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Discussion Starter · #1 ·
Okay. So. 2012, GMC 3500 desiel dually. I had a 2007 Chevy, same model, that had no exhaust brake and it stopped my damn trailer better. I bought this "new" 2012 truck for the exhaust brake and the "better" towing capacity. It has no suck back and stop. It is weak as well. Everything on it is stock. Exhaust started coming in the cab. I took it to the GMC dealer which was a COMPLETE waste of time. They actually told me that the problem was there is a button on the dash that you have to push to turn it on. No shit. When you do that it doesn't work, hence me bringing it in here. My tow haul is on too for those who are going to ask. They were beyond incompetent and misdiagnosed the problem twice. I took it to a desiel machanic who was worth his salt and he took 4 hours cleaning out the whole system. It got a little better. The exhaust smell is gone. The exhaust brake still doesn't work well but a smidge better. The turbo was replaced two years ago. Does anyone have advice? The machanic worth his salt said that we might have to repeat the 4 hour clearing out process. Would that help?

Thank you so much! I'm so aggravated with GMC.

~Katie
 

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Did you have the turbo replaced or was it done prior to your ownership? Any idea if its an OEM replacement or something different was used?

One thing worth noting is, unlike the Cummins which our Dmax exhaust brake are often compared too, they are not ON/OFF. They are variable and will change how hard they work based upon load. Some see this as a pro and some a con.
 

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Sounds like the second guy cleaned the soot out of the turbo vanes and possibly sealed up an exhaust leak.

Further to Bsimster's comment on it being variable, it's pretty RPM sensitive as well. Higher RPM's = much more braking power. At normal highway speed say around 2000 RPM, you won't notice a lot of braking. Wind it up to 3000 - 3500 range and it will provide much more braking power. My 2012 would typically hold a 14,000# trailer back going down a 6% mountain grade in 4th gear, which is drive.

So if you're in T/H mode and kick the exhaust brake on then start applying brakes to stop, where are your RPM's running as the transmission kicks down?
 

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Discussion Starter · #4 ·
Did you have the turbo replaced or was it done prior to your ownership? Any idea if its an OEM replacement or something different was used?

One thing worth noting is, unlike the Cummins which our Dmax exhaust brake are often compared too, they are not ON/OFF. They are variable and will change how hard they work based upon load. Some see this as a pro and some a con.
Hi it was done by the previous owner but I can find out if it is important? Can I adjust how the exhaust break kicks in? That is a big con for me. I haul about 20k through cities and I need the exhaust brake to kick in when I take my foot off the break.
 

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Discussion Starter · #5 ·
Sounds like the second guy cleaned the soot out of the turbo vanes and possibly sealed up an exhaust leak.

Further to Bsimster's comment on it being variable, it's pretty RPM sensitive as well. Higher RPM's = much more braking power. At normal highway speed say around 2000 RPM, you won't notice a lot of braking. Wind it up to 3000 - 3500 range and it will provide much more braking power. My 2012 would typically hold a 14,000# trailer back going down a 6% mountain grade in 4th gear, which is drive.

So if you're in T/H mode and kick the exhaust brake on then start applying brakes to stop, where are your RPM's running as the transmission kicks down?

Hi! How can I adjust this? I need it to kick in when I take my foot off the brake. I'm sometimes hauling 20k lbs through cities. Honestly when I am hauling 8k lbs I don't feel safe or like the exhaust brake or the transmission helps me. It's feels like the truck wants to keep going like a wind up toy.

Help please!
 

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2017 GMC Denali 2500HD, 3.5" Rough Country Lift, 305/55R20 Yokohama Geolandar A/T
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You can't adjust the exhaust brake to be on/off. It's designed to apply proportional amount of braking power as you apply the brakes. It works in tandem with the transmission.

One thing you could try if you aren't already is to use the Manual Mode on the gear selector to lock out 6th gear. You should consider doing this regardless, but it will help with how much exhaust brake you feel as well. Shift the truck down to M, then hit the + button on the shift handle until M5 shows on the dash. This locks out 6th gear and will only let the truck shift up to 5th. What you're trying to do is keep the truck between 1800 and 2200 rpms while towing. This keeps the motor in its optimal rpm range which actually keeps everything cooler and the transmission much happier. The byproduct that you would be interested in is that the exhaust brake really doesn't activate until 2000 rpm anyway. I think there was a TSB or something that I read a while back talking about where the exhaust brake on the Duramax is designed to function and it's at the 2000 rpm mark.

So, knowing that, while you're driving through cities with that much of a load, use the manual shift mode to keep your RPM above 2000 and when that exhaust brake kicks in you'll definitely feel it. Below 2000 rpm you're going to be relying on the transmission and your truck/trailer brakes to provide all the stopping power.

The exhaust brake in these trucks really does work well. I tow a 13000 lb camper and I have to keep the rpm around 2000 if I want the exhaust brake on my L5P to do the work.
 

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When you left off the throttle, the exhaust brake comes in pretty slow, probably about 2-3 seconds for full power. It's not nearly as quick as a big truck if that's what you're expecting.

Like Mr. Melon mentioned, manual mode will probably be best for you. In city driving you might even lock out 5th too. 4th is direct drive, 5th and 6th are both overdrives. That might suit your driving even better, depending on what speeds you travel and which rear gear you have.
 

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Discussion Starter · #8 ·
When you left off the throttle, the exhaust brake comes in pretty slow, probably about 2-3 seconds for full power. It's not nearly as quick as a big truck if that's what you're expecting.

Like Mr. Melon mentioned, manual mode will probably be best for you. In city driving you might even lock out 5th too. 4th is direct drive, 5th and 6th are both overdrives. That might suit your driving even better, depending on what speeds you travel and which rear gear you have.
It is a big truck... The dodges and Ford's seem to work just fine? How can I adjust this to make it work when I take my foot off the brake?
 

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It is a big truck... The dodges and Ford's seem to work just fine? How can I adjust this to make it work when I take my foot off the brake?
Then buy a Dodge or a Ford? The exhaust brake works exactly as intended in these trucks and slows you down quite well without putting your chest into the steering wheel every time you take your foot off the skinny pedal. If you want that type of reaction, you should probably consider a different truck because you just won't get it from the Duramax.
 

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Long story short:

Keep your RPM at or above 2000 using manual mode

Keep using tow/haul (which you said you are doing)

Make sure your trailer brakes are adjusted properly

Make sure exhaust brake is turned on (which you said you're doing)

The exhaust brake will kick in, and will work in tandem with the transmission to give you a reliable deceleration for your truck and towed trailer. If you don't feel safe towing 8k lbs with your setup, you should get a different setup, and you certainly should not be hooking up to anything that weighs 20k lbs.
 

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And "big trucks" is trucker talk for Kenworth, Peterbilt, Freightliner, etc. Apples and oranges.

And it's not adjustable. Maybe a tuner could make it come in quicker but its maximum braking as designed is all it's going to do.

Although it's really intended for controlling loads down grades it will provide some braking force to "help" your service brakes. It's not intended nor never was intended to stop the truck. Sounds like you're looking for it to provide substantial braking in traffic, maybe even in panic stops. It AIN'T for that, not even close.

If your competent mechanic says it's all in order and working as intended and it's not doing what you want/need, I'm with Melon, sounds like you need a different truck.

Assuming you're pulling a trailer with electric brakes, maybe they need inspection/adjustment/repair? They're known for becoming sub-par fairly quickly.
 

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And you won't have much exhaust brake if you take your foot off the brake. When you take your foot off the brake the ecm thinks you want to coast, so it lets up too. If you want to see how good it can work. Get up to 60 mph, not in manual mode, then try a panic stop with a lot of pressure on the brake panel. Turn your trailer brakes down some so you don't skid the trailer tires.

Don't be too surprised when your rpm's go to 4300 and your forehead is in the dash.

My friend has a dodge 2014 I believe and his is selectable to work like ours does or a max effort type like the bigger trucks.
 

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Discussion Starter · #14 ·
And "big trucks" is trucker talk for Kenworth, Peterbilt, Freightliner, etc. Apples and oranges.

And it's not adjustable. Maybe a tuner could make it come in quicker but its maximum braking as designed is all it's going to do.

Although it's really intended for controlling loads down grades it will provide some braking force to "help" your service brakes. It's not intended nor never was intended to stop the truck. Sounds like you're looking for it to provide substantial braking in traffic, maybe even in panic stops. It AIN'T for that, not even close.

If your competent mechanic says it's all in order and working as intended and it's not doing what you want/need, I'm with Melon, sounds like you need a different truck.

Assuming you're pulling a trailer with electric brakes, maybe they need inspection/adjustment/repair? They're known for becoming sub-par fairly quickly.

My other Duramax did a great job and it was a 1 ton dually as well
 

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Discussion Starter · #15 ·
Hi All!

Thank you for your answers they are helpful! I am not looking for panic stops at all. I'm looking for the truck to use it's turbo and tranny to slow me down. All of my friends trucks with exhaust brakes do this. I like it because instead of shifting my horses forward when you brake it is a more subtle suck back for them. I just had my trailer brakes redone and still have this problem. I do it annually. I like for my truck to start sucking back when I take my foot off the gas. I suppose for emissions and fuel efficiency they have mixed this. It's a shame that it is not adjustable. If anyone has further tips on how to activate the exhaust brake under 2000 RPMS I'd very much appreciate it!
 

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Towing live horses… smoothness is important, right? No need to slam their chest into the tack box… right?

with TH on, and tow mode, if I keep my foot on brakes lightly, the shifting and exhaust brake are more pronounced. As mentioned, speed is definitely a factor and the nut munchers want you to coast as much as possible.

when in traffic with live or heavy load in tow, I just go easy and watch the special needs operators bump and grind each other..

I have had Thor’s RPM at 4K when in a 14% grade, 35 MPH and 10k# pushing us. The locals told me the hay bales along the edges were the way folks stop over speed rigs. The brakes on truck and trailer got warm. I thought I would blow something out on Thor.. so would allow speed to build to about 35-40 then haul it down so brakes could cool and maintain control.

the best control of the deceleration process was first to choose a correct speed. Then, TH and EB on and transmission in “manual” .. this takes the ECM deceleration software out of the “automatic mode”, from what I have experienced. Hope that is an option you want to try.. to see if actually “driving” the truck yourself will give you the response expected.
 

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I just had another thought... and yeah it kinda hurt.

It makes no sense that an older non-exhaust brake truck stopped the horse trailer better than the LML with exhaust brake. So....I wonder if the torque converter is not staying locked up. I think that might explain the conditions being described.

Could it be that it's not being commanded to stay locked up or maybe it's just shot. These torque converters are known to go bad sometimes.

It's just a thought, maybe someone else that knows if this makes sense or not can jump in.
 

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Check into EFI live tuning. They will be able to adjust the transmission to engage quicker at lower RPMs and also stronger exhaust braking. Cost roughly around $750.00
With a DSP 5 switch you have five individual tunes for your truck. One tune is for heavy towing with maximum engine exhaust braking, another tune is for light towing stock engine braking.

Your other option is to leave it as it is use manual mode keep the RPMs up above 2000.
 
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