Speedo woes

[plc]

G'day All,

Last year I had my speedo serviced and all was good. Then after I changed the clutch early this year the speedo would start to wobble after 90-100 km/h and then still be shaky after slowing to 70 km/h after I had been at 100 km/h for a while. I read some other posts here and suspected the cable. So I cleaned and lubed the cable, no better.

So then I bought a new cable. This was a Venhill cable which was a real tight fit on the speedo. It seemed OK at first but when I got to 100 km/h the speedo would start dropping 20-30 km/h then jump back up. At 60 km/h now it will even drop down to zero then jump back up. This happens all the time with the old cable and new cable.

So I pulled off the speedo and connected it to a drill. It could only get to 90 km/h but rock solid. Checked both cables connected to the speedo driven by the drill, both fine.

Last time I checked the drive gear looked OK, maybe slighly worn. Is this an item that often fails? When I had the gearbox off it was upside sown for a while, and oil ran out the speedo drive. other than that I am baffled. It seems like some part in the speedo drive is slipping and then has no registering input. I don't think it is sticking or the cable would snap.

Has anyone else had these woes? I think I am safe in saying cables and speedo are fine. Advice would be greatly appreciated.

Best wishes,
Paul

[Bengt_Phorqs]

Paul, BMW speedos are notorious for their inaccuracy.  Seldom will they provide accurate speed although if the odometer works that's generally close enough.  Usually you can count on a 10% overspeed indication and lots of bounce.  About the only way to be happy is to install something like a Vapor unit  http://trailtech.net/vapor.html
I'm not selling them or promoting the unit, and the display can seem to fade out if let in the bright sunshine for a while.  Otherwise, there are several choices for speedo repair, none of which are cheap.

[Bob_Roller]

How's the routing of the speedometer drive cable ?

A tight turn in it's routing may cause speedometer indication problems .

[nhmaf]

The cable needs to be lubed once in a great while, and like Bob said, tight bends or pinches inthe cable will cause it to act "jumpy" and/or start to fray the cable strands, which then catch on the inside of the housing and cause the speedometer to be jumpy... that said, the BMW speedometers are famous for being jumpy, though the odometers are generally spot-on accurate.   Often it is the drive gear that is either worn or else doesn't mate fully with the cable end, or sometimes there is a bit of sloppiness that allows the gears to partially disengage when they start spinning fast enough.   Make sure that there is also a bit of grease down at the other end of the cable where it goes into the transmission housing.    You may also check that the special, hollow bolt that retains that end in the transmission cover still has the narrow "nose" that is supposed to intersect with the groove in the speedometer cable - if that "nose" is broken or someone has substituted an incorrect bolt, that end of the cable may be jumping in/out of gear as you go over bumps, etc.

[Justin B.]

The upper part of the drive gear in the speedo might be hogged/rusted out where the cable slides down into it.  It's square and if it's starting to get rounded out might cause symptoms like you are describing.