John in RI

iTrader: (167)

I Just bought a replacement speedo gear to correct the speedo reading due to a rear end change. The gear I bought is significantly smaller than the driven gear it's replacing. ( See picture)

Both gears are from Cable sending units and both gears are for an automatic tranny. Once the new gear is installed the speedometer needle will not work because the new driven gear is not making contact with the drive gear on the tail shaft.

If I re-install the original gear and spin the tranny tailshaft by hand I can see the cable end of the sending unit turning. After installing the new Driven gear and turning the tailshaft by hand --- the cable end of the sending unit is not turning. What is the deal ??

P.S. There was no "sleeve" or other "sensor" specified in any of the gear charts I have looked at and the 37 tooth gear was the only one I could find ( PN = 25522481 ) The gearing changed from 3.42 to 2.73. Highway gears- yes, but it's a POSI DISK rear end !

cdartz

I wish I could help you John since you helped me, but unfortunately I know less than you.

Apeiron

There are two different housings for the different sized gears. I don't have the P/N's for VSS cars.

JamesC

iTrader: (5)

I don't know if this will help or not, but check the link. Go to Speedo Calibration Utility, enter your numbers and you'll get drive gear/driven gear ratios.

http://www.hanlonmotorsports.com/




JamesC

John in RI

iTrader: (167)

When you mentioned "housing"......... are you talking about the tranny tailshaft housing ???

I got a new sending unit along with the new driven gear and the speedo sending unit is exactly the same as the one that was already in the tranny ( with the larger driven gear.) I tried swapping them back and forth and the same result was noticed each time....... The new driven gear would not contact the drive gear.



That's why I assume you mean there is a different tailshaft housing. Is that it ??? That would be logical since it should re-position the driven gear closer to the drive gear.

All my previous experience with sending units has been with the "larger" sized speedo gears. I have never seen a small gear like this in an automatic tranny before. ( Manual tranny gears are real small) I do know that the drive gears from an electric sending unit & a cable sending unit are NOT the same and that is not the problem here.



--> CDARTZ <--

While looking thru the boards for information on these wierd gear sizes I read your post. Since the charts were handy to me I wanted to pass the info you needed along. I hope it helps !

John in RI

iTrader: (167)

Hi Jim,

I've got the right numers --- I got the gears directly from GM. They just don't fit right !!

cdartz

Yes it did. Thanks John. I really appreciate you finding me the part number I needed. It's no longer available from GM, but I managed to find a dealer in Mississippi who still had one. They are going to mail it to me, so hopefully I'll have it soon.

Motopsyco

are you sure they are for the same car, i went from 2.73 to 3.42, and switched the red gear with a grey on and they were the same size. so thats just really odd that your new gear is smaller, cuz with 3.42 or less you dont have to change the tailshaft gear they should be the same size, unless its for a different tranny

John in RI

iTrader: (167)

-->stormr<--

If all you did was swap the Drive gear on the tail shaft from the 15 gray to the 17 red than your speedo is still off. You should have also replaced the the 37 (or 38) tooth driven gear with the 'larger' 41 tooth as well (depending on your tire size).

I just found this old post from a previous speed gear swap. This guy also swapped 2.73 gears to 3.42:




Now - knowing that he had to "change out" the sleeve in order for the larger driven gear to fit right,...... I would assume that I will need to add this sleeve.

ANYONE know where, what, how this sleeve is used ?? I've never delt with this "sleeve" in the past !!!!

v8unleashed

iTrader: (3)

There is a sleeve that fits gears less than 45 tooth, and one that fits 45 tooth only. If I counted right, you have the latter.






The following was in our FAQ section.....

Some applications may use Sleeve No. 25007224 or 10456092 in place of 25007338, or 25007308 or1045089 in place of 25007339.

From my records, the sleeve I used swapping from 2.73 to 3.42 was p/n 10456089....apparently we have a typo in the FAQ section since since GM part numbers are 8 digits. So most likely 10456089 is what you have on there now. Maybe you need the 25007339 one. But I would think any GM parts dealer could get on their computer and tell you what the opposite of 10456089 was. The little piece of crap cost me $36.

John in RI

iTrader: (167)

All the mention of a "sleeve" made me think I needed some additional part to make this speedo problem disapear ! I have finally figured out the a "sleeve" simply means the Sending unit that the driven gear sits on !!!

I was using the wrong sensor (or "sleeve") with the right gear.

The cable driven units are designed for 2 different sized DRIVEN gears. One sensor is for 34 to 39 tooth DRIVEN gears and the other is made for 40 to 45 tooth DRIVEN Gears.

As you can see in the picture,....... all you have to do is look at the sensor ("sleeve") to see what tooth count it will work with !!


When I had previously tried to set the new gear in the tranny,.... I simply swapped the gear and used the same speedo sending unit. That's why the thing would not spin when I rotated the tailshaft by hand.

Bandit5

Tell me your tire size and rear gear ratio and I will find you the most accurate gears possible.

Beast5spdGTA

You probably need to change the gear on the output shaft as well. I've heard it can be done with an auto still in the car, but I know it was a major PITA on a manual on the ground (damn snap rings).

Bandit5

Seriously. Just give me those specs and I can do the calculations to get you the most accurate gears possible. Some of those online calculators are not as accurate as they claim... sometimes clearly omitting certain gear calculations which are the most accurate and instead using more common combinations.

John in RI

iTrader: (167)

It's all good ----------->

I looked up the correct gears directly from the GM Parts book and used a red DRIVE gear along with a red DRIVEN gear. I took the Tranny type, Axle ratio, and Tire size into consideration when I was referencing the factory gear charts.

What screwed me up was the physical size of the gear. It would not line up properly causing a trouble code to be stored in the ECM. (#24 Speedo sensor output) Since I had to get the car to pass a state inseption after a V6MPFI to V8 Carb motor swap I HAD to get the speedo working.

I was using the correct speedo gears and the wrong sending unit.

I've got the correct speedo sending unit now ( AKA = "sleeve" ) and the correct speedo gears have been installed in the car already. No More guessing what the speed is when driving and no more computer trouble codes !

Bandit5

Good to hear. I had problems like this earlier, only now resolving all problems... since then I have become sort of an expert on the subject.