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GM 3800 II Tensioner & Idler Pulleys Replacement Guide
Pictures illustrated instructions for replacing the idler and tensioner pulleys in a 1997-2003 GM Pontiac Grand Prix GTP.

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This "how to" automotive repair guide was specifically written to assist owners of the 1997-2003 General Motors Pontiac Grand Prix GTP in replacing a tensioner pulley and idler pulley. Owners of other GM cars with engines similar to the 3800 Series II 3.8L V6 may also find the guide to be useful. These other vehicles include the following: Buick Park Avenue Ultra, Olds Eighty-Eight LS, Oldsmobile Eighty Eight LSS, Olds Ninety-Eight, Pontiac Bonneville (SLE, SSE, SSEi), Buick Riviera, Buick Regal (GS, GSX, SLP), Chevy Impala SS, and the Chevrolet Monte Carlo SS. I am not a professional mechanic. I assume no responsibility for damage to your vehicle, persons, property or pets. If you have any doubts, please consult an ASE certified mechanic. Please proceed with caution at your own risk.
GM 3800 Series II Engine
Dayco Serpentine Belt
Supercharger Belt

A few days ago the serpentine or "accessory" belt in my 2001 Pontiac Grand Prix GTP tore itself apart after some spirited driving.

While replacing the Serpentine Belt and the Supercharger Belt, I noticed that a tensioner pulley and an idler pulley didn't spin easily due to their bearings being worn out.

Rather than wait for them to seize and destroy another belt, I decided to replace both of the stubborn pulleys.

The directions below will cover how to access the belts, remove the belts, remove the pulleys, re-install new pulleys, and re-install the belt.

The tools needed include the following: 13mm socket, 15mm socket, 10mm socket, 8mm socket, long handled socket wrench, and a ratcheting socket wrench.

Half of Serpentine Belt
13mm Socket
Buick STB Bolts
The parts you may need to complete this procedure include the following: Dayco 89007 3" Smooth Pulley, Dayco 89006 3.5" Smooth Pulley, Dayco 89051 3" Ribbed Pulley, Dayco 5060918 Serpentine Drive Belt, and the Dayco 5060665 PolyRib Supercharger Belt.
Buick Strut Tower Brace
Removing STB Bolts
10mm Socket
Some of the symptoms of an idler or tensioner pulley that needs to be replaced include squeaking sounds, squealing, vibrations, chirping, and/or rapid belt wear.
Coolant Overflow Bottle
Removing Coolant Bottle
Removing Coolant Hose
To access the belts more easily, you'll need to remove the coolant overflow bottle and unbolt the left side of the Buick STB (strut tower brace) if you're car is equipped with one.
Coolant Hose Covered
8mm Socket
Removing Battery Cables
For extra safety, I recommend covering the coolant overflow bottle's hose and remove the battery terminals with an 8mm socket. I also covered the battery terminals with tape to prevent the possibility of an electrical shock.
Battery Terminals Covered
15mm Socket
Belt Routing Diagram
The supercharger belt must be removed first on GM 3800 Series II engines equipped with the Eaton M90 Supercharger. If you have a naturally aspirated GM 3800 Series II engine (L36), skip down past the next block of text.
15mm On SC Tensioner
Pull Towards Front of Car
Supercharger Belt Off Pulley
To remove the supercharger belt, place the 15mm socket and long handled wrench on the supercharger tensioner pulley. The supercharger tensioner pulley is located near the front of the car right behind a black 3" grooved idler pulley. Then push the wrench towards the front of the car to relieve the tension on the belt. With the tension relieved, slip the supercharger belt off the supercharger pulley. Then you can pull the supercharger belt off the two idlers and the crank shaft pulley.
Removing Supercharger Belt
SC Belt Off Crank Shaft
Old Supercharger Belt
SC Belt Pits & Cracks
Supercharger Belt Removed
15mm On Serpentine Tensioner
To remove the serpentine belt, place the 15mm socket and long handled wrench on the serpentine belt tensioner. The serpentine belt tensioner is located right below the alternator. To relieve the tension on the serpentine belt, push the long handled wrench towards the rear of the car and then pull the serpentine belt off the alternator.
Push Towards Rear of Car
Slip Serpentine Off Alternator
Old Serpentine Belt
Then pull the serpentine belt off the power steering pump, the tensioner, the water pump, the crank shaft, and the air conditioning pulley.
Half Missing, Cracks, Pits
New Serpentine Belt
Power Steering Fluid Reservoir
Since you already have the coolant bottle and belts removed, now is a great time to check the level in the power steering fluid reservoir. My car has a very slow leak that requires topping off the fluid every 6 months to prevent the PS from whining.
SC Tensioner & Idler Pulleys
Spinning Pulleys By Hand
Serpentine Belt $40
The first pulley I replaced was the serpentine belt tensioner pulley located just below the alternator. To remove the pulley, place the 15mm socket and long handled wrench on the pulley's bolt. The pulley's bolt is reverse threaded so to the left is tighten and to the right is loosen.


Removing 3" Tensioner Pulley

3" Serpentine Tensioner Mount

Installing New 3" Tensioner
After loosening the tenionser pulley's bolt, it will come off with a large metal washer attached. The 3" smooth tensioner pulley itself can be removed by gently rocking it while pulling it away from the engine. Clean the tensioner pulley's mount with some compressed air and then install the new pulley. Remember that the bolt is reverse threaded (A.K.A. "left hand threaded). Torque it down to about 50 Nm or 37 lb ft. I tightened the bolt snugly and then turned the wrench another 1/8 to 1/4 turn.
Pulling Off Old 3.5" Idler
3.5" SC Idler Removed
Rear Of Old 3.5" Pulley
The larger 3.5" smooth supercharger idler pulley is located just above the crank shaft pulley (lowest & largest) and slightly closer to the front of the car. To remove the 3.5" SC idler pulley, place the 15mm socket and long handled wrench on the pulley's bolt. The SC idler pulley is threaded normally so the "lefty loosy and righty tighty" rule applies. After loosening the 15mm bolt all the way, the bolt will come off with a large metal washer attached. To completely remove the pulley, gently rock it back and forth until it slips off the mount.
Front of Old Pulley
New Dayco Pulleys
89007 3", 89006 3.5"
I bought the new Dayco 89007 and 89006 pulleys for about $20 each at Advance Auto Parts. They come with a 1 year guarantee so make sure you save your receipt in case they seize up prematurely.
Supercharger Idler Pulley 3.5"
SC Belt Idler Pulley Mount
New 3.5" SC Idler
I cleaned the 3.5" SC idler pulley's mounting location with compressed air before pressing on the new pulley by hand. Then I threaded the bolt and large washer on a few turns by hand. If you have a torque wrench the bolt should be torqued to about 50Nm or 37 lb ft. Alternatively, you can tighten it snugly and then go another 1/8 to 1/4 of a turn.
Idler Pulley Bolt & Washer
Tighten With 15mm Socket
New Serpentine Belt
Both New Pulleys Installed
Belt Routing Diagram
Once any stubborn or seized pulley has been replaced, you can replace or re-install the belts. The serpentine or "accessory" belt goes on first. Keep in mind that the flat side of the belt goes around smooth pulleys and the ribbed side of the belt goes against any ribbed pulleys.
Routing Serpentine Belt
Hold Serpentine Near Alternator
15mm On Tensioner
The easiest way to install the serpentine belt is to first wrap the ribbed side around the inner part of the crank shaft pulley. The crank shaft is the largest and lowest pulley. The outer set of ribs on the crank shaft are for the supercharger belt. Then route the serpentine belt around or over the water pump, air conditioner, power steering and tensioner pulleys. Hold the serpentine belt near the alternator pulley with one hand. Then put the 15mm socket and long handled wrench on the tensioner pulley just below the alternator with the other hand. Push the wrench towards the rear of the car to release the tension on the belt and slip the serpentine belt over the alternator's pulley.
Push Towards Rear of Car
Checking Belt Routing
New Supercharger Belt
If you have a N.A. or Naturally Aspirated GM 3800 Series II engine, you can skip down past the next block of text.
Routing SC Belt
Supercharger Belt On Crank
Hold Near Supercharger Pulley

To install the Supercharger belt, first wrap the ribbed side around the outer set of ribs on the crank shaft pulley (lowest and largest). Remember that smooth pulleys get the smooth side of the belt and ribbed pulleys get the ribbed side of the belt. Route the supercharger belt over or around the 3" smooth tensioner pulley, the 3" ribbed idler pulley, and the 3.5" smooth idler pulley.

Push 15mm Towards Front
Slip SC Belt Over Pulley
Both Belts Installed
Hold the supercharger belt near the supercharger pulley with one hand. Place the 15mm socket and long handled wrench on the supercharger tensioner pulley (just below the SC pulley and towards the front of the car) with the other hand. Push the wrench towards the front of car to relieve the tension on the belt. Slip the SC belt over the SC pulley. Double check the routing and fit of the belts. There should only be a tiny amount of slack in each belt. If either belt feels loose, you may need to replace a tensioner mechanism.
Re-Install Coolant Bottle
Re-Install Battery Terminals
Attach Coolant Bottle
Now re-install the coolant bottle, re-attach the battery terminals, and re-attach the passenger side of the Buick STB (if equipped with one). If you did everything correctly, the motor should sound & look like this - GM 3800 Series II Engine Video.
Re-Attach Buick STB
Job Complete
Pulleys - About $20 Each
For more of my automotive "how-to" instruction guides, click on the following links: Pontiac Grand Prix Supercharger Belt Replacement Guide, GM 3800 Series II Serpentine Belt Replacement Guide, Pontiac Grand Prix Front Brake Pads Replacement Guide, Grand Prix Rear Brake Pads Replacement Guide, Pontiac Grand Prix Brake Lines Bleeding Guide, GM 3800 Series II Power Steering Fluid Maintenance Guide, Pontiac Grand Prix Alternator Replacement Guide, Pontiac Grand Prix PCV Valve Replacement Guide, Grand Prix TCS/ABS/SES Troubleshooting Guide, GM Pontiac Grand Prix Power Window Motor & Regulator Replacement Guide, GM Wheel Bearing Hub Replacement Guide, GM Pontiac Grand Prix Engine Oil Change Guide, Eaton M90 Supercharger Oil Change Guide, and the Tail Light or Headlight Condensation Removal Guide.
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