UnderDrive Pulleys for 4.6L GT/Cobra

Guide to installing piggybacked underdrive pulley systems for 4.6L GTs and Cobras
by Ben West (nick BenW on SN, Corral, SCOA, etc etc) see bottom for contact info.

Tools needed
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- ratchet
- ratchet extensions
- 10mm, 11mm, 18mm sockets plus others
- torque wrench
- breaker bar or impact wrench
- harmonic balancer puller tool (place deposit at O'Reilly or AutoZone, get $ back when done)
- 3/4" drive ratchet OR massive screwdriver
- Loc-tite Red
- high temperature silicon RTV sealer (ultra black OEM)
- floor jack and 2 jack stands (optional)
- a helper (optional)

1.) Disconnect the negative battery terminal. Just a preventative measurement.

2.) Put the car into first gear if manual, park if automatic, set parking brake.

3.) Begin by removing the Degas container's three bolts and washers. They secure the overflow container for the radiator to the fan as well as a pedestal in back.

4.) Position a catch pan of some sort beneath the driver's side headlight, underneath the radiator's bottom corner.

5.) On the Degas container there is a small hose running from the container into one of the main radiator lines. Using a pair of pliers, squeeze the hose clamp tabs towards each other and gently rock the clamp away from the fitting. Remove the hose, and be prepared for a bit of coolant to seep out of the plastic nipple. * you may want to stuff a rag or towel into the crack where the nipple leaks coolant, or let the catch pan do it.

6.) grasp the Degas container by the left and right sides as if handling a package. Rotate one side of the container under the other so it rotates away from the pulley area, giving you clean access to the pulley system. On my 4.6L GT there was a plastic tab which conveniently held the overflow container away from the work area without stretching hose lines.

7.) Using a 10mm socket, loosen the water pump pulley from the water pump. It is helpful to have an assistant put counterforce on an opposing bolt with another 10mm socket tightening while you are loosening. When your bolt breaks loose, stop and repeat for the rest. Leave the pulley on with the bolts slightly broken.

8.) Remove the accessory belt. Using a 3/4" ratchet (one of the biggies), put the bare ratchet into the belt tensioner's hole and turn the handle in the direction indicated by the tensioner pulley. The pulley will move away from the belt, allowing you to slip it off the top of the alternator pulley at the top of the engine. Once it is off the alternator, the belt will have plenty of slack and you can remove it from the rest. ALTERNATE METHOD: if you do not own a huge 3/4" ratchet, you can put a massive flathead screwdriver into the tensioner hole and lean into it, pressing the tensioner down and away, pulsating on the tensioner. An assistant will be able to barely and laboriously remove the belt from the alternator pulley.

9.) If you are using the alternator pulley from the new set, remove the alternator nut with an impact wrench. If you do not have one, it will not come off. Either use the stock one as I did, or unbolt the alternator, drive to your neighborhood garage, and ask them politely to install the underdrive.

10.) Remove the water pump pulley and set it aside.

11.) Now remove the crank pulley. This is what you ate your Wheaties for this morning. Use a 18mm socket on this bolt. It is NOT cross-threaded, it is conventionally threaded, just takes brute force to get it off. A long pipe or breaker bar should afford you the leverage you need to break the nut. After that, its all downhill. Remove the bolt and set it aside, retaining the large washer.

12.) Pull the crank pulley off the crankshaft using the puller tool. It is very simple to use and all the bolts you need will be in the box you rented it from. If there are not any bolts, use the ones in your pulley set temporarily. This is hard to describe how to use but it is very simple you will figure it out. The puller tool serves one function: to pull circular objects off their center bolt by applying perfect equal force to all three sides.

13.) Now the 2 main pulleys are off - water pump and crank. The next step is to bolt the underdrive crank and the stock crank together. Why? Because the stock crank pulley acts as a dampener and is needed to smooth out crankshaft operation, that's why. Use the three bolts included in your kit to sandwich the pulleys together. Use loc-tite here. Tighten WELL.

14.) Using your 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.

15.) Now slide the 2-pulley array onto the crankshaft, underdrive first. Gently work it inward as much as you can. Then insert the new longer crank bolt with your stock old washer. Use this to further draw the assembly onto the crankshaft. Torque to 60-65 ft/lbs (tight).

16.) Install the new water pump pulley and secure it using the stock bolts. Torque to ~ 20 ft/lbs.

17.) reinstall the belt. Make sure it goes on the underdrive crank pulley, not the stock crank pulley which is also right there.

18.) Position the Degas container back where it goes and bolt it down.

19.) Re-attach the small radiator hose to the Degas container.

20.) Start the car and let it idle, observing the pulleys and belt. Watch for any loose bolts on the sandwiched pulleys or a pulley spinning out of round. If everything is OK and the belt is no slipping, go ahead and take a spin. Your radiator lost a little bit of coolant, so top it off with some water.

That's it. Be sure to re-torque the crank pulley bolt and water pump bolts a couple days afterwards to make sure they are holding their torque. Enjoy your 5 horsepower improvement!

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Contact Info
Ben West | [email protected]
ICQ: 1380121
AIM: Stack97GT and Ben MMDS

1997 GT coupe, crystal white, black cloth, 5-speed, 3.27s, Tri-Ax, underdrives, ram air, K&N.
1994 Cobra coupe, rio red, black leather, 5-speed, 3.08s, Tri-Ax, stock.