Alternator Replacement - Volkswagen Upright (Type I) Motor




Recently the battery in my 1971 Westy died.... Normally this is no big deal. However, this battery is less than 2 months old. A newer battery should not go dead, as the alternator re-charges the battery as you drive. Obviously this was not happening for me. I got out my trusty volt-meter, and sure enough, the alternator was putting out 0 volts (more on how to check it in a minute). So I called a good friend of mine that has a mini parts-warehouse at his house and he provided me with a new alternator. This is how to swap them.

Note: Disconnect your battery before beginning any of this work.


19mm socket and ratchet
10mm socket and ratchet
8 mm wrench
10mm wrench
13mm wrench

Note: If any parts are unknown to you, refer back to the photo on this page with the labels on it.
Note: Disconnect your battery before beginning any of this work.

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Step 1: Check New Alternator Out

There is a shaft that comes out of the back of the alternator and spins a fan. The fan is what provides the main cooling for the motor. The fan lives inside the giant shroud at the back of the motor. It is fixed onto the alternator shaft with a great amount of torque. It is pretty difficult to remove without an impact driver. If your new alternator does not have a fan on it, you can follow the next few steps, remove your alternator, then have a shop (or yourself) switch the fan from the old alternator to the new. If you are unsure if you have the torque to do it, get professional help. If this fan comes off at speed...... I shudder to think... Anyhow....

I wanted to make sure the new alternator I had was going to work. I made a visual inspection of the fan to make sure it was not damaged.

I put the alternator next to the battery (which I had out of the vehicle) (Interesting side note, someone once told me if you leave a battery on concrete it will discharge. I can't attest to the veracity of that claim, but to be sure I set mine on a rag, on some bricks) that I had removed. I alligator clipped a wire from the body (shroud cover) of the alternator to the negative terminal of the battery because in the vehicle it would be grounded. I clipped the negative lead of my voltmeter to the negative of the battery, and the positive to the B+ terminal on the alternator. I set my voltmeter to the millivolt-DC reading and spun the fan as fast as I could by hand. It registered on the meter. Good enough for me. (When I hooked my meter to the B+ of the dead alternator in the car, it showed 0. Later when I did the by-hand test on it, it went -0.3 then .2 then 0 then -5... not sure what was up with it, but it obviously wasnt working)

Step 2: Removing the Pulley

To begin taking out the alternator, we have to remove the belt that drives it. The pulley on the front of the alternator is actually 2 pieces. Once you pull the nut off the front and take the belt out, the front half of the pulley comes off and there are circular shims inside (see pic). The shims are what allow you to adjust the tension of the belt. Weird, right? Yes, but also wicked smart. When you get it apart you will see that the pulley halves are dished. The belt rides in that groove. As you separate the halves, the belt rides deeper in that groove, and is effectively "looser". As you remove shims, the halves get closer together, pushing the belt further out towards the circumference of the pulley. Nifty!

If you look down at the top of the pulley, you will see a little nib behind it. We're going to use that and a screwdriver to hang up the pulley so it doesn't turn as we loosen the nut. Look for the notch in the back half of the pulley and stick your screw-driver in there a couple of inches. Use the 19mm socket and begin to turn the nut to the left. When the screw driver hits the nib the pulley will not turn, and you can take the nut off.

Once the nut is off, there may be shims right under it (for safekeeping, theyre not actually doing anyting on the outside of the pulley). Take the front of the pulley off and take the shims out and the belt as well.

Step 3: Shroud Bolts

The alternator is held in-place by 4 bolts in the shroud, and a strap that holds it down to the stand that it's on. These are 10mm bolts, and only 1 is readily accessible by a mortal. Go ahead an take it out. There is one below that is right behind the intake manifold. If you're careful you can get that one as well. The other two screws are blocked by other motor parts, so we're going to have to do some more tearing down.

Step 4: Carburetor Removal

One of our bolts is behind the carburetor, and really, it's just all in the way. Let's get it out of the way.

First, lift off the air-cleaner and set it aside. Take a paper towel or a rag and put it in the top of the carb. The last thing we need is something falling in there. Then you will have real problems.

Note that there may be wires hooked up on the left and right of your carb. Make a note of where they are and maybe take a picture of them for reference later. They're for the automatic choke!

On the bottom left of the carb you will see a little barrel connector that has the accellerator cable poking through it. We need to remove it and make absolutely sure we dont lose it. The barrel connector is an 8mm bolt.

At the bottom of the carb are two 13mm nuts that hold the carb in place on top of the intake manifold. There is one right out front, and one that is pretty much impossible to get to with the distributor in the way.

We have to get the distributor out of the way...

Note: Make extra sure that you do not rotate the distributor at all or else your timing will be off. Also, the cap has to go back on the same way it came off.

The distributor cap has two clamps on it. Push down on the top of the clamp and pull it off. Lift off the cap, and move it out of the way.

Now we can take off the distributor nuts!

Note: You do not need to disconnect the fuel line to the carburetor. However, when you get the carburetor off, do not tip it, as it is full of gasoline.

Once you get the nuts off, lift the carburetor up and set it up front. Also lift up the gasket with it and try not to destroy that. you can put the nuts back on the carb so you dont lose them. You need to put a towel into the throat of the intake manifold. Remeber my note about having real trouble? Yea, drop something in the intake manifold and you are going to be really hating life.

Step 5: Strap, Wiring, and Shroud

On the alternator, behind the terminals, you will see a 1/2" metal band. This is a strap that holds the alternator to the stand it's on. Use a 10mm wrench and socket to loosen that up. Loosen it to the point where you can slide the strap all the way forward to the shroud.

Go ahead and loosen any wiring that may be fastened to the shroud as well.

At this point you should be able to rock the alternator towards you. As it begins to pull away from the shroud you will be able to see the fan. You will most likely only be able to get it part-way out before the bottom part of the fan cover hits up against the intake manifold. If that's the case, we have to loosen the shroud, lift it up and then pull the alternator out.

Be careful when lifting the shroud, as your oil cooler is also under there and you dont want to damage it. It may help to have a friend help with this part. Around left and right sides of the shroud is a 10mm nut holding the shroud to the tins below it (see photo). Loosen those, then lift it straight up about 2 inches and the fan should clear the shroud.

Step 6: New Alternator In

Reversing your steps exactly, place the new alternator in position, and lower the shroud. Tighten the shroud bolts, and re-secure any wiring that was on the shroud. Slide the strap towards you, over the stand, and tighten. Replace the 4 alternator shroud bolts.

Replace the distributor and carburetor. Re-wire the automatic choke if necessary. Replace the B+ and light wires on the alternator.

Step 7: Pulley Adjustment

First, hang the belt on the bottom, crankshaft pulley, then put it up and over the alternator shaft. Place the front of the alternator pulley back on (ensuring it's seated properly) and tighten the bolt. Using your index finger, push on the belt. The belt should only deflect 1/2 to 1 inch or so. If it's too loose it wont drive the alternator. If it's too tight, it may snap. If it is too loose, take shims OUT of the middle of the pulley. This will bring the pulley halves in closer and tighten the belt. If the belt is too tight, add shims INTO the middle of the pulley.

Congratulations! You've just replaced your alternator!

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    19 Discussions


    7 years ago on Introduction

    Pretty sure the battery going flat on concrete is an urban myth that originated about 40 years ago when auto batteries had hard rubber cases. Still not too sure about how it was supposed to discharge, but storing a battery on a nice cool concrete floor is probably the best thing for it. I have stored batteries this way for many years (charging them every couple of months) and they have always worked fine. One of them was under my bench for about 3 years after being salvaged from a wreck, and is now in it's 5th year under the hood of my car. Not definitive proof, but a pretty good argument.

    2 replies
    Philip J Frycaarntedd

    Reply 7 years ago on Introduction

    Not a myth, It's the cold from the concrete that does it, lead acid batteries and cold are not good bed fellows.

    What BS, the concrete floor isn't any colder than say, Minnesota. It was the old rubber cased batteries and the salts in the concrete that were the basis of the story. New plastic cased batteries have no such issuses.


    7 years ago on Introduction

    I'm unsure about your particular VW, but many of the air cooled engines used a generator, not an alternator. From time to time, generators need to be polarized with the voltage regulator or they will not charge. Generators get replaced a lot when all they need is polarizing. Not to say yours didn't need replaced, just my 2 cents. Awesome job though.

    1 reply

    Reply 7 years ago on Introduction

    Thanks! It was an alternator, and I did some subsequent testing once I had it out.

    Thanks for the tip, and the feedback!


    7 years ago on Introduction

    Good job. But, you didn't explain how you determined the failure in the alternator. The test you described on the first page does not accurately show anything beyond the condition of the bearings of the rotor. If you have no voltage across the rotor windings, the alternator will not produce anything. Alternators are very robust, especially those from Wolfsburg. They have no moving parts except the rotor which cannot be overloaded, and thus rarely fails. If the stator diodes are OK, then the commonest reason for a problem is the voltage regulator. The Voltage Regulator monitors the condition of the battery and when the voltage decreases it turns on the rotor winding by connecting the battery to the alternator.

    The greater the need at the battery, the more voltage is across the rotor winding. If the voltage regulator fails, the battery goes dead. If the battery was not charged before installation, it will not charge either. (Although, the car will run fine on the drive home!) If the alternator has a built-in regulator then you have fixed the problem, whatever it is.  If the battery was charged.

    Articles like this, however, are very valid and important  instructables.  They explain how-to repairs for automobiles.  Often a handman (woman) hesitates to fix his car because (s)he has never done this before.

    4 replies

    Reply 7 years ago on Introduction

    As I read the instructable this is exactly what I was thinking.

    Not only is it a faulty alternator a common misdiagnosis, but in fact a failed voltage regulator is a very common problem. That said, it does depend on the particular alternator you are replacing as it is common to find both alternators with a built-in voltage regulator as well as with an external voltage regulator. if the voltage regulator is built in, then the solution is in fact replacing the entire unit.


    Reply 7 years ago on Introduction

    Thanks for the feedback. I basically did not get very detailed in my diagnosis due to my own ignorance :) I saw that the old alternator was putting out 0V at the B+ terminal, and that's about as far as I can go. Perhaps I need to educate myself in this area.

    Thanks again!

    Phil Bhirod3

    Reply 7 years ago on Introduction

    I cannot say for certain about your alternator, but I had an alternator fail on a Chevy 350 cu. in. V-8. My battery was much older than yours with side post connectors. Someone had over-torqued one of the side posts and it was partially broken off inside. According to the Chilton manual I had, a bad internal battery connection can cause an alternator to fail. That failure causes the rotor to short out. The test in that case was to use an ohmmeter on the slip rings to read the resistance in the rotor windings. The resistance was to be 1.5 ohms, which is tiny. Anything less meant the windings had shorted out. Mine read 0 ohms. Anyway, a new battery and a new alternator fixed me up. It sounds like your battery is still OK.

    Thank you for your Instructable. I do not have a VW, but I may someday have a friend who will need help with his.


    7 years ago on Step 6

    Just fyi: I had a volkswagen in which I replaced the alternator and after doing so the fan started rattling in a rhythmic fashion (you'll know it if you hear it). After months of frustration an old man at a volkswagen shop informed me that there is supposed to be a shim the thickness of about three business cards between the stand and the alternator. So cut a piece out of the back of a notepad and put it in there. Problem solved. Now you know, just in case.

    2 replies

    Reply 7 years ago on Step 6

    Glad to make suggestions. I only do so because I have such traumatic memories of this experience. It was awful! I had replaced the squirrel cage, messed with shims, tightened every nut. I even drilled holes and put screws in the squirrel cage in order to balance it. The second I put that shim in there, problem solved! But boy...the mountain I had to climb before I found that old guru. Phew! I loved that car, but it was a quirky little bugger.


    7 years ago on Introduction

    Very clear, concise instructable! I don't own a VW but I feel I can take this task on thanks to this!! Great job!

    A neat way to test an alternator: With the engine off, check the voltage across the battery. If it is above 12V, you're in good starting shape. If it is below that, this test will not work and it is probably your battery.

    Start the engine and check the voltage across the battery again. It should be above 13V. Give it some gas and increase the RPM's; you should see the voltage fluctuate between 13-15V. If there is no increase in voltage from the first 12V measurement, there is no voltage coming from you alternator.

    To test amps, you need to run the multimeter inline. I would suggest taking it to Autozone since they test an alternator for free!

    Great job!


    7 years ago on Introduction

    Loved your ible. it brought me back to when I had a 77' beetle that I got in 86'. rebuilt the engine twice. And made me remember why I ALWAYS carried ALL of my tools needed to work on the car. One day on the way home from work my belt came off. I pulled into parking lot put my old belt that I had saved for just such an occasion and back an the road in less then 10 min.

    1 reply

    7 years ago on Step 7

    Ah Dud, thanks this one brought back some fond Memories of my first ride back in 1978 mine was 69 VW Bug, however I replaced the Engine with a 4/11 Porch Engine, it took a little Modification of the Engine Comp and had to Mod the Trans-axles, I kept snapping the off the the 6 bolts at the CV joint, also had to use the friction and pressure plate from the 4/11 want more info feel free to contact me.