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Servicing a Denso

15A

World's Oldest Brewery
Joined
May 7, 2004
Location
OH-MI....just like it sounds
I asked about how to service regulators or brushes awhile ago and got no response, so went digging myself. Found these are some of the easiest to rebuild out there.

A long time alt rebuilder on another site posted his tests as to the most efficient alternators out there. Densos were one of the highest, and Bosch one of the worst. A 100A Bosch at idle will put out about 45-55A. A 100A Denso will put out about 65-70A. On our 945T, when the electric fan kicks on when sitting in traffic its like a gut punch to the car. If it cycles at the same moment the AC compressor does also, I have moments of the dummy lights flickering. The 400w stereo and headlamps dont help either. :cool:

I recently had 2 Denso's in 2 different cars have the battery lamp illuminate with the key off or out.....which is indicative of a bad diode. Changing out the rectifier bridge, regulator and brushes - with new OE Denso parts, cost about $75 and took less than 15 minutes. You need a phillips screw driver, 8mm socket and 12mm socket (nut on the positive cable is an 8mm and can be a 13 if someone has replaced it).

Here is the patient.
Denso01b.jpg


Cover removed - if you only need to replace the brushes or regulator, this is as far as you'll need to go.
Denso02.jpg


5 phillips screws to remove the brushes and regulator. Only 1 and 2 hold the brushes - all 5 hold the regulator. Make sure your new brushes come with the plastic guard and transfer it if not. Most do - some dont.
Denso02b.jpg


Next up - removing the rectifier bridge (diodes).
Denso03b.jpg

4 phillips screws is all that holds it in.

Denso04.jpg


This particular one had 1 bad diode. I've had them that as many as 3-4 were blown. They're not hard to find.
Denso05b.jpg


Installation is the reverse....takes about 15min tops.
Denso08.jpg

Denso09.jpg

Denso10.jpg

Denso11.jpg

Denso01.jpg


I have been buying the brush-regulator set on feebay HERE Less than $35 shipped. Great quality too.

The rectifier bridge / diodes can be bought from Maniac Electric Motors. What you need is PN 77904018 $37 shipped. Great quality.

The last one I had go bad wasn't charging the battery - putting out 12.4V at the posts. It had 3 bad diodes. Most of the other 5 didn't look too good either.
Diodes2.jpg


After changing everything out, it now puts out 13.8 - 14.2V.

Anyways.....hope this is clear as mud and helps some. :cool:

ONE OTHER THING TO NOTE......

The regulator I linked to is an IN442. There are also some for these labeled as an IN443. Both PNs and styles Denso lists for a 14V/100A Volvo alt. Only difference between them is the IN443 has Load Response Control (LRC) - from what I have heard, its helpful when you have something like a high load stereo system - but you can look it up to see if you want/need that or not. I have opened up about 10-12 of these and the last one was the first one I found that had it - here is the difference:

VoltReg.jpg
 
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Just what i needed, thanks Chris!:cool:

Say, is this pretty much everything needed in order to 'bulletproof' my denso? I don’t like charging issues..
 
Think it's a good idea to service bearings too while it's out and on the bench?
Wonder how hard that is on these, and if there's a good source for quality bearings?

Thanks for the write up. I figured I'd just take mine to a local alternator rebuilder when it goes out, but this looks surprisingly underwhelming.
 
I had one of these that was REALLY fried totally apart (housing totally removed, etc) - its bearings sounded like sand - had 380k on it before it went. 99% of any issues in these is at the shown level. The cost and hassles of going deeper, IMO, is cost prohibitive - I'd just find another alt at that point....but thats just me.
 
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They sell reman units at advance Auto and AutoZone for relatively cheap with a lifetime warranty, pay for one and never buy another one.

But are they any good? I?d prefer a good used one over most reman units, at least when it comes to a Bosch. Wonder if it?s the same story with the denso.
 
I have all but given up on the reman garbage. They take a 300k whipped unit, replace the regulator or bearing or whatever single item failed, blast it and put it in a new box. I had a Bosch unit I bought from a blister pack store in the dead of winter. The regulator brushes were well worn and "Made in W Germany". 8 months later I was getting a flickering battery light. I returned it and got my $ back.

Sure they'll give you another after your car is towed home and you pull it. After seeing the efficiency ratings as well as my own experience with them, I wont have a Bosch on mine again.

About 35 yrs ago I remember an old mechanic telling me that these blister pack stores - that were just starting to spring up about then - that he would buy parts there except anything electrical. This was before the flight to sweatshops in Mehico and China.
 
I have all but given up on the reman garbage. They take a 300k whipped unit, replace the regulator or bearing or whatever single item failed, blast it and put it in a new box. I had a Bosch unit I bought from a blister pack store in the dead of winter. The regulator brushes were well worn and "Made in W Germany". 8 months later I was getting a flickering battery light. I returned it and got my $ back.

Sure they'll give you another after your car is towed home and you pull it. After seeing the efficiency ratings as well as my own experience with them, I wont have a Bosch on mine again.

About 35 yrs ago I remember an old mechanic telling me that these blister pack stores - that were just starting to spring up about then - that he would buy parts there except anything electrical. This was before the flight to sweatshops in Mehico and China.

Noted. I?ll follow your wroteup and spend the ~$75 in order to have a fresh high output denso.
 
I've changed both of my sig cars to Denso alternators. Thanks for that write up. In my experience the bearings are easier to replace than the bosch. The small bearing can get stuck but it's easy to use a dremel on it to get the inner race off the shaft. The large bearing is bigger than the bosch ones even though the alternator is half the size.

I do have one thing to add. When installing the brush set. Use a sleeve made up of paper so you can slide the brushes down onto the shaft without any issues. Then pull the sleeve out and the brushes are installed. I saw this on Youtube if you want to watch a video.
The bearings are 6303 and 6202 if I recall correctly.
 
That small screw driver I think thats in the one pic.....thats what I use to hold the brushes back when I put them in - lol. They dont seem to be that high strung like the Bosch brushes.
 
Thanks for this. I ordered a new regulator, brush, and diode pack for mine.
Has anyone done the diode "mod" to up the voltage? Just two reverse parallel diodes between the regulator ground point and the case should up the output voltage by whatever the forward voltage of said diodes are. Is it even necessary? or is voltage drop not as much of a problem unlike the bosch alts under the exhaust manifold of a 240
 
It would be nice to up it to something like 14.7 volts at cold start like Dave Barton does with his Bosch regulators. Once it is warmed up the voltage drops and then you start adding loads like heater/ac, e-fan (if applicable) radio, wipers, lights, stereo and it easily drops to 13.5 - 14.0 volts.
 
I just placed an order for both parts, we'll see if it brings this 200k Denso back around. None of the diodes on mine were as obviously blown apart as the ones pictured, but most had visible cracking and two had what look like scorching. The brushes only had about half a centimeter of meat left on them.

Anyway, thanks for the write-up!
 
As someone else mentioned, blown diodes and regulators can often be related to electrical system overloads like high power stereo amplifiers. But there also can be a faulty IAC or other short in the system. Mine started squeaking at about 100K. I had the electrical shop replace bearings, brushes and diodes.

-L
 
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