Speedometer lag
Thread Starter
Advanced
Joined: Oct 2010
Posts: 78
Likes: 1
From: maryland
Speedometer lag
Anyone have problems with their speedometer in colder weather?? lately I am noticing that it takes along time for the speedometer to get up to speed. If it's cold out it takes forever. The warmer the outside temp is the faster it begins to work properly. In the summer on a warm day after a little while it does show the correct speed. Is this a plastic gear issue or does the cable need lubrication somewhere along the line?? It doesn't make any noise so I have to wonder.. thanks for any help mark..
Race Director
Joined: Jan 2002
Posts: 15,340
Likes: 2,716
From: Close to DC
C2 of the Year Finalist - Modified 2020
Mark,
It's probably the cable and the casing it spins in. This could lead to a gauge cluster redo, also know as "project creep". If you want some help, let me know. I would suggest pulling the cluster, disconnect the case at the trans, then pull the cable, and clean it out. Relube the cable from 6-8 in. away from the speedo head toward the trans. You don't want the lube to get into the speedo head.
Dennis
It's probably the cable and the casing it spins in. This could lead to a gauge cluster redo, also know as "project creep". If you want some help, let me know. I would suggest pulling the cluster, disconnect the case at the trans, then pull the cable, and clean it out. Relube the cable from 6-8 in. away from the speedo head toward the trans. You don't want the lube to get into the speedo head.
Dennis
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Anyone have problems with their speedometer in colder weather?? lately I am noticing that it takes along time for the speedometer to get up to speed. If it's cold out it takes forever. The warmer the outside temp is the faster it begins to work properly. In the summer on a warm day after a little while it does show the correct speed.
Burning Brakes
Joined: Mar 2008
Posts: 859
Likes: 53
From: Magnolia Texas
More than likely, it's the lube on the bearings in the head itself getting stiff in the cold. The cable can't twist much without breaking so one turn at the tranny results in one turn at the speedo head with little delay. If it twisted enough to cause a noticeable lag, it would most likely break.
There IS a phenomenon with mid-year speedos that if they have too much end play in the needle assembly, they will lag under acceleration as the cup moves away from the magnet under acceleration and then jump up as you stop accelerating. That doesn't sound like what you are experiencing though. On my '67, I can easily get a 10 MPH drop under acceleration, even though it was rebuilt less than 3000 miles ago with a NEW cup assembly.
Steve
There IS a phenomenon with mid-year speedos that if they have too much end play in the needle assembly, they will lag under acceleration as the cup moves away from the magnet under acceleration and then jump up as you stop accelerating. That doesn't sound like what you are experiencing though. On my '67, I can easily get a 10 MPH drop under acceleration, even though it was rebuilt less than 3000 miles ago with a NEW cup assembly.
Steve
Thread Starter
Advanced
Joined: Oct 2010
Posts: 78
Likes: 1
From: maryland
Steve, Without pulling the whole dash cluster, is it easy to get to the cable to inspect at the speedometer or am I in for a cluster rebuild as Dennis said earlier? Not that worried about the speedo working correctly immediately because the odometer seems to work fine. With gas being what it is I guess I really don't wanna know how fast I'm going!!!!!!
Burning Brakes
Joined: Mar 2008
Posts: 859
Likes: 53
From: Magnolia Texas
I don't know if you'd call it "easy" but you can remove the cable from the back of the speedo without pulling the cluster. It's easiest if you remove the driver's seat so you can lay down on your back and see what you're doing. I find it easiest to remove the cluster screws and replace them with 1/4-20 bolts, 6 inches (or longer) long. Then you can slide the cluster toward the rear of the car which will make it a little easier to get to the nut on the back of the speedo that holds the cable into the speedo head.
As I recall, the drive cable is removable from the sheath from the transmission end of the cable. However, I don't see any way that lubing the cable is going to address your problem. The drive cable can't absorb enough "twist" to make the head lag that far behind.
Hope that helps,
Steve
As I recall, the drive cable is removable from the sheath from the transmission end of the cable. However, I don't see any way that lubing the cable is going to address your problem. The drive cable can't absorb enough "twist" to make the head lag that far behind.
Hope that helps,
Steve
Race Director
Joined: Feb 2007
Posts: 15,422
Likes: 8,873
From: northern california
C2 of Year Finalist (track prepared) 2019
I've got this exact problem on two '63 clusters.... one has a tach that lags (NOT good on a track car!) and the other has a speedo that lags (inconvenient but not tragic).
What do you do about it? Any suggestions?
Jim
Burning Brakes
Joined: Mar 2008
Posts: 859
Likes: 53
From: Magnolia Texas
Hi Jim,
I have not fixed it in my '67 just because I don't want to pull it out again but I did get a speedometer cup and proved to myself what is causing it. I posted a YouTube video that I believe explains it here.
http://www.youtube.com/watch?v=6Hqse4dhgPY
As for fixing it, I am virtually certain that if I had the end play removed from the shaft, as is shown in the video, that would fix it but until I have a reason to pull the cluster, I've decided to live with it. It's very irritating, especially after having the cluster rebuilt but it is what it is. I believe the reason it happens in C2's is that the instruments are virtually horizontal so it doesn't take much acceleration to move the shaft back. If the speedo was at an angle, like it is in most cars, I don't think you would see this issue. Incidentally, the tach is the same mechanism and as far as I can tell, my tach is fine.
I would advise anyone having one rebuilt to request the rebuilder set the end play of the shaft at the minimum. If I was doing it, I'd ask for .005 or so and I bet the problem would be gone.
Steve
I have not fixed it in my '67 just because I don't want to pull it out again but I did get a speedometer cup and proved to myself what is causing it. I posted a YouTube video that I believe explains it here.
http://www.youtube.com/watch?v=6Hqse4dhgPY
As for fixing it, I am virtually certain that if I had the end play removed from the shaft, as is shown in the video, that would fix it but until I have a reason to pull the cluster, I've decided to live with it. It's very irritating, especially after having the cluster rebuilt but it is what it is. I believe the reason it happens in C2's is that the instruments are virtually horizontal so it doesn't take much acceleration to move the shaft back. If the speedo was at an angle, like it is in most cars, I don't think you would see this issue. Incidentally, the tach is the same mechanism and as far as I can tell, my tach is fine.
I would advise anyone having one rebuilt to request the rebuilder set the end play of the shaft at the minimum. If I was doing it, I'd ask for .005 or so and I bet the problem would be gone.
Steve
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Race Director
Joined: Feb 2007
Posts: 15,422
Likes: 8,873
From: northern california
C2 of Year Finalist (track prepared) 2019
I have not fixed it in my '67 just because I don't want to pull it out again but I did get a speedometer cup and proved to myself what is causing it. I posted a YouTube video that I believe explains it here.
http://www.youtube.com/watch?v=6Hqse4dhgPY
As for fixing it, I am virtually certain that if I had the end play removed from the shaft, as is shown in the video, that would fix it but until I have a reason to pull the cluster, I've decided to live with it.
That video is compelling (and very nicely edited). Your explanation makes plenty of sense. Now the problem becomes working up the enthusiasm to pull the cluster .... Ugh.
Thanks for posting that.
Jim
