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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.
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.
You'll find this site has a lot of generous people who want to share their information. In that respect, it is unlike the car sites that you must be comparing it to.
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!
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?
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.
Given that the problem started out of nowhere after working correctly for six years, it's unlikely to be the gears. I've had stripped gears cause a slow or non-functioning speedo, but they can't physically make it turn faster than the output shaft.
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.
I thought the speeding up speedo was from a binding speedo cable. Binding and snapping free should make speedo jump up.IDK
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.
FYI. Just a recommendation if you need a place for speedo repair. Dicks Speedo- tach in Tempe Az. This shop is run by the good son. The other shop and other son ruined his portion of the business.
Yes this is the correct one. My boss bought the building from the bad son as he ran it in the ground. It was a cash purchase and get out. I went and looked and pallots of 50's and newer used speedos. Dont know if the speedos went to the good shop.
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.
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?
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?
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!!!
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 have had incorrect speedometers before with error proportional to speed as you describe. the error is pretty consistent so I don't think it temperature related. The transmission is a new th400 and I had the builder use the correct gear for the 323 rear end and tires. I will try checking at a higher speed to test your theory which sounds plausible. Hopefully no tickets
