What causes really bad vibration and steering wheel shake when my 1993 grand cherokee hits a bump at a speed over 55 mph

SOURCE: 1996 grand chorkee 4x4

Having just purchased a used 96 Grand Cherokee I know exactly what you are talking about. You have a condition known in the Jeep world as DW (Death Wobble).Now this condition can just happen over time with wear and tear. Orcan be caused by lifting the Jeep with a kit to 3 or more inches in heightand adding larger tires. In my case DW had reached a severe point and was caused by multipleproblems all in the front end steering equipment. You may or may nothave all these problems. But all can contribute or any one cancause DW. I started with the visible loose or bad components. Ball joints: Loose.
Universal Joints in front driveshafts: Worn and rusted inside the bearing caps.
Brakes: Not the pads themselves but the rubber covers for the sliders on the disk brake calipers. They had torn and allowed water and dirtto get inside causing sticking and uneven braking. The pads were worn at a angle instead of evenly.
Steering Gear. The seal above the Pitman arm had fallen out and allowed dirt and water into the needle bearings. Eventually the bearings failed allowingexcessive play in the shaft the pitman arm was attached to.
Shocks: Just plain shot
Tires: Brand new but needed balanced. I recommend computer spin balancing.Mine when purchased were done on an old bubble Balance machine. This turned out not to have the accuracy necessary for a jeep.
Tire inflation: Yes the amount of air in the tires can cause this. If you have added larger tires and inflate them to the max recommended PSI you will get DW or make it more severe. Mine are 31x10.50s mounted on 15" x 10" wheels.At 45 psi DW is very severe. At 25 psi it is hardly noticible.
Steering Stabilizer: Mine was leaking.
Alignment: After all this work Alignment was the last step. Make sure you replace anypart that is loose in the front end before the Alignment or you'll have to haveit done again. Find a shop that does four wheel alignment. It costs a bit more but front and back wheels are aligned for proper tracking. Now after all that, in my case, I still have DW. But it now only happensonce and awhile at about 44 mph and quickly leaves by slowing downor speeding up. On the plus side compared to when I started at least I am no longer worried that the front end will shake itself loose and fall out. I have a 3" lift on mine so next step is a Adjustable Track Bar. This is necessary to adjust the proper centering of the front axle. There is a shift usually to the left when raising the vehicle 3 or more inches which can also cause DW. Your problem is likely not as severe as mine was. But any or all of these parts can cause DW. Ones I did not mention was Tie Rod Ends and any rubberbushings at mounting points in the front end. Mine were fine. So jack it up and start looking for anything loose or worn in the front end steering and mounting components. Then change anything that looks worn or loose. Good Luck.

SOURCE: Steering shakes violently when I hit a bump

I had the same problem and it was a small shock sitting horizontally called the steering stabalizer your something close to that. Eazy fix.

Jason

SOURCE: The front end shakes badly when going over a bump

That and other bushings and idler arms worn. I would suggest a free inspection somewhere for them to show you what needs repaired.

SOURCE: When appling brakes on a 2000 Jeep Grand Cherokee, steeing wheel

New revised calipers. and have the new rotors machined right out of the box before installing

SOURCE: my front end shakes when i hit a bump at 50 mph, the front tires

could be a bent rim ? have you changed the universal joints? how about the tie rods and stabilizer bar

Testimonial: "thank you very much, i will do this first thing. i have had several people look at it , and of course they have told me it was not the tie rods,i knew"