Upgrading alternator, should I install a clutched drive pulley? 1991 350SDL
 

I'm planning on upgrading the wimpy 75a? alternator on my SDL with a nice 115a one. VW diesels with 90+ amp alternators have a one way clutch on the drive pulley so that as you shift, etc, the alternator isn't trying to drive the engine. This saves wear on the harmonic balancer and the drive belt. Early TDIs and 1.9l IDI engines have problems with the crank sprocket coming loose / ruining the crankshaft, and putting a clutched pulley on the alt helps mitigate that.

Would it be worth installing one of these on the Mercedes? I haven't heard about issues with the crank bolt / balancer, but it would be easy to do if the VW pulley is the right length...

-Jason

There seems to be problems with those overrunning clutch pulleys on VWs pretty frequently which i think you have seen on TDI club, and i am not sure they were beneficial even when they were functioning correctly.I dont recall any of the people who replaced their failed ones with a conventional pulley having reported any problems caused by them.I would not even consider putting one on my cars,a standard pulley has been pretty much fool proof for many years on many cars.maybe VW needed it as a work around for a bad balancer attachment design but My Mercedes does not need one. Don

If it ain't broke don't fix it!

The alternators on most any Benz ever equipped with one are often good for a couple of hundred thousand miles. My 300E went about 275,000 miles before it gave any trouble. At that p;oint, a $14 regulator with fresh brushes put it back on the road and it now has a half million kilometers without the alternator ever being removed from the vehicle.

Most any other MB model I'm aware of has an alternator of equal quality and reliability.

I don't understand why you need more than a 75 Amp alternator. Do you plan on beefing up the appropriate wiring to match it? Are you sure you're not opening a Pandora's box?

Best of luck,

The alternator upgrade is a good one, sorely overlooked by Mercedes IMO as the stock system discharges at idle when any amount of equipment is on. I've been very happy with the upgrade on my early cars, especially since my '91 alternator only lasted 60,000miles / 3 years and failed in a blizzard. Fortunately Mercedes figured it out in the mid '90s and put on a respectable size alternator.

The over-run clutch is not necessary IMO on the Mercedes, there are several other items with inertia on the belt system and the car is an automatic transmission which doesn't drop RPMs quickly like a stickshift could.

I get to learn something new as I had never before read of a ?clutched drive pulley".

There are many threads about upgrades to alts based on a 115amp (I think) that is fitted to a saab. Have a search.

Your talking about comparing a heavy Mercedes diesel to a light VW diesel. These engines will not benefit from a clutch, especially on an automatic. I've \contemplated removing my clutch on my own TDI if it gave me problems since I have an automatic. But haven't gotten there yet.



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I have had a 143A on my SDL for years without issues. Just upgrade the cable, 2awg is what I have here. 300sel is rocking a 150A.

The rpms not changing quickly on the benz is a good point. I think ill save the spare I have for my Tdi then. Fwiw the height on both is the same.

-J

The rpms not changing quickly on the benz is a good point. I think ill save the spare I have for my Tdi then. Fwiw the height on both is the same.

-J

And yes, I do need to upgrade the alt... 12.5 volts at idle with the lights and air on is not acceptable. Even my lowly 92 jetta, which cost 1/5th as much as the mercedes did, puts out 13.6 volts with everything on, even the 450 watt radiator fan!

Seems to me mine came from a later W140. I also recall the M117 400E had around a 110a unit you could probably steal for hardly anything.

I just installed a 120A on my 300SD

upgrading the cable is unnecessary unless you are adding electrical load to the system. an alternator will not put out more load than is drawn! and if it does, having a small wire will act like a fuse to protect the rest of the car!

My '85 Jetta came with a 90a bosch.
My '85 quattro came with a 90a bosch.
My '91 300TE 4matic with heated everything, came with a 65a bosch.

I am not going to risk a melt down with 25 year old cable to save $30. If you want to with your vehicle, knock yourself out.



My SDL has heated seats, rear recline, AC that works, headlights, wipers, etc. The stock alternator could not keep up for its life. My 560 is similar, it turns accessories OFF as it cannot keep up. Lame.