Well this is my first caddy, but I have always wanted one since I was a little kid. I purchased the car from a guy that lived like two house away from my work which was just luck cause my 87 t bird wasn't really a lady killer. So I bought the car in which had been taken really good car of by the previous owner which was an old rich women who had just bought the car to get suffured around in. anyways long story short my car shakes at just 45. I have balanced the tires rotated them and they are all in spec, I am really hoping this isn't a tranny problem but I don't feel the vibration on the seat it feels mostly everywhere pleaese help :)

Rob

Perhaps it is a timing issue; but that would happen at other speeds too. Is it past 45 and 45? Or does it only happen when you reach that threshold?
Could even be the driveshaft.

Two words: Torque Converter.

hmm sounds like a fun job but I don't understand about the torque converter? How would that cause a shutter at 45? O and to answer you question it is between 42-48 but I rounded it to 45 because that were it is most severe. I think it may be the driveshaft, how should I go about checking that without a lift for my car??

Yes, it could be the driveshaft. Have a look at the linkage and the universal joint. Don't tighten anything or loosen anything, just check to see that it is secure. You can have a driveshaft/transmission shop to check this to be sure. Get a few opinions if one wants to do something drastic. I am sure it is not the torque converter in this case. Also, it could be a suspension problem - check your shocks. Especially if the vibration seems to be coming from one of the corners of the car.

Hey thanks I think I will have a look under my car tonight and check and see if there is any slop

I certainly didn't mean torque converter was the only possible cause. Around 45 mph is where you'll go into overdrive, as well as having the torque converter clutch lock-up, if you're at cruising speed or light acceleration. Perfect MPH for a converter shudder. There are certainly other possibilities, but that's my first inclination.

im having the same problem at somewhere at 55mph can u help me

My bronco was like that,, at first only at really high speeds,, then it go worse by the day,, to the point where it was real violent all the time,, i put it on a lift and found where my driveshaft bolted to the tranny was loose,, the two of the four bolts had worked thenself 3/4 of the way out, and i could move the driveshaft up and down with my hand,, sounds like u could have the same thing.

Check u-joints. Also a seized fan clutch can do some pretty goofy things. See if the fan freewheels. Tires full of fix-a-flat are fun too.

I have a similer problem, except mine is when i break at anyspeed over 50 mph. Is this a balancing issue? It just started when i put my summer wheels and tires on about a week ago.

I have seen a bent driveshaft do it too (65 Mustang 200 cid 6 cyl, 3 speed stick), weak motor mounts compounded the issue. It took us 3 shafts to get a straight one.