Odd speedometer and Odo issue
#1
Odd speedometer and Odo issue
So I have/had a 1970 Olds Rallye 350 that I just sold. Took me two years but I tracked down one of the original owners from 1986. He was elated to get it back!
Anyway I'm trying to help him fix the Speedometer and odometer.
Yes before the haters start I did a ton of research online and in this site.
Here's the issue.
The car had a TH400 in it when I purchased it from him way back when. I found a correct 1970 JL or JO (can't remember) TH350 for it. Its the none W-31 trans. Had it rebuilt and put it into the car 15 years ago. I never had an issue with the speedo being off or odometer at all that I noticed, miniscule if anything. Then 6 years later and about 4,000 miles more, it started to act up. At 60mph it would read 90mph and the ODO would rack up really quick. Agrivated, I parked it and life happened. Never had time to dig into it. I told him about it when I sold it to him and I want to help him. The car has the original 3:23 gear (verified) still in it. Stock size tires.
See the pic of the ODO. The first digit is between the 2 and 3. It was never like that until it acted up. Everything I read it says the gear in the tranny. But it worked ok for years. Doesnt make sense. I did hear a weird clicking whiring noise behind the dash before I parked it. That never happened before.
Could it be a ODO and speedo issue?
Anyway I'm trying to help him fix the Speedometer and odometer.
Yes before the haters start I did a ton of research online and in this site.
Here's the issue.
The car had a TH400 in it when I purchased it from him way back when. I found a correct 1970 JL or JO (can't remember) TH350 for it. Its the none W-31 trans. Had it rebuilt and put it into the car 15 years ago. I never had an issue with the speedo being off or odometer at all that I noticed, miniscule if anything. Then 6 years later and about 4,000 miles more, it started to act up. At 60mph it would read 90mph and the ODO would rack up really quick. Agrivated, I parked it and life happened. Never had time to dig into it. I told him about it when I sold it to him and I want to help him. The car has the original 3:23 gear (verified) still in it. Stock size tires.
See the pic of the ODO. The first digit is between the 2 and 3. It was never like that until it acted up. Everything I read it says the gear in the tranny. But it worked ok for years. Doesnt make sense. I did hear a weird clicking whiring noise behind the dash before I parked it. That never happened before.
Could it be a ODO and speedo issue?
#2
The odometer wheel has thin plastic tabs between each of the wheels that lock the number wheels into alignment. These were designed to break and cause the misaligned digits like that in an attempt to thwart odo rollback. First, it REALLY isn't that difficult to take the odometer apart and reset the mileage despite this, and second, that fifty year old plastic is now very brittle. You need a new or good used odo wheel to fix this.
The odo on my 1962 used metal tabs, not plastic, but you get the idea.
The odo on my 1962 used metal tabs, not plastic, but you get the idea.
#3
Thanks so much!
My main question is that the miles rack up really fast and the speed reads 90mph at 60mph. What odd is it just started to do this randomly one day.
Could it be associated with this turn back feature?
My main question is that the miles rack up really fast and the speed reads 90mph at 60mph. What odd is it just started to do this randomly one day.
Could it be associated with this turn back feature?
#5
#7
Thanks guys, I really do appreciate it!!! Im use to other car forums with a bunch of arm chair warrior's.
I love my Oldsmobiles. Some Olds guys up here in the Northeast think they poop ice cream but for the most part Olds guys are very generous humble people. I've met a ton of great people through the years.
I got my 1st one at 15 years old. I was an advisor for the Olds Club of America for many years until it became hard to balance all the calls between family and work.
Due to a career change and raising a child, I've been out of the Olds World for a few years now. It feels great to get back into it!
Here's some of the great people I met sign my car!
I love my Oldsmobiles. Some Olds guys up here in the Northeast think they poop ice cream but for the most part Olds guys are very generous humble people. I've met a ton of great people through the years.
I got my 1st one at 15 years old. I was an advisor for the Olds Club of America for many years until it became hard to balance all the calls between family and work.
Due to a career change and raising a child, I've been out of the Olds World for a few years now. It feels great to get back into it!
Here's some of the great people I met sign my car!
#8
Incorrect mileage can definitely be related to the broken tabs. Speed inaccuracy is not. It might indicate a larger problem in the speedo head, but typically it's due to incorrect speedo drive gears in the trans. Has the trans or rear axle been changed? If not, and this just started all of a sudden, there's a problem in the speedo head. If something broke, causing the inaccurate speed reading, that debris might also have damaged the plastic tabs.
#9
The inexpensive attempt to fix would be to match the "pencil"/driven gear at the trans. That gear needs to match the rear end gear ratio.
https://www.tciauto.com/speedometer-gear-calculator
But, it sounds worse than that. Also, stumbled on this
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
But, it sounds worse than that. Also, stumbled on this
https://www.hotrod.com/articles/cali...-speedometers/
#10
The inexpensive attempt to fix would be to match the "pencil"/driven gear at the trans. That gear needs to match the rear end gear ratio.
https://www.tciauto.com/speedometer-gear-calculator
But, it sounds worse than that. Also, stumbled on this
https://www.hotrod.com/articles/cali...-speedometers/
https://www.tciauto.com/speedometer-gear-calculator
But, it sounds worse than that. Also, stumbled on this
https://www.hotrod.com/articles/cali...-speedometers/
I never had an issue with the speedo being off or odometer at all that I noticed, miniscule if anything. Then 6 years later and about 4,000 miles more, it started to act up.
#12
A mechanical speedo has a drive wheel and cup. The spring counteracts the magnetic force from the cup. A broken spring or other debris in the speedo head can increase the drive force in the cup and cause a consistently high reading. That debris could also break the plastic tabs on the odo drum.
#15
#17
#18
Jumping periodically is not constantly indicating 30 MPH fast.
A mechanical speedo has a drive wheel and cup. The spring counteracts the magnetic force from the cup. A broken spring or other debris in the speedo head can increase the drive force in the cup and cause a consistently high reading. That debris could also break the plastic tabs on the odo drum.
A mechanical speedo has a drive wheel and cup. The spring counteracts the magnetic force from the cup. A broken spring or other debris in the speedo head can increase the drive force in the cup and cause a consistently high reading. That debris could also break the plastic tabs on the odo drum.
#19
this is an interesting topic. I have issues with my speedometer. It reads 34 mph when GPS confirms 30 mph and reads 62 when GPS confirms 60 mph. This seems inexplicable since the absolute error should increase with an increase in speed in a direct proportion not an inverse proportion. What would cause this?
i would guess the faster speed overcomes whatever resistance (over and beyond the normal expected amount) the hairspring is designed to provide. You could test my theory by driving 90mph, if the speedo reads correctly you know it’s internal resistance. 😏
On the other hand, I’d expect the amount of error to change with temperature. So maybe my idea is stupid. Wouldn’t be the first time, or the lady time I’m sure!!!
#20
Speedometers inaccuracy is best though of as a percentage. Yours reads 34indicated at a actual 30 (the actual speed is 1.13333 times faster than indicated) the 64 indicated is 1.0333333 faster than actual 60. Unless my math or methods of calculating the difference is wrong, the percentage of inaccuracy is changing. That suggests something other than simple speedo gear mismatch is messing up the indicated vs actual speed.
i would guess the faster speed overcomes whatever resistance (over and beyond the normal expected amount) the hairspring is designed to provide. You could test my theory by driving 90mph, if the speedo reads correctly you know it’s internal resistance. 😏
On the other hand, I’d expect the amount of error to change with temperature. So maybe my idea is stupid. Wouldn’t be the first time, or the lady time I’m sure!!!
i would guess the faster speed overcomes whatever resistance (over and beyond the normal expected amount) the hairspring is designed to provide. You could test my theory by driving 90mph, if the speedo reads correctly you know it’s internal resistance. 😏
On the other hand, I’d expect the amount of error to change with temperature. So maybe my idea is stupid. Wouldn’t be the first time, or the lady time I’m sure!!!
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