92 240sx speedometer problem

[tsnider]

Speedometer is very erratic showing anywhere from 50-95 mph going about 40. Showing varies greatly with speed. How can I tell if it's the cable, sending unit, or cluster.

Been rebuilt from wreck with salvage title - BAD BAD shimmy in wheel at any speed - amount also varies - seems worst @ about 2500 rpms. but happens all the time. 4 places over the years have said the alignment is fine - tires are new.thx

[Wc240]

search for speedo. more pages cover that topic than any other. for vibration, get under the car and look for things that are damaged, cracked, check the drive line, and search for vibration

[AZ89two4Tsx]

Take the speed sensor out. Crank it by hand. Judge accordingly.

[Steady_One_S13]

Take the speed sensor out. Crank it by hand. Judge accordingly.

^True that. The FSM can show you how to do this using a multimeter.

[Second Shadow]

I'm also having a little trouble with my speedo. For the most part it works fine, but when you rev past about 2500 to 3k RPM the needle shakes, and it also shakes intermittently past 50 MpH. It just seems to kind of wobble a little, about 3 to 5 MpH plus or minus.

I remembered seeing a topic that said most problems with speedo shaking were due to poor grounding but I couldn't find it. I did find an old post where the guy said on his car it was harmonic vibration. Now, I have solid engine mounts, and I don't remember when the shake started but it could have been around the same time.

is excessive vibration a common cause for speedo needle shake?