Speedometer issues

Guys,

My BRM wagon rested over the Christmas holidays for about two weeks due to the battery what was broken again as usual every 2 years
But thats not the problem. After replacing it some days before, my wife drove some km and told me that the speedometer had some strange issues. First it didn´t work at all, then it waked up and worked strange with stucking and showed way too less speed, then started to come up, then the speed stuck at 60 mph thou the car slowed down to 10 mph and after some driving, it worked ok again. The last two days when I drove the car myself it worked without issues. My question is if the speedometer is an electronic item what maybe faulty inside or is there an cable drive involved what might be stuck?

Just to know about in case it happens again…..

The 91-93 is an electronic unit run by a gear driven pulse generator. There is a splitter under the dash to   to give a 4000 ppm signal to the speedo, and cruise control, and a 2000 ppm to the computer. The  ground for the speedo is at the base of the A pillar.

The 94-96 speedo is an electronic unit driven by a reluctor driven pulse generator. The signal from the pulse generator feeds to the computer that adjusts the pulse rate by internal settings, then to the speedo. The ground for the speedo is at the base of the A pillar.

I would check, and reestablish the ground at the A pillar first.

I have some replacement clusters for the 91-93 cars. The 94-96 units can be replaced as well. Both the sedan and wagon clusters are interchangeable, but you may have to swap a couple of light bulbs for the correct display.

The sending units (VSS) are replaceable, but you will have about 2 qts of trans fluid pour out when changing them. The 91-93s have two types of VSS units, one for 40 tooth, and larger driven gears, and one for 39 tooth, and smaller gears. If you have 2.73 gears, you have the 39 tooth minus unit, and if you have 3.23 gears, you have the 40 tooth plus unit. The 94-96 VSS units are all the same.

Thanks Fred. As told, in the moment the speedo is working perfect again. Anyway, I will have a look to the ground at the pillar.

Bringing this topic back to life, my speedometer is behaving just like the OP's speedo. Sometimes it doesn't read, sometimes it reads only up to 12 MPH, 0r 20 MPH or it will run up to 60 and just die after a mile or two. And then, like this afternoon, work just fine for 80 miles other than reading 7-9 MPH fast at 60 MPH.

That ground Fred speaks of, is that the wire that clips to the inner top of the e-brake mount under the dash?

I have a correction that I learned recently. The 96 VSS is different from the 94-95, and the tail shaft housing is different as well.

I just finshed a rear spring and sway bar install tonight, and when I got the car back on the ground, I fired it up to warm it up before a test drive, and while idling, the speedo needle was gently moving up and down to about 10 MPH to below zero.

I'm confused. We'll see if the speedo works on the test drive.