BMW Repair: instruments, 1990 bmw 535i, bmw 535i

Question
I have a 1990 BMW 535i.  Lately I have noticed that the instruments on the dash panel have been acting up a lot.  The speedomoter will jump when the car comes to a stop, the gas gauge will read accurately to the best of my knowledge until it gets to a 1/4 of a tank, and then it just drops to empty.  I have drove close to a 100 miles with it on E, so I don't believe it is empty, and lately the Temp gauge seems to be getting to the center line on the gauge very rapidly, but it never exceeds that center line.  The car does not seem to be overheating, but I fear that the gauge might not be telling me the right info.  Any ideas on what could be causing this?

Respectfully,
Donovan Farrald
Eugene, Oregon

Answer
It's unlikely that the elecric signal from the fuel gauge, temp gauge and speedo are all flustered at the same time.  My best guess would be that the cluster itself is bad.  I replaced one because i put a 3-4inch crack in the clear plastic cover. The cluster was working great when i removed it to replace the backlight bulbs.  I would be willing to let you put it in your car to test it so long as your willing to pay shipping from seattle WA and if it doesn't solve the problem ship it to Phoenix AZ.  
Check all the grounds also, sparatic readings can sometimes be linked to a bad or intermittant ground.  Either way a known good unit to test it with would determine the problem.
As for price, whatever the average price they sell for on ebay minus some $ for the cracked display sounds fair to me since i was going to put it on ebay anyway.  other good sources for a display is www.junkyarddog.com and sometimes the message boards http://www.roadfly.org/bmw/forums/
.  If you can convince a local junkyard to let you test the gauge before you buy it you could save some time and money however generaly speaking junkyards will demand the highest price for used parts because it's an expensive car and few are ruined due to accidents or premature failure.
-cheers
scheidmiwa@hotmail.com