Jeep won't start stopped suddenly while going 50 mph won't fire.

SOURCE: 2001 silverado thumps when going 40 to 50 mph

Maybe check for loose u-joints, transmission mount, or carrier bearing if you have a two piece driveshaft.

SOURCE: 99 jeep cherokee died going down the road. will not start. has fuel but no fire

Check spark to plugs. Possible crankshaft position sensor. Located at rear of engine between engine and trans.

SOURCE: HAVE 2004 JEEP GRAND CHEROKEE,HAS LOW WHINING

the whinning noise is definalty a signiture of the bearing, and they do on occasion start making the noise long before other systoms of a bad bearing appear. There is really nothing else in the suspension that moves in a manner to cause the whinning pitched sound, other than the axel, but there signature has allways been a clicking around turns, so id definatly look cloesr at the bearings......good luck

SOURCE: speedometer stopped working

It's covered to 7 years or 70,000 miles. If you are past the coverage check out gmgaugerepair.webs.com They are much cheaper than the dealership and have a 24 hour turn-around time.

SOURCE: 1975 cj5 jeep starts to shake badly at about 40 mph.

check you tires for seperation or unbalace...