so it is still in my trunk. If the old VR is suspect, toss it.

Yes, do not forget about cleaning all the connections of the alternator

1. the 3 pin plug
2. the spring leaf electrode in the alternator (scrape it clean with a flat blade screwdriver) and it's corresponding connection on the regulator (scrape it clean also).

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

In my case, the 3 pin plug was OK but the wiring inside the plastic connector was degraded so the wires were barely connected. I finally figured that out by watching the voltage at the battery change when I wiggled the wires with the engine running.

You have (Or Have Had) a COOLANT LEAK,down onto the Alternator.
(Being blown THROUGH the Alternator? 'Won't know unless you dis-assemble the
Alternator).

That's whats causing ALL that NASTY stuff on/in the V.R.

If you can't get another 10 to 12 MM s Length out of the "Cleaned" V.R. Brushes
I'd not even bother re-installing.
(The New Brushes.On the New V.R., will provide all the Diagnostic Capabilities you'll want.)

Compare previous Bad / Good V.R. Brush length:

Attached Thumbnails

   

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'84 300SD sold
124.128

I think that was also the problem with my old alternator, which I have been nursing along for almost 2 years before replacing it with a 120 amp alternator with lugs so should not have to worry about the pesky 3 pin connector anymore). My alternator would charge fine for a few months then the battery light would flicker. I brought the old alternator to Autozone for a bench test and it tested good so it was likely the 3 pin harness connector that was intermittent.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked