77 Speedometer issue
Thread Starter
3rd Gear
Joined: Aug 2020
Posts: 3
Likes: 0
From: Cobourg, Ontario
77 Speedometer issue
Hi everyone, this is my first post as I just purchased my first Corvette. Its a 77 with L48 engine, no cruise.
My speedo was stuck at 10 mph when I bought it. To trouble shoot I have:
a) disconnected at transmission end, gauge went to 0.
b) red driven gear is not worn. I see the green drive gear in transmission. It looks good. Tried to wiggle it with screwdriver to see if it was loose and it does not move.
c) bullet looks good
b) used cordless drill backwards on transmission end of cable and got a steady read on speedometer.
e) disconnected cable at speedo end, removed inner cable and cleaned and lubed it although it looked pretty good IMO
f) re-assembled everything and speedo is stuck at zero and non functional
I'm stumped. Seems like the issue is in the transmission. Hoping someone might have another though as I have never ventured into a transmission before.
Thanks everyone for any suggestions you have.
My speedo was stuck at 10 mph when I bought it. To trouble shoot I have:
a) disconnected at transmission end, gauge went to 0.
b) red driven gear is not worn. I see the green drive gear in transmission. It looks good. Tried to wiggle it with screwdriver to see if it was loose and it does not move.
c) bullet looks good
b) used cordless drill backwards on transmission end of cable and got a steady read on speedometer.
e) disconnected cable at speedo end, removed inner cable and cleaned and lubed it although it looked pretty good IMO
f) re-assembled everything and speedo is stuck at zero and non functional
I'm stumped. Seems like the issue is in the transmission. Hoping someone might have another though as I have never ventured into a transmission before.
Thanks everyone for any suggestions you have.
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are you certain you have the bullet all the way in?? it's easy to not get it right as the groves can be confusing.
Safety Car
Joined: Oct 2007
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From: Seattle Area Washington
When you pulled the inner cable and lubed it what did you use as a lube?
Only use dry graphite lube, this product works great for many things. LINK:
Make sure where the square speedometer cable end fits into the red speedometer gear is not wallowed out that the gear turns but not the cable.
If you need to inspect/change the Drive Gear, at about the 0:50 mark in the video is when the tail shaft is pulled. LINK:
Simple, remove 4 bolts and drive shaft. Make sure when you drop the drive shaft wrap some tape around the rear "U" joint caps.
Also a good time to replace the rear seal of the trans housing.
Use ONLY Transmission Assembly lube for the new seal and "O" ring when going back together.
Only use dry graphite lube, this product works great for many things. LINK:
Make sure where the square speedometer cable end fits into the red speedometer gear is not wallowed out that the gear turns but not the cable.
If you need to inspect/change the Drive Gear, at about the 0:50 mark in the video is when the tail shaft is pulled. LINK:
Also a good time to replace the rear seal of the trans housing.
Use ONLY Transmission Assembly lube for the new seal and "O" ring when going back together.
Last edited by bmotojoe; Dec 30, 2020 at 07:35 AM.
Thread Starter
3rd Gear
Joined: Aug 2020
Posts: 3
Likes: 0
From: Cobourg, Ontario
Thread Starter
3rd Gear
Joined: Aug 2020
Posts: 3
Likes: 0
From: Cobourg, Ontario
Thanks bmotojoe for the reply - great video showing the replacement of the drive gear. I used lithium grease on the bottom 2/3 of the cable. Thought I read that some where here on the forum. With the cable detached from transmission, I inspected the red driven gear and it had a nice square hole (and no crack in its shaft) and the cable is basically square with a little wear on the corners. When I insert cable into the driven gear, they seem to lock up nicely and spin together when I turn by hand.
On another thread I read that sometimes the cable will "shrink" in length so the driven gear no longer makes proper contact with the drive gear. Anyone heard of this? This is the only other thought I have. Otherwise I think it must be a drive gear issue.
On another thread I read that sometimes the cable will "shrink" in length so the driven gear no longer makes proper contact with the drive gear. Anyone heard of this? This is the only other thought I have. Otherwise I think it must be a drive gear issue.
