could someone please help me diagnose the problem on my 1990 ls400. it keeps breaking serpentine belts. all pulley's (except crank) spun freely except last time it broke i noticed the pulley behind the fan did not spin. is that suppose to spin freely? is that the water pump behind the fan and if so could that be my problem? i noticed after i put the last belt on and engine was running the pulley behind fan would wobble now and then. thanks for any help you can give.

 

Yes the pulley you are refering to is called the fan clutch pulley, if it is not spinning than it needs to be replaced. To my knowledge when the waterpump freezes it usually means that the timing belt is broken and not the drive belt.

 

Sounds like the fan shaft bearing to me.

 

The part that you are referring to is called a fan bracket and yes the pulley on it is suppose to move just as freely as the others. It will haveto be replaced. The waterpump is behind the timing belt cover and directly drives the timing belt. Snap that one, and the car is dead. Only good thing is the 1st gen LS motors were non-interference motors so no harm would be doe be snapping a tming belt. Second gen and above, where VVTI is offered, snap that timing belt and start ooking for a new motor.

 

Yes, sounds like your fan bracket needs replacing. I just did this a week ago on my '91 with 174k miles.

The fan pulley itself is just a shell (no moving parts in the part itself), so that is probably fine. It is held onto the "fan bracket" by the 4 nuts that hold the fan clutch to the fan bracket. When you re-seat the pulley while installing the fan, make sure all is well-seated (relieve belt tension while doing it).

The "fan bracket" is a fairly big cast Aluminum piece with a bearing pressed in there. It is the bearing, which is for the fan pulley, that has failed.

Unfortunately, it is fairly involved to remove the fan bracket - many of the steps of the T-belt job are involved. T-belt covers, AC bolts, etc.

A new fan bracket will cost ~$230 for OEM and ~$120 for aftermarket. I was in a rush when I did mine so I bought aftermarket from my local Kragen. Turns out that part did not fit well. I had to use a jigsaw to cut down one end of the bracket where an AC-screw comes in by about 1/8 inch. Also had to use my dremel cutoff tool to trim down one of the T-belt covers since the casting was a little off. I would not have done either of those, except that I was already late for leaving on my trip and had no real choice.

 

If you do have to trim off part of the T-belt cover, like oldskewel says, make sure you seal it up with some sealer. You don't want dirt and oil getting into the T-belt. I needed to do it with my lower cover, there was no way I was paying $40 for a new gasket when a $5 tube works just as good.
The thing with aftermarket parts is you run into problems like these, that's why they are cheaper. But yeah, they should do a better job copying a part.