I'm going to be changing rears in my 76 Cutlass soon. Going from 2.41 to 3.73. The speedo will be off, I know. I'll get the right gears for it (speedometer) as I go on with the whole project. But in the meantime, to test drive the car, can I just disconnect it from the tranny, tie it out of the way and plug the hole for now? Is there a recommended way to seal the hole? Certain "Plug" that anyone had luck with? If I leave it connected I'm afraid I might "Pin the speedo" and break something because of the major difference in rear gears. Thanks. Tom

 

I'm no expert, but I don't think you will break the speedometer pinning it.
My speedo only goes up to 85mph, but the car has been well over that for an extended period of time.
As a rough estimate, I've had it pegged for at least 6 straight miles and was probably going in excess of 110Mph. Gotta love those old 2.41 rear gears. Not even any burning belt stench, just a cool, calm and collected ride.

 

I don't think you need to worry. I had a 91 Buick Estate Wagon with a 2004R transmission and a bad speedo gear. The speedo would jump and bounce until I replaced the speedo gear with one I got from a junkyard out of a sedan. When I got the new one in the speedo was about 20 miles per hour off. Apparently the wagons had a different gear ratio... probably for towing. Anyways, I drove it like that until I sold the car a year later.

 

Just hook it up. You won"t hurt the speedo. For completeness, however, the trans will work just fine without the speedo cable connected.

 

OK. I won't worry about it. Thanks. The rear is coming tommorow. 3.73's should give her a bit more snot off the line. Although her highway days are over until I get the OD tranny, maybe next year if I have a good year with work. But thats what my 1970 Ninety Eight is for. Highway cruiser. Tom.