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41 Oldsmobile speedometer inop

Hi I was driving my Oldsmobile the other day and the speedometer needle seemed to “bounce” up and down and then stop. I removed the cable and it is intact I can spin it and the other end spins. I jacked the rear end up (both wheels off the ground and started it up and put it in HI. I did not see the output shaft turning. Which leads me to ask a whole bunch of questions. Can I get a new output shaft (aftermarket) or do I need to find another Hydramatic and cannibalize it. I also wonder if the fact that two years ago my speedometer cable came loose at the transmission and the road wore the end off so I replaced the core with an aftermarket one’

My car is a dynamic Cruiser series 76 but those options don’t show on this page.

I am not even sure how to remove the speedometer output so if anyone could help me there I would be thankful.

Though I’m not familiar with a 41 Olds…all the old cable type that I’ve worked on…there is a bolt next to the input on the tranny. This bolt loosens a plate that covers the “input shaft” (as you call it) and removing this plate gives access to the gear inside…which is most likely stripped of it’s teeth.

But if you did wear off part of that cable core when it came loose…the cable may be too short now.


I’m not familiar with this transmission much at all but decided to rummage through an old MOTOR manual in my pile. It covers '40-'46 Oldsmobiles and there’s about 8 pages on the transmission.
However, there was no reference to the speedometer drive gear. There is one large cutaway diagram that shows what appears to be a speedometer drive gear near the end of the tail housing much like modern era transmissions.

You should be able to eyeball up in the speedometer cable output hole and determine if the gear is good. Keeping in mind that my knowledge of this trans is near zero would that gear have even been made of nylon back in the day? I thought most of them were brass.
The input on the back of the speedometer heads back in the day were also usually made of brass so it’s difficult to see wear or breakage on those 2 items anyway.

I would tend to think maybe the ends of the cable have worn down. I’m assuming this is a running driving car with an inoperative speedo so I don’t see the need for an output shaft.

IF by some weird chance you needed a speedo drive gear the tailhousing should be easily removed without pulling the transmission. Drop the driveshaft, remove a few bolts around the perimeter, and wiggle it off. The speedo drive gear generally just slides onto the output shaft.

In the old days when the speedo jumped liked that, it meant the cable needed to be lubed. That usually took care of it. So maybe it sheared the end off or something and you just need a new cable.

Just as an off comment, I remember having to replace the cable on my 59 VW. The cable went from the speedo right through the hub of the left front wheel. So as the wheel turned, the cable turned. Weird and always wondered what the piece of wire was on the wheel until I had to replace the cable.

I did replace the speedometer cable and it did work for a short time then it started bouncing and then just stopped I used a whole tube of graphite when I put the new core in. I will try this Thursday when I have a day off to remove the output shaft and see what is in there.

Never used graphite. There was a special light oil for speedo cables, like a 3in1 oil.

Is the odometer working. If it is, then the cable is OK and the speedometer itself is bad. The cable first turns a gear inside the speedometer that turns the odometer, then it goes to a steel cup with a magnet attached tot he end of the cable. The magnet spins and causes the steel cup to rotate, the speedometer needle is attached to the cup.

If the magnet comes loose, it hits the cup and causes it to bounce before the magnet finally falls off and the speedometer goes to zero.

The NAPA speedometer lubricant that I used was graphite. The odometer is not working.