Gear change

[royg]

I want to change my gear ratio on my 2006 GMC 1500 sierra. Can I program the new gear ratio so that my speedo reads correct? If so do I do it with the Tech2 and TIS 2000? Is there an option in the TIS to do this? If not how would I be able to do this?

 

Thank you

[GM-Tech]

There is no option within TIS or the Tech 2 to recalibrate the speedometer in any way. You can set the tire size (but not gear ratio) in ABS, but that does not affect the speedometer.

 

Your best bet is to look to an aftermarket solution.

[naturalbornmudder]

while we are on this topic, I would like to know if there are any special tools involved ina GM gear change. I have done several gear installations so I already know about dial indicators and dial calpiers, shimming, pre-load, etc. Is it simply pull the old ones, install and properly shim and gear mesh the new ones, then figure out a speedo aftermarket fix?

 

I too want to do a gear swap in my 06 GMC Sierra 4wd. I want to go from 3.42 to 3.73

 

Advice?

[GM-Tech]

There's a special tool that's needed to determine the pinion depth. There's a shim between the pinion and the bearing that needs to be the correct one. Some guys just reuse the same shim, but that doesn't always workout.

[royg]

There is no option within TIS or the Tech 2 to recalibrate the speedometer in any way.  You can set the tire size (but not gear ratio) in ABS, but that does not affect the speedometer.

 

Your best bet is to look to an aftermarket solution.

 

<{POST_SNAPBACK}>

 

 

Thank you very much

[naturalbornmudder]

isn't paint shadowing and preload used to determine pinion depth?

[GM-Tech]

isn't paint shadowing and preload used to determine pinion depth?

 

<{POST_SNAPBACK}>

 

 

 

Preload has nothing to do with pinion depth, but yes, you could do a pattern check (I assume that's what you mean by "paint shadowing"--never heard that term before) and skip the depth setting with the special tool.

 

The problem with that method is that if the pattern check determines there's a pinion depth problem, now you have to pull the pinion back out, press off the bearing without damaging it, take your best guess at what thickness shim you need to use, put the shim on, press the bearing back on, install a new crush sleeve, re-install the pinion, set pinion preload and start all over and hope you got it right this time.

 

It's obviously much easier to know in advance what shim you need by using the special tool. Is it worth several hundred dollars you'll pay for the tools to do this? Probably not to the person who's going to do this one time, but hey, you asked and that's a tool that's needed to do the job "by the book."

[C & A s Dad]

I have no idea but is the carrier the same for the 3:42 and the 3:73 gears? I know that when you cross a certain line the carrier itself is different. For example, I am pretty sure you could not go from a 3:42 to a 4:10. Just something to consider.

[naturalbornmudder]

Preload has nothing to do with pinion depth, but yes, you could do a pattern check (I assume that's what you mean by "paint shadowing"--never heard that term before) and skip the depth setting with the special tool.

 

The problem with that method is that if the pattern check determines there's a pinion depth problem, now you have to pull the pinion back out, press off the bearing without damaging it, take your best guess at what thickness shim you need to use, put the shim on, press the bearing back on, install a new crush sleeve, re-install the pinion, set pinion preload and start all over and hope you got it right this time.

 

It's obviously much easier to know in advance what shim you need by using the special tool. Is it worth several hundred dollars you'll pay for the tools to do this? Probably not to the person who's going to do this one time, but hey, you asked and that's a tool that's needed to do the job "by the book."

 

Good info GM Tech. Thanks for taking the time to type it all out.

 

Preload has nothing to do with pinion depth

I am not trying to call you out, but from what I know, a pinion that is shimmed too much gives the feel of too much preload, essentially the pinion gear teeth are bottoming out in the ring gear and makes for a "tight fit". From what I gather, preload is set by the tightness of the pinion nut and the crushing of the crush sleeve and it's effect on the amount of pressure that the pinion bearing has against the bearing cap or race, so what I was trying to relay in my earlier post was that an overshimmed pinion is often mistaken for too much preload and most folks would rather try to loosen the pinion nut as opposed to pressing off the pinion bearing and shimming out the pinion more.

From my experince, when you get a foul pattern, obviously depending on the gear shadow indications(pattern check) it is usually a combination of both pinion and carrier shimming that needs adjusted, not just one

 

I am glad to see that a gear install is still a feesible option for me to do on my 06 once I get settled stateside. On a side not, I would like to see how the special tool works.

[GM-Tech]

I am not trying to call you out, but from what I know, a pinion that is shimmed too much gives the feel of too much preload, essentially the pinion gear teeth are bottoming out in the ring gear and makes for a "tight fit".

 

Sorry, I have to totally disagree on this one. Pinion preload is set with just the pinion in place, not the ring gear. So the preload that is set at that point is what it is. The amount of the shim on it, which in most cases is going to vary just a few thousandths of an inch, will have no effect whatsoever on preload. You could put a .010" shim or a two inch shim (just an example!) and preload will not be affected. All I can say is, changing the depth that the pinion is into the ring gear has no effect on this preload. It's not as if changing the depth jams the pinion horizontally more into the ring gear. It does not "bottom out". Against what?

 

Now, if you're talking about insufficient backlash, that theoretically could cause the pinion to bite way to deep into ring gear and maybe even bottom out, though I've never seen it. In that case, it may feel as if there is too much side bearing preload, not pinion preload.

[naturalbornmudder]

You could put a .010" shim or a two inch shim (just an example!) and preload will not be affected.

So basically what you are saying is to set the preload on the pinion first and adjust the carrier shims to that. In essence, you would only have to press on the pinion bearing once. I sort of understand, but let me bounce what I think I understand off of you and tell me if I am wrong.

 

Let's say that:

- the pinion depth is axis X

-the carrier shimming side to side is axis Y

- a single ring gear tooth is made up of 3 faces, shaped in a V with a flat internal bottom where the right side of the V is face 1, the left side of the V is Face 2 and the bottom of the V is Face 3.

 

Set axis X with the oil slinger and bearings. Install. Do not remove.

Set axis Y with shims,pattern paint

 

If the gear mesh is too tight or too loose, only adjust the carrier shims?

Here is where I am doing it differently.

I would, depending on the paint shadow, either adjust the carrier shims or the pinion shims. The thought process behind this is that if the pinion is pushed out too far on the X axis, that the gear mesh will bind because it will bottom out on "Face 3." In doing so, it pushes the pinion off of it's correct alignment on the X axis and puts tension on one side of the pinion bearing more than the other. That is where the whole preload thing I spoke of comes in. I may have used the wrong term, calling it preload.

 

Now, I am not sure that what I am doing is exactly right , but it isn't all wrong. If you take the time to work this out with me, I will understand further and maybe save some time the next time I do a gear install.

Thanks for the help thus far.

[GM-Tech]

Your terminology, analogy, x/y axis whatever, is confusing. So let me just say this. Pinion preload is a measurement of the amount of rotational torque needed to rotate the pinion (no ring gear in place). I don't have the specs in my head, but I believe it's around 25 lb. in. if reusing the old bearings and 45 lb. in. if using new bearings. That is, as you tighten the pinion nut and begin to collapse the spacer, you have to constantly measure the amount of force needed to rotate the pinion using an inch pound torque wrench.

 

So yeah, I think your use of incorrect terminology is confusing matters even more. Also, the pinion ain't never gonna bottom out on "face 3" if I'm understanding THAT definition correctly.

 

Once again, and for the last time I hope, this setting has no effect whatsoever on the pattern you're going to get from the ring/pinion when doing a pattern check. Preload does not change the pinion depth.

 

In fact, neither the pinion preload or the preload on the side bearings is going to affect the pattern, as long as the gears are not just flopping around in there with no preload. What will effect the pattern is the depth the pinion rides into the ring gear (shim decides this), and the position of the ring gear side to side, which also affects backlash.

 

If the gear mesh is too tight or too loose, only adjust the carrier shims?

 

If by "gear mesh" you mean backlash, absolutely. I like 'em tight, around .005"-.006" backlash. If it's say .015", you're going to add thickness to the left side shims and remove thickness from the right side, all the while keeping the same total thickness of both shim packs. That will simply move the ring gear over to the right, while keeping the same side bearing preload, and reducing the backlash. You don't set/change backlash by messing with the pinion whatsoever.

 

This is all getting way more complicated than I care to get into any more, plus really, I'm not a top notch expert/teacher of this stuff but do have a good, basic understanding.

 

I suggest you get yourself a good book (or maybe google it) on setting up a rear end and it will tell you what all the various pattern results mean. They will no doubt explain it a whole lot better than I can.

 

You must be doing something right if it's quiet when you're done and it stays quiet. I guess that's what counts. If they're off even the slightest amount, you'll get a helluva ring/pinion whine.

[Brain]

Hi Royg you can change your gear ratio and program with tech 2 and tis but you will have to stay with a stock gear ratio (ex 3:42 to 3:73) You need to find out what gear ratio and tires could have come on your truck. Then the dealer has to phone a 1 800 number to get a vci number to reprogram your changes.

 

 

hope this helps

[drumset5994]

I was actually going to ask this about changing my 3.08's to 3.73's.

 

From the depth of this topic, i'll stick with my 3.08's

[naturalbornmudder]

RoyG, sorry about hijacking your thread.

 

I'm out.