[pilot737]

My speedometer stopped working yesterday. Sits at 0 while driving around... not the common 'noisy' or 'bouncing' issue that some have.

Broken cable?

Is there a plastic gear part that is attached to transmission end of cable like my 65 Mustang?

[Sirrotica]

Yes most GM transmissions use a nylon driven gear, manual, or automatic. You weren't specific of what you're working on so I included both in possible scenarios.

Possible problems I have seen, broken cables, stripped teeth on the nylon gears, and the square section of the inside of the nylon gear rounded out. Usually dragging speedometer cables proceed the gear problems, so before replacing a gear make sure the cable is properly lubed so the same problem won't reoccur.

If the cable and gears are intact that leaves the speedometer head as a source of your problem.

Hope this helps, 50 years turning wrenches, so I've seen most of the common problems, and repaired them.

[pilot737]

Thanks for those ideas. It's a 67 GTO w/ 4 speed.

I assume the first place to start is where the cable connects to transmission to check condition of nylon gears?

Then disconnect cable from speedometer and have someone watch end of cable while I'm underneath spinning the nylon gear piece?...to check condition of cable?

[Sirrotica]

Disassembling it at the lower connection on the transmission would be the logical place to start. Cables breaking are the most common problem, followed by the driven gears stripping.

Many times the cable will shear on the square portion that goes into the gear, you then have to fish the broken piece out of the inside of the gear with a strong magnet, pick etc.

[pilot737]

Thank you, great info.

[FirebirdHank]

Is the odometer still adding miles? If it is the problem is probably in the speedo head. If not then it is somewhere between the head and the transmission. Good luck.

[pilot737]

Ah, good suggestion. I just went for a test drive and mileage is not moving.

Thanks for the help.

[shifty]

Take the speedometer cable loose from the transmission. Then connect a drill to the cable and spin it slowly in the reverse direction. A helper in the car should watch the speedometer for operation. Any movement will determine the cable and speedometer are okay.

[pilot737]

Got it back from the shop today. He said the cable was okay... replaced the gear (nylon?) piece inside the trans.

Something he said makes me think the gear had broken off and wasn't in place... he said "some came with a metal gear, some with nylon" as if he wasn't sure what was originally there before the speedo quit working.

If the gear broke off and wasn't attached to end of cable, are the pieces in the transmission?? If so, is that harmful?

I will return and ask more questions Monday.

[Mister Pontiac]

Originally Posted by pilot737

Got it back from the shop today. He said the cable was okay... replaced the gear (nylon?) piece inside the trans.

Something he said makes me think the gear had broken off and wasn't in place... he said "some came with a metal gear, some with nylon" as if he wasn't sure what was originally there before the speedo quit working.

If the gear broke off and wasn't attached to end of cable, are the pieces in the transmission?? If so, is that harmful?

I will return and ask more questions Monday.

Should be a nylon gear. Both the drive (inside the trans) and driven gear (in the housing the cable screws onto). I've not seen any metal ones in Muncie's, ST-10's, or even Turbo 400's, but that's personal experience talking. I suppose there could have been metal ones somewhere, but I've never seen them.

I have had problems with a bad combination of drive/driven gears not meshing when trying to compensate for rear gear changes. There are only certain driven gears that will work with certain drive gears. Sometimes, they both need to be replaced to have a proper matching 'mesh' between the gears. Otherwise, they can strip, or jump around.

I doubt the gear broke off, but if it did and it's floating around inside the trans, then no. It won't hurt anything. As long as it's working again now, I'd keep driving it.

Hope that helps.

[pilot737]

Originally Posted by Mister Pontiac

Should be a nylon gear. Both the drive (inside the trans) and driven gear (in the housing the cable screws onto). I've not seen any metal ones in Muncie's, ST-10's, or even Turbo 400's, but that's personal experience talking. I suppose there could have been metal ones somewhere, but I've never seen them.

I have had problems with a bad combination of drive/driven gears not meshing when trying to compensate for rear gear changes. There are only certain driven gears that will work with certain drive gears. Sometimes, they both need to be replaced to have a proper matching 'mesh' between the gears. Otherwise, they can strip, or jump around.

I doubt the gear broke off, but if it did and it's floating around inside the trans, then no. It won't hurt anything. As long as it's working again now, I'd keep driving it.

Hope that helps.

Thanks Mr Pontiac, big help with that info.