jumping speedo
Thread Starter
Instructor
Joined: Dec 2000
Posts: 178
Likes: 0
From: Twin Lake MI
jumping speedo
about 6 years ago I replaced a broken speedo cable, last week it started jumping around and after a few miles it quit altogether. After setting while at work for 8.5 hours it worked good for a few miles then started jumping again then again went to "0". Is it time for another new cable or does it just need lubrication or is it something else? This happens on a daily basis
Racer
Joined: Apr 2006
Posts: 417
Likes: 0
From: Tacoma Washington
I had the same problem. The speedo repair shop calibrated my speedo and that problem went away. The adapter they put on worked for awhile, but now my speedo is not working again and sits at zero like yours. Are you positive your speedo shows the correct speed? Getting it calibrated may help the issue. just my .02
Thread Starter
Instructor
Joined: Dec 2000
Posts: 178
Likes: 0
From: Twin Lake MI
It always has showed correctly. I'm gonna pull panel and disconnect and pull cable and lube for a start, need a new wiper switch anyhow so I'll kill two birds. If it doesn't help I'll change speedometer, it still has original and gets pegged often.
Pro
Joined: Mar 2001
Posts: 633
Likes: 1
From: Hamilton, ON, Canada
There was a problem with the C3 speedo driven gear in the transmission, although I don't think all years were involved. There's a GM service bulletin out on the problem. I changed my driven gear several times before the problem was solved. I'd suggest lubing the cable first to see if that solves the problem. If it doesn't, change the driven gear. The only proper speedo cable lube I can locate out there is available from NAPA and is called "cable lube".
Pro
Joined: Mar 2001
Posts: 633
Likes: 1
From: Hamilton, ON, Canada
Found the service bulletin. Looks like it covered only 1974-75 but it may also be applicable to later years..
1974-1975: Service Bulletin: Stripped Speedometer Driven Gear, 1974-1975 Corvette with 4-Spd. Transmission
Model Year: 1974-1975
Subject: Stripped Speedometer Driven Gear, 1974-1975 Corvette with 4-Spd. Transmission
Source: Chevrolet Dealer Service Technical Bulletin
Number: 75-T-3
Date: Jan. 17, 1975
TO: ALL CHEVROLET DEALERS
On 1974 and 1975 Corvettes with 4-speed transmission, an inoperative speedometer due to a stripped driven gear may be the result of relatively high internal friction in the speedometer adapter.
a new low friction adapter and key will be phased into production in January, 1975 and will be available for service under the numbers listed below:
1565211 ---- Adapter
6476870 ---- Key
For service, vehciles exhibiting this problem may be corrected by the following method:
Remove driven gear and replace with new gear of same part number and color.
Remove and discard production adapter and key and install new adpater and key.
1974-1975: Service Bulletin: Stripped Speedometer Driven Gear, 1974-1975 Corvette with 4-Spd. Transmission
Model Year: 1974-1975
Subject: Stripped Speedometer Driven Gear, 1974-1975 Corvette with 4-Spd. Transmission
Source: Chevrolet Dealer Service Technical Bulletin
Number: 75-T-3
Date: Jan. 17, 1975
TO: ALL CHEVROLET DEALERS
On 1974 and 1975 Corvettes with 4-speed transmission, an inoperative speedometer due to a stripped driven gear may be the result of relatively high internal friction in the speedometer adapter.
a new low friction adapter and key will be phased into production in January, 1975 and will be available for service under the numbers listed below:
1565211 ---- Adapter
6476870 ---- Key
For service, vehciles exhibiting this problem may be corrected by the following method:
Remove driven gear and replace with new gear of same part number and color.
Remove and discard production adapter and key and install new adpater and key.
Instructor
Joined: Dec 2004
Posts: 198
Likes: 0
From: Newmarket Ontario
Mine did the same thing and the cause was the cruise transducer. The plate inside the unit was siezing and causing the cable to snap. Ended up just removing the plate. One day I will get a rebuilt transducer but until then I have no cruise but the speedo works.
