635 Speedometer bounce

My 85 635 speedometer just started to bounce and I have had about three different stories on what would cause it. Batteries, gears, need new cable or ground may have come loose??? Wondered if anyone has anything I should look for before paying out the money to have it fixed?
154,000 miles

Thank you
Troy

It could be any of those 3+

Check for an earthproblem as the cheapest option
They dont have a speedo cable!
It could be the service interval batteries inside the clocks, over time they have a habit of leaking all over the circuit board. They are usually accompanied by other instruments/gauges misbehaving tho

A likely culprit would likely be the speed sensor on the rear diff reasonably cheap and easy to fix

I have a similar problem--'85 635 CSI--first speedo bounce, now no speedo, no tach, no temp, just a slightly erratic fuel gauge operational. The tach stopped working just after some engine electrical work.--Help! Where do I start looking? The car has been in a very humid environment--grounding issues?

Thanks for any help you can provide.

aron

I have a similar problem--'85 635 CSI--first speedo bounce, now no speedo, no tach, no temp, just a slightly erratic fuel gauge operational. The tach stopped working just after some engine electrical work.--Help! Where do I start looking? The car has been in a very humid environment--grounding issues?

Thanks for any help you can provide.

aron

Aron,

I would bet that your service light batteries have leaked acid all over your Service Indicator board. Remove the gauge cluster and pull the back off of it; you will find a circuit board in the center with acid damage. If you dont see damage you are most fortunate as this means that you only need to replace the batteries.

Blake

My 85 635 speedometer just started to bounce and I have had about three different stories on what would cause it. Batteries, gears, need new cable or ground may have come loose??? Wondered if anyone has anything I should look for before paying out the money to have it fixed?
154,000 miles

Thank you
Troy

Batteries yes, gears???, poor connection at the sensor on the differential. I am not clear about what bounce is.

Blake

Thanks for your quick reply! So the service indicator board has never been operational--was disabled as I understand it, by the previous owner. Never having removed the instrument cluster, is it possible that the service indicator board was removed and therefore is not the problem, or is that not an option so even being disabled, it has batteries which leaked all over the place?

I guess the first coarse of action would be to remove the cluster and take a look--is there somewhere you could point me which describes how to do that?

Thanks so much.

Aaron





Aron,

I would bet that your service light batteries have leaked acid all over your Service Indicator board. Remove the gauge cluster and pull the back off of it; you will find a circuit board in the center with acid damage. If you dont see damage you are most fortunate as this means that you only need to replace the batteries.

Blake

You need to pry the check light cluster from the bottom. Once that is removed you'll see several screws to remove the instrument panel. On the right side you'll see a blank immediately next to the instrument cluster. Pry this off, very slowly. Once removed you'll see several more screws. As far as the fog lamp and headlamp switches, I opted not to remove them. Instead I disconnected the wiring from the rear.
Also in order to remove the cluster, you will have to unscrew the two bolts holding the steering column in place and let it slowly down. You'll have ti remove the knee bolster to access the column bolts.

On the back of the instrument cluster there are several locking connectors. Locate the locking tang and sqeeze it to release the connector. The SI batteries are located within the instrument cluster. There are, if I remember, two black knobs that you twist to unlock the back cover. Be very careful to not pull any wires or worse as you work on this.

If you find no damage then you can unsolder the batteries and find the replacements at Radio Shack.

If the board is damaged I have found that soldering in wires to replace the dissolved traces is a doable fix. Otherwise you could always send your cluster to Programa Inc and they can repair it for you.

HTH,
Blake