Speedo Cable

[roadking77]

There was a question posted on the py forum about 2 piece speedo cables for 78/79 4 speed cars. Not much other info.  I have a 79 4 sp but it came to me in pieces so I have no idea on this part. Could it be in 2 pieces as a way to deal with the removal of the cruise control servo?

[jonathonar89]

Mine was only piece on my ‘79 400.  Direct from speedo to transmission.  Two piece would be if you have cruise control.

[firebirdparts]

They're talking about the cars using a calibration gearbox and in those cases, with a 4 speed, they used little short cable and the box wasn't screwed directly into the transmission.  Lo and behold, I found a source of new cables for that setup:
https://www.ebay.com/itm/281117655486

[roadking77]

Good work Joe, now the question is... What is a calibration gearbox?

[firebirdparts]

They used a lot of them, although it seems like they really weren't necessary.  If you look at the parts books they had multiple speedo gear ratio options for the same gear ratio and tire size.  They were made by Stewart Warner.  they were made to screw directly into the transmission, but the 4-speeds that had them, at least some I've seen, had a little short cable there instead.

Appearance is like this: 

[roadking77]

Very good. As a cross reference going back to the PY thread, there is a company Speedometercablesusa.com that has this stuff.

[Jack]

Good info., thanks for sharing. Did not know of a calibration gearbox.

[jonathonar89]

This has eluded me.  Learn something new every day with these old cars.

[5th T/A]

Going back a long time ago I recall many cars with manual transmissions had these. I never thought much about it but maybe it was necessary for certain rear axle ratios.

[firebirdparts]

They are.  Each one is a fixed ratio and there are a bunch of different ratios.

They were used on 1978 L78 automatics (2.56 axle), so due to that one application they're somewhat common.  They made a lot of those.  but in that case it was screwed directly to the transmission and the cables were just ordinary.

I never took one apart, but now that i think about it, I am so curious.  I wish I had.