Land Rover Repair: vibration, driveline vibrations, wheel balancing

Question
Hi John!
 I have a 95 discovery with approx 95,000 miles on it. I have two different driveline vibrations that may or may not be connected to each other. They are causing me some concern.
 One vibration starts at approx 70mph or so. I haven't ever had the car above 75, so I don't know if it goes away with higher speed. I don't believe it's tire balance or alignment - I've had both checked & there's no shaking or vibration coming up thru the steering wheel. It feels as if it's coming from the rear of the car or from underneath it. Almost as if the driveshaft is out of balance.
 The other vibration is much more severe, although  intermittant, it seems to be happening a little more frequently lately. This vibration only comes on above 45mph or so. Below 45, the car is as smooth as silk. Under acceleration or going up hills, the car starts to shudder & shake, if I let off the gas it goes away somewhat, & sometimes by babying or feathering the gas I can get the car up to 65 or so. Manually downshifting helps a little as well.
 Any thoughts or recommendations would be greatly appreciated - I don't have the budget to start throwing parts at the car without having a good idea of what the problem may be.
 Thanks so much!

    Jim Scholten

Answer
Hi Jim,

I understand your situation.  I too hate throwing money at a problem and prefer to know as much as I can before opening my wallet!

Could be two separate vibrations.  You're in luck about the first vibration:  I too have a slight vibration at high speeds and it usually starts around 75mph. I rarely get to this speed and usually maintain a comfortable 60 as much as possible.  I always thought it was alignment and wheel balancing coupled with the weight of the Disco. Since I rarely drive at those speeds, I've ignored this and the problem has never progressed.

The second vibration may be related to fuel/ignition timing.  It could be a timing adjustment that is needed on your engine, it could be the injectors, general tuneup, distributor cap and rotor.  By your description, I'd start looking at the ignition components I just mentioned.  It could also be the TPS (throttle position sensor) beginning to fail.  Lastly, it could be vacuum related. A seasoned mechanic could test your system to see if you have a leak.  I also heard of leak in the gasline that could cause the engine to bring in more air than required and cause those same shudders under load.

I hope this helps,

Regards,

JohnMc