How do you replace the alternator on a 1991 Chevy Astro?

New for the Chevrolet Astro/GMC Safari

I just did this on a 1992 Astro EXT cargo van having the Z-code 4.3-liter V6 and automatic transmission; I previously performed this operation on a 1994 Starcraft Conversion Astro (EXT) having the W-code 4.3-liter V6 and automatic transmission.

On all the Astro/Safari vans I've seen, the alternator is located on the passenger side of the engine.

Recommended tools:

  1. 8mm box-end wrench or socket (not all will need)
  2. 10mm DEEP box-end wrench or socket
  3. 13mm box-end wrench or socket
  4. 14mm DEEP box-end wrench or socket
  5. 15mm box-end wrench or socket
  6. 3-inch socket extension
  7. 3/8-inch-drive ratchet
  8. steel "butter knife" or suitable substitute
  9. teflon tape or other "thread sealer"

If you elect to use a 1/4-inch-drive ratchet in lieu of the 3/8-inch-drive ratchet, limit its use to 10mm-or-smaller sockets: the threaded fasteners in this application having larger heads require greater torque than can be safely and reliably applied using 1/4-inch-drive hardware.

Read this entire procedure first, then decide whether this is a project for you to attempt.

There are significant minor differences to the specific procedures involved, to wit:

(1) Always observe all applicable safety procedures.

(2) Disconnect the cable from the positive (+) battery terminal. For some vans, you will need an 8mm socket or wrench; for others, you will need a 10mm socket or wrench.

(3) The power steering reservoir is in the way on vans having the Z-code engine: leaving the hoses attached and avoiding tipping of the reservoir, remove and save the screws that hold the reservoir to the cowl; then bend the hoses and rest the reservoir on the driver's side of the radiator shroud.

The air filter box is in the way on vans having the W-code engine. Open the clamps that seal the box, remove the filter: the nuts and bolts holding the airbox in place are visible. Remove the airbox, saving the hardware.

(4) The ductwork supplying the engine with fresh air is in the way. Usually, these plastic pieces just click together, but there may be one or more clamps, nuts and/or bolts, or screws holding some of it in place. The offending portion consists of the following pieces:

(a) the lower part that turns the air about 90-degrees, so that the air flows upwards,

(b) the upright section that channels the air upwards (it looks like an accordion's bellows on the Z-code engine),

(c) the upper ductwork connecting the upright section with the air filter housing.

I have heard that some ductwork installations are secured using #2 Phillips threaded fasteners (screws); if yours is such an application, you will also need a #2 Phillips screwdriver.

(5) Remove serpentine belt. The ratcheting tool that looks like a long, flat handle -- it came with the vehicle as part of the lug wrench kit -- has an opening that fits the pulley on the tensioner. Using the tool, loosen the tensioner with one hand and slip the belt off using the other hand.

At this point, whether you need to remove the fan from the front of the engine should be obvious. If you must, be aware that so doing without removing the shroud really isn't going to give you much room (about 1/2 an inch, maybe an inch).

If you need more than that, the shroud has to come off so that you can remove the fan. Although at 13.5 inches (34.3mm) circumference and 14.5 inches (37.9mm) circumference respectively, my forearms and upper arms are rather small, I think that needing to remove the fan to have enough room is a highly unlikely condition.

(6) Remove the engine oil dipstick bracket from the stud holding the alternator to the bracket. The nut securing the dipstick bracket is probably a 10mm. Remove the dipstick bracket from the stud. Be aware the dipstick tube could slide from the engine.

(7) The alternator bracket should be loosened from the front of the engine. Remove the bolts (it should be a trio of 14mm bolts) and save them. This allows the bracket, tensioner and alternator to be tilted away from the engine. At least one bolt may be wet with engine coolant; seal the threads of any such bolt before reinstalling it.

(8) Use an appropriate tool to unclip the plug from the alternator (I used a "butter knife), and remove the red wire from the lug at the back of the alternator. The nut securing the red wire to the alternator is probably a 10mm; the stud in the alternator is probably a 15mm (menitoned just in case the new one needs snugging).

(9) Remove the bolt from the rear of the old alternator holding it to the bracket (either a 13mm or a 14mm); then remove the stud holding the old alternator to the bracket (either a 13mm or a 14mm); then remove the "hinge" bolt holding the old alternator to the bracket (either a 13mm or a 14mm bolt screwed into a 15mm nut).

Installation of the new unit is done by reversing the steps of disassembly.

SAFETY NOTES: Be aware that there can exist pinch hazards during this procedure. Also be aware of the possible hazard of falling tools and/or debris.

Helpful hint: if possible, have someone else hold the bracket/alternator/tensioner assembly in-place while you start the lower 14mm bolt by hand from underneath the passenger side. This makes installing the upper bolts much easier.

Start ALL the bolts before tightening any of them. Generally, it goes pretty quickly if you begin with the "all bolts finger-tight, then all bolts hand (wrench/socket) tight, then all bolts torqued" method.

NOTE: Conspicuously dexterous people may not have to remove the alternator bracket, but in my opinion, the procedure is much easier if this is done. You should never have to remove the doghouse (engine cover inside the van) to replace the alternator. If a mechanic told you he/she did it that way, you should be going to a different mechanic.

There are two bolts visible on the front side of the alternator, and one on the BACK side which you can only feel, not see. The trick to remove this back side bolt is to remove the engine shroud in the passenger compartment, and remove the bolt securing the dip sticks to the firewall. With the dipsticks loose, you can push them aside enough to get a long socket extension on this back-side bolt (might be 10mm, I forget) from the passenger footwell area. An alternate method used by Pros, is to raise the vehicle on a hoist and use a 3-foot socket extension from the ground to reach up to this rear bolt. IMPORTANT NOTE: If this job is done by someone other than yourself, check to make sure this rear bolt was re-installed. Some unscrupulous individuals will omit replacing this bolt because it is such a PITA. You wil have problems a hundred miles down the road, failed alternator, thrown belt, cracked accessory mounting bracket, etc.