Speedometer bouncing

[Hooptybass]

My 94 GMC K2500 Suburban the speedo is acting up . Its wont work right , or its bouncing all over the place and then sometimes it just stays on 0 mph
Anyone have any ideas on where to start chasing this down ?

Thanks Brian

[a5150nut]

Check your plug going to the sending unit on transfer case. If it is good go ahead and pull sending unit to see if it is full of filings on the bottom end.

Might check connections at VSB too. Pull glove box out and it will be a white plastic box about the size of a cigarette pack just left of the opening where the glove box was.

[CoyleJR]

If it is cable driven remove the cable from the back of the speedometer. Put some wheel bearing grease on the tip of your finger and put it on the cable behind the speedometer and put it back on to the speedometer snug. If the cable is loose at the back of the speedometer it causes the needle to jump around. If it is electric check for a bad ground or bad sending unit.
Good luck
John

[a5150nut]

If it is cable driven remove the cable from the back of the speedometer. Put some wheel bearing grease on the tip of your finger and put it on the cable behind the speedometer and put it back on to the speedometer snug. If the cable is loose at the back of the speedometer it causes the needle to jump around. If it is electric check for a bad ground or bad sending unit.
Good luck
John

94 is electronic not cable driven.

[Hooptybass]

ok thanks ill give that stuff a try this weekend ....

[john8662]

Sounds like speed sensor, wiring, or VSSB/DRAC Module behind glove box near the PCM.

If you need a new VSSB you can get one at www.uniquediesel.com/drac

Thanks,

John