Is my 4 speed tranny only 4 speed, or does it have 4 spd + overdrive?

jlrosine · May 16, 2018

This might be a stupid question, but I feel like I'm missing overdrive in my 4speed on my yukon. Is it 4 speed + overdrive? Or is 4th the overdrive?

2004 GMC Yukon XL 2500 - 4spd with 8.1L Vortec

My axle codes from the glovebox read that I have the 3.73 gearing, however when I'm travelling down the road I notice at about 60mph, I'm around 2000rpm which seems high for 3.73.

Here's a video (couldn't accelerate fast due to other traffic): https://photos.app.goo.gl/9hS6brqufCsYdquA2

From a stop, just counting the shift points, I have 4 total shifts, and no overdrive (rpms don't drop after I reach 4th gear).

Is this normal? I'm new to the 4L80/4L85

davester · May 16, 2018

The 4l80e has 4 speeds. 2000rpm sounds about in the ballpark, I believe my truck revs a bit higher than that for 60mph, but I've also got 4.10 gears.

garagerog · May 16, 2018

Need a little clarification, you say you feel 4 shift points, 1-2, 2-3, 3-4, and then TQ lockup above 45 mph or so? If so it's operating correctly and yes 4th gear is OD. But if you meant you're only feeling 4 gears, 1,2,3,4 and don't see about a 100 rpm dropoff above 45 mph or so you may have an issue.

jlrosine · May 16, 2018

Thanks guys.

garagerog: Yes I feel 1 => 2, 2 => 3, 3 => 4 . I've just read some other threads where I thought the 4.10 ratio folks were at about 2000rpm @ 60mph, so then I wondered if I was missing OD or something.

I was expecting it to hit 4th gear, and then go in to overdrive at higher speed when letting off the gas or setting cruise. I could have sworn my 2004 yukon denali was like that...but it was a different transmission and drivetrain altogether.

Edit: I just re-read what you stated. I think I'll have to go out and drive it again, I'm not sure I feel any dropoff after going in to 4th. 4th just feels like 4th all the time, I'm not sure I feel any dropoff in rpm until I completely let off the throttle.

Thanks again,

-Jeremy

newdude · May 16, 2018

4 Speed with overdrive is the usual marketing term. 4th gear in the 4L85 being overdrive. What size tires are on the truck currently?

jlrosine · May 16, 2018

@newdude

265/75/16

Raptordude · May 17, 2018

As said, it has 4 forward gears and a torque converter lockup that comes in around 45 mph, which feels like a 5th gear to someone who doesn't know what's going on. 4th gear is overdrive, but also as said I think it depends on your diff ratio whether or not it is actually a true "overdrive"

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Grumpy Bear · May 17, 2018

Overdrive just means a gear whose ratio is less than direct drive and hasn't anything to do with the final driver ratio of the differential(s). For the 4L80/85E the ratios are:

1.) 2.48

2.) 1.48

3.) 1.00 (direct drive)

4.) 0.75 (Overdrive)

R.) 2.07

Converter lock up is actually a single plate clutch that is electronically controlled thus the E at the end of 4L80/85E

A torque converter is a variable slip liquid coupling. It has a stall speed. A speed where converter stator and rotor an running nearly identical speeds. Nearly. That stall speed can be found by power braking and observing a tachometer. Say for example it's has a stall of 1500 rpm. IF road speed RPM is greater than the stall speed RPM when the clutch locks up you wont feel it although you may see it on a good tachometer. Stall speed isn't direct coupling and there is a small percentage of slip. This was ignored before lockup converters and in normal day to day it didn't generate enough heat or waist enough gas to be a bother. But as economy numbers required by law began to rise and buyers begged for more tow capacity removing that last little bit of slip was considered by bean counters and engineers alike worth going after.

On newer transmissions that have tall final drives and higher stalls the clutch can actually be placed in a controlled 'slip' as part or the strategy to prevent step down to a lower gear in light load situations such as hill assent and at times during gear changes. Lock up is no longer the domain of high gear only, especially in tow mode.

jlrosine · May 17, 2018

Thanks Grumpy.

I did some calcs on rpm/gear ratios here > http://www.csgnetwork.com/multirpmcalc.html

Looks like my RPMs are where they should be given the ratios, rear axle and tire size.

Thanks!

Raptordude · May 19, 2018

Overdrive just means a gear whose ratio is less than direct drive and hasn't anything to do with the final driver ratio of the differential(s). For the 4L80/85E the ratios are:

1.) 2.48
2.) 1.48
3.) 1.00 (direct drive)
4.) 0.75 (Overdrive)
R.) 2.07

Converter lock up is actually a single plate clutch that is electronically controlled thus the E at the end of 4L80/85E

A torque converter is a variable slip liquid coupling. It has a stall speed. A speed where converter stator and rotor an running nearly identical speeds. Nearly. That stall speed can be found by power braking and observing a tachometer. Say for example it's has a stall of 1500 rpm. IF road speed RPM is greater than the stall speed RPM when the clutch locks up you wont feel it although you may see it on a good tachometer. Stall speed isn't direct coupling and there is a small percentage of slip. This was ignored before lockup converters and in normal day to day it didn't generate enough heat or waist enough gas to be a bother. But as economy numbers required by law began to rise and buyers begged for more tow capacity removing that last little bit of slip was considered by bean counters and engineers alike worth going after.

On newer transmissions that have tall final drives and higher stalls the clutch can actually be placed in a controlled 'slip' as part or the strategy to prevent step down to a lower gear in light load situations such as hill assent and at times during gear changes. Lock up is no longer the domain of high gear only, especially in tow mode.

I can't stand newer vehicles that "slip" gears rather than downshift. I like to be in a gear, know I'm in a gear, and pull that gear. Then go to the next. As it should be

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Supreme Pizza · May 19, 2018

11 minutes ago, Raptordude said:

I can't stand newer vehicles that "slip" gears rather than downshift. I like to be in a gear, know I'm in a gear, and pull that gear. Then go to the next. As it should be

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I'm guessing that you would not be a huge fan of the CVT system.