Mark_1

Newbie 1st post.

I purchased an 85 GSL SE about three weeks ago. This week the speedometer started acting up and started to display the speed approximately 2X actual. The behavior disappeared for a few days then jumped briefly this evening. The tachometer and odometer seem to be working normally. If he speedometer cable is going bad I would expect less than actual and it does not make sense to indicate 2X. Any ideas?

Thanks
Mark_1

steve84GS TII

Possible one of the internal clock springs has broke or gone weak and is not holding the needle in the right place.If the odometer is dead on accurate,then that is a likely answer.
Id start off by pulling the cable and lubing the core.Probably easiest to do this from below.Then,get under the dash and check the connection at the back of the cluster.Mine has popped out a couple time in the past,although it usually causes bouncing when the cable starts to walk out.Never seen one display HIGHER than actual speed!

IronMonkeyL255

I have had a speedo 'bounce' from not enough lube on the cable, but never up to 2x actual speed.....

t_g_farrell

iTrader: (1)

I have a similiar issue. My speedo never falls lower than 40 or 50 mph and seems fairly accurate about 50 mph. Its not the cable, I pulled and lubed it and put it back in. I'm going to pull the cluster next and hit the speedo with some canned air to see if it cleans it out and gets it back in shape.

I've heard that sometimes its just a matter of cleaning that will fix it, but other problems with the mechanism can crop up as well. Besides springs, theres a magnetic coupling that acts on the needle to make it go up as the speedo cable spins faster and that can get out of whack as well.

These are old cars, who needs accurate speedos and gas gauges anyway

Mark_1

Thanks! Will check out the cable this weekend.

mustanghammer

iTrader: (3)

I used to repair speedometers for a living. The problem is in the speedometer itself, not the cable. In your case my guess is that the magnet (it is connected directly to the cable) is contacting the speed cup (it is connected to the needle) and that is why speeds are reading high. The magnet and the speed cup are not supposed to touch one another and there is a lubrication point that is critical.

To fix this the instrument cluster needs to be removed from the car and the speedometer removed from the cluster. The problem is most likely a lack of lubrication in the jewel bearing in the magnet. The jewel bearing supports the bottom of the shaft that runs through the speed cup. This is the same shaft that the needle is pressed on to. When you see the needle jump you are seeing the shaft seize in the jewel bearing. There are other possible causes like bad magnet bearings or a bent speed cup. Disassembly is required in all cases.

Beyond repair, the other option is to swap out the speedometer with one in better condition. There are some draw backs to this option, however. First you will loose the mileage that is accummulated on the odometer that is in your failing speedometer. Second, to perform the swap I believe that you have to pull the needle off of the speedometer and then remove instrument from the cluster from behind. Once the needle is removed the speedometer will need to be recalibrated. This cannot be done without a calibration machine that is dedicated to the task.

In my opinion, unless you just swap the entire cluster none of the options above can be performed by a do-it-yourselfer. Speedometers are not complicated but without some experience, the correct lubricants and a calibration machine you cannot perform this task on your own. In my time in the business I had more than one speedometer arrive at the counter in pieces because somebody got brave!

A speedometer shop should be able to lube/recalibrate the speedo you have now or swap in a good instrument and set the mileage to match what is on your bad speedo's Odometer.

Here is a shop that I can recommed:

Metro Speedometer
225 S Main St, Independence, MO 64050
Phone: (816) 421-5996

The owner has developed some repairs for older mechanical speedometers so call and ask for Zevee (spelling??)

There is also United Speedometer in California - www.speedometershop.com/
We bought VDO gears and rebuilt GM cruise controls from them....good people.

t_g_farrell

iTrader: (1)

Good info. So not to highjack (much) but a if I took my cluster out and hit the speedo with some canned air and maybe a light spray of wd40 it won't help at all? My issue is slightly different in that the needle doesn't fall back to zero and hangs up around 40 to 50 mph but above that seems good.

Mark_1

Great information. The erratic behavior seems to initiated by cold temperatures. Once the behavior starts, there also seems to be an influence by the engine rpm. For example while at rest and at idle, the needle will only drop to 40 mph, but will swing upward with an increase in rpm (still at rest). Will be interesting checking things out this weekend.

mustanghammer

iTrader: (3)

Mark, T_G,

A needle that doesn't return to zero is caused by a broken return spring. No amount of compressed air or WD40 will fix that. I would find a good replacement speedometer and take it to a speedo shop. Your speedometers have broken parts that are not available.

As an asside I would never spray WD40 into a speedo head. WD40 has solvent properties as well as lubricating properties. Not a good fit for the parts inside of a mech speedo. At a minimum all WD40 would do is attract more dust. A speedo needs lube, but not that much.