Technical how does a spedometer cable work?

school me on how a speedometer cable works heres my 1956 olds one and theres the port on the new 700 r4...do i just screw it on? or is there a special way i need to go about it?

 

You're end of the cable is messes up, should be square, like the tranny 'hole".

Does the cable spin freely inside the housing?...something happened to keep the cable from spinning and twisted the end off.

 

Well first you have to have at least a new inner cable as that one is destroyed. Somewhere along the line you have to figure out why the hell that one got destroyed.
That can be because the speedometer head is froze up. Because there is a kink in the cable housing housing or other damage to the cable housing.
You can buy a replacement cable that you cut to length and crimp the top end on at any parts house and then figure out how long it has to be. Or buy a new cable and housing assembly and universal ones the correct length aren't that spendy. That involves pulling your housing out of the car (make mental notes of how it's routed) and taking it to a parts house (preferably a real parts house like NAPA and telling them you need one to replace this. That should get you a new cable assembly with the right length cable and the right ends.

As far as how it works, The drive gear in the trans turns the cable and the cable turns the mechanism in the speedometer. The square end of the cable goes in the square hole in the gear and your square end is twisted off.

 

Really? It TURNS.

 

It is like a round-wound bass guitar string inside. On each end the roundness has been pressed into a square, to facilitate it turning with the driven gear in the transmission, and the speedometer head, at the other end.

Over that inner cable is a jacket or housing, with ends that attach via a one or another means to both the transmission and speedometer housing. This can be a screw on fitting, push on fitting with a clip, or push on with a bolt and tab. I am sure there are others.

You may or may not have been able to simply unscrew the cable from the old transmission, and attach it to the new, were that cable not trashed.

If you can get the whole cable out, you can replace the whole thing, with one that just re-attaches, with the new transmission.

There are different drive gears that can be had for inside the transmission, to calibrate the speedometer.

I have happily purchased a fair quantity of stuff from these guys:

http://www.transmissioncenter.com/7..._Performance_Transmission_Parts_from_PATC.htm

The end of your cable once looked like, and will again need to look like this:

The "nut" will likely not be that size, though.

 

Come on Tman. Dude has to start somewhere.

 

More good stuff here: http://www.bowtieoverdrives.com/catalog/catalog.php?Action=GETSUBCAT&CATID=DA2

 

Like a 30 second Google search?

 

Sometimes us old farts just assume everybody knows what a speedometer cable should look like,but then again looking at the photo it should be apparent that the cable won't work with the end being snapped off.

Check your local napa store for a replacement,,does the speedometer head work or is it froze up. HRP

 

And check to make sure that both ends of the outer part of the cable screw into their respective threaded ends

 

They work better if they're all there!

You will need to figure out why the old one broke. It could be that the cable itself got stuck in the housing. Or maybe the speedometer locked up, which can happen. The odometers on the old GM speedos often get stuck, usually when it has to turn several numbers at once...I've found a few that were caught in the act of turning over, stripped the cable or internal gears, and never moved again. If you want to test the speedometer first, you can use the old broken cable, and a reversible cordless drill.


Also you need to make sure the new cable is long enough, and I'd also suggest buying a complete new cable, not just the inner part. Some new cables come lubricated, some come with a small packet of grease that you have to apply yourself. Make sure it gets grease on it, one way or another.

 

TRIVIA: A Corvette mechanical tach cable is wound the opposite direction compared with a speedo cable because the cable spins the opposite direction.

 

thanks everyone... I got my 700 r4 transmission from monster transmission and had to tell them my tire size and rear end gears..do I need to contact them? or can I tell the speedo cable people that and that the transmission was build on those numbers? thanks

 

After you verify the speedometer is not stuck, pull the housing out along with the cable...when shopping for a new one, you want to make sure the speedometer "nut" is the same as you have, then you want the tranny "nut" for a 700r4...
I couldn't tell by your pics if it was correct (tranny side) or not.

The shop won't care/need to know tire size/etc.

 

I haven't added anyone to my ignore list yet this year... done.

 

You cable doesn't care anything about gear ratios. But it does care about thread sizes of the fittings it screws to. And the square holes in the trans and speedo could be different sizes.

Best thing you can do is remove the old cable&housing and the transmission's fitting, and take them to the parts store with you. Find the oldest parts man in the store, and show him your stuff. Hopefully he can find you a cable with the proper ends on it, and close to the proper length. If not, try an even older store with an older parts man. No O'Reilly's or Autozones need apply.

 

The dash part (speedometer head) ends are pretty much standard. The one out of my Ford was 61" and I needed one to go to the Muncie 4-speed. I found one on eBay 63" long that fit a '63 Belair and it was perfect.

 

There are only a few lengths that speedo cables come in these days...and this one will fit most older cars, like GMs from the 30s to the mid 60s.

http://www.oreillyauto.com/site/c/detail/PIO0/CA3002.oap?

And as mentioned, the cable has a ratio of one to one

The thing you have to worry about is the speedometer, if it has not been worked on for a while, it will probably give you trouble.

 

Speedometer shops are becoming increasingly rare these days, too.

 

and this car has been sitting since 1980 so who knows

 

I would play with the speedometer before connecting the cable to it. There is a little collar that the cable fits into, remove the old cable from it, and see if you can turn the collar easily by hand. If it's sticky or stuck, you will just damage the new cable or speedo gear when you take your first drive.

 

will do I will get under the dash tonight thanks

 

Cobalt, I'll chime in here since I didn't read anything about it. I would leave the end attached to the speedo andspin that broken part to prove the speedo works; you can use a variable speed reversible drill under the car to do this. Have someone watch the speedo in the car. GO SLOW you don't want screw anything up. If it works grab the bad end with vice grips and pull it out. It will have a square end in the speedo. In the old days a repair kit came with only the inner cable extra long. You lubed it and put it in from under the car. Once u had the proper length u pulled it out again, cut it, heated the end and put the plastic part that came with the kit onto the cut end following the instructions. Make sure it's well lubed, we used that white lubricate same on brake backing plates, and reattach it...I've done hundreds of these and rarely ever disconnected the speedo end....Good Luck

 

X2 on the reversible drill and the go slow to test speedo, if the cable will turn by hand first.

 

not so fast there! there is a collar on the upper end of the cable, that prevents it from being pulled out the lower end of the housing.

 

Squ...I couldn't agree with you less. On the replacement cables the plastic end you heat up the cable and put on has the shoulder which keeps it "centered" . None of the ones I fixed in a shop had a collar on the speedo end. The hardest thing was "hoping" the top was lined up good enough for the squared end to slide in; if not sometimes we had to go under the dash but other times an older mechanic took a file and gave it a little 4 side taper and it went in from the bottom. This was always done on the lift and was completed in less than 15 minutes with 1 hour flag time....

 

that's strange, I own several old GMs and all of them have a metal collar crimped on the top end of the cable, which prevents it sliding down into the casing, you can't pull it out the bottom without damaging something.

 

Same results here.

 

Speedometer cables on American cars always go in from the top, unless they are put in backwards. That is unless the speedometer driven gear uses a keyed (flag) tip.