2005 Mustang GT Under Drive pulley Installation Instructions

By Octavio Diaz




These instructions are for installing a set of MotoBlue Underdrive pulleys on a 2005 For Mustang GT, but these instructions may be applicable for other UD pulleys.


Before you start, make sure you have all the necessary tools, rent them if you have to. My local Auto zone has a loan a tool program and they lent me most of what I needed except for the power tools.

Quick inventory first. The MotoBlue kit comes with an idler pulley, a bolt for the idler, the water pump pulley and the Crankshaft pulley. During the install you will reuse the 4 original 10 mm bolts form the water pump pulley and the 18 mm crankshaft pulley bolt.  Other underdrive pulley systems may not include the idler pulley.  Steeda does not.

Get a paper and pencil and draw out all of the pulleys and how the belt goes around them. Believe me you will need this. I did not do it and had a really tough time trying to figure out how to put the #$$%%% belt back on.  I recently found the following diagram that shows the propper belt routing:

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1) Compressor

2) 5" or smaller impact wrench gun (an impact ratchet does not have enough power for the crankshaft bolt)

3) 10 MM socket, 18 MM impact socket and 24 MM socket

4) 1/2" ratchet

5) Harmonic balancer install kit. ; OEM Part Number 27144 or equivalent (shown on left in picture below

6) Harmonic balancer puller - OEM Part Number 27139 or equivalent (shown on right in picture below.

7) Large Rubber band

8) Dremmel tool with metal cut off wheel or smaller bolt for alternator bracket (see step 11 below)

9) two adjustable wrenches

I could not find any instructions for the MotoBlue pulleys but I was able to reference some Steeda instructions. Though the pulleys might be different, the procedure is the same. Here are the steps for the removal/installation:

1) The Steeda instructions say to disconnect the battery but I don't see the need for it, I'm not going to be touching anything electrical.

2) Remove your air cleaner tubes. This will give you more clearance.  Othesr have recommended removing the radiator fan but this involves draining the Antifreeze reservoir and the Power Steering reservoir and removing them first.  I did not see the need for this.  The clearance is tight, but sufficient to complete the job.

3) Loosen ALL of the bolts BEFORE removing the belt. I made the mistake of removing the belt first and then all of the pulleys turned freely. The 4 bolts on the water pump are 10mm. The bolt on the crank shaft is 18 MM. Others have said you can remove it with an impact ratchet but I wasn't able to. Most impact ratchets are only rated for 40-60 Ft-lbs of Torque.  I tried a very long torque wrench on the crankshaft bolt and it had over 120 Ft-lbs on it. I tried getting a long pipe to fit over the end of the torque wrench for more leverage, but that did not work either. I wound up having to go to Sears and buy their smallest impact gun. It only measured 5" and it was just small enough to fit.

4)Make sure the torque gun is set to counterclockwise. This new gun I was using had a little push button to control the direction and the fit was so tight that the button kept getting pushed in and the bolt kept getting tightened instead of loosened. Also, make sure your air compressor is set at the maximum rating for the gun (mine was 90lbs but I set the compressor to 100) and that the compressor stays on . My compressor blew a circuit breaker and just kept emptying. I didn't realize it did not have enough air for the gun until the tank was almost empty.
5) Verify your belt orientation picture is correct and remove the belt. To remove the belt, use a 1/2 ratchet and insert it into the square hole on the tensioner pulley (this is the idler pulley with the long arm) and push down on it. After removing the belt, remove the pulley on the water pump. Don't put the new one on yet, this way you'll have more room to work. Screw the waterpump bolts back into the water pump so you won't loose the bolts.

6) Remove the old idler pulley and bolt. You wont' need the old bolt, you'll be using the new one. Install the new idler pulley. It works great, much less friction then the stock pulley. The pulley goes on with the C clip pointing towards you. If you put it on the other way, the pulley binds up against the engine. Once you have the pulley installed, tighten it with the bolt they provide you. The washer on the stock bolt is much too large and will restrict the pulley. When you're all done tightening the idler pulley, it should turn freely.

7) Remove the crank pulley. Make sure you use the right tool. The first time, Autozone gave me a pulley puller and it was not big enough. You need a harmonic balancer removal tool. There are 2 types. The first is a flat piece of metal with three long slots. There are long bolts that fit into these slots and screw into the crank shaft pulley. Then there is a very long bolt that screws in the middle. The other type has three claws that fit inside the crank pulley. There is a pin (use the shorter one) that goes inside the crank shaft and then a long screw that screws through the claw and pulls the pulley out. The MotoBlue crank shaft pulley takes the first type but the one in the car takes the second. This claw puller is very difficult to use, the claws keep slipping. I worked on this for several hours before I thought of putting a rubber band around the jaws to keep them closed. This worked like a charm. Use a 24 MM socket to tighten the bolt on the tool. The following picture shows how the puller fits around the crankshaft.  It’s impossible to see this on the car but by seeing the pictures below, you should get a better idea of how the tool fits on the crankshaft.


8) Boil the new crankshaft pulley for about 10 minutes, not much longer. The idea here is that the heat will make the pulley expand and thus make it easier to install. While it is boiling, put some grease on the crank shaft to help the pulley go on. Not too much, keep it clean. Using ultra black gasket sealer put a dab in the notch key area of the underdrive pulley so when you install it no oil can get out.

The pictures below show the old and new crank shaft pulleys.  Notice how much smaller the new underdrive pulley on the right is.


Conversely, the new water pump pulley (on the right) is much larger then the original:

9)Iinstall the crank shaft pulley lining up the key notches. You'll need a good set of gloves so you don't burn your hands. Use a harmonic balancer install tool to "press" the new pulley onto the crank shaft nice and even.  You will need to use the M12x1.5 mm adaptor on the tool.  The picture below show how the tool is put together.  Install the adaptor onto tool.  Install the bearing and then the nut as shown below.




Using the tool is quite simple.  Screw the tool onto the crankshaft and tichten the nut as much as possible by hand.  Then, just hold the end of the tool with a wrench and use another wrench to tighten the large nut.

10) An alternate method of installing the crankshaft pulley is recommended by Steeda. They recommend the torque turn method. Steeda claims it is more accurate. The torque turn method measures how much the bolt is stretched which is really what is desired. Friction from the bolt head and washer is a factor which leads to inaccurate torque of a fastener. Use the original 18 MM bolt and tighten as follows.

Torque to 67lb-ft. this step seats the balancer

Loosen half turn. this step relieves all stress on the bolt

Torque to 37lb-ft , this step pre-torques the bolt before bolt to washer friction becomes an issue

Tighten an addition 90 degrees, the fourth step stretches the bolt to the proper tension

11) install the water pump pulley using the original bolts. Finally, install your belt using the diagram you drew. Make sure the belt sits properly on all of the pulleys.  Note that there is a bolt coming out of the lower alternator bracket on the left side of the engine that interferes with the MotoBlue water pump pulley.  Make sure that there is sufficient clearance between this bolt and the Water Pump pulley and the belt.  I did not notice this at first and it destroyed the belt when the engine started.  To solve this problem, I cut 1/16” from the end of the bolt using a cut off wheel on a dremmel tool.  Start the engine and watch the belt to make sure it is properly aligned.


12) Reinstall your intake tubes and enjoy the extra HP.

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