Speedometer off??

10ringarcher · Post by **10ringarcher** » Fri Sep 23, 2016 9:08 am

I believe my speedometer is off by 5 to 10 mph or more depending at what speed I am doing. At 25-35 mph it seems it's off by about 5mph, then when I am doing 35-45 or more it's off by 10mph or more. What gives?

I noticed while doing a nice long drive on highway, looked down and speedometer said 138 mph?? What the heck??

Then confirmed it was off by asking a friend to drive next to me at the same speed. Yep, it was off. Then opened my waze app and then again confirmed.

Only 86k on the car. Stock tire and rim size all around. All original drivetrain and components.
Anyone else have or has had this issue? Anything in particular to look for?
I am really concerned that I am adding additional mileage to the car thinking the odometer is spinning faster than it should be.

T.Hanson · Post by **T.Hanson** » Fri Sep 23, 2016 9:49 am

Relax, see previous posts on Odometergears. All will be well through Jeff.

https://www.bmwtechinfo.com/

If you are of a mind to investigate the cause yourself, perhaps clean, lubricate the cable. Instructions for removing the instrument box are fairly simple and straight forward. If your efforts fall short of fixing the problem the speedometer will be accessible for removal and sending to Jeff.

Properly packed !

10ringarcher · Post by **10ringarcher** » Fri Sep 23, 2016 11:37 am

Thanks T.Hanson,
Was hoping Jeff would chime in. May have to try that.

Mike W. · Post by **Mike W.** » Sat Sep 24, 2016 12:51 pm

It's pretty unlikely you are adding extra miles, the odo is driven by a gear off the transmission, the speedo is a little different, it uses the same drive, but it turns a magnet that moves the needle against a spring. So it sounds like the spring is weak or stretched. I had an optimistic one on a Bav one time and I kind of recalibrated it by changing the preload of the spring. But it turned out to be non linear, so I could only get it accurate at one speed. A speedo shop may very well be able to do better.

But no extra miles on the odo.

RonDwyer · Post by **RonDwyer** » Thu Sep 29, 2016 9:39 pm

I'd make sure the cable is well lubricated. Did you put bigger wheels on the car? The only way the speedo can read higher than actual input revolutions is if it is roached. There's a spinning magnet that lifts the needle. This stuff is getting to be almost 40 years old. Time for a few new parts or an overhaul.

I have a 140 Mph and a slower one if you want a spare. Palo Alto Speedometer can work on them.

10ringarcher · Post by **10ringarcher** » Fri Sep 30, 2016 3:54 am

Thanks guys.
Will try to lube the speedo cable. As long as it's not adding additional miles, I am going to leave it alone for now. "But officer....."

Odometergears · Post by **Odometergears** » Mon Oct 17, 2016 2:32 pm

The guys are correct along with your own thoughts. The reading is done in a percentage. If it's off 5 MPH at 35, it will be off 10 MPH at 60. You can make the adjustment yourself if you like. I'm going to guess you are not the original owner and have no idea if this is the original speedo head. None of them are so don't kid yourself. There were different calibrations for all the speedometers not just 85MPH or 140MPH. There is a "K" number on each speedo. The best way to make it accurate is to send it to Palo Alto Speedo or mount your phone to the windshield and run Waze, which is an excellent app if you like to go fast!

Take the speedometer out of the metal back case. Use a drill in reverse to run the speedometer. Either a small square bit or an old speedo cable will work to run it. See what it reads on speed 2 of the drill in REVERSE.

If your speedometer is reading slow:
You need less preload on the clock spring. On the back side you will see the empty screw holes that held the backing plate on. Insert a small flat blade to lock or jam the speed cup from turning. Being VERY careful, you will have to twist the speedo needle clockwise about a 1/8 inch. This is a big adjustment believe it or not. Run the drill again and get an idea of where you need to be.

If your speedometer is reading fast:
Same as above but twist the needle counter-clockwise.

If your needle doesn't want to move, which is probably the case, I use a drop of bicycle chain oil carefully placed where the sleeve of the needle meets the speedometer shaft coming up from the face. You then leave it upside down on a soft surface for a few hours to let the oil work it's way into the joint. Then try and move the needle again with the above method.

Best result: you fix it.
Worst result: you break the needle. Don't call me. I have given away all I have.

GL,

Jeff

RonDwyer · Post by **RonDwyer** » Mon Oct 17, 2016 8:37 pm

Or resign yourself to lightening your wallet a bit and having the remnants of a dying art fix it before they are all gone. Sort of like the guys at Pacific Fuel injection, you cannot get mechanical bosch gasoline pumps rebuilt many places anymore.