4.10 vs 4.56

[Charlie207]

It's a funny coincidence, because I've been thinking about regearing too. When I switch to my smaller winter tires (factory size) I can feel the mechanical advantage, and would like that when I go back to my 33" summer tires.

Im sure it would help shift the RPMs up slightly into a meatier part of this cam's power-curve.

 

[j91z28d1]

It's a funny coincidence, because I've been thinking about regearing too. When I switch to my smaller winter tires (factory size) I can feel the mechanical advantage, and would like that when I go back to my 33" summer tires.

Im sure it would help shift the RPMs up slightly into a meatier part of this cam's power-curve.

you'd have to check, but I believe shift points are rpm and tq request (your right foot) based. if so, and you calibrate your speedo correctly. it will shift at the same time with any gear swap or tire size. it doesn't know any better. you'd need to chance settings in the tcm with hptuners or the like to move shift points up to take advantage of the cam power band. and probably make the tranny last longer and engine happier. the oem bogs the heck out of engines to keep rpm low for fuel mileage

 

[Charlie207]

you'd have to check, but I believe shift points are rpm and tq request (your right foot) based. if so, and you calibrate your speedo correctly. it will shift at the same time with any gear swap or tire size. it doesn't know any better. you'd need to chance settings in the tcm with hptuners or the like to move shift points up to take advantage of the cam power band. and probably make the tranny last longer and engine happier. the oem bogs the heck out of engines to keep rpm low for fuel mileage

You're absolutely correct, but I can certainly feel the difference in a 1.5" shorter tire, especially in Tow Mode.

Edit: I also leave it in Manual shift mode most of the time, so it'd be nice.

 

[Marky Dissod]

I believe shift points are rpm and tq request (your right foot) based. if so, and you calibrate your speedo correctly,
it will shift at the same time with any gear swap or tire size. it doesn't know any better.

Long story short:
Shift points are MpH (not RpM) & TPS% based. If you calibrate your speedo correctly,
it will shift at the same INDICATED speed on the speedometer.
With shorter tires or better gears, it would upshift sooner due to more power put to the ground while the speedo is being deceived by some percentage.

 

[Tozan]

Long story short:
Shift points are MpH (not RpM) & TPS% based. If you calibrate your speedo correctly,
it will shift at the same INDICATED speed on the speedometer.
With shorter tires or better gears, it would upshift sooner due to more power put to the ground while the speedo is being deceived by some percentage.

I know from first hand experience with a calibrated speedo if you run 35's with 4.88 it will shift into 6th gear as low as 35 MPH... and around town MPG will be terrible as will highway speeds. Mine got 8-10 MPG or less.

Even with 35's my 4.10 gears on the street seems a little to much. Off road when it gets rough I am normally in low range and it will pull just about anything. For my needs I don't think running any higher gears would be beneficial and it might overall be a step down for how and where I drive. Pulling heavy loads with a trailer might be slightly better as long as you don't plan to drive over 65. At 75mph coming across Texas with a trailer it would start overheating my transmission (255+ degrees) so I kept it under 60mph.

 

[Marky Dissod]

... from first hand experience with a calibrated speedo if you run 35's with 4.88 it will shift into 6th as low as 35MpH ...

Your speedo was calibrated. To what extent did you have your ecm & tcm tuned?

 

[swathdiver]

Long story short:
Shift points are MpH (not RpM) & TPS% based. If you calibrate your speedo correctly,
it will shift at the same INDICATED speed on the speedometer.
With shorter tires or better gears, it would upshift sooner due to more power put to the ground while the speedo is being deceived by some percentage.

Not sure about that. My 1-2 shift at WOT with 3.42s was about 5800 rpms. If I tried that with 3.73s she'd be over 6000 rpms. If memory serves she does the 1-2 shift at 35 mph now.

 

[mikez71]

All shift tables I have seen for our gen IV's are mph vs tps. It should shift at same indicated speed regardless of tire size. Unless you are using a gps speedo..

 

[j91z28d1]

All shift tables I have seen for our gen IV's are mph vs tps. It should shift at same indicated speed regardless of tire size. Unless you are using a gps speedo..

I haven't looked, is it really just straight tps % on hpt? I'm surprised it's not some kinda math value from a map/mag blend like the vve/timing tables.

if it doesn't look at rpm at all, it might be smart to adjust the mph the shifts happen after changing gears and speed recal. if not, seems like the shift points at wot would be way passed the power band. I've I remember right, a good shift point is to have the next gear drop the rpm down to just before peak tq and then run out to around peak hp.

of course less than 100% tps would be much different rpm

 

[Marky Dissod]

Not sure about that. My 1Up2 @ WOT with 3.42 was about 5800RpM. If I tried that with 3.73 she'd be over 6000RpM.
If memory serves she does the 1Up2 @ 35MpH now.

I'm sure, because there's a big caveat, a safety feature built in to the shift logic.
Once the TPS% exceeds a certain angle (80s or low 90s, depending on other factors),
the Normal Shift table is temporarily set aside, and the crank & cam sensor readings are prioritized to prevent overreving.
GM OE tunes as well as thorough aftermarket tunes SHOULD deliberately underestimate UpShift road speeds @ 100%, 93%, & 87% TPS
so that the major criteria remains the RpM at the most fun TPS% angles. In older stuff it was called KickDown Mode.

I.E.: If the 1Up2 @ 100%, 93%, & 87% TPS is written to begin @ (let's say) 28MpH (when it'd actully begin @ 31MpH),
the KickDown Enable TPS Threshold is set @ 85%, and the Upper RpM is set @ 5600RpM, then the upshifts will always occur on time (if not a bit early to be safe).
Once you get below the KickDown Disable TPS Threshold (obviously slightly lower than the Upshift threshold), it reverts back to using the main table.

If the driver has the Tow / Haul shift map enabled, however, then the Tow / Haul KickDown Mode will also be enabled over a certain TPS%.
To protect the drivetrain, Tow / Haul Mode's KickDown RpM will be a bit lower - say, 5200RpM - as well as the upper road speed limits -25MpH for this example -
and the KickDown TPS% Enable & Disable thresholds - 82% & 81% TPS respectively.

So tuning for different axle gear(s) is not just about adjusting shift tables, but also each of those tables respective KickDown tables.

 

[Marky Dissod]

VCM Suite Online Help

For the 6L80 and younger transmissions it's no longer called KickDown, it's called Wide Open Throttle.
There are Wide Open Throttle UpShift '(road) Speeds' & 'RpMs' for the following modes:
'Normal' ... 'Performance' or 'Tow / Haul' (depends how you choose to write it) ... 'Cruise' ... '4WD Low' ... 'Hot Trans' ... 'Hot Engine' ... & TapUp/TapDn
Once the TPS% angle is exceeded, the appropriate Wide Open Throttle shift tables take precedence.
Again the road speed should deliberately underestimate the RpM, for all seven modes.

Tip: If you've disabled but not yet deleted Engine Half@$$, doesn't hurt to slightly lower WOT upshift speeds & RpMs to take it easy on the 2mode lifters

 

[Tozan]

Your speedo was calibrated. To what extent did you have your ecm & tcm tuned?

I used a tuner to adjust for the gearing and tire size changes that were made. Then adjusted it to a radar and also compared it to a couple gps speedos.

 

[gmartin1215]

I finally saved enough $$$$ to do a gear change.

After getting everyone's feedback on this forum, and talking to a few diff shops, I decided to go for the 4.56 ratio. With my rig, plus towing, the diff math showed 4.56 will be my best option. I was undecided between 4.10 and 4.56, and I was worried about engine stress at 70-75mph, but all numbers showed I should be about 2200 rpms in 6th gear with better climbing power on the hills. As one diff shop told me, get the biggest bang for your buck. One thing that will really helps is the 6-speed with the 2 overdrives. I could use 5th in the mountains and 6th on the flat roads. With 4.56 gears, my transmission should run cooler than with 3.42 ratio I have now, but I also have a transmission cooler already installed. Also, I shouldn't have to to press the gas pedal down as far to get the power. So run 4th or 5th in the mountains and 6th on the open highway. Who knows, I might actully get a bit better mileage, too, with more power on the low-end. Highway speeds will eat more gas, but with more power on the low-end, I may have a net benefit in mileage. We'll see. Anyway I decided to go for the 4.56 instead of saying Would've, Should've or Could've later on.

I am scheduled to bring her in mid-March.

I'll let everyone know how it turns out after this job gets done and I drive it around a bit (with and without a load).

 

[Marky Dissod]

What you lose in MpGs, you'll get back in how much longer the 6L80 lasts before its next rebuild, plus smiles per gallon.

 

[gmartin1215]

I got the work done to re-gear the truck to 4:56. I also got the main drive-line u-joints replaced. The u-joints were the original ones with 160K on them and were quite loose.

Driving around town, it definitely improves over the 3:42 and gets to 5th and 6th sooner. On the highway at 75 MPH, I was hitting about 2300 RPMs when it reached 6th gear. I have not tried towing with it yet.

One thing that's interesting: while it is in 6th gear, when I let up on the gas, I briefly hear a bit of buzzing from the transmission/transfer case area. It only lasts for a couple of seconds and goes away, and also goes away when I put a little pressure on the gas pedal.

I had not noticed this sound in the past, but maybe its louder now with the tighter driveshaft and new gears? After I let off the gas, I do see the RPM jump down a little, and the sound occurs between me letting up on the gas and when the RPM goes down. There is a like a second or two when this happens

I tried to get a video of it. Not great for sound because my phone was in the cup holder, but you can hear at around :09, :19, :40, :53 and 1:00, 1:07, 1:13 on the video.

gear sound video

Might be normal, but its louder than it used to be. Makes me wonder if I got some worn gears in my transmission, but just speculating. Had not really heard this before the diff gear change, and the sound is not coming from the front or back of the differentials.

Any thoughts?

 

[SpareParts]

Wonder if a 08 Suburban has the same rear end as my Yukon. Guy about 2 miles away from me is parting out a Suburban and will sell the front diff and rear end together for $350.
It is G80, GT5, 6lug.
Here is the RPO tag

 

[gmartin1215]

I got the work done to re-gear the truck to 4:56. I also got the main drive-line u-joints replaced. The u-joints were the original ones with 160K on them and were quite loose.

Driving around town, it definitely improves over the 3:42 and gets to 5th and 6th sooner. On the highway at 75 MPH, I was hitting about 2300 RPMs when it reached 6th gear. I have not tried towing with it yet.

One thing that's interesting: while it is in 6th gear, when I let up on the gas, I briefly hear a bit of buzzing from the transmission/transfer case area. It only lasts for a couple of seconds and goes away, and also goes away when I put a little pressure on the gas pedal.

I had not noticed this sound in the past, but maybe its louder now with the tighter driveshaft and new gears? After I let off the gas, I do see the RPM jump down a little, and the sound occurs between me letting up on the gas and when the RPM goes down. There is a like a second or two when this happens

I tried to get a video of it. Not great for sound because my phone was in the cup holder, but you can hear at around :09, :19, :40, :53 and 1:00, 1:07, 1:13 on the video.

gear sound video

Might be normal, but its louder than it used to be. Makes me wonder if I got some worn gears in my transmission, but just speculating. Had not really heard this before the diff gear change, and the sound is not coming from the front or back of the differentials.

Any thoughts?

Took the truck for another drive on the highway again. It could be that the 4:56 is just louder gears than what I am used to hearing with the 3:42. Just guessing, at this point. Hoping it's not the tranny. That too will probably need to be done, but just spent big $$$$ on the regear and have no budget for the tranny yet.

 

[j91z28d1]

I got the work done to re-gear the truck to 4:56. I also got the main drive-line u-joints replaced. The u-joints were the original ones with 160K on them and were quite loose.

Driving around town, it definitely improves over the 3:42 and gets to 5th and 6th sooner. On the highway at 75 MPH, I was hitting about 2300 RPMs when it reached 6th gear. I have not tried towing with it yet.

One thing that's interesting: while it is in 6th gear, when I let up on the gas, I briefly hear a bit of buzzing from the transmission/transfer case area. It only lasts for a couple of seconds and goes away, and also goes away when I put a little pressure on the gas pedal.

I had not noticed this sound in the past, but maybe its louder now with the tighter driveshaft and new gears? After I let off the gas, I do see the RPM jump down a little, and the sound occurs between me letting up on the gas and when the RPM goes down. There is a like a second or two when this happens

I tried to get a video of it. Not great for sound because my phone was in the cup holder, but you can hear at around :09, :19, :40, :53 and 1:00, 1:07, 1:13 on the video.

gear sound video

Might be normal, but its louder than it used to be. Makes me wonder if I got some worn gears in my transmission, but just speculating. Had not really heard this before the diff gear change, and the sound is not coming from the front or back of the differentials.

Any thoughts?

since you had the u joints changed and it's just on that unloading time between acceleration and deceleration load. my 2 cents is it's drive shaft vibration.

next time you have to 75-80 pop it in neutral and let it coast down. see if you can feel it get better and worst as it slows done. usually drive shafta have a harmonics to them that very with speed and seem better under load.


others seem to change u joints without issue, any time I touch them of have them touched it end up with vibration. at this point I just buy new drive shafts if I need u joints.

have you had the speed o calibrated to the new gear. you can check your speed with a GPS app to see.

 

[Marky Dissod]

Wonder if a 08 Suburban has the same rear end as my Yukon XL?
Guy about 2 miles away from me is parting out a Suburban, and will sell the front diff and rear end together for $350.
It is G80, GT5, 6lug. Here is the RPO tag:
View attachment 480452

A Yukon XL basically IS a Suburban, so,
Yes.

 

[SpareParts]

A Yukon XL basically IS a Suburban, so,
Yes.

Was almost positive it was the same. Thanks!