Bosch Alternator Rebuild Info

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
97 Passat
Two reasons I haven't bit the bullet on this yet.
1) for $75, I can buy the big bearing version of the plastic roller (for the hub) and a metal roller from Amazon for less
Right on... an understandable dilemma which I've also thought of. If you want to score the cheap roller on eBay just for the collar and bushing, it's totally understandable. My selling point here would be:
  • I make the collar and bushing assembly from stainless, which is higher-quality than what the Chinese use
  • I make the press-fit collar/sleeve with a larger OD in order to have more surface area against the flat spot on the rod
  • If I make the entire part here in the shop, then I can also assemble it all - saving you from having to press it all together.
  • I'm only charging $25 extra for the collar and bushing, which isn't much more than you'd be paying for the entire plastic roller assembly.
  • You're supporting a family business! :p

As for my billet roller vs the stamped metal you can buy, I guess you'll just have to decide that mine is worth the extra cash.

2) don't know the mass difference between the two
I can weigh it for you somehow if you're curious, that'll be no issue. I do have some spare 410 stainless sitting here if you want me to make one from that - no worries about that not being heavy enough.

I may still buy one off you with a reduced diameter since I'm running a larger alternator pulley, thus belt tension is higher.
Due to the stock roller being 3.075" in diameter, and 3.25/3.5" roundstock being substantially more expensive than 3.00" roundstock, I've been making the aluminum ones from 3" and cleaning up the OD, which brings it to about 2.985." Making a smaller OD (70mm/2.755" as you suggested) will be no problem.

Now for your PM'd question...

Each and every roller I've seen has the belt riding right up on the outer edge. If the mount for the bearing, which you have @ 0.2638 or 6.7 mm was at 8 mm, this would be fixed.
I guess you're suggesting that I move the bearing further "right" in the pulley in order for the pulley to ride closer to the rod. That's something I've also looked at, and it's not really feasible to change the design. As you can see from this drawing, there is only 1mm difference between the rod land and the edge of the pulley as it is. This dimension is determined by the thickness of the press-fit sleeve that goes over the 17mm bushing.



Not to say that I couldn't make the left-hand outer edge of the pulley extend further, like this:



The easiest solution I've thought of is to remove the spring tensioner and place a very small washer on the end of the rod to shim it further in the left-hand direction.

And again, the larger bearing size will be no big deal at all.
 
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thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
97 Passat
Well I just had a chance to make my shim and grease the rod. I measured the width of the shiny spot on the edge of my roller, which was about .100, so I made the washer .050" thick. (.375 OD, .240 ID)



Definitely centered up now.

 

Chris_TDI_98

Veteran Member
Joined
Jul 19, 2012
Location
Hartford, CT
TDI
1998 Jetta TDI 1.9L mk3 1Z AHU
How about adding some info on diagnosing and repairing the rectifier boards on these alternators.
For example, my 120 amp alternator received a voltage surge, and blew a few of the six big heavy duty rectifier diodes on the board.
Good sources of quality parts, plus suggestions about the optimal way to go about doing it - replacing the entire board, or just the diodes - would be great.
 

Digital Corpus

Top Post Dawg
Joined
Mar 14, 2008
Location
Ontario, California
TDI
'97 B4 w/ 236K mi body, 46K mi soul
I've never looked into that, honestly. When I last had mine apart, I never was able to identify anything that resembles descrete components and I've read the whole black mass is a diode. I have quite a few things on my plate, and rebuilding one of these and making a tutorial is on the list. I'll look into breaking some spot welds and soldering things back up if I get to that bit during my vacation that starts Monday.
 

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
97 Passat
I've been noticing some rattle coming from under the hood at idle, and it seems that my idler pulley bearing is getting a bit wobbly. Not as bad as the old one yet, but wobbly nonetheless. Not sure if it's the size, brand, or type of bearing that is causing it to be worn out so fast.

EDIT: After disassembly, it seems that the bearing wasn't that worn out after all. Seems identical to the other new one I had in my trunk. What I did discover was that the wheel bearing grease I used on the rod wasn't such a good idea - it was all gummed up, inhibiting both the movement of the rod and the tensioner spring. It even caused some galling on the end of the rod, which I cleaned up with sandpaper. I sprayed it all down with some white lithium grease-type lubricant I have here at shop, at am getting ready to reassemble. I cleaned out the tensioner really well and the travel is much better. This will probably fix things.

But in the future, I'll probably just start using the big bearings only - like what Digital Corpus has. By the way, how's yours holding up?

EDIT 2: Yes, it is much better.

EDIT 3: I managed to find one of those 6303 bearings on Amazon for about $5 shipped. It appears to be a new one that has a damaged box or something. Score for me!
 
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Digital Corpus

Top Post Dawg
Joined
Mar 14, 2008
Location
Ontario, California
TDI
'97 B4 w/ 236K mi body, 46K mi soul
Our other B4 needs some parts so I’m looking around for alternates again. If you have a 17mm hub and want a full metal pulley for its inertial properties, then this guy might work for you since it is a mass produced part:
http://www.daycoproducts.com/part?part_number=89105

At 74 mm diameter, and assumed 90° of contact with the serpentine belt, it’ll have a little less tension as the belt will get ~0.2 more “slack”. Amazon is selling it for about $36 shipped. It is also a 2 bearing pulley.

If you have an A4 clutched pulley, you loose about 0.4” inches of belt length from the added diameter. This pulley would drop that delta to loosing only about 0.2” of belt length.

Less belt length in the path is greater tension and vice versa, more belt length is less tension.


Edit, so far my custom one is running beautifully.
 
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Digital Corpus

Top Post Dawg
Joined
Mar 14, 2008
Location
Ontario, California
TDI
'97 B4 w/ 236K mi body, 46K mi soul
Corrected.

Also, the Gates 38087 has a 17mm hub and aa single 6203 bearing. The composite is PA66 with 35% glass fill, but is overmolded so once the bearing is gone, you cannot replace it. The 2-part, 16.8 mm hub is easily removable though, fwiw.
 

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
97 Passat
Our other B4 needs some parts so I’m looking around for alternates again. If you have a 17mm hub and want a full metal pulley for its inertial properties, then this guy might work for you since it is a mass produced part:
http://www.daycoproducts.com/part?part_number=89105

At 74 mm diameter, and assumed 90° of contact with the serpentine belt, it’ll have a little less tension as the belt will get ~0.2 more “slack”. Amazon is selling it for about $36 shipped. It is also a 2 bearing pulley.

If you have an A4 clutched pulley, you loose about 0.4” inches of belt length from the added diameter. This pulley would drop that delta to loosing only about 0.2” of belt length.

Less belt length in the path is greater tension and vice versa, more belt length is less tension.


Edit, so far my custom one is running beautifully.
I've had a spare 6203 aluminum pulley sitting on my desk for several months. Send me a PM if you want it and I'll cut you a deal.
 

coronan

Veteran Member
Joined
May 4, 2009
Location
Reno, NV
TDI
01 Golf
Can someone fix the broken pictures?
Thanks!

I dont see where to remve / solder the brushes.

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hey_allen

Veteran Member
Joined
Nov 25, 2006
Location
Tacoma, WA
TDI
2000 Jetta TDI
Coronan,

The brushes are secured under the plastic cover that is in the lower left in the picture you posted, opposite the end where the brushes stick out.

That said, I tried replacing brushes, and couldn't solder onto the steel bus bar that Bosch used in the regulator. They appear to have spot welded the brush pig-tails.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Bumping an old thread….

Disassembled the alt from Rotbox, to install on the pick up. Bearings were noisy and I figures I’d replace them and clean up the alt.

The only thing replaced were the bearings. I ordered Koyo and SKF. Everything that came out of this alt went back in. I did not touch the slip rings, since they looked decent. The issue I’m having is, the regulator brushes are not lining up with the wear marks on the slip rings.

- If I push the rotor to the rear to make the brushes line up with the wear marks, the rear fan is contacting the housing to the point that it locks up.
- If I push the rotor to the front to avoid fan to housing contact, a portion of both brushes are no longer in contact with the slip rings. I also notice the rear bearing is not fully seated in the plastic shim/cup, when I do this.



Any ideas? The only thing I can think of is, when I pressed the front shaft washer onto the shaft, I supported the rotor by the slip ring… I did some light research and I didn’t see anything saying not to do this.

-Todd
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Bumping an old thread….

Disassembled the alt from Rotbox, to install on the pick up. Bearings were noisy and I figures I’d replace them and clean up the alt.

The only thing replaced were the bearings. I ordered Koyo and SKF. Everything that came out of this alt went back in. I did not touch the slip rings, since they looked decent. The issue I’m having is, the regulator brushes are not lining up with the wear marks on the slip rings.

- If I push the rotor to the rear to make the brushes line up with the wear marks, the rear fan is contacting the housing to the point that it locks up.
- If I push the rotor to the front to avoid fan to housing contact, a portion of both brushes are no longer in contact with the slip rings. I also notice the rear bearing is not fully seated in the plastic shim/cup, when I do this.



Any ideas? The only thing I can think of is, when I pressed the front shaft washer onto the shaft, I supported the rotor by the slip ring… I did some light research and I didn’t see anything saying not to do this.

-Todd
I'd guess you forgot to install/lost the spacer on the front of the rotor, unless the two halves aren't seated together. The rotor is supposed to be pulled forward by the pulley and held forward. If the spacer is missing, it'll slide too far forward and the slip rings won't line up, or if the two halves aren't seated together enough, there will be too much space between, and it won't line up either.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Is that spacer seen from the front, under the pulley? The thick one that’s a press fit? If so, that’s what I was referring to as “front shaft washer“.

If not, I didn’t remove a spacer from this alt. I took 2 alts apart and I have the identical parts, from both.



The halves are pulled together as much as possible. The one I’m working on is 90A, although the 120A uses the same hardware.

Thanks for the reply.

-Todd
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
Started taking apart another 120A alt, for comparison. Disassembled the 90A, reassembled the 90A, measured some parts, stared at some parts, etc.. Everything checked out, as it should. For a very brief second, I thought about leaving it alone and running it. For another brief second I thought about grinding down the mounting posts for the regulator, to lower the brushes… couldn’t bring myself to do either.

The only thing I can think of is, when I pressed the front shaft washer onto the shaft, I supported the rotor by the slip ring…

The slip rings did not look like what was on the 120A rotor, or the spare alt. Everything inside was replaced with aftermarket parts. I took a measurement from the inner race to the top of the slip rings, on the 120A and compared it to the 90A.

1.6mm less than expected…. so, the slip rings did slip!




From the above pic, you can see I was already digging in there with screwdrivers. I was lightly levering on the outer race and Robert Bosch called me, and told me to stop. Better do this the right(?) way, before I ruin something.

A couple nuts and washers to support the outer race, some prybar action, and it instantly popped.



If I moved it another .5mm, it’d be perfect, but I decided to leave it alone, before I ruined something. The brushes are fully landing on the slip rings, but not exactly where they were previously riding. Good enough for me….




Reassembled





I need to disassemble it again, because one of the threaded case holes washed out. If I’m installing thread coils in one, I may as well do all…. I’ll probably spray the rear cover satin black, since the nameplate markings look like crap.

Takeaways… don’t do what I did.
  • Don’t use a press to press the front washer (Bosch calls it a spacer) onto the shaft. Use the pulley, washer and nut to press It on.
  • Don’t use a tie rod/pitman arm puller to remove the rear bearing. This probably didn’t cause the issue, but I can’t guarantee it.
This should have been easy. My mistakes cost me at least 4 extra hours.

-Todd
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Started taking apart another 120A alt, for comparison. Disassembled the 90A, reassembled the 90A, measured some parts, stared at some parts, etc.. Everything checked out, as it should. For a very brief second, I thought about leaving it alone and running it. For another brief second I thought about grinding down the mounting posts for the regulator, to lower the brushes… couldn’t bring myself to do either.




The slip rings did not look like what was on the 120A rotor, or the spare alt. Everything inside was replaced with aftermarket parts. I took a measurement from the inner race to the top of the slip rings, on the 120A and compared it to the 90A.

1.6mm less than expected…. so, the slip rings did slip!




From the above pic, you can see I was already digging in there with screwdrivers. I was lightly levering on the outer race and Robert Bosch called me, and told me to stop. Better do this the right(?) way, before I ruin something.

A couple nuts and washers to support the outer race, some prybar action, and it instantly popped.



If I moved it another .5mm, it’d be perfect, but I decided to leave it alone, before I ruined something. The brushes are fully landing on the slip rings, but not exactly where they were previously riding. Good enough for me….




Reassembled




I need to disassemble it again, because one of the threaded case holes washed out. If I’m installing thread coils in one, I may as well do all…. I’ll probably spray the rear cover satin black, since the nameplate markings look like crap.

Takeaways… don’t do what I did.
  • Don’t use a press to press the front washer (Bosch calls it a spacer) onto the shaft. Use the pulley, washer and nut to press It on.
  • Don’t use a tie rod/pitman arm puller to remove the rear bearing. This probably didn’t cause the issue, but I can’t guarantee it.
This should have been easy. My mistakes cost me at least 4 extra hours.

-Todd
Good you figured out the issue! Make sure you still have continuity between the two slip rings. It shouldn't have broken the wire in there, but you'll probably want to make sure of that. I've not really had that specific issue before, as I generally am replacing the slip ring when I rebuild an alternator.
 

ToddA1

Top Post Dawg
Joined
Aug 3, 2011
Location
NJ 08002
TDI
'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
I do have continuity. That’s something I did glean from the many videos, when I was trying to figure this out.

Being that you’ve replaced slip rings, are you taking before and after height measurements, to ensure they line up with the brushes?

I did assemble the 120A, tonight. I assembled the front half as usual, but did not crimp the stator leads to the rectifier.… makes everything much easier to see. Bolted the halves together and the slip rings were low, again… I’m two for two!. This time, I carefully cut the base of the slip rings with a hacksaw, to form a ledge for the pry bars to grab. A few trial and errors, and the height was perfect.

This one was assembled much faster. I’d estimate 2.5 hours, including set up and clean up.… I’m working a bit slower, so I’m not scratching the refreshed parts.







I realized the slip rings have an open top. Using the puller to remove the rear bearing, couldn’t have caused these issues, since the puller is pushing directly off the rotor shaft. On both alts, the rear bearing does not entirely seat in the plastic spacer cup. Learning new stuff..,,

-Todd
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
I do have continuity. That’s something I did glean from the many videos, when I was trying to figure this out.

Being that you’ve replaced slip rings, are you taking before and after height measurements, to ensure they line up with the brushes?

I did assemble the 120A, tonight. I assembled the front half as usual, but did not crimp the stator leads to the rectifier.… makes everything much easier to see. Bolted the halves together and the slip rings were low, again… I’m two for two!. This time, I carefully cut the base of the slip rings with a hacksaw, to form a ledge for the pry bars to grab. A few trial and errors, and the height was perfect.

This one was assembled much faster. I’d estimate 2.5 hours, including set up and clean up.… I’m working a bit slower, so I’m not scratching the refreshed parts.





I realized the slip rings have an open top. Using the puller to remove the rear bearing, couldn’t have caused these issues, since the puller is pushing directly off the rotor shaft. On both alts, the rear bearing does not entirely seat in the plastic spacer cup. Learning new stuff..,,

-Todd
I don't measure it, as as long as one brush is touching each slip ring, it doesn't matter too much if it's exactly centered, as there's no groove to line up. I press them down until they touch the step.
The end of the slip ring often goes past the end of the metal core, so pressing on that can cause the slip ring to slightly collapse, which would be what caused yours to not line up. I use the same method to pull the bearings, but I'm most often replacing the slip rings as well, so haven't actually dealt with that issue.
 

finyuk2005

New member
Joined
Jan 19, 2022
Location
scotland
TDI
T4
Hi there, im new here and im glad i found this thread as i am having issues with my 120 amp alternator and couldn't find much info on them!
I had to replace the regulator a few months back as the brushes quit on me with a 150 mile drive to go! I did manage to get home because i have about 180aH of leisure battery and that kept the headlights on!
now i have replaced the regulator with this one

https://www.justkampers.com/028903803d-voltage-regulator-for-14v-bosch-alternator-t4-1996-2003.html

but i never see much more that 13.6 on my volt meter, although i did just put my multimeter directly on the battery and it was showing 13.8v, but i would still like to see it more like 14.something, also the first time i start the van every day i need to blip the throttle to get the alternator to start charging, that didnt happen with the old regulator, any ideas why?
I did find this adjustable regulator that would be perfect because i think with the leisure battery i could do with the extra voltage to help charge it fully,

you have to scroll down a bit to see the internal adjustable regulator which to me looks like it would fit fine, but i emailed the guy and he said it wouldnt work, i gave him the bosch part number 0123-515-020

anyone know if this would work or have any alternative ideas?
I know i need to check for things like voltage drop across cables and such, and i may take the alternator off again and check i did a good enough job of cleaning the slip rings.

anyway sorry for the long essay!!
cheers for any help!

almost forgot, i got myself a clamp meter in the post today and it read 40amps at idle revs on the cable between the starter and the battery, which i didnt think was too bad at idle rpm, but the voltage is still lower than i would like.
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Hi there, im new here and im glad i found this thread as i am having issues with my 120 amp alternator and couldn't find much info on them!
I had to replace the regulator a few months back as the brushes quit on me with a 150 mile drive to go! I did manage to get home because i have about 180aH of leisure battery and that kept the headlights on!
now i have replaced the regulator with this one

https://www.justkampers.com/028903803d-voltage-regulator-for-14v-bosch-alternator-t4-1996-2003.html

but i never see much more that 13.6 on my volt meter, although i did just put my multimeter directly on the battery and it was showing 13.8v, but i would still like to see it more like 14.something, also the first time i start the van every day i need to blip the throttle to get the alternator to start charging, that didnt happen with the old regulator, any ideas why?
I did find this adjustable regulator that would be perfect because i think with the leisure battery i could do with the extra voltage to help charge it fully,

you have to scroll down a bit to see the internal adjustable regulator which to me looks like it would fit fine, but i emailed the guy and he said it wouldnt work, i gave him the bosch part number 0123-515-020

anyone know if this would work or have any alternative ideas?
I know i need to check for things like voltage drop across cables and such, and i may take the alternator off again and check i did a good enough job of cleaning the slip rings.

anyway sorry for the long essay!!
cheers for any help!

almost forgot, i got myself a clamp meter in the post today and it read 40amps at idle revs on the cable between the starter and the battery, which i didnt think was too bad at idle rpm, but the voltage is still lower than i would like.
Sounds like the original one you have is a 13.8v set point regulator. The ones I sell are 14.2 volt set point.
The reason that the one from the Volvo guy won't work is that it's for the alternator with a 28mm slip ring, the VW one has a 14mm slip ring.
Where are you located?
 

finyuk2005

New member
Joined
Jan 19, 2022
Location
scotland
TDI
T4
Sounds like the original one you have is a 13.8v set point regulator. The ones I sell are 14.2 volt set point.
The reason that the one from the Volvo guy won't work is that it's for the alternator with a 28mm slip ring, the VW one has a 14mm slip ring.
Where are you located?
Ahhh thanks for clearing that up, makes sense now!
i might have a look for a higher voltage one in that case
I am in scotland
cheers!
 
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