Originally posted by Redtruck-VA:

Ok, you made me do the math using 4:56 with a 32" tire it's 2245 rpm @ 70mph and 2570 rpm @ 80 mph.[/QUOTE]

Hi Greg,
I just was able to take a trip on the highway. At 80MPH my RPM is 2450 and at 70MPH 2200RPM or so with the 4:10 gears. My tires are just under 32" So the 4:56 is not that of an big RPM jump from 4:10 if your math is correct.[/QUOTE]

The math shows the difference between the two gears as 10%.
4.10/4.56=.899 (90) subtracted from 1= 10%
Using your actual rpm of 2450rpm at 80mph, 4.56 would become 2695rpm at 80mph.
When I compare my calculator with my truck it is correct with 2144rpm at 65mph with 28" tires.
Since we don't have an identical setup we have to use apples and oranges a little. But I believe what you say and I believe my calculations are good. So we need to figure why there is a difference. Your rpm should have been closer to 2020 and 2310. Anyone wants to pitch in you are certainly welcome to.

Edit: I checked my calculator with a online calculator and they matched. So messing with the numbers I can only say it looks like you are running a 3:92 gear in 4th gear. Tell us about your truck and who installed the gear.

Edit#2: I just looked over the thread, all I can say is wow, If I was you I'd use chalk and mark the tire amd driveshaft. With the tire off the ground rotate it and count the shaft rotations. A little more than 4 it's a 4:10. Just short of 4 than it's a 3.92. Good luck..[/QUOTE]

I know they put in the 4:10 I have the box with my stock 3:92 in it.And I can tell the difference in RPM. Did you use my tire size 275/55/20? Thanks PS Do I go with the 4:56?

 

I got a feeling that you may be running in 4th gear which would acount for the higher rpm at 80mph. IMO, cruising at 2700 rpm is more than what I would want personally. Did your truck come with factory 20" rims?

 

Originally posted by Redtruck-VA:
I got a feeling that you may be running in 4th gear which would acount for the higher rpm at 80mph. IMO, cruising at 2700 rpm is more than what I would want personally. Did your truck come with factory 20" rims?

Yes it did. But I'm not at 2700RMP @80MPH I'm @2450RMP

 

Originally posted by bada44:

Originally posted by Redtruck-VA:
I got a feeling that you may be running in 4th gear which would acount for the higher rpm at 80mph. IMO, cruising at 2700 rpm is more than what I would want personally. Did your truck come with factory 20" rims?

Yes it did. But I'm not at 2700RMP @80MPH I'm @2450RMP

Yes, but 4:56 is 10% deeper than 4:10's. Using your numbers 2450rpm + 245 (10%) = 2695rpm.

 

Originally posted by Redtruck-VA:

Originally posted by bada44:

Originally posted by Redtruck-VA:
I got a feeling that you may be running in 4th gear which would acount for the higher rpm at 80mph. IMO, cruising at 2700 rpm is more than what I would want personally. Did your truck come with factory 20" rims?

Yes it did. But I'm not at 2700RMP @80MPH I'm @2450RMP

Yes, but 4:56 is 10% deeper than 4:10's. Using your numbers 2450rpm + 245 (10%) = 2695rpm.

So do you think it's the gearing in my trans or is 5th gear not working?

 

I don't know what to tell you. Using your numbers the only thing that matches is a 3.92 gear running in 4th. I would check the rear gear ratio by marking the tire and drive shaft to confirm the ratio. Then accurately measure the tires. (275/55-20 should be 31.8") Then compare your Tach to see if it is reading correctly. Once all these are checked then do another test run at 60, 70 and 80mph and see if we can match the numbers. Anyone who wants to pitch in on this pls do.

 

Originally posted by Redtruck-VA:
I don't know what to tell you. Using your numbers the only thing that matches is a 3.92 gear running in 4th. I would check the rear gear ratio by marking the tire and drive shaft to confirm the ratio. Then accurately measure the tires. (275/55-20 should be 31.8") Then compare your Tach to see if it is reading correctly. Once all these are checked then do another test run at 60, 70 and 80mph and see if we can match the numbers. Anyone who wants to pitch in on this pls do.

I did a test 50MPH @ 1500RPM And I think it's in 5th gear.

 

50MPH @ 1500RPM And I think it's in 5th gear.

By my calculation is still 48 rpm off what you should be seeing at 50mph 4:10 32" tires in 5th. But with that said it is also only 54 rpm off of 50mph 3:92 32" tires in 4th. So doesn't prove anything either way. Need accurate speed, any chance at using a GPS to measure speed?

 

Originally posted by Redtruck-VA:
50MPH @ 1500RPM And I think it's in 5th gear.

By my calculation is still 48 rpm off what you should be seeing at 50mph 4:10 32" tires in 5th. But with that said it is also only 54 rpm off of 50mph 3:92 32" tires in 4th. So doesn't prove anything either way. Need accurate speed, any chance at using a GPS to measure speed?

Yes I'll do that next. Thanks

 

I did a GPS test and my speedo is right on. How would I check my Tachometer? The idle speed is a little more then 600RPM.

 

Ok, good. check the differential ratio either by your own method or the way I previously posted. Anyone with any ideas here is welcome to state them. How about turning off your OD and see what the rpm is at 30, 40 and 50 mph.

 

What is the OD?

 

Overdrive push the tow/haul button

 

OK I'll do an RPM test with the OD off today. Thanks guys!!!

 

OK I got some numbers. OD off 30MPH 1375-1400RMP ,40MPH 1775-1800RPM, 50MPH 2200RPM. And OD on 30 MPH 1200RPM,40MPH1400RPM,50MPH 1500RPM. Tire size 275/55/20 that makes the tire 31.8in hope this helps.Thanks..PS My truck came with factory 20in wheels. And the gear is G2 4:10

 

What was the question again? LOL
How many rpm's should the truck be turning at 80mph with a 4:56 gear? Using your latest numbers I conclude your OD "off" numbers are very close to what I see on my spreadsheet (+/- 40rpm), in 3rd gear. With OD "on" the only number close to what I have is your 50mph 5th gear. This makes sense as the truck increases in speed the converter should become tighter (lockup). Your 30/40mph OD numbers are way off but that could be from not being in 5th and not calculating for converter slippage. Meaning I am unable to calculate when your converter locks up and slippage throws the lower speed numbers off.
Using your latest numbers to calculate 70/80 mph rpm it comes to 70mph=2260rpm. And 80=2585rpm. This is with 31.8" tires, 4:56 gear.
Hope that helps.

 

My truck up until recently had 4.56 gears with 31.8 inch tires on it at 70 I turned 2600-2700 rpm at 80 was 2700-2900 now I have 4.10 and have not been on highway yet

 

Why did you take out the 4:56? To many RPM on the highway I bet! And your gas mileage was 10-11 miles to the gallon.

 

Actually with the tuning my truck has on the road trip to last years rally in Alabama averaged 15-18 highway very nice but before that trip I changed out pinion bearings and forgot to measure my
Backlash so I set it up diff than removal and they slowly destroyed themselves and two back to back 1.60 60' launches at pbir did them in and I picked up a set of 4.10 from fasthemiram05 in orlando for cheap I loved them 4.56 and highway didn't bother me one bit but they sure made the tires spin real good

 

What tune are you using I don't get anywhere near that! city 11.8 highway 14.5 or so

 

Full custom tune by white lightning we have played with the fueling a little bit and its real nice is all I can say

 

Hi guy's

Has anyone heard of this? The place where I had my gears installed is telling me that he just found out that you have to modify the aftermarket carrier AKA my Yukon Carrier so the gear oil can get to the pinion bearings. They think that's why I keep getting that noise back. PS. I'm going to get the 4:56 gears this time.

Anyone!

 

Hi guy's

Has anyone heard of this? The place where I had my gears installed is telling me that he just found out that you have to modify the aftermarket carrier AKA my Yukon Carrier so the gear oil can get to the pinion bearings. They think that's why I keep getting that noise back. PS. I'm going to get the 4:56 gears this time.

Anyone!

I have not heard of this, and find it unbeiveable. I agree they need to show some documentation supporting that theory as it smells like BS. Good luck..

 

Never heard of that before sounds like they are giving you the runaround so they don't have to eat any costs call there bluff or have them show you something saying that from Yukon

 

There going to replace the gears at no cost to me!

 

Just got off highway 2350 @75 with 4.10 gears

 

Little update I have a set of 4:56 gears on the way. And Ricks Gears has the info on the mod that needs to be done on some rear ends you have to file the ends of the teeth on the ring gear for clearance. Maybe someone can call these guys who can ask the right questions. Thanks

 

Usually the housings from 06 to 09 have that issue of some gears interfering with the housing. Usually inside top front section for like a 3" to 5" of gear travel
I just clearance the housing, it's not much and its so much less annoying than machining the gear.
Some gears need the tooth filed so that the cross pin can be removed and reinstalled for the c-clips
The later trucks from 2010 and current need different machining/or new holes drilled in the carrier
I suspect that hopefully soon that will be addressed.

.

 

That I have heard off taking the tips off the teeth to clear the case almost had to do mine it is very close but not touching got lucky

 

Depending on the differential istalling the axle pin may require either ring gear grinding or pin modification. DDT's do not require any grinding.

 

Update: 4:56 are in But I have not got the truck back yet. The shop got the gears from Rick's Gears I think Yukon gears This time with all new bearings and axial bearings. Rick's gears told him you can expect some high pitch noise from 50 to 70 MPH I hope not.What do you think thanks?