Servicing a Denso

[15A]

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.

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.


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


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.


Next up - removing the rectifier bridge (diodes).

4 phillips screws is all that holds it in.



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.


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






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.


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

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

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:

[mblue240]

Thanks for the detail. My denso doesn't perform as well as I'd like and was just thinking it might be time for a tune up.

[cleanflametrap]

Nice give-back!

[iHateVolvoPeople]

Just what i needed, thanks Chris!

Say, is this pretty much everything needed in order to 'bulletproof' my denso? I don’t like charging issues..

[IansPlatinum]

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.

[15A]

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.

[VB242]

They sell reman units at advance Auto and AutoZone for relatively cheap with a lifetime warranty, pay for one and never buy another one.

[iHateVolvoPeople]

Originally Posted by VB242

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.

[15A]

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.

[VB242]

Originally Posted by iHateVolvoPeople

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.

Mine has lived for a couple years next to the turbo on my B21 no issues, maybe 5-6000 miles. It's hot down there too!

[iHateVolvoPeople]

Originally Posted by 15A

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.

[dl242gt]

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.

[15A]

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.

[esmth]

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

[holtzboy]

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.

[Dicktater]

Great write up.....I may need this, Thanks Chris!

[15A]

Glad its of some help to some.

Carry on gentlemen.

[ortho stice]

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!

[Lazarus]

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

[ortho stice]

No dice unfortunately. The alt will only charge over 2k rpms. I suppose that’s an improvement over not charging at all but...

[apachechef]

Originally Posted by ortho stice

No dice unfortunately. The alt will only charge over 2k rpms. I suppose that’s an improvement over not charging at all but...

Sounds like a fault in exciter circuit. confirm by applying 12+ to exciter contact on back of alternator at idle, and see if it starts charging

[AndrewNance]

Have you ever come across a faulty Denso that drains your battery? Recently I’ve been trying to track down the source of my battery draw in my 142 and narrowed it down to the alternator. I replaced the rectifier bridge and threw in some new brushes but it didn’t fix my issue. I still see a 150 milliamp draw in a car with no extra accessories requiring constant 12v even though it still charges ~14v. I ended up just buying another alternator to try.

[apachechef]

Originally Posted by AndrewNance

Have you ever come across a faulty Denso that drains your battery? Recently I’ve been trying to track down the source of my battery draw in my 142 and narrowed it down to the alternator. I replaced the rectifier bridge and threw in some new brushes but it didn’t fix my issue. I still see a 150 milliamp draw in a car with no extra accessories requiring constant 12v even though it still charges ~14v. I ended up just buying another alternator to try.

what feeds your excviter circuit?

[AndrewNance]

Whatever fed the factory one I guess. When I swapped to the Denso I just used the original exciter wire in the harness and it worked fine until recently (I assume it would trace back to the cluster but I didn’t really dive into it since it worked). I only started to doubt the alternator when I was searching for the draw and couldn’t find it by pulling any of the fuses out. When I’d disconnect the battery cable from the alternator, the draw would drop back to like 1 milliamp.

[122power]

Thanks for that write up! Should be a sticky!