2nd Gen Non-Engine/Transmission Speedo Correction on Pre-98's?

[CnH2n+2]

Ok, I think I have this right. The Pre-98 trucks use a gear driven speedo cable still correct? In the transfer case? The later trucks use an electronic signal from the ABS I believe.



So I need to get my speedo recalibrated. If my above thinking is correct, I can not use the DRBIII tool to do so. I need to change the speedo gear correct? So where do I begin? How would one go about doing this?



Thanks.

 

[GAmes]

Partially correct. Pre 98 has a gear in the trans that drives a sending unit for the speedo. You can correct the speedo by buying gears with more or less teeth than your current one. The sender is easy to pull, one bolt holding it in if I remember correctly. Maybe someone else can provide the correction factor.

 

[mschoenheider]

It should be a gear. You need to pull the sensor out (noting the orientation of the sensor’s rotation to the clamp), then pull the gear off the end of the sensor. it will have the number of teeth stamped on it. If you put bigger tires on, you need a smaller (lower tooth count) gear. If you put smaller tires on, you need a bigger gear.

Take your old tire diameter, divide it by your new tire diameter and multiply that by the number of teeth on your old gear. Round that answer to the nearest whole number, and that is how many teeth you need on the new gear.

Example:

old tire diameter = 29"

new tire diameter = 33"

old gear had 34 teeth

29/33*34=30. 8 ~31 teeth for the new gear

Mark

 

[CnH2n+2]

Thank you. That is exactly what I needed. I can figure it out from here.



Now for new gears, I'm assuming just call the dealer?

 

[RustyJC]

If the dealer can't fix you up, the speedometer shops used to supply an adapter gearbox that had 2 gears to correct the cable output speed. I suspect some of them can still do that.



Rusty

 

[vssman]

Rickson can also help you out. A couple of things to remember:

1) remove the bolt holding the VSS adapter to the transfer case and not the VSS unit from the black plastic adapter.

2) Pull straight out, don't twist it or you'll probably end up cutting the o-ring and have a leak.

3) Pull the gear off of the shaft. It just snaps on. push the new one on - you'll know when it's engaged.

4) Changing the numebr of teeth may require a new 'clocking' postion in that its rotated in a different position from where it was. There's a couple of positions for each group of teeth (i. e. as an example only 25 - 27 teeth may have the orientation bolt that holds the VSS unit into the adapter at 2:00, etc... )

5) Whatever you do, don't rotate it when pushing the adapter back into the hole.

6) The o-ring for a non-adapter required VSS unit (i. e. from a car) is not the same as for the adapter required unit. The mfg that made the adapter had a roundness tolerance that required a slightly larger o-ring on the VSS unit. Later models were blue in color with a teflon coating.



I used to make those things before my job went to Mexico...

 

[CnH2n+2]

Thanks guys. Looks like my stock gear is 31T. I will need a 29T. The only problem I fear I will run into at the dealer is they will only have optional teeth for factory equipment. I think they only offered 225/75, 245/75 and 265/75. Probably a 265/75 for a 3. 54 gear will probably be the smallest one and 225/75 with a 4. 10 (if that was even offered) will probably be the largest one. I guess I'll try there first.



Thanks again everyone.

 

[RDelissen]

or you can install the Superlift Truespeed and correct it that way. Then you don't have to worry about the right tooth gear and even when you change tire size in the future, all you have to do is dial in the reading again.



Downside -> more labor involved and it's more pricy than a tooth gear ...



Got the Truespeed on my Jeep Grand Cherokee and it works flawlessly

 

[CnH2n+2]

Is the Truespeed a universal application? How hard is the install, just splicing wires? What would you hook it up to on a gear driven speedo? How hard is it to use once installed?



Thanks.



P. S. I confirmed my previous post that in fact the 30T is the smallest I can get. I'd like to get a 29T. What would be the best place to look? Or depending on more info about the truespeed, perhaps that is the way to go?

 

[RDelissen]

here's a link where to get it + some general info

http://www.4x4rockshop.com/scripts/prodView.asp?idproduct=10148



and the install ain't that hard

 

[vssman]

P. S. I confirmed my previous post that in fact the 30T is the smallest I can get. I'd like to get a 29T. What would be the best place to look? Or depending on more info about the truespeed, perhaps that is the way to go?

That's strange! Mine is a 20-something tooth gear. Try a different dealer or even one of the wheel vendors? Maybe there off of a different model vehicle?

 

[CnH2n+2]

here's a link where to get it + some general info

http://www.4x4rockshop.com/scripts/prodView.asp?idproduct=10148



and the install ain't that hard

See the thing that gets me is is says in the application guide "on vehicles with an electric (non cable-driven) speedometer". That's what gets me. I have a cable driven speedo, which is why I was wondering how it works on my truck.

 

[CnH2n+2]

That's strange! Mine is a 20-something tooth gear. Try a different dealer or even one of the wheel vendors? Maybe there off of a different model vehicle?

What gear and tire size do you have? I called two different Dodge dealership. The one that the dealership I work for deals with actually let me look at the parts catalog with them and they show a listing and it has tire size and gear size and then it tells you how many teeth are on the speedo gear. For example mine was 3. 54 gear and 245/75/16 and it had 31T. The 265/75/16 and 3. 54 gear had 30T. I'm running 285/75/16's and 3. 54 gear so I need a 29T. I didn't see one anywhere on there. I mean if you think about it the 265/75 and 3. 54 should be the smallest tooth one. A smaller tire size and shorter gear (4. 10) will add teeth.

 

[CnH2n+2]

Anyone have any other input?

 

[vssman]

I am running a 255/85 tire (33. 5" tall) with 3. 54 gears. I changed the gear a couple of years ago so I don't remember the exact tooth count. I know that one gear was green and the other was black - just can't remember which. At that time I was able to get the correct gear and o-ring from Rickson for around $10. 00 Instead I went into the lab work and grabbed the right gear off of a tester. If I had another one, I'd send it to you.

 

[CnH2n+2]

No sweat thanks for the help. I'm just going to call up Rickson and order one from them.



I wish I had the $$$ for 19. 5's!