oldskewel

iTrader: (1)

Has anyone ever replaced the slip rings in their OE Denso alternator?

I replaced my alternator in my '91, now at 200+k miles, about 10 years ago, after it failed. Also rebuilt the PS pump around that time, did other fixes to the PS system. All good since then.

But yesterday I was clearing out the garage, and came across the old alternator. It had been installed by the PO's mechanic a few years before I replaced it. On the side is a label - Denso 210-0170, indicating it's rebuilt by Denso. Should have been high quality, and lasted only about 25k miles, so I thought I'd open it up to try to see what failed.

I had read many times on here how the PS fluid causes the slip rings to fail, and had doubts about that since they're just copper, and I could not see how ...

But this one definitely has a failed slip ring. Amazing. It is worn all the way through the copper to the plastic substrate, over almost half the circumference. So the legend is true. I can guess that the PS fluid holds the graphite debris from escaping, and maybe makes a grinding grit to accelerate wear on the copper slip rings.

Having done it on a different car / alternator manufacturer, I'm considering replacing the slip rings. Searching on here does not reveal any other reports, short of replacing the whole alternator, or replacing easier parts like the VR or brushes.

So, has anyone replaced the slip rings on this alternator?

Here's a pic of the part I think I need. Any comments about whether that is the correct one?

oldskewel

iTrader: (1)

I guess not even Bueller has done this one. In case anyone ever comes across this thread, please respond at any time.

If I do follow through with this, I'll post the findings here.

From the experience with other alternators, slip ring replacement is by far the toughest thing to do on an alternator. The lead wires are encased in epoxy, covering the connection to the field windings. And the task is to chip away the epoxy without damaging the pure copper wire underneath so the new slip ring assembly can be attached.

So it is an understandably rare procedure. I just like a challenge sometimes, and rather than storing a broken alternator in my garage, I could be storing a spare one.

jaaa

If you end up doing it, take pictures for the rest of us.

Superfast1

Of my 40+ years of driving, I've rebuilt the alternators a few times & they worked well. Based on my experiences, the brushes tend to wear out much quicker than the slip rings & other components i.e. the stator (stationary set of wire coil windings), rectifier (diodes), voltage regulators, bearings, etc.. so when it comes to rebuild, most people only need to replace the brushes to get the alternator back in good working condition. I know this doesn't directly answer your question but since your slip ring(s) is/are worn out, I'm sure you can find a replacement but it'll be a bit harder to find than the brushes. Some auto part stores carry alternator rebuilt kits which consist of brushes, brush holders & voltage regulator. I haven't seen any kits that also included the slip rings. Perhaps, you can stop by some local shops that specialize in alternator rebuild, I'm sure they can help you finding the correct replacement. Good luck.

oldskewel

iTrader: (1)

Yes, all that fits with my experience too. So I had some doubts about the oft-cited slip ring failure due to PS fluid leaking on the alternator. But it is clear as day looking at this one.

And as I mentioned, this is a Denso rebuild that lasted 25k miles. The brushes look like they only have about 25k miles of wear on them, so my guess is that when Denso rebuilt it, they replaced the brushes, maybe some other things, and did not replace the slip rings.

Given the abnormal PS fluid issue these cars have with their alternators, it makes some sense that it is not a common problem for other cars.

Yes, I'll take some pics if I tackle this. I think that pic in post #1 is what I'll be getting.

Superfast1

The last alternator that I had to replace on my 97 LS400, the leaking fluid from the ps pump had caused the bearing to go bad & it made a grinding noise so if you want to fix your alternator, make sure to check the bearing as well & replace it if needed then you'll have a known good spare alternator. Bearing brands to be consider: Timken, NSK & SKF. They are all OEM bearing suppliers so can't go wrong w/ any of them.

oldskewel

iTrader: (1)

The alternator has come apart very easily. It looks like a quality rebuild except for the slip rings, unfortunately. So the brushes and bearings look good. Diodes test perfectly.

The manual shows how to test and repair everything, then when it gets to the slip rings, if they are worn too much it says to replace the rotor (the whole thing, vs. just the slip rings).

**** So this might be something to consider when buying a Denso-remanufactured alternator ... they might truly rebuild it as good as new except for the slip rings. In most cases, that's good enough, but not in my case.

I took some pics of the failed slip rings, which I found pretty amazing. The brown patch you see there on the top ring is the plastic substrate - i.e., all the copper is worn away in that whole area. I used some Scotchbrite to clean things up to make them easier to see.

I did buy that replacement part I asked about earlier, but am having some doubts about whether it can be made to work. I'm pretty sure it is not the right part, but whether I can get it to work is a different story. Not sure if I want to try though.

fixmiester

I took my '99 alternator apart about ten years ago, because it wasn't charging properly. The car had about 80K miles then. I've repaired several GM alternators, including new brushes, regulator, diode packs, etc., so I felt comfortable that I could fix this one. And yes, I had a leaking PS pump for quite awhile, before I put new o-rings in it, but when I began taking the alternator apart, I found that it was a little more difficult to separate than other manufacturers. I did find a bad diode pack, and replaced it.. I was surprised that the brushes were only about 30% worn, and the slip rings were neat perfect condition. That's after several years of PS fluid soaking everything under the engine, including the alternator. Since the brush assembly was soldered in and not an easy replacement, I just polished a little discoloration off the slip rings and put it all back together. It worked fine until about two years ago, with similar diode issues, so I just bought a new one, and it works fine. So, like you, I'm a little skeptical that your severe slip rings wear is due to the leaking PS fluid issue. However, I would be curious about the rebuilt brushes, and whether they may have caused severe wear due to improper material composition, or compatibility.
I too stubbornly spend hours creatively fixing things that could be very easily replaced, simply because "I can"! But in this case, I think someone would have to be really desperate, or a glutton for punishment to pursue a slip rings extraction and rebuild. But, like I've said for years "Hey, it's completely broken now, so what have I got to lose?"
Good luck.

oldskewel

iTrader: (1)

To clarify - I was formerly a doubter in the PS-killing-slip-rings theory, but am now a believer.

When I opened it up, the brushes holder was stuffed with debris from the brushes wearing away. I will guess that if things were dry, the graphite would gradually wear away and fall out, get blown out, etc. But being wet from the PS, the graphite powder sticks around, and becomes a gritty paste that can very quickly wear out the slip rings. So it's not a chemical thing.

I don't think there is a problem with the brushes. They're pretty hard to get wrong, and I can't imagine Denso putting something wrong in there.

And the other lesson is that this is the weak spot of the highly regarded Denso rebuilds. Pretty safe bet that Denso will not replace slip rings during the rebuild, and if they start out thin, and you have a PSF leak issue, you may end up like this one did.

I completely hear you on the stubborn fixmeister mentality on this. I know it does not make sense. Better things to do with my time. Hopefully nobody tells me it's impossible, then I'll definitely have to do it.

YODAONE

Denso should set themselves apart by replacing slip rings.

Rebuilt auto parts, on an individual basis, do not provide adequate information to allow the consumer to make a fully informed decision as to exactly what they are purchasing...

At best they are vague.

An excerpt from Denso on their rebuilt alternators:

Remanufacturing Process Includes:

1. Bearing - 100% tested to OEM specifications and repacked with premium OE-standard lubricant.
2. Stator - Insulation tested to 600 volts.
3. Rotor - Performance and insulation tested to 600 volts.
4. Housing - Re-tapped to OEM specifications and damage-checked for heat warping, corrosion, or improper surface alignment.
5. Hardware - 100% stripped and replated.
6. Rectifier - Performance tested to 300 volts.
7. Voltage Regulator - 100% voltage tested to OEM specification.
8. Slip Ring - Re-machined to an average of 8 microns (20 micron run-out maximum), minimizing brush wear and abrasion.

While Denso says a lot about testing, it does not actually provide us with a parts list or specific measurements or exactly what components were replaced on each rebuilt unit (I have installed a Denso rebuilt alternator)...no mention of brush assembly in this list. It does not say bearings are replaced...really?


A cut away view of a Denso alternator.


It is the authors belief should parts rebuilders be required to generate a list, then consumers would gravitate towards more reputable rebuilders resulting in far fewer returns.

Lifetime warranties offered by parts stores mean little and are a hassle when required to perform the same repair numerous times.
My expectation is to repair once, and that rebuilt part be at least as durable as the original.

razvy

I think fixmeister it's right at least 50% , the brushes could your problem , hard or abrasive brushes can go thru that cooper like butte or you the car was driven in a dusty environment and dust got in there and act like abrasive oil + dust ..
I try my self to take the alternator apart and I stop when I seen the rectifier and voltage regulator brazed , looked like brass or cooper welds in there , haw you guys deal whit that ?

spuds

Can you elaborate,did you buy a new Denso and the cost,or did you buy a new china brand?
Thanks a lot.....

fixmiester

I forget all the details, but since it was brand new, and half the cost of a Denso, and had a full warranty, I gave it a shot. When it arrived it included a full spec sheet, for that specific alt of the final QA bench test, with voltage output at full load, and a printout of the diodes output waveforms, plus some other parameters. I was impressed, and it has worked fine ever since. Although I am pretty sure it was from China, all bolt holes, and casting details were a carbon copy of the Denso original. Cannot remember the brand name, unfortunately.

spuds

Thanks fixmiester,I also have had good luck with the newly built China (On my Jeep,super easy to access) but horrible with the rebuilds.Nice to see this can be an option.

oldskewel

iTrader: (1)

Update, after scouring the interwebs for info ...

for those interested in doing an alternator rebuild, not including slip rings, this video seems pretty good. I prefer to use pullers rather than hammers, and did not need to bend and then un-bend the fan blades, but still, this is the best I found:

There, as with almost everywhere that looked legit, they don't actually replace the slip rings. Looking down in the comments where a few people ask for that, the author of that video basically says they don't recommend or sell parts for it because it is not likely to succeed. I will guess that is good advice, but still may not follow it myself, having nothing to lose other than some time.

But to show the extent of my search, I did find a video of a determined guy in India(?) - the slip ring work comes about midway, right when the pair of stray cats come to inspect the work, but I've got to say that is not something I would put in my car. And it looks like he's actually doing a re-repair of a failed previous rebuild attempt. Still amazing to me what some people can get done with things that barely pass for tools. Sorry, can't find the video again, right now.

EDIT - Found it, turns out it's for a Bosch, not Denso. Still amazing ... ly scary (cats enter around 16:20):


After sending in the pics and asking for more info, I think the eBay seller realized the part they sent is not an ideal fit, so they refunded the cost. I'd of course much rather have the exact part.

So anyway, this means it will be about 2 hours of R+D surgery to make a decent attempt. Best I can do, but I am not in any rush since it looks like it will not be successful. If I do it, it will be for the challenge and to see how close to impossible it really is.

Recap
- That video looks very good for anyone wanting to get an idea what's invovled in rebuilding everything except the slip rings.
- Slip ring replacement on these Denso alternators seems close to impossible, and I have not found any reports of success.