CK5 Network
Become a member of the largest online community for Chevy K5 Blazer, Suburban and C/K series truck owners!

speedometers repairable?

ramack

1/2 ton status
Premium Member
Joined
Jun 20, 2004
Posts
1,184
Reaction score
1,564
Location
Centennial, CO
The 79 K5 speedometer never worked since I bought several years ago. Over the weekend I replaced the speedometer cable since I knew it was bad. Taking it out for a test drive, the speedometer and odometer were working. The indicated speed was off about 20% due to the taller tires, but that's ok.

About .2 miles the odometer stopped rolling over and probably 10-15 miles after that the speedometer stopped indicating speed and the needle dropped to zero. Are the speedometers "repairable"? Or should I just get a new one from LMC, Rock Auto etc..?

I don't really need a speedometer, I've been using a speedometer app on my phone, just like stuff to work the way it's suppose to.
Rich
 

K5wrench

1/2 ton status
Joined
Apr 29, 2018
Posts
1,063
Reaction score
2,840
Location
Wyoming
This happened to my 76.
In my case the square hole in the converter on the NP203 tcase had become so lose it allowed the speedo cable to slip (not turn).
I fixed it by wrapping the end of the speedo cable with duct tape.

edit: The converter I am talkin about is that metal cube on the output of the tcase to which thr cable attaches.
you could also try attaching the cable directly to the tcase without converter.
 

ramack

1/2 ton status
Premium Member
Joined
Jun 20, 2004
Posts
1,184
Reaction score
1,564
Location
Centennial, CO
I haven't visually confirmed, but I'm pretty sure the cable is still good. I can "hear" movement in the dash, so I'm assuming that the cable is still rotating and something in the speedo assy is still turning, just that something in the speedo itself is stripped or broken.

The transfer case end of the cable I took off was all mangled, ie , the square end was a bird's nest. The gauge end of the cable looked ok, but after I took the dash apart, it wasn't connected to the speedometer, it was just hanging loose in the dash.

The converter between the speedometer cable and transfer case turns freely. So I'm assuming I'm finding out why the cable I took off was shredded, something is wrong with the speedometer itself.
 

K5wrench

1/2 ton status
Joined
Apr 29, 2018
Posts
1,063
Reaction score
2,840
Location
Wyoming
I haven't visually confirmed, but I'm pretty sure the cable is still good. I can "hear" movement in the dash, so I'm assuming that the cable is still rotating and something in the speedo assy is still turning, just that something in the speedo itself is stripped or broken.

The transfer case end of the cable I took off was all mangled, ie , the square end was a bird's nest. The gauge end of the cable looked ok, but after I took the dash apart, it wasn't connected to the speedometer, it was just hanging loose in the dash.

The converter between the speedometer cable and transfer case turns freely. So I'm assuming I'm finding out why the cable I took off was shredded, something is wrong with the speedometer itself.
Yeppers.
Sounds like something bound up in the speedo.
I'd find another one.
 

ramack

1/2 ton status
Premium Member
Joined
Jun 20, 2004
Posts
1,184
Reaction score
1,564
Location
Centennial, CO
Speedo01.png Speedo02.png Speedo03.png

So...I pulled the speedometer back out of the dash this afternoon. Using a drill and the speedometer cable I took off yesterday (yup, dumpster dive) I spun the assembly to see what was and was not spinning. Best I could see and feel, everything was turning freely. A couple of screws were loose which was allowing the worm gear to not fully engage the intermediate spur gear. In addition to that, the worm gear shaft that mates to a through hole in the loose bracket was much smaller than the though hole, which allowed the teeth to not fully engage as well. I was able to make a band-aid adjustment to correct the alignment and shaft OD to plate ID mate.

The cable that I installed yesterday was shredded, but I'm pretty sure there was too sharp of a radius in the cable housing between back of the instrument cluster and the firewall. I bought another speedometer cable from Orielly's which was a lot shorter than the one I installed yesterday. I'm guessing 12-18 inches shorter.

We'll see how long this lasts. I'm heading up to Leadville in a few weeks, hopefully fix will at least make it there and back, ha. If not, the cell phone app will have to do until the speedometer is replaced..
 

ramack

1/2 ton status
Premium Member
Joined
Jun 20, 2004
Posts
1,184
Reaction score
1,564
Location
Centennial, CO
My son and I installed the new LMC speedometer and cable this afternoon. It worked for about 100 feet then stopped registering MPH. Taking off the ratio adapter and spinning it with a drill the speedometer registers. I'm thinking the inside of the transfer case speedometer output shaft is rounded out. I think I'll give your duct tape solution a shot. Replacement shafts are ~$150.
 
Top Bottom