Are 63 to 67 Speedometers Interchangeable?

[Norm B.]

Just want a working speedometer for now so I can comfortably drive the car for the next year or so while I decide what I am going to do with the interior.

I am going to Carlisle and who knows what I might come across there. So the question is; will any 63 to 67 speedometer fit into a 63 cluster and is the 63 cable compatible?

[Wayne W.]

Re: Are 63 to 67 Speedometers Interchangeable?

Should be functionally.

[Paul Y.]

Re: Are 63 to 67 Speedometers Interchangeable?

Just want a working speedometer for now so I can comfortably drive the car for the next year or so while I decide what I am going to do with the interior.

I am going to Carlisle and who knows what I might come across there. So the question is; will any 63 to 67 speedometer fit into a 63 cluster and is the 63 cable compatible?

The speedo head is close enough that it can be installed on your 63 speedo face and used, as a lot of the heads were interchangeable.

[Duke W.]

Re: Are 63 to 67 Speedometers Interchangeable?

GM used a standard cable speed/speedometer reading factor. IIRC it's 1000 cable revs/min at 60 MPH, so all GM speedometer heads of that era should be functionally identical.

A 3.36 axle and 760 revs/mile tires yields 2554 revs at 60.

The speedometer gearing is 8/20 = 0.400

And 2554 x 0.400 = 1022

So, the theoretical speedometer error is 2.2 percent high with new tires, which is about 1.3 MPH at 60 MPH.

Speedometer error increases with tire wear, which increases revs/mile about another two percent at minimum tread depth.

An additional 1.5 percent error on the high side was introduced with the switch to 7.75-15 and F70-15 tires, which are both rated at about 775 revs/mile, but this was eliminated with the switch to GR70-15 and 225/70-15 tires which are rated at 760, the same as the early 6.70-15 tires.

Changes in tire sizes did not affect most OE speedometer gearing for most axle ratios, but there were changes for some axle ratios (3.55 comes to mine) with 7.75-15 and F70-15 tires to minimize speedometer error since each change in driven gear tooth count changes speedometer readings by about 4 percent. I think there were also some cases where Stewart Warner geared adapters were used on the transmission.

Duke

[Norm B.]

Re: Are 63 to 67 Speedometers Interchangeable?

Thanks guys, you've answered my question. Functionality is all I need for now.