ECO Hubs Who needs 3:07 gears?

[MatthewWBailey]

As I contemplating eco-hubs. My truck is a 2003, 3126 tuned to 330hp with 3.07 gears, weighing 27,600lbs. One of my favorite aspects is the exhaust brake especially going down step 10% grades, narrow 2 lane roads with switch backs every few hundred feet, with no shoulders for miles. Is that I can keep my speed down to 15-20mph without ever touching the service brakes. Any faster and things get a little sketchy. Between 10-15 is when the exhaust brake disengages, I'm guessing second gear and I have to use the service brakes.

With Eco-hubs installed in the same scenario as above at approximately what speed can I expect the exhaust brakes to stop working with 3.07 gears and 3.90 gears?

I observed this change with mine. Leaving my house starts with a 5 mile 5-7% varying, continuous downhill grade. Speed limit 45. With 3.07 without ECO, I hit the pacbrake at 50mph and it downshifted to 5 and slowed the truck to sub 40 pretty easily. I have to turn off the pacbrake otherwise speed will
Drop below 35. With ECO, the trans must've relearned, bc in the same scenario, it downshifts to 3, makes the same noise, and slows below 40 pretty quickly. I feel like there is a difference as the truck stayed at 40 for longer with ECO and without having to turn off the pacbrake. So depending on grade and load, the effects will vary. I like it better bc the pacbrake is not so abrupt now, which makes sense.

 

[GeneralDisorder]

You can see the exhaust brake lamp on my annunciator panel and the current gear to the right on my trans display. This is coming to a stop from around 40 mph.

PXL_20240710_161405245.TS.mp4

drive.google.com

 

[hike]

1,600 to 2,400 rpm with 3.07's and EcoHubs in 3L would be about 32mph to 49mph; 1,600 to 2,400 rpm with 3.07's alone in 3L would be about 16mph to 24mph.

To be at 16mph with 3.07's and EcoHubs the pacbrake would have to lower the rpm's to 800 and the torque converter would need to remain locked. In our M1078A1 the torque converter can be locked or not in 3rd gear.

Would changing the downshift rpm settings help?

 

[Lostchain]

I'll take a video of coming to a stop in my truck. Yes the exhaust brake disengages when you hit 2nd gear

You can see the exhaust brake lamp on my annunciator panel and the current gear to the right on my trans display. This is coming to a stop from around 40 mph.

In my A1 truck If you manually downshift to 2nd gear the pac brake will kick back on, default programming is requesting only 3rd gear automatically. Have you tried that on yours?

 

[Ronmar]

1,600 to 2,400 rpm with 3.07's and EcoHubs in 3L would be about 32mph to 49mph; 1,600 to 2,400 rpm with 3.07's alone in 3L would be about 16mph to 24mph.

To be at 16mph with 3.07's and EcoHubs the pacbrake would have to lower the rpm's to 800 and the torque converter would need to remain locked. In our M1078A1 the torque converter can be locked or not in 3rd gear.

Would changing the downshift rpm settings help?

The TC on the Allison locks in 3rd gear and above, 100% of the time; probably why the 2-3 shift hits so hard in an empty truck with the reduction hubs, as the mechanical advantage they create allows the trans to satisfy its parameters to engage lockup almost immediately after the 2-3 shift occurs. Pretty sure It should maintain lockup in 3rd all the way down to the low RPM shift point, where it commands the 3-2 downshift. not sure how much difference altering the low RPM downshift would make…

 

[hike]

The TC on the Allison locks in 3rd gear and above, 100% of the time; probably why the 2-3 shift hits so hard in an empty truck with the reduction hubs, as the mechanical advantage they create allows the trans to satisfy its parameters to engage lockup almost immediately after the 2-3 shift occurs. Pretty sure It should maintain lockup in 3rd all the way down to the low RPM shift point, where it commands the 3-2 downshift. not sure how much difference altering the low RPM downshift would make…

In our 2003 M1078A1 the lower rpm range of 3rd gear is not locked. When watching the gear status either on Bluefire or using the DPA III+ connected to a laptop you can seen the torque converter locked status change. And you certainly feel the change in the seat as well.

I'll try to pay attention to the rpms when the locked status transitions to locked and unlocked and see if I can get a video to share. Perhaps something is wrong with ours?

 

[Ronmar]

Well your live data is probably better than my learned info from Allison and I have not encountered any specific RPM details for lockup operation. I have never looked at it live, just felt the lockup during accelerations at a few different weights. Cannot say that I have ever felt it unlock. IRT to lockup control it might be possible to modify that a little also to extend it into 2nd. Standalone converter lock is an available operation mode when these trucks are used in oil-field/pumper service, and we might be able to persuade it to activate in our 2nd gear, but would need a way to insure it definitely releases at a low RPM limit before you try to fully stop a vehicle...

 

[Ronmar]

There is a WTEC 2 config(not sure about wtec3) for manual or auto TC operation with a manual on/off setting when in manual mode. You of course would not want to try and bring the vehicle to a stop with the TC manually locked, You could probably use a latching relay powered by the de-energized contacts of the brake relay, so any brake pedal application would revert the trans to automatic TC lockup control… It appears this would allow lockup all the way down into 1st gear…

 

[Keith Knight]

So Rick in your video it looks like it released the exhaust brake around 22 mph.
Your rig still has 3.90 correct? So with my 3.07 I could expect it to release more around 25-30?
I wish my trans display was like yours showing what gear its in.

 

[Lostchain]

As I contemplating eco-hubs. My truck is a 2003, 3126 tuned to 330hp with 3.07 gears, weighing 27,600lbs. One of my favorite aspects is the exhaust brake especially going down step 10% grades, narrow 2 lane roads with switch backs every few hundred feet, with no shoulders for miles. Is that I can keep my speed down to 15-20mph without ever touching the service brakes. Any faster and things get a little sketchy. Between 10-15 is when the exhaust brake disengages, I'm guessing second gear and I have to use the service brakes.

With Eco-hubs installed in the same scenario as above at approximately what speed can I expect the exhaust brakes to stop working with 3.07 gears and 3.90 gears?

What you would do here is just lock the truck in 2nd gear and let the exhaust brake do its thing. I just tested this on my ECO hub truck with stock gears and the exhaust brake was effective to just below 10mph, with your 3.07s 2nd gear would have a very nice effective range for the situation you are describing. The below photo is me decelerating in 2nd and exhaust brake is still activated just below 10. Contrary to forum lore, the TC will lock up in 2nd automatically.

 

[GeneralDisorder]

Yeah I observed mine again and it stayed engaged till about 10 mph. The speedo doesn't respond fast enough if you are stopping quickly.

 

[Keith Knight]

Ok those numbers are perfectly acceptable. So knowing I weigh in at 27,600lbs. Stick with 3.07 or go back to 3.90 considering power and fuel economy?

 

[Ronmar]

Well i don’t know about forum lore, but I gleaned that lockup information from an Allison Freightliner lecture, linked below… The Ex brake may stay engaged, but is the TC lockup still engaged? It would make sense to do so and retain good engine braking right up until a stop is impending(decrease rate and RPM proximity to engine idle?) but they did not indicate that in this lecture, and it is the only place I have ever seen lockup operation actually described…

Allison also does not indicate lockup operation in the lowest two gears in the pressure spec info(low and 1st/our 1st and 2nd) in the 3060/3070 troubleshooting manual. You would probably have to put a pressure sensor on the LU test port or look at live data with Allison dock to confirm if Lockup clutch pressure is still applied or not… Thats a cool datapoint, not seen anywhere else!

Other option configurations have the 132 wire that we use to control an exhaust brake solenoid, designated to provide a lockup indicator/signal. But some Allison screenshots I have seen show it with PTO options… Wether it is active without an ex brake preselect switch input(power into wire 119) would be easy enough to test, simply remove the ex brake relay and monitor its pin 85 to ground. The TCU grounds this line to energize the ex brake relay. If it energized after the first upshift without the ex brake switch energized, it probably is driven by lockup operation…

Right near the end, 1hr 15min into the vid, the rep goes over lockup operation in more detail in response to a question… keep in mind the 1st-2nd shift he is referring to is the 2nd-3rd shift in our 3070 transmissions since we start in 2nd(1st on the core 3060 transmission).

 

[GeneralDisorder]

Monitoring lockup state in Allison DOC should clear this up. There are many options both in DOC and even more available to Allison engineering in the base program they load for the specific application. I'm sure they can make it function however they want as long as they can unlock it fast enough to ensure no stumbling or stalling behavior.

I can try this later. @hike - the laptop I sent you can do this also.

 

[Keith Knight]

Still waiting for opinions on my last comment! LOL!!!

 

[GeneralDisorder]

Still waiting for opinions on my last comment! LOL!!!

Go back to 3.90's. The 3.07's don't realize the full potential fuel economy gains. Neither do the 3.90's but no one makes 4.50's (yet ).

3.07 vs 3.90 - seems to be about 1 mpg difference. The 3.07's are on the wrong side of the bell curve for fuel economy and performance.

 

[hike]

Monitoring lockup state in Allison DOC should clear this up. There are many options both in DOC and even more available to Allison engineering in the base program they load for the specific application. I'm sure they can make it function however they want as long as they can unlock it fast enough to ensure no stumbling or stalling behavior.

I can try this later. @hike - the laptop I sent you can do this also.

We have the rear axle out of service at the moment. Once it is all back together we will hook it all up and see what we learn.

That laptop is very nice—

 

[Lostchain]

Still waiting for opinions on my last comment! LOL!!!

I would do the ECO hubs first and decide on the final drive ratio later. 3.07s won’t be unusable by any stretch of the imagination.

 

[Lostchain]

look at live data with Allison dock to confirm if Lockup clutch pressure is still applied or not… Thats a cool datapoint, not seen anywhere else!

Other option configurations have the 132 wire that we use to control an exhaust brake solenoid, designated to provide a lockup indicator/signal.

As you can see in the below screenshot, descending a steep grade in “2” on the keypad (1 as far as the Allison is concerned) has the transmission locked up and wire #132 enabled. Input speed and turbine speed are within an rpm of each other so that also confirms lockup. side note: TPS appears to come from the J1587( J1708 ) DATABUS

 

[Ronmar]

Cool, lockup down into 2nd, thats good news…