What Speedo (and/or) Driven Gear?

[Terbro]

When I bought the car, the speedo gauge was working okay, but as with some of my older cars, it would fluctuate wildly when cold, sometimes giving out and dropping to 0 mph for a few minutes (until it warmed up, or I was at lower speeds).

So I replaced it a few months ago. That caused a charging issue, which I've just resolved (for the most part; another story). Point being, I just got it back on the road yesterday, and discovered that the new cable not only didn't fix the problem, it isn't working at all.

In troubleshooting, I disconnected it at the gauge cluster, and determined that it's not spinning. So obviously the problem is at the transmission. A call to a local trans shop guy had him advise it's either the speed gear or the driven gear. I'm not familiar with these, but he's explained that the speedo gear is accessible right at the interface between the cable and the housing, and that the driven gear is farther inside, and requires dropping the pan. He suggested replacing both. I asked how much he would charge and quoted $100.

My local Advance Auto Parts store has two speedo gears, one orange or yellow and the other red, or dark brown. One was 19-tooth, and the other 20-tooth; forget which color coincided with which tooth count. The red or brown one had a tube running through the gear; the yellow did not (looking at the photos on their system).

Searching the forum, I read some posts mentioning 30-tooth and even 27-tooth gears...so now I'm confused.

1) What speedo gear do I need?
2) What's the probability that changing that alone is sufficient and I need not worry about changing the driven gear?

I suppose I could pull it and answer the question of color/tooth-count. But I already pulled it once and trans fluid drained, and so if possible, I'd rather have the new one at the ready, so I don't have to worry about trying to plug it or lose too much fluid by pulling the speedo gear housing twice.

 

[GNRick]

When I changed mine I don't remember any fluid coming out. If it did, it would have been minimal, as the fluid should be in the pan. As stated in your other post, one gear is blue and one is orange. I think the gear at the cable is blue but you will soon find out.

 

[INEEDAGN]

As long as the car has stock 3:42 gears and stock 26" tall tires you can use one of two configurations. Stock is an 11 tooth orange drive gear (which is part of the governor gear) and a 30 tooth blue driven gear. The 11 tooth governor gear is getting scarce these days and therefore expensive. So an alternate combo is to use a green 10 tooth drive (governor) gear and a black 27 tooth driven gear. This combo is available on eBay for $30-40 for the pair and has the same ratio as the expensive 11 tooth gear. I have the part numbers but I'm on vacation this week and can help more when I get home.

The charging issue was caused by not getting the cluster back in correctly. But you probably already figured that out. Since it's a 2 piece cable you should triple check that it's installed correctly at all connections.

If I was in your spot and wasn't familiar with the trans internals, I'd buy the eBay gears and pay the $100 to have a trans shop swap them out for you. That's a fair price considering you're getting a fluid change at the same time and when it's done it'll just be done with no mess or future leaks etc. assuming it's a reputable shop.

 

[Terbro]

As long as the car has stock 3:42 gears and stock 26" tall tires you can use one of two configurations. Stock is an 11 tooth orange drive gear (which is part of the governor gear) and a 30 tooth blue driven gear. The 11 tooth governor gear is getting scarce these days and therefore expensive. So an alternate combo is to use a green 10 tooth drive (governor) gear and a black 27 tooth driven gear. This combo is available on eBay for $30-40 for the pair and has the same ratio as the expensive 11 tooth gear. I have the part numbers but I'm on vacation this week and can help more when I get home.

The charging issue was caused by not getting the cluster back in correctly. But you probably already figured that out. Since it's a 2 piece cable you should triple check that it's installed correctly at all connections.

If I was in your spot and wasn't familiar with the trans internals, I'd buy the eBay gears and pay the $100 to have a trans shop swap them out for you. That's a fair price considering you're getting a fluid change at the same time and when it's done it'll just be done with no mess or future leaks etc. assuming it's a reputable shop.

Thanks for the info. Please do tell me the part numbers when you return from vacay.

When I originally bought the new cable, I was only given one piece. And that's all there was existing. I was confused when I went to check the size of the cable yesterday, and saw a short piece of cable, only a few inches long. It looked like it had the same connectors as the new one I bought a few months back. So...I'm confused about what you're saying about a "2 piece cable". I was given one long cable, obviously one end attaching to the trans and the other directly to the back of the gauge cluster.

 

[INEEDAGN]

Governor (drive) gears
Stock 11 tooth: 8634965 "good luck"
10 tooth green gear: 8639906

Driven gears:
stock 30 tooth blue: 561035
27 tooth black:410731

Use the 10/27 combo. Should be able to find them typing in the part numbers on eBay. Doubt you find them at your gm dealer.

 

[David Husek]

Unscrew cable from transmission and spin the cable. The speedometer will bounce when cable is turned. If it does not, there is a problem with the cable or the speedometer itself. I would try this before opening the trans. The gears very rarely have issues. If you need stock oem parts, I do have them but are very costly. With the 10 and 27 gear combination, the speedometer will read 1 mph less than actual speed with a 26" tall tire. I have all the gears mentioned in this post

 

[Terbro]

Governor (drive) gears
Stock 11 tooth: 8634965 "good luck"
10 tooth green gear: 8639906

Driven gears:
stock 30 tooth blue: 561035
27 tooth black:410731

Use the 10/27 combo. Should be able to find them typing in the part numbers on eBay. Doubt you find them at your gm dealer.

Thanks for the good info. Found the 10-tooth green on Ebay for $18.50 shipped and the 27-tooth black for $13 shipped.

 

[Terbro]

Unscrew cable from transmission and spin the cable. The speedometer will bounce when cable is turned. If it does not, there is a problem with the cable or the speedometer itself. I would try this before opening the trans. The gears very rarely have issues. If you need stock oem parts, I do have them but are very costly. With the 10 and 27 gear combination, the speedometer will read 1 mph less than actual speed with a 26" tall tire. I have all the gears mentioned in this post

Just to review: My speedo was giving out past 45 mph with increasing regularity. It would usually come back after warming up (~20 min. driving). Still worked at times if I remember correctly.

Bought new cable, but now doesn't work at all.

Disconnected cable at cluster, drove and discovered that cable is not spinning (only a turn or so on rare occasion, typically when shifting from fwd to rev or visa versa).

With that info, we can conclude the problem isn't with the gauge at least.

What's odd, is that it went from working sometimes to not working at all with the new cable. So at this point, one can't conclude that one of the problems isn't the speedo gauge. We might have a problem with the new cable (which I'd bet is the least likely, being new).

I went back to the parts store, and another clerk pulled up different, two-piece speedo cable, include an add'l section of cable that looked 7"-10" long in the photo. As far as I know (my mechanic and I did the job together), the original speedo cable we pulled was a single piece just like the new replacement. Just mentioning this, in case that's been part of the original as well as my current problem.

 

[INEEDAGN]

I don't know for sure but I know my cars both have two piece cables. As long as it reaches the cluster I doubt it matters.

Gear failures are indeed rare but I have seen it once on a 200-4r. You can pull the speedometer bullet out of the trans case and inspect the driven gear and see the drive gear with a flashlight. Assuming the bullet isn't seized in the case

 

[INEEDAGN]

I've done the math before but didn't record it so I did it again: The ratio of the 11/30 combo is 2.7272727272 (repeating) and the ratio of the 10/27 is 2.7 flat. A difference of 1.01 percent. Meaning if you are traveling at an actual 60 mph ground speed, the speedometer and vss data will be showing 60.6 mph if you are using the 10/27 combo instead of the 11/30. It's up to the individual to decide if that difference is worth paying for stock gears in the event you need a governor gear. Especially since it's off in the direction that will help prevent you from getting a ticket.

Other math for numbers nerds. Stock tires and rear gears give you a driveshaft rate of 2732.58 revolutions per mile, 11/30 speedometer gears give you a speedometer cable rate of 1001.946 rev/mile and the 10/27 combo gives you a cable rate of 1012.0666(repeating) rev/mile.

 

[Terbro]

I've done the math before but didn't record it so I did it again: The ratio of the 11/30 combo is 2.7272727272 (repeating) and the ratio of the 10/27 is 2.7 flat. A difference of 1.01 percent. Meaning if you are traveling at an actual 60 mph ground speed, the speedometer and vss data will be showing 60.6 mph if you are using the 10/27 combo instead of the 11/30. It's up to the individual to decide if that difference is worth paying for stock gears in the event you need a governor gear. Especially since it's off in the direction that will help prevent you from getting a ticket.

Other math for numbers nerds. Stock tires and rear gears give you a driveshaft rate of 2732.58 revolutions per mile, 11/30 speedometer gears give you a speedometer cable rate of 1001.946 rev/mile and the 10/27 combo gives you a cable rate of 1012.0666(repeating) rev/mile.

That's good info.

So what if one has 275/60R-15 Nitto DRs (diameter = 27.76"). Haven't checked on the stock tire's diameter, but the DRs are surely taller. I'm thinking if one goes with the 10/27 combo, being that it would read a smidge higher, the larger rear tire would bring it down a smidge. Something tells me it's a bigger smidge than 1.01%.