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Hey guys-

I'm not sure if anyone remembers the thread from a few months ago, but I posted about problems I was having with a front-end vibration only when accelerating (please see it at http://www.mx-3.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=000940#000000 for details).

Well, I'd replaced the tires, both front axles and got it re-aligned (again), and I STILL had the problem. Also, my MS engine/tranny mounts and struts were just fine. I then had it in the shop for a weird high-pitched noise coming from one of the pulleys, and my mechanic told me my crank pulley was toast. Honestly, I can't remember exactly the way he put it, but I know that the harmonic balancer was almost completely gone, and the pulley(s) were just spinning erratically.

He thought that this could very well cause the front-end vibration I was experiencing, so I got myself a new underdrive pulley from R&R Racing (same specs as the UO pulley, but about $125 cheaper). I had doubts that this would fix anything at all, but since the pulley seemed to be causing a problem with my water pump anyway, I went ahead and had it installed.

Well, to my great surprise, the vibration is now all but gone. Acceleration is completely smooth. AND, I'm not having any of the adverse effects that some people report after installing an underdrive pulley (weak battery charging, etc).
I never even considered the crank pulley as a possible cause for this, and my advice to anyone having this problem as well (I remember a few with similar issues) is to check this thing out. I was focusing on my suspension parts, and it turns out everything was fine there.

I can post a pic of my old pulley if anyone wants to see what kind of shape it was in. In case anyone doesn't know, it's a dual-pulley that's supposed to be one solid unit, and I could actually yank the two pulleys apart...
Anyway, just thought I'd share my experience. It's the end of a long and frustrating 6 months of troubleshooting.

Thanks...

Interesting. Good job. I'd be interested in seeing pictures. How difficult was it to put on the new pulley?

notice any gains from when the normal pulley was on and it running right

To answer both of the above questions:

The pulley itself is not difficult to put on, however I knew going in there would be a need to cut off part of the flange from the oil pump housing. I would have done this job myself, but since I needed the water pump replaced as well (a tough job for me to do in my driveway), I just had my mechanic do the whole thing. He told me he had to cut quite a bit off the oil pump housing, which is contrary to what I've read from others.

It's hard to tell if it's had any effect on performance, mainly because the car feels so much different without the vibration I was getting before -- much smoother, more responsive acceleration. Also, I haven't driven the car all that much since the install because my battery decided to start dying on me (unrelated issue due to an old battery). But it does seem like the engine revs just a little faster now, and it seems I'm getting more power to the wheels. But again, this could simply be because my old crank pulley was so messed up. I was having a hard time breaking the tires loose even in first gear before!

I have to be honest, I don't quite understand how this all affects the drivetrain, and if anyone would like to shed some light on this, I'd be very interested in hearing it. If anyone has other questions about the UD pulley, please let me know and I'll try my best to answer!

As I understand it, the lower wieght of the underdrive pulley makes a bigger difference than the smaller diameter. It does the same thing as shaving weight from your crank or flywheel to give you more power.

As for your vibrations, I know from experience that all kinds of things can cause all kinds of vibrations, so I'm not surprised that the crank pulley fixed it for you.

I didn't hear about having to shave down the water pump, but I haven't researched the underdrive pulleys very much at all.

Originally posted by JasonH:
I didn't hear about having to shave down the water pump, but I haven't researched the underdrive pulleys very much at all.

Well, it wasn't the water pump that needed to be shaved, but rather the oil pump housing. I'm not sure if he had to shave some off the timing belt cover, or not... but I've heard that may be necessary.

Yeah, I meant oil pump.