I have a 70 F85. There has been this loose cable hanging around in the engine bay forever, and I finally connected the dots today when I found another cut cable on the transmission.

Why would someone do this, and (if it’s worth it) how would I route a replacement?

 

Yes it's a thing.

Its done on purpose when a driver wants more control over an automatic. But should be deleted correctly.

I don't recommend it, unless you never want to relax when on the go.

 

Look at a Chassis Service Manual for routing and adjustment. (For 1971, its pages 7-242 and 7-243; that should get you close to where it is in a 1970.)

The last time I replaced one, I used GM part number 411340. That appears to be discontinued, but there are still some out there for sale.

The throttle end of a new cable will probably look a little different than the original. The original style had a metal clip that slid on a metal rod for adjustment. A new one will probably have a hard rubber tube (looks like an inch long piece hose) that slides over a metal ball.

In theory, you install everything, then the last step is to press the accelerator pedal to the floor, and it should adjust itself. I had to push the ball a little further into the tube so it wouldn't kick down too soon.

 

Here is one on Amazon for reference.

 

Here's the diagrams from the 1970 Oldsmobile Chassis Service Manual, pages 7-228, 229.

I have the 1970 service manual for sale in the Miscellaneous Classifieds section:
https://classicoldsmobile.com/forums...manual-172409/

 

Unlike a 200/700R4, a TH350 does not care if the kickdown cable is connected. It won’t burn up, it will shift normally just fine. The only hangup: you have no WOT downshifts, and the trans will tend to “short shift” when accelerating hard.

Personally, I’d fix it. The cables aren’t terribly expensive, and it makes the car much more responsive, without driver input. Get a good quality pan gasket and filter. When you remove the cable, some fluid will come out of the hole. It’s much easier and cleaner to replace when your not fighting a waterfall of atf.

 

Thanks for all the info everyone. Seems worthwhile to replace, though up to this point I've been satisfied with a 2 barrel and no kickdown. I guess I'll really be smoking the tire now. I'm going to avoid changing the filter and fluid because I did that a few months ago.