Hello fellow Mercurymen! I’ve had my car since '96 and she always had bad vibrations seemingly in the ass-end. She doesn’t shake 'til I hit 55mph. Faster I go, worse it gets! I’ve replaced all u-joints and front end parts. I’m thinking the driveshaft. That’s not the only problem. I get bad spark knock w/premium fuel. Timing is spot-on. Plugs and wires are good. Anyone with any input is much appreciated! Thanks!!!
She has more problems but I get really stressed out when I talked about it! It’s the life long lesson:“If you want it done right do it yourself or find someone that’s not gonna f*** you over and over and over…”
The driveshaft would be the first thing to have checked, not likely but pinon angle can cause vibs too. If you are absolutely sure your timing is correct, sometimes carbon buildup on the piston can cause pre-ignition due to a hot spot. Some fuel additive may fix it, but an old mechanic’s trick is to slowly pour ATF down the carb while you rev the engine up and down. It will smoke a lot but I’ve seen this work.
Also, check the rear pinion yoke. Make sure the rear u joint is centered in the yoke correctly. Could also be rear end axle bearings.
check your rims too - might have lost a weight or bent a rim.
Thanks all for the input! The wheels-n-tires have been balanced. I need to get this car out of my brothers pole barn and over to my place so I can work on it!
Check to make sure your weights have not fallin off either of your brake drums. I had that happen on one of mine caused a vibration.