This is my 2nd question from an earlier post on 3-4-18, just got the car 2 weeks ago, speedometer was not working, took the speedo cable off at the transmission and turned it counter clockwise, the needle went up to 40-50 mph, I put in a new pencil gear (green) color, no luck speedo still doesn't work, so now I'm assuming it must be the gear on the tail shaft that drives the pencil gear. So now I have to take the transmission out, I would like to have the gear on hand when the transmission comes out, but I don't know which 1 to buy, here are 2 p/ns I see on the trans,3857584 and 3925661, does this help define the p/n I need for the tail shaft gear. Also 1 more question, I plan to have all the gauges rebuilt because they work, but poorly. Do you all know of a good source to perform the rebuild of these original gauges?
Thank You for all the help I've received and in the future, really enjoy this forum and all the great information.

D.Sperle

 

Before you do all that are you sure that the cable in the sheath is long enough to make contact with the plastic gear? Has the cable been replaced recently ? Does it look new? Last year I had the same issue with my 65 coupe. It was the length of the interior cable that was short by about 1/8". Try pulling it out as much as you can and make sure that it slides into the plastic gear. Then test it. That solved my problem and I think it is worth a try. i have heard that some of the internal cables being produced today are too short.

 

Thanks, sure would be a cheaper fix, I'll try it

 

It probably IS the cable length, however if it is not easy to tell and you are sure the cable is not broken, you can also disconnect it at the speedo and see if it turns when the car is moving.

 

rarely is the problem the tail shaft drive gear. although in some cases it is plastic, but is harder and your softer pencil gear is designed to strip first.

try to get a mirror up there with a flashlight, perhaps you can eyeball it to see if it is stripped.

also some pencil gears will not mate correctly with some drive gears. don't know the specifics, but perhaps someone here can chime in with the specifics.

 

D.. not sure what a pencil gear is, but in our terms you have a drive and a driven gear. The drive gear is on the rear shaft, the driven gear is what you can remove from the tranny without taking the tranny apart.

If you can spooled up the cable at the tranny with a reversed drill and the speedo worked, then your issue is more than likely inside the tranny on the drive gear. While it's not real common, the retaining clip can break or come loose which will cause the drive gear to fail.

So.. my questions would be at this point..

What did the old driven gear look like when you removed it?

If the driven gear was missing teeth or chewed up then replacement would be justified. But if the condition of the original gear appeared in good condition again I would lean toward the drive gear.... which is a royal PITA to fix. You'll have to remove the tranny and tear down the rear section for replacement.

In regards to your gauges... you lost me there too... What are the gauges doing? Working poorly is a confusing statement since you can use the actual dash unit to diagnose issues. Most issues with center dash gauges are caused by faulty senders and not the actual gauges themselves. You can learn more about these issue by going to this link and reading more info... and there are even video's to help you. http://repairs.willcoxcorvette.com/?yt=1972&s=gauge

Temperature gauge issues can be corrected by installing an adjustable resistor behind it... Reproduction senders (and I don't care which brand you buy) are all wrong and will make your temperature gauge read incorrectly.... You can lean more about this at this link http://repairs.willcoxcorvette.com/w...deo-1968-1976/

IMHO,

Willcox

 

The driven gear I took out looked good except a little wallowed out in the center of the dia. I have bought a new driven gear (green)
and I purchased a right-angle drive adaptor to attach the speedo cable to at the transmission, thinking maybe the steel drive inside the cable was to short to engage the driven gear. As far as the gauges go the tach needle has a lot of bounce above 3000 rpm, clock works for 5 min
then quits, fuel gauge registers between 1 quarter when empty and 3 quarters when full, amp gauge never moves and water temp goes
up to 1 quarter when fully warmed up. I just thought they would need some attention after 48 years. Thank you for all the useful information
I'll try the websites

D. Sperle

 

Sorry for your problems. To get the proper speedometer gear you need to match the gear to the rear differential ratio. The bottom of the differential is coded. You need to translate the code to figure out the ratio. You should also decode the transmission near the mid-plate. Wilcox has the speedometer gear selector on their website but you will need the aforementioned info first. If the plastic gear is showing wear there is a good chance the speedo gear on the shaft of the transmission is misaligned.

 

There are three steel drive gears used in Muncie transmissions. Working from memory, one drive gear works with 3.70 and higher , one works with 3.55 and lower. There is a third rarely seen gear that is used with 4.56 gears. If someone has changed the rear gear across the 3.55/3.70 line then you need to change the internal steel drive gear. The plastic driven gears must be used with their respective drive gears.

 

You probably should manually determine what rear axle ratio you have. Jack it up and see how many revolutions the rear tire makes to one revolution of the drive shaft.
While you are doing that, see if the "pencil" gear turns.

 

Regarding instrument rebuild: Morris Mintz at West Valley Instrument Specialists in Reseda CA is the BEST we know of. Amazingly knowledgeable. We hope he never retires! He has helped us numerous times, as well as plenty of folks we have sent there. He even has access to a lot of parts nobody else seems to have. Call 818-758-9500 or toll free 877-818-9402, or check his web site westvalleyinstruments for more information.