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Duct_Taper
05-17-2009, 02:17 PM
Anyone else have this?

My odometer reads accurate within 1% (checked over 100km using the markers on the 401) but my speedo reads close to 10% high (like when I'm actually going 120 it reads a little over 130).

Not a huge deal, but a bit annoying to have to do mental math every time I want to figure out how fast I'm actually going.

I saw this thread (http://forums.bimmerforums.com/forum/showthread.php?t=875056) on Bf.c for a repair on E36s... anyone tried it on an E30 cluster?

Or know of another way of fixing this?

Cheers,
-Paul

Ceeker
05-17-2009, 02:32 PM
do you have the correct tire size on the car? If it is larger diameter it will throw the speedo off a bit making you drive slower then what is displayed. if the rolling diameter is smaller then factory, your speedo will show you are going slower then the actual speed of the car. also check the wheel speed sensor. there is also a sensor in the diff which sometimes goes wonky. That usually just dies and it's either working or not. I don't know of anything else unless someone else has had a different experience.

SamE30e
05-17-2009, 02:33 PM
BMW's are known to read high. My friend 03 540i reads about 5km/h over.

Duct_Taper
05-17-2009, 02:37 PM
Yes, my tires are a touch smaller than stock, but that's not the issue here.

Like I said, the odometer reads correct within 1% - so the cluster _does_ get the correct data (or close enough).

The speedo is just calibrated high, and like SamE30e said, it's a known issue with BMWs.

I just didn't realize how far off mine was until I tested it by following my dad's car on the highway and comparing speeds. Then I did the math based on tire diameter, gear ratio, and rpm... and at 3800rpm I should be doing about 120 but my speedo shows a little over 130.

Wannabe
05-17-2009, 02:59 PM
I knew of a 300C that read 10km/h too low! hahaha

its better to read too high

Duct_Taper
05-17-2009, 03:00 PM
Yeah, I guess if it's going to be inaccurate it's better to be high (probably why BMW calibrates them that way), but I'd rather it just be correct.

SamE30e
05-17-2009, 03:19 PM
I think on the motometer clusters there is a pot in the back that you can adjust to correct it.

Duct_Taper
05-17-2009, 11:21 PM
Ooohhh... interesting. My cluster is a motometer. I'll check on it and post back with a write up if I figure anything out.

SamE30e
05-18-2009, 01:02 AM
It's either motometer or the VDO ones.

everlast
05-18-2009, 12:11 PM
It's motometer, but it not for the faint of heart. You need a square wave signal generator and a small op-amp circuit. There is a great (i mean AMAZING) write up somewhere.... I just can't remember where lol.

Edit: found it!

http://www.e30tech.com/forum/showthread.php?t=73541

SamE30e
05-18-2009, 12:24 PM
It's motometer, but it not for the faint of heart. You need a square wave signal generator and a small op-amp circuit. There is a great (i mean AMAZING) write up somewhere.... I just can't remember where lol.

Edit: found it!

http://www.e30tech.com/forum/showthread.php?t=73541


Or a GPS and screwdriver.. lol

everlast
05-18-2009, 01:06 PM
And a friend. Driving with your cluster ripped apart while adjusting the speedo = not recommended lol. :)

Duct_Taper
05-18-2009, 08:25 PM
Yeah... if I do this, I'll pull it apart, adjust, assemble, test, repeat.

One thing though... anyone know if this adjustment affects the odometer as well or just the speedo?

Edit: Found it, looks like it only affects the speedo. Sweet!

echo
05-19-2009, 08:13 AM
I did mine with a GPS. Just move the needle by hand in the direction of the required adjustment and retest.

Piece of cake - 40min job.

everlast
05-19-2009, 11:29 AM
Moving the needle would only add or remove an offset, not adjust the ratio of correction. At 50, the speedo is 4 fast, at 100 it would be 8 fast. Offsetting the needle could only hope to split the difference, or correct for one speed.

Duct_Taper
05-19-2009, 11:53 AM
Like everlast said - moving the needle will only make the speedometer correct at one speed. Might help a bit all around, but this other adjustment should completely correct it for all speeds. I'm going to give it a shot tonight.

guibo
05-19-2009, 03:48 PM
first step is to grab a good 12 channel gps unit and test different speeds. graph the two and you should be able to determine your offset and gain error.

Duct_Taper
05-19-2009, 07:06 PM
Don't need a GPS to do this - if you know your tire size you can get (reasonably) accurate speeds from the tach (assuming the tach is accurate, which it generally is).