drwet

I have a 79 with cruise. Originally TH350 now has a TKO 600. Speedo started jumping very slightly last fall before I put it away, and there is a faint clicking noise coming from under the dash. Obviously the possible causes include the speedo head, the cables, and the cruise transducer. I'm thinking of trying the cables first since they are both 37 years old and my experience tells me that is the most likely cause. Couple of questions: Can I lubricate the cable from the cruise transducer to the speedo head on the car if I disconnect it at the transducer and slide the cable out of the housing? Is there merit in lubricating the cables or should I just plan on replacing them? And what is the best cable lubricant to use now that GM doesn't have their ST640 available any more?

blk79nj

If there is a bad cable, more then likely it's the lower cable. As the transducer wares/gets old it becomes harder to turn. This will put more tension on the lower cable. The upper cable basically has no tension on it.

On my 79, that is what happened. The speedo started jumping...then just stopped, and it was the lower cable that snapped. Since my cruse wasn't working anyway, I put in one long cable, and bypassed the transducer.

I"m not sure if you can lubricate the cable without removing it.

I hope this helps.

drwet

Anybody else care to weight in? Anyone ever lubricated their speedo cable?

mark79,80

I also have a 1979 and had a problem with the speedometer needle jumping. It turned out the cruise transducer was bad. To test for this, remove the cable that runs from the transducer to the transmission. Then spin the shaft on the transducer that the cable was attached to. If it does not spin easily, the transducer is the problem. I replaced the transducer.
I did lubricate both cables with a cable lubricant.
To lubricate the cables you pull the cable out from the sleeve. They only pull out from one end. The speedometer cable pulls out from the speedometer end. I cannot remember from which end the transmission cable pulls out. Then put some lube in the sleeve and start feeding the cable back in. Add more lube as needed as the cable is pushed in the sleeve. Do not lubricate the cable end close to the speedometer to keep lube out of the speedometer.

drwet

That's great information. Thanks. Of course GM designed it so the cable comes out from the speedo end. It would be way too easy if it came out from the other end.

Sluefoot

My '79 cable was jittery & makin' some noise.....I already had that portion of the
dash out to fix the tach, so I disconnected the speedo cable, at both ends, so I could
see when the lube was coming out of the tranny end as well.....put it back together,
and it's been nice & smooth & quiet ever since!!

drwet

I've been shopping around for a suitable lubricant. Years ago it was a common product and I'm pretty sure I have a tube of it around someplace, but do you think I can find it? And nowadays no one has heard of the stuff. What is an appropriate lubricant for a speedo cable these days?

mark79,80

Purchased it from a NAPA store. Currently listed on their web site at $3.50 a tube.

7t9l82

We used to use graphite on speedo cables.

drwet

I checked the NAPA web site for 'speedometer cable lubricant' but nothing came up. You have a name for it?

newbie2vette

I have not done this to the 79 I am reviving, but I did lubricate the cable for my 72 LT1 when I installed a new cable. I used the same grease used on the CV Joints. Removed the core (cable) and coat it with that grease, then I use a grease attachment to force grease in the housing so when you re-install te cable it will force the grease in the housing.

mark79,80

Part no. BK 7651378

I entered "cable lubricant" in the search box.

tonak

Mine was jumpy and then froze years ago. I disconnected the transducer to speedometer cable and chucked the transducer end into an electric drill. Run the drill in REVERSE and apply minimal lube while running. I used WD40 sparingly and the gauge has worked well ever since.