HELP car shakes horribly only when going downhill

[Sambo]

OK so my car has been doin really good untill a few months ago it started Violently shaking when traveling down Steep Grades. I was Driving Over a pass coming home from work and my wheel had a shake so violent you would think the car couldnt be driveable. Then as soon as I got a few miles down the road there was nothing. I decided to drive real slow and speed up to 60 to see if it was that but nothing. then i went really fast closer to 80 or 90 and still no more shake.

I had this problem while driving in the high rockies in the winter on random occasions but it was nothing i could ever get to happen. I took it to a shop and they looked thru the car and couldnt figure it out. they said maybe the Viscous coupling but would have to tear my transmission apart and i didnt have the money for that at the time.

I just drove 3000 miles and i didnt feel it once even going up and down mountain ranges. but going down the Altamont Pass in the Bay Area CA it definatly was one of the worst times ive seen it happen.

Does anyone know what this could be?? and why it would be so random ?

Thanks

[Wiscon_Mark]

So if the shop looked at it, I'm guessing they ruled out:

-Wheel balance
-Alignment
-Suspension bushings/bolts

I'm not really sure what it is, but does it only happen off-throttle?

I doubt it would be the viscous coupling (not ruling it out) as that happened to my old Outback and it drove pretty normally other than being FWD only until it got fixed.

[Sambo]

Recent events might have revealed the problem! Last night driving in town my front caliper locked up. I belive that could have been my problem the whole time. There was no pulling or anything. That's what really bothered me. But I fixed it and now to wait and see if it fixed the problem.

[Wiscon_Mark]

Frozen calipers can be weird. My left caliper froze up and the car was pulling to the right. It also made it feel like I had a flat tire (little bit of whumming).

[Huffer]

As soon as you said intermittent, my brain said frozen caliper.