65 Speedometer / Cable /Gear Issue?

[Randal M.]

After 45+ years, the speedometer just quit. I found a seized cable which was replaced. I also found that the plastic gear inside the tailshaft was not contacting the drive gear on the output shaft, probably the result of the cable failure, so I replaced that too. I found a 'natural' 19 tooth gear inside the tailshaft, so that is what I put back in. Still no reading on the speedometer...

I spun the cable with a cordless drill, and got 20 MPH, so I assuming the speedometer and the new cable are not the culprit. I also tried turning the plastic gear, which has a little play, but seems engaged with the drive gear. Also checked to be sure that the square end of the cable went into the plastic gear which it does. After all the checking, the speedometer still reads zero.

Based on past threads, I am wondering if the diameter of the plastic gear is somehow the issue. Instead of the natural gear, do I need to switch to another color with a different diameter? I assumed that replacing the worn gear with the same type would work.

Thanks for any ideas, as this has totally stumped me....

[Joe R.]

Re: 65 Speedometer / Cable /Gear Issue?

Randal,

The first step would be to determine what rear end ratio your 67 has and then it can be determined from a GM chart what driven gear in the trans you should have.

JR

[Ray K.]

Re: 65 Speedometer / Cable /Gear Issue?

Randall

Are you sure that the replacement speedo cable is long enough so that it engages both the driven gear and the speedo head?

Ray

[Wayne M.]

Re: 65 Speedometer / Cable /Gear Issue?

Randal -- 1st step is to check rear axle ratio, per Joe R's description.

I doubt your '65 came from the factory with a "natural" plastic 19-tooth gear, as a 3.08 axle with 7.75 x 15 rubber called for the 18-tooth brown gear, and 3.36 needed the blue 20-tooth. Unless you've owned the car since new, maybe a previous owner has wrongly installed the 19-tooth, depending on whether the gearing determined in step #1 is original.

But even if the drive gear on the trans output shaft is too small a diameter (ie. the one meant for the 22-25 gear count plastic driven gears) a new plastic gear usually has enough "meat" to operate for a short period (depending on the speedo cable load) before the center of the teeth are worn and the skipping begins. Was there concave wear on the 19-tooth, or wear to one side ?

[Randal M.]

Re: 65 Speedometer / Cable /Gear Issue?

Thanks for the responses!

The rear-end is 3.55, and and is not original to the car, based on the stamped code. The trans may have also been replaced at some point, as the car was heavily raced in it's early days.

This means what I should have found a red 22 tooth gear. I seem to recall I put in the 19 tooth gear years ago to true-up the speedometer reading. I think the original have had 20 teeth, but was reduced one tooth to increase the read-out, which was slow.

The square trans end of the cable goes right into the plastic gear before I even start to thread on the nut, so I think I am OK there...

I expected the old gear to be chewed up because the cable locked up, but the weird thing was that although noticeably smaller in diameter than the new one, it seem to be uniformly worn all across the surface - no concave depressions in the middle.

I also agree with Wayne that even if the new gear is smaller, there should be enough material to get it working even for a short period of time - as opposed to not working at all. I can't figure how the new gear seems to engage inside the trans, but not turn the cable. Maybe my next move should be to get the rear wheels off the ground, rotate the tires by hand, and see if I can detect any movement of the new plastic gear...

Thanks again for the suggestions so far!

[Bob R.]

Re: 65 Speedometer / Cable /Gear Issue?

The drive gear in the transmission for 355 to 411 is different then the drive gear for the 308 and 336 gears. The plastice gear for a 308 will not work in a transmission with a 355 drive gear. It won't reach the teeth. Try using the correct gear for the 355 and see if that works. If your speedometer is not running at the correct speed after installing the gear the only fix is to relpace the drive gear in the transmission with the correct part for your rear differential and that is a pain in the neck.

[Randal M.]

Re: 65 Speedometer / Cable /Gear Issue?

I put the car up on jackstands todayso I could remove the cable and driven gear to look around inside the tailshaft...I was very surprised to find out the steel gear on the output shaft does not line up with the hole for the nylon driven gear - it was shifted to the right.

Can someone please confirm the relation between the steel gear and the driven gear opening in the tailshaft? I am assuming the hole and the steel gear should line up...

Thanks for the help!

[Dan B.]

Re: 65 Speedometer / Cable /Gear Issue?

I doubt your problem is in the driven (metal) gear in the Tranny, they are pressed on the tailshaft and not easily moved. I'd take a closer look at your replacement speedo cable. I have had many problems with replacement Tach and speedo cables in the past few years that needed work. Most recently had a repro Tach cable in my 59 that was manufactured just slightly too short. It worked but made a racket that sounded like a bad Tach.

I fixed the problem by buying a new cable core and cutting it to the exact length and reusing my original housing. That may be your problem here. Dan

[Ken A.]

Re: 65 Speedometer / Cable /Gear Issue?

AC Delco always recommended replacing the cable & the casing TOGETHER. The casing wears out internally & causes cable whip which causes bouncing pointers & noise. In addition, unless you have a Speedo shop make you a new cable & hand them the casing to measure, you're unlikely to get the correct length cable.

[Bob R.]

Re: 65 Speedometer / Cable /Gear Issue?

If the driven gear in the tail shaft does not line up with the plastic gear I would wonder if that transmission was once in a different car possibly a Ponitac. Maybe a car with the speedo connection on the passengers side not the drivers side. I had this problem on a transmission I had in my 63. I was fortunate to find the problem before the transmission was mounted in the car. I had the wrong drive gear for my ratio transmission and it was located on the wrong spot on the tail shaft. We were able to purchase and install the correct gear in the correct location and my speedometer works perfectly now. My car has a 336 rear.

[Pete L.]

Re: 65 Speedometer / Cable /Gear Issue?

My 66 AIM shows clearly that the location of the speedo cable routing is on the pass. side. I would like to know if the previous question asked "should the steel drive gear in the tail shaft be centered below the nylon gear"? My steel gear is also not centered, but offset to the right while looking in. I am also having problems with speedo and not sure if this is the issue.

[Wayne M.]

Re: 65 Speedometer / Cable /Gear Issue?

If the driven gear in the tail shaft does not line up with the plastic gear I would wonder if that transmission was once in a different car possibly a Ponitac. Maybe a car with the speedo connection on the passengers side not the drivers side. I had this problem on a transmission I had in my 63. I was fortunate to find the problem before the transmission was mounted in the car. I had the wrong drive gear for my ratio transmission and it was located on the wrong spot on the tail shaft. We were able to purchase and install the correct gear in the correct location and my speedometer works perfectly now. My car has a 336 rear.

Bob R. and Pete L. -- position of steel drive gear on the tailshaft could be the problem if not visually centered when looking through the "bullet" hole for the plastic gear. The spec for location of steel gear for the '65-up '584' tailhousing was 9/16" further rearward from that used for the '429' [driver side speedo] '63-4 Muncie tailshaft. If it's the original '64 mainshaft that's being reused, the raised, machined circumferential 'pad' on the shaft may not be long enough to retain the drive gear that's now moved back. There are three different mainshaft part #'s for '63, '64, and '65 transmissions, and pad length is the reason for the new # for '65 (made long enough to service '64s).

[George C.]

Re: 65 Speedometer / Cable /Gear Issue?

Guys I need some help. I just installed the larger speedometer drive gear in my Munci transmission. This is in a 65 car, and some previous owner has changed out the low gears to a 3:36 unit.
My problem is that after pressing the new drive gear to a measurement of 4 7/8 inches from the bearing plate it is not centered in the bullet hole in the case.
Waynes note above says the drive gear should be centered in the hole, so I am going back to the garage to do that. Can someone explain the
4 7/8 dimension in the service manual, I am guessing that I am measuring it incorrectly?

Thank you,
George

[Michael C.]

[George C.]

Re: 65 Speedometer / Cable /Gear Issue?

Michael,
Hi, I was able to figure out that I had the smaller 1.74 Drive Gear, and needed the 1.85, and I have the new blue 20 tooth gear for the 3:36. I also figured out the problem with my measurement, I was measuring from the back of the drive gear, not the front.
Damn, back to the garage.

Thank you for the information,
George