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Just wanted to circle back on my experience with the GDE trans tune and GDE after taking some time to do some additional tow tests. My memory was fuzzy about which shift/RPM drop was the problem, turns out it was the 1-2 upshift and not TCC lock as it was the first RPM drop, not the second.

So, I went to the barn today and hitched up the horse trailer to test D, L, and T/H modes. Here's what I experienced and what I've passed on to GDE.
  • D, T/H disabled, trailer hitched up, starting from a stop with like 30-50% throttle there's a thud/bump as it upshifts from 1-2. TCC lockup is fine.
  • D, T/H enabled, trailer hitched up, starting from a stop with the same throttle input the thud/bump is much less pronounced and I don't see it as an issue. The difference here is that with T/H enabled the transmission isn't short-shifting for the 1-2 upshift and is holding 1st gear longer. The 1-2 upshift is firm but not harsh. The grade braking will downshift to the moon with minimal brake input even on flat ground.
  • L, T/H enabled, trailer hitched up, slowing from 55 to a stop it doesn't trigger grade braking on flat ground like in D. Apparently it only goes into rage mode in L with T/H when there are actual hills and it thinks it needs to downshift because the truck isn't slowing fast enough?
Anyway, GDE is going to try and reproduce the harsh 1-2 upshift while towing but without T/H enabled. Even if there's no fix, I can at least work around the issue by changing trans or T/H settings to run where it and I are both generally happy. Going back to the stock trans tune is a last resort, and the main test is going to see what our off-road trailer tows like once it arrives next year. It's much lighter than the other trailers I tow/have towed and I'll do whatever needs to be done to make sure the truck is happy towing it as we're planning on putting a lot of miles behind us with it.

It's interesting because my 1st to 2nd shifts are fine and I can feel (and see on my idash) when the TC locks and it's pretty smooth. the shifts are the same whether I am towing my trailer or not. I'm running the same TCM rev you are.
 

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It's interesting because my 1st to 2nd shifts are fine and I can feel (and see on my idash) when the TC locks and it's pretty smooth. the shifts are the same whether I am towing my trailer or not. I'm running the same TCM rev you are.
Right, the TCC lockup is fine. The 1-2 upshift when towing 3,500+LB with T/H disabled feels like someone rear-ended me at a slow speed and gave me a bump. If I'm not towing then it's fine. No harsh 1-2 upshift, etc. I did have my trans fluid serviced about 20k miles ago but it was done by the dealer using whatever Dex6 they had on-hand, the trans has shifted better than new since that was done (with the stock trans tune) and is fine with the GDE trans tune unless I'm towing a decent weight with T/H disabled.
 
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Some videos that help explain when it's happening. The shift logic with T/H disabled seems to be just a little different with the 1-2 upshift compared to with T/H enabled. Just to be clear, it's the first RPM drop, not the second, where I get the bump/thud.


 
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Thanks for your observations! Watched your videos, mine definitely slips more on the 1-2 upshift than yours. 1-2 is the only shift it does that on. Running the LVHP Mobil 1 blue label fluid, but I believe it did the same thing before the fluid change.

Yes, when Tow/Haul is on in L mode, it grade brakes like crazy. My loaded dirt bike trailer is not nearly has heavy (probably 1,500 pounds) as yours, but when I go down the "Ike Gauntlet" my usual workaround to get the exhaust brake without revving the nuts off my motor as I exit the tunnel at the top of the hill is to put it in L mode, which drops it to 5th gear, then thumb 6th gear on the handle and once it is in 6th, engage Tow/Haul, which drops it to 5th again. Then as I descend the hill, I select the gear needed for the desired engine braking. I have not found excessive grade braking down that hill as long as I don't touch the brake pedal. If one so much as goes near the brake pedal while in L + Tow/Haul mode, it is rod stretching, high RPM city. If I feel the need to use the brakes, I turn off Tow/Haul first.

All this maneuvering around the transmission's programming to get it to do my desired bidding does give me something to do on long drives 😆
 
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@Dunken

I'm sitting in my trailer at a camp site and your comments about the selecting of gears came up in conversation with some others in our group.

I was saying to them today that I love my truck but it's the first automatic I ever purchased since I started driving in 1977. My statement to them today was I have always felt connected / one with my vehicles. For a good portion of my life I've done field service, driving an average of 100 to 200 miles a day. Now driving an auto I don't have to pay as much attention to the workings and I think that's the difference. When driving a manual it just gets into your life and they're s a certain rhythm about it. You instinctively run through the gears without even remembering doing it because just the sound and pitch of the motor, the view of road ahead, decline or incline of what's in front you all plays a subconscious roll in gear selection. It's not that the TCM tune I'm running is bad ( it's WAY better then what came from GM) it's just not me controlling it (yeah yeah yeah control freak I hear ya's) but they're s still plenty of times now that I hear the motor pitch and think I wish they made this truck in a manual.

If GM came out with a manual tomorrow I would trade mine in a hart beat. I too go for manual mode when towing to keep things where I want them but it's just not the same.

I live in Dillon on the 80's for a year. I worked for a national company and I requested a transfer to CO and got it. I was also doing field service back then so driving 8 to 10 hours a day on I-70 through the tunnel regularly. I can remember what a POS the naturally aspirated company car was at those elevations. I remember doing 90+ down hill so I could make it up the other side still doing 55, that was until the red and blues adjusted my thinking process and bank my account a bit...lol...

A manual... A boy can dream!
 

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@Dunken

I'm sitting in my at a camp site and your comments about the selecting of gears came up in conversation with some others in our group.

If GM came out with a manual tomorrow I would trade mine in a hart beat. I too go for manual mode when towing to keep things where I want them but it's just not the same.

A manual... A boy can dream!
Grew up riding motorcycles, still ride them, they are all manual of course. I get what you are saying about how a manual becomes "automatic" for the driver, my bikes are certainly that way. Had a few manual 4 wheelers over the years, including my '79 Dodge truck with a "3 on the tree" as a kid. A friend has a modified Corvette with stupid amount of power and a 6 speed. Driving that car with the nannies turned off was insane, it would light the tires at will in 3rd gear at freeway speed, at Denver's mile high elevation no less.

The most intense manuals I have piloted are these 125cc, 14,000 RPM bad boys. I can do 5 laps and then my brain was mashed potatoes from the G forces and constant shifting. If you have not driven one, you gotta go to a Kart track and rent one. They are a riot :LOL:



Tire Wheel Car Vehicle Automotive tire
 

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Grew up riding motorcycles, still ride them, they are all manual of course. I get what you are saying about how a manual becomes "automatic" for the driver, my bikes are certainly that way. Had a few manual 4 wheelers over the years, including my '79 Dodge truck with a "3 on the tree" as a kid. A friend has a modified Corvette with stupid amount of power and a 6 speed. Driving that car with the nannies turned off was insane, it would light the tires at will in 3rd gear at freeway speed, at Denver's mile high elevation no less.

The most intense manuals I have piloted are these 125cc, 14,000 RPM bad boys. I can do 5 laps and then my brain was mashed potatoes from the G forces and constant shifting. If you have not driven one, you gotta go to a Kart track and rent one. They are a riot :LOL:



View attachment 417048
HAHA.... I had a coyote Bullet, had 2 100cc Yami's, fluid clutch set to grab at 9,500 and the wonderful smell of Klots 2 stroke racing fuel..... WOW man you just brought me back and the cart is still hanging on the wall in the garage at my best friends house.... serious flashback....
 

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Just wanted to circle back on my experience with the GDE trans tune and GDE after taking some time to do some additional tow tests. My memory was fuzzy about which shift/RPM drop was the problem, turns out it was the 1-2 upshift and not TCC lock as it was the first RPM drop, not the second.

So, I went to the barn today and hitched up the horse trailer to test D, L, and T/H modes. Here's what I experienced and what I've passed on to GDE.
  • D, T/H disabled, trailer hitched up, starting from a stop with like 30-50% throttle there's a thud/bump as it upshifts from 1-2. TCC lockup is fine.
  • D, T/H enabled, trailer hitched up, starting from a stop with the same throttle input the thud/bump is much less pronounced and I don't see it as an issue. The difference here is that with T/H enabled the transmission isn't short-shifting for the 1-2 upshift and is holding 1st gear longer. The 1-2 upshift is firm but not harsh. The grade braking will downshift to the moon with minimal brake input even on flat ground.
  • L, T/H enabled, trailer hitched up, slowing from 55 to a stop it doesn't trigger grade braking on flat ground like in D. Apparently it only goes into rage mode in L with T/H when there are actual hills and it thinks it needs to downshift because the truck isn't slowing fast enough?
Anyway, GDE is going to try and reproduce the harsh 1-2 upshift while towing but without T/H enabled. Even if there's no fix, I can at least work around the issue by changing trans or T/H settings to run where it and I are both generally happy. Going back to the stock trans tune is a last resort, and the main test is going to see what our off-road trailer tows like once it arrives next year. It's much lighter than the other trailers I tow/have towed and I'll do whatever needs to be done to make sure the truck is happy towing it as we're planning on putting a lot of miles behind us with it.
I wonder if your adaptive shift for 1-2 isnt quite right too. I have the banks idash on my truck, still stock. Torque converter doesnt lock until 3rd gear on mine. Mine banged from 3-4 upshift from new when warmed up on certain engine load. Ended up being a bad clutch piston seal from new, put together with dirt in it. GM assembler I blame. :cautious:
 
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