1968 GMC Speedometer Cable Help
 

My truck’s speedometer has never worked. A while back I pulled the old cable out and it had broken apart and someone had removed the pieces, so all I had was a portion of it. I ordered a new cable from Rock Auto that was 38” long and it was way too short, so I measured the housing like I should have from the beginning and ordered the next size up, 63” long. That length is too long by roughly 5”. Does anybody know what length speedometer cable I need? Is this something if I go to the old guy at NAPA he can probably help me with? I’m a little confused because LMC (I know they aren’t the best) says it should be one of those two lengths, but nobody seems to have a length in between those two.

It’s a 1968 C20 with an NP435 transmission. I’m guessing the transmission is why I’m having a hard time finding the right length of speedometer cable.

Thanks in advance for any help.

Re: 1968 GMC Speedometer Cable Help
 

I just ordered a cable from O-Reilly's but I got the longest one they showed at 112" because I installed a 700-R4 in it.:chevy:

Re: 1968 GMC Speedometer Cable Help
 

Five inches too long isn't enough to worry about.. Just reroute the cable in such a way as to take up the access.. No sharp bends, don't allow the cable to come in contact with the hot exhaust parts.. Did the thought ever occur to you that the reason the old cable broke was because it was 5 inches too short?????

Re: 1968 GMC Speedometer Cable Help
 

I’m looking at trying to reuse the housing that’s in the truck. The way it’s routed doesn’t look like I can remove it and then reinstall a new one. It goes through a small hole in the frame that either end won’t fit through. I’m sure this is making it harder than it should be, but if it gets to that point I can pull the old one and install the new one and route it as you described.

Re: 1968 GMC Speedometer Cable Help
 

Cut it 5' shorter ….or am I not understanding. Both ends are just raw.

Re: 1968 GMC Speedometer Cable Help
 

One end is square to fit into the transmission and the other end has a “nock” on it. I’m not sure what purpose the nock serves, I figured it was for the speedometer.

Re: 1968 GMC Speedometer Cable Help
 

The speedometer cable shouldn't go through the frame. I just pulled 2 of them. One out of the LWB frame trans and one out of the SWB and neither one goes through the frame.


The e brake cable does go though the frame right under the drivers floor and it look's a lot like a speedometer cable. The speedometer cable does not go through the frame on any of these model trucks that I have ever seen.

Here is a thread on the speedometer routing.:chevy:


http://67-72chevytrucks.com/vboard/s...d.php?t=445001

Re: 1968 GMC Speedometer Cable Help
 

Interesting. I’ll get out there and take a look this week. I might have gotten it confused with the e-brake housing. Thanks for the link. I’ll report back soon!

Re: 1968 GMC Speedometer Cable Help
 

You can measure and cut the longer cable to use as a replacement and buy one of these cheap universal kits to swedge a bead on the speedometer side .:chevy:

https://www.ebay.com/itm/Universal-S...-/142957131769

https://www.ebay.com/itm/Dorman-9-18...cAAOSwBahU4S3r

Re: 1968 GMC Speedometer Cable Help
 

Genius! I appreciate all the help, guys. And Grumpy, you always offer sound advice! I’ll report back soon. I had knee surgery on Thursday so once I can get around a little better I’ll go take a look.

Re: 1968 GMC Speedometer Cable Help
 

I have the same transmission, and just bought a speedo cable a couple weeks ago, Let me go grab the package to see where I bought it,
Dont get a longer than needed cable.

Re: 1968 GMC Speedometer Cable Help
 

Mine came today and I had to take it back. It worked but was way to long by about 30". I took it back out and pulled it to where I needed it. 65" total. I went back to O-Reilly's and we found one at 63", it should work it will be here tomorrow. I'll post once I get it and see how it fit's. If it's 5" to long it should be fine you don't want it to have any sharp bends.:chevy:

Re: 1968 GMC Speedometer Cable Help
 

That will only work if the outer cover is in good shape. If the outer cover are the ends are bad it want work. The OP never has said but he said parts where missing. ????:chevy:

Re: 1968 GMC Speedometer Cable Help
 

Thanks all, I appreciate the help! Astro-Balls, that might be exactly what I need!

Re: 1968 GMC Speedometer Cable Help
 

63" cable with housing worked perfectly. I would have liked a 65" but the 63" is fine. That's a 700-R4 also.

First picture is box from O-Reilly's auto.
Last picture is e brake coming through the frame under the drivers side.:chevy:

Re: 1968 GMC Speedometer Cable Help
 

Try here..

https://www.classicindustries.com/pr...SABEgIRo_D_BwE

Re: 1968 GMC Speedometer Cable Help
 

An older thread, but very helpful in locating Speed-O-Cable for my '68 (C20 396, w/NP435 trans).

Attached pic of OER one that AstoBalls linked, along with what I ordered.


I did end up ordering from Ebay (since I found a 70" with metal housing).
Brand: Fargo Automotive
Mfg. PN: 47-17260-MH