LMM Towing Question

[duramaxdiesel]

I'm heading to Indiana tomorrow to haul an RV. Question I have is, whenever I'm towing and have the cruise set, I notice that the tranny is constantly downshifting into 5th in the slightest hill. Is there a way to stop that annoying problem? When using any other of my LB7's I never have this problem. Obviously because they are 5 speeds, I know and are already in 5th gear. Will towing all the way back ( about 800 miles ) in 5th in the LMM yield me much worse fuel economy?

Thanks



Nick

 

[WVRigrat05]

Mine gets better mileage in 5th. I rarely ran 6th gear

 

[2004LB7]

engine load is lowered while RPM is raised in 5th while towing. net result can be better or the same MPG, rarely is it worse

 

[duramaxdiesel]

Really? Interesting. I never knew that. But it does make sense that the engine load is lower. I'm going to do a hand calculated MPG figure to see what kind of mileage I get towing. Only did one trip with the LMM before and I never calculated it.

 

[WolfLMM]

When I did tow with my lmm, the mileage was worse in 5th than in 6th. I never had the constant downshifting problem though.

 

[gmduramax]

I'm heading to Indiana tomorrow to haul an RV. Question I have is, whenever I'm towing and have the cruise set, I notice that the tranny is constantly downshifting into 5th in the slightest hill. Is there a way to stop that annoying problem? When using any other of my LB7's I never have this problem. Obviously because they are 5 speeds, I know and are already in 5th gear. Will towing all the way back ( about 800 miles ) in 5th in the LMM yield me much worse fuel economy?

Thanks



Nick

Drive faster

 

[duramaxdiesel]

I usually keep her in the 60-70 range with my DSP-5 in the Tow tune. Faster than that isn't for me hauling one of these things.

 

[2004LB7]

what size tires are you running?

 

[duramaxdiesel]

Ah yes. There is that little factor that I neglected to mention. I'm rolling on 315/70/17's. I have my speedo adjusted for those tires too.

 

[2004LB7]

so, are you having to press down on the accelerator more to maintain speed on inclines? if so that may be why it is downshifting more. i would agree with the above advice and try locking out 6th and see how it runs

 

[malibu795]

Ah yes. There is that little factor that I neglected to mention. I'm rolling on 315/70/17's. I have my speedo adjusted for those tires too.

With stock 3.73.. 6th puts you substantually under the power band.. which is usually starts around 1700-1900 pending tune and how big of load you're dragging..

5th with ~35" tires and 3.73 at 68 is ~1700rpm
I'd set it to M5/ in tow haul.. trans will shift Normally but not go over 5th gear. I'm hardly running in drive while towing

 

[hondarider552]

5th. I never ran 6th in my LBZ or my pile of shit Cummins.

 

[duramaxdiesel]

Thanks for the advice guys:hug: Adam, I'm going to try that method and report back on how it did

Running on flat ground there isn't a problem. It stays in 6th. It's inly when I come to a slight incline that it downshifts. This only happens when I have it in cruise. Not in cruise, it hardly happens.

 

[2004LB7]

Cruise control seems to be a little bit more aggressive in the application of power when it senses a reduction in speed then when driving manually. This is why it downshifts more in cruise control. Same thing would happen if you where more aggressive too. The issue is the truck can't anticipate up coming hills like we can so when you start climbing it drops speed more quickly than when you are controlling the throttle. Then it ramps it up more quickly, the transmission sees a larger throttle input compared to speed and downshifts

 

[NC-smokinlmm]

Drive faster

This^^^ When I pull big boats with lots of windage I just pick up my speed 1 or 2 mph and it usually would stop downshifting. You just need to add a couple clicks on the acc button before you see an overpass or hill coming, then slow back down on the downside...

 

[malibu795]

Thanks for the advice guys:hug: Adam, I'm going to try that method and report back on how it did��

Running on flat ground there isn't a problem. It stays in 6th. It's inly when I come to a slight incline that it downshifts. This only happens when I have it in cruise. Not in cruise, it hardly happens.

Problem with cruise is there's a delay from when truck drops certians mph off the set speed then it basically floors the truck to get back up to speed, which results in over shooting the set speed, then goes to into grade braking to slow everything down to set speed.. it's an annoying cycle.
Two things
Either Accel the truck by the pedal while in cruise to catch the hill, being pre-emptive vs reactive
Or run hills without out cruise on

Only way I've been able to shorten the delay of the cruise control is to bring/make the fuel/timing/throttle sooner/more aggressive
Down side it's extremely almost annoyingly touchy/responsive when empty

Basically allowing you to lugg a gear better under load
Or more throttle per pedal movement

Other way would increase the amount of pedal the TCM needs to see before down shifting.

 

[WVRigrat05]

Thanks for the advice guys:hug: Adam, I'm going to try that method and report back on how it did��

Running on flat ground there isn't a problem. It stays in 6th. It's inly when I come to a slight incline that it downshifts. This only happens when I have it in cruise. Not in cruise, it hardly happens.

If I'm not in tune 4-5 (built trans tunes) mine will upshift-downshift 6-10 times depending on the hill if I let it. So I just run 5th all the time unless I'm going over 85

 

[WolfLMM]

I never had a problem towing a huge boat in 6th. I do run 75+ and it's pretty flat here as well, so that must be it.

 

[NC-smokinlmm]

I never had a problem towing a huge boat in 6th. I do run 75+ and it's pretty flat here as well, so that must be it.

I forget that some guys don't live in the flat land.:spit:

 

[2008lmmchopper]

I tow a fifth wheel all over the place with my lmm and I'm decently built but I've always heard and known that when towing you shouldn't use cruise control if you put your foot in it you'll find that it doesn't down shift nearly as much. I don't know if this is credible I just know the less downshift you have while towing is obviously going to be better.

Sent from my STV100-2 using Tapatalk