D80 speedo cable

[68Zproject]

On page 241 of the 68 AIM it lists an adapter for the 4-speed trans with posi.  What is that thing?  Does anyone have this and can you buy it anywhere?  It also shows the one-piece speedo cable.  Which cars used the two-piece cable  and did they used this adapter?  I'm totally confused.

[Jerry@CHP]

The adapter is a gear reduction box that calibrates the speedo to read correctly in the case of rear axle ratios of 4.56 and 4.88.  This was required in cases like this.  For 4.10 and higher ratios, it is not needed.

So, if your car has a 4.10 or higher ratio, then it is not needed.  Most 4.10 ratios will use a 25 tooth driven gear and 1.750" drive gear.  3.73 ratios will use the same drive gear and a 23 tooth driven gear.  The driven gears are color coded. 23-t 3.73, black and 25-t 4.10 orange.

Jerry

[sd1968z28]

jerry this is jason in south dakota.  the speedo in my camaro reads perfect now with the 4.10 rear axle.  when i replace the diff with the original one will i have to replace the plastic gears in the trans or just install the adapter. i am pretty sure i have a few of those lying around.  the look the same as the one on a 70s 4x4 pickup that runs speedo out of transfer case.  i only want to do this once so any help would be greatly appreciated.

[Jerry@CHP]

Jason,

You should be able to use a 25 tooth driven gear without the adapter.

Keep me posted,

Jerry

[68Zproject]

Thanks again Jerry.  Did the 68 Z's use the two piece cable?

[Jerry@CHP]

My white 22K survivor and many others that I've seen have had the one piece cable.

Jerry

[sd1968z28]

is this using the 3.73 gear?  i am thinking of leaving the dealer installed 4.88s in the diff.

[1968RSZ28]

is this using the 3.73 gear?  i am thinking of leaving the dealer installed 4.88s in the diff.

Jason -

Keep it original, PLEASE!  

Paul

[sd1968z28]

great, now i have to find the original ring and pinion.  i don't think the dealer kept them around for nearly 40 years but who knowns.  i've lucky so far.  but seriosly can install a set of richmond gears or should i find a correct date codded used set or nos set.

[1968RSZ28]

Jason -

I mean keep the gear ratio original, as stamped on the axle tube.  With a 4.88:1 rear axle ratio you will reach redline at highway speeds!  Just my two cents worth.  

Paul  

[Jerry@CHP]

Don't use the Richmond gears or any aftermarket if you can help it.  Most will whine when coasting or under accelration.  Find a good set of used GM gears.

Jason,

Have you received the engine yet, or how did that play out,

Jerry

[sd1968z28]

i am supposed to be picking up the engine this month.  he had sent i arizona to sell at a big swap meet.  i caught him and he is bringing it back with him.  where in the world do you find a used set of gears.  most people i know are scared to install used gears?  would the 4.88 be so bad?

[JohnZ]

would the 4.88 be so bad?

4.88's are a nightmare in anything approximating normal driving; 70mph is 4300 rpm.

[sd1968z28]

i do not necessasarly care about the rpm thing.  this car dosen't get driven down the interstate.  4.88 would be fun around town.  i am talking about originality.  the 4.88 were dealer installed shortly after the car was purchased new. would i have to change the carrier to go back to 3.73 gears? if any body has a set of oem 3.73 please let me know?
my 1971 z28 had 4.88 in high school, i drove it all over the place, but the speed limit was 55 then so no big deal.

[JohnZ]

Yes, you'd have to change - the 3.73 uses a Series 3 carrier, and 4.10/4.56/4.88 use a Series 4 carrier.