Speedo hand bouncing around
Thread Starter
Advanced
Joined: Mar 2008
Posts: 79
Likes: 0
From: Concord North Carolina
Speedo hand bouncing around
Hey guys.
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?
Thanks,
Randy
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?
Thanks,
Randy
Safety Car
Joined: Jun 2003
Posts: 3,596
Likes: 8
From: Grosse Ile MI
Hey guys.
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?
Thanks,
Randy
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?
Thanks,
Randy
Go to Long Island Corvette and do a search for Speedo Gears
Le Mans Master
Joined: Feb 2001
Posts: 6,317
Likes: 292
From: Ocala FL
You need to lube the cable or replace it. The speedometer is bouncing because of drag inside the cable sheathing that makes the inner cable twist tight, then it releases like a spring, and then twists tight again.
This also puts a huge load on a plastic gear that is not designed for a load, and eats the gear up.
This is why the old mechanical cruise control transducers used to eat up speedometer gears and cables on the primary cable side. The transducers would go bad, put a load on, and wipe out the gears.
Also, be sure you don't have too tight of a bend anywhere as it will make the cable drag inside the sheath even with lube.
BTW, you lube them with graphite, not oil. You used to get it at any auto parts store, but I have no idea if you can at half the computerized chain stores now.
This also puts a huge load on a plastic gear that is not designed for a load, and eats the gear up.
This is why the old mechanical cruise control transducers used to eat up speedometer gears and cables on the primary cable side. The transducers would go bad, put a load on, and wipe out the gears.
Also, be sure you don't have too tight of a bend anywhere as it will make the cable drag inside the sheath even with lube.
BTW, you lube them with graphite, not oil. You used to get it at any auto parts store, but I have no idea if you can at half the computerized chain stores now.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Randy,
There are several things that could cause this problem.
1) The drive gear in the transmission.
2) A defective cable
3) A problem in the speedometer head.
If the drive gear clip has slipped, the gear could off center with the driven gear. This would cause the driven gear to get wiped out pretty quickly. The drive gear could be bad, but I doubt it. When GM went to the plastic driven gears it pretty much stopped the problem with taking out the main drive gear.
If the clip is indeed off or loose then the gear can move on the shaft and eat up the driven gears.
If your cable is defective it could cause the driven gear to be eaten up.
If the speedo head is binding up in the car then it would cause this same problem. But. . . If the speedo head is binding up in the car it will normally snap off the end of the plastic tip on the drive cable and not eat up the driven gear.
I think for now I would check the speedo cable as mentioned above. If the cable is fine, I would then go to the drive gear, and since it’s eating up the driven gear I would put off the speedometer as the problem until last.
Willcox Inc.
There are several things that could cause this problem.
1) The drive gear in the transmission.
2) A defective cable
3) A problem in the speedometer head.
If the drive gear clip has slipped, the gear could off center with the driven gear. This would cause the driven gear to get wiped out pretty quickly. The drive gear could be bad, but I doubt it. When GM went to the plastic driven gears it pretty much stopped the problem with taking out the main drive gear.
If the clip is indeed off or loose then the gear can move on the shaft and eat up the driven gears.
If your cable is defective it could cause the driven gear to be eaten up.
If the speedo head is binding up in the car then it would cause this same problem. But. . . If the speedo head is binding up in the car it will normally snap off the end of the plastic tip on the drive cable and not eat up the driven gear.
I think for now I would check the speedo cable as mentioned above. If the cable is fine, I would then go to the drive gear, and since it’s eating up the driven gear I would put off the speedometer as the problem until last.
Willcox Inc.
Thread Starter
Advanced
Joined: Mar 2008
Posts: 79
Likes: 0
From: Concord North Carolina
Randy,
There are several things that could cause this problem.
1) The drive gear in the transmission.
2) A defective cable
3) A problem in the speedometer head.
If the drive gear clip has slipped, the gear could off center with the driven gear. This would cause the driven gear to get wiped out pretty quickly. The drive gear could be bad, but I doubt it. When GM went to the plastic driven gears it pretty much stopped the problem with taking out the main drive gear.
If the clip is indeed off or loose then the gear can move on the shaft and eat up the driven gears.
If your cable is defective it could cause the driven gear to be eaten up.
If the speedo head is binding up in the car then it would cause this same problem. But. . . If the speedo head is binding up in the car it will normally snap off the end of the plastic tip on the drive cable and not eat up the driven gear.
I think for now I would check the speedo cable as mentioned above. If the cable is fine, I would then go to the drive gear, and since it’s eating up the driven gear I would put off the speedometer as the problem until last.
Willcox Inc.
There are several things that could cause this problem.
1) The drive gear in the transmission.
2) A defective cable
3) A problem in the speedometer head.
If the drive gear clip has slipped, the gear could off center with the driven gear. This would cause the driven gear to get wiped out pretty quickly. The drive gear could be bad, but I doubt it. When GM went to the plastic driven gears it pretty much stopped the problem with taking out the main drive gear.
If the clip is indeed off or loose then the gear can move on the shaft and eat up the driven gears.
If your cable is defective it could cause the driven gear to be eaten up.
If the speedo head is binding up in the car then it would cause this same problem. But. . . If the speedo head is binding up in the car it will normally snap off the end of the plastic tip on the drive cable and not eat up the driven gear.
I think for now I would check the speedo cable as mentioned above. If the cable is fine, I would then go to the drive gear, and since it’s eating up the driven gear I would put off the speedometer as the problem until last.
Willcox Inc.
Randy
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
The plastic drive gear on the output shaft with a retainer clip didn't start until 1970 Muncies - prior to that, they were pressed-on steel gears.
There were two "families" of drive and driven gears, depending on axle ratios; a "large" diameter drive gear and "small" diameter driven gears, and a "small" diameter drive gear and "large" diameter driven gears.
If you mismatch them, and use a "small" driven gear with a "small" drive gear, the teeth have minimal engagement, and the steel drive gear will tear up the teeth on the plastic driven gear in short order.
What color and teeth-count plastic driven gears are you tearing up?
There were two "families" of drive and driven gears, depending on axle ratios; a "large" diameter drive gear and "small" diameter driven gears, and a "small" diameter drive gear and "large" diameter driven gears.
If you mismatch them, and use a "small" driven gear with a "small" drive gear, the teeth have minimal engagement, and the steel drive gear will tear up the teeth on the plastic driven gear in short order.
What color and teeth-count plastic driven gears are you tearing up?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
John,
The OP’s car is a mid year and you are correct about the steel press on gear vs. the plastic with the clip. However, I’m not so sure GM started this in 70, we just took apart a 69 transmission last Thursday and it had the clip. The car was purchased March 1st 1969. (The owner always tells us when he drops the car off so it’s embedded in my brain).
This car is still in the hands or the original owner and the transmission is the original as far as I’m aware. We still have the tail housing off the car right now, it should not be hard to verify. We’ve worked on this car for the past 15 years and I know we never replaced the transmission, but that’s not to say that someone years ago did not.
You are dead on about a gear miss-match. In fact the OP could be out of his gear range with the drive gear vs. the driven gear. This would as you described cause this exact problem. . . I never thought about that and should have.
People that change rear ends in their cars don’t think about this and it will bite them in the rear (no pun) from time to time trying to get the correct ratio for their speedometer.
Food for thought on the transmission, I’ll be in my office around noon and if they have not put this back together I’ll check it.
Willcox Inc.
The OP’s car is a mid year and you are correct about the steel press on gear vs. the plastic with the clip. However, I’m not so sure GM started this in 70, we just took apart a 69 transmission last Thursday and it had the clip. The car was purchased March 1st 1969. (The owner always tells us when he drops the car off so it’s embedded in my brain).
This car is still in the hands or the original owner and the transmission is the original as far as I’m aware. We still have the tail housing off the car right now, it should not be hard to verify. We’ve worked on this car for the past 15 years and I know we never replaced the transmission, but that’s not to say that someone years ago did not.
You are dead on about a gear miss-match. In fact the OP could be out of his gear range with the drive gear vs. the driven gear. This would as you described cause this exact problem. . . I never thought about that and should have.
People that change rear ends in their cars don’t think about this and it will bite them in the rear (no pun) from time to time trying to get the correct ratio for their speedometer.
Food for thought on the transmission, I’ll be in my office around noon and if they have not put this back together I’ll check it.
Willcox Inc.
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Burning Brakes
Joined: Nov 2001
Posts: 989
Likes: 13
From: Gloucester Point VA
Asimple test.
[QUOTE=Randys66;1566657296]Hey guys.
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?/QUOTE]
I simple test would be to replace the gear once again and leave the cable off at the trans. Drive the car for a couple of days and check the gear, if it's OK the problem is the cable or the speedo. Next connect the cable at the trans and disconnect it at the speedo. Again drive the car for a couple of days and check the gear. Instead of just replacing parts this may help you isolate the problem.
I have replaced the plastic colored gear that goes in the transmission 3 times. Each time the speedometer will work great for about 2 days. Then the hand will start bouncing around and finally stop and go to zero. The teeth on the gears are chewed a little but not that bad. Is the problem in the transmission?/QUOTE]
I simple test would be to replace the gear once again and leave the cable off at the trans. Drive the car for a couple of days and check the gear, if it's OK the problem is the cable or the speedo. Next connect the cable at the trans and disconnect it at the speedo. Again drive the car for a couple of days and check the gear. Instead of just replacing parts this may help you isolate the problem.
Instructor
Joined: Nov 2005
Posts: 146
Likes: 0
From: East Grand Rapids MI
Slightly different problem
What would cause the needle to bounce sometimes and other times be steady as can be? Also what would cause a clicking sound in the speedo head when the car is slowing down from say 25 to 0 mph? The head has been rebuilt and bench tested to be within original specs. I have had the cable off, replaced and lubed but nothing seems to changed.
Thanks,
Scott
Thanks,
Scott
Safety Car
Joined: Jun 2003
Posts: 3,596
Likes: 8
From: Grosse Ile MI
What would cause the needle to bounce sometimes and other times be steady as can be? Also what would cause a clicking sound in the speedo head when the car is slowing down from say 25 to 0 mph? The head has been rebuilt and bench tested to be within original specs. I have had the cable off, replaced and lubed but nothing seems to changed.
Thanks,
Scott
Thanks,
Scott
