Speedometer not working properly

[Gorillasoldier]

First, I will apologize if this is a worn out subject. BUT...
I recently bought my son a 1981 CJ7 , 258ci, 3 speed manual, Dana 300 Transfer Case with short rear output, rear diff has the "DD" stamp, also running on 33's.
The speedometer is NOT working correctly. It will run up to 35'ish mph and no higher. I have checked it vs. a gps and it is about 1-2mph fast through out that range. I have taken the cable loose from the Transfer Case and spun it with a drill, Speedo will go above 85mph on the drill. I have read several posts but haven't found any that have updated with a solution/solved post. I have also read a few posts that say there is no way to fix it.
Suggestions or links to actual fixes greatly appreciated. We won't let him drive it until I know the speed is accurate as a 16 yr old boy doesn't need any tickets.
Thank you

 

[jp360cj]

Sounds like the issue may be on the tcase side. How does the cable look where it connects to the tcase?

Also, idk if it would make a difference, but are you sure it's a Dana 300 tcase? A 3 speed manual wasn't offered in '81 and the only Dana 300 I know of that can be mated to 3 speed would be a Scout Dana 300 . It would have the same backwards texas bolt pattern as a Jeep/Scout Dana 20 and a short rear ouput, but they are rare. If you do have one, then definitely hold on to it. The easiest way to tell a Dana 300 from a Dana 20 is the casting number on the rear of the case. The Dana 300 has a C300-xxxx casting and the Dana 20 is a C18-xxxx.

 

[Lumpy Grits]

:ww:

Pull the speedo drive gear out of the t'case and check it for damage.
Lube the cable with Sta-Lube Engine Assembly lube.
LG

 

[cglax6]

:ww:

Pull the speedo drive gear out of the t'case and check it for damage.
Lube the cable with Sta-Lube Engine Assembly lube.
LG

Exactly what he said. Could be either, or both.

If there's nothing wrong with the gear and the cable is the right length and lubed up, and it still doesn't work, you may be hosed. Not sure what else it could be if it works when you take a drill to it. Doesn't sound like it's something in the speedo housing.

If all else fails, you could replace the speedo with a replacement from Speedhut. They make a very nice GPS speedo. They're pretty pricey though. I have one on my wish list, but can't quite justify the expense when everything works fine...maybe I need to just bash mine up with my foot...

 

[Gorillasoldier]

Sounds like the issue may be on the tcase side. How does the cable look where it connects to the tcase?

Also, idk if it would make a difference, but are you sure it's a Dana 300 tcase? A 3 speed manual wasn't offered in '81 and the only Dana 300 I know of that can be mated to 3 speed would be a Scout Dana 300 . It would have the same backwards texas bolt pattern as a Jeep/Scout Dana 20 and a short rear ouput, but they are rare. If you do have one, then definitely hold on to it. The easiest way to tell a Dana 300 from a Dana 20 is the casting number on the rear of the case. The Dana 300 has a C300-xxxx casting and the Dana 20 is a C18-xxxx.

Well I was pretty sure till you said that. I stand corrected as it has the 18series casting numbers.
The cable at the tcase looks fine it is square no obvious wear. I was going to pull the tcase sleep plug out but do not have a narrow wall socket that will fit. I'll need to run to town and get one.

 

[Gorillasoldier]

:ww:

Pull the speedo drive gear out of the t'case and check it for damage.
Lube the cable with Sta-Lube Engine Assembly lube.
LG

Will do, I will just need to go buy a narrow wall socket first. Thank you

 

[Gorillasoldier]

Exactly what he said. Could be either, or both.

If there's nothing wrong with the gear and the cable is the right length and lubed up, and it still doesn't work, you may be hosed. Not sure what else it could be if it works when you take a drill to it. Doesn't sound like it's something in the speedo housing.

If all else fails, you could replace the speedo with a replacement from Speedhut. They make a very nice GPS speedo. They're pretty pricey though. I have one on my wish list, but can't quite justify the expense when everything works fine...maybe I need to just bash mine up with my foot...

Cable seems to be proper length as there is no excess and makes no weird rerouting, did spin fine on a drill, Speedo is also very new along with cable.
I'll get the socket and pull it.

 

[Lumpy Grits]

Will do, I will just need to go buy a narrow wall socket first. Thank you

My comment was for a later D/300 t'case.
Don't know what to do for a D/20.......
LG