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Old 09-17-2021, 02:01 PM   #1
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Brand: Thor Motor Coach
Model: 40RT
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THOR #20989
VGT Exhaust Brake

Hello all,
I have a 2018 Tuscany which (I have been told) has the Cummings VGT Exhaust brake. The brake does not appear to work properly.

When going down a hill (doesn't matter how steep but the more steep the worse it is) the Allison transmission appears to down shift, usually form 6th to 2.4, which I suppose is the pre set gear but the engine only slows down a bit and many times does not slow but gains speed. My last trip I am sure I burnt my coach brakes trying to slow and for the first time in my life was looking for the emergency hill to pull off the road.

I have tried to manually down shift but that didn't work. I called Freightliner and they said it is a Cummins issue and Cummins said it was the after market vendor. Everything I have read indicates that this product is Cummins.

Not withstanding the finger pointing has anyone had this issue? Yes it is under warranty but checking with the Forum.

Thanks

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Old 09-17-2021, 02:38 PM   #2
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THOR #1469
I have the Cummins VGT brake and it works fine going downhill. Cummins did state at a seminar that if the cruise control is set the VGT brake will not engage until speed is 5 to 7 miles over the set cruise speed.
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Old 09-17-2021, 02:41 PM   #3
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THOR #6411
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Originally Posted by Glenn D View Post
Hello all,
I have a 2018 Tuscany which (I have been told) has the Cummings VGT Exhaust break. The break does not appear to work properly.

When going down a hill (doesn't matter how steep but the more steep the worse it is) the Allison transmission appears to down shift, usually form 6th to 2.4, which I suppose is the pre set gear but the engine only slows down a bit and many times does not slow but gains speed. My last trip I am sure I burnt my coach breaks trying to slow and for the first time in my life was looking for the emergency hill to pull off the road.

I have tried to manually down shift but that didn't work. I called Freightliner and they said it is a Cummins issue and Cummins said it was the after market vendor. Everything I have read indicates that this product is Cummins.

Not withstanding the finger pointing has anyone had this issue? Yes it is under warranty but checking with the Forum.

Thanks
It is a Freightliner problem. Take it to the Freightliner Factory Service Center in Gaffney, SC.
https://www.fcccrv.com/parts-and-ser...ervice-center/
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Old 09-17-2021, 02:45 PM   #4
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THOR #20989
Thanks...cruise control is off...Freightliner said it is a Cummins problem and take it to them. I did make an appointment with Cummins (Can't get in until November) for both this and the fuel rail recall. My concern was that Cummins had no idea what the VGT was...maybe the local dealer here in AZ?
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Old 09-22-2021, 07:43 PM   #5
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The vgt is short for variable geometry turbo and has nothing to do with the engine brake, as the engine brake uses solenoids on the first three cylinders to hold the valves closed and building compression in the cylinders that is why they are called a compression brake or engine retarder, Cummins engine should have a button to toggle engine brake on or off and in the engine controller are settings that can be changed for engine brake only comes on when brake pedal applied or when you left off the throttle, and can toggle brake lights on with engine brake.
Also all freightliner dealers are also authorized Cummins dealers but they don’t like working on motor homes and blew you off.
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Old 09-22-2021, 07:53 PM   #6
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THOR #1808
you have the VGT style on your engine


it does produce back pressure brake HP but not NEAR as much as a jake brake or engine brake


yes is will indicate a drop to 2 or 3 gear but WILL not downshift if road speed and resultant engine speed would exceed safe RPM


i have found on mine that its best to use it on exit ramps and the like and if your in hills or mountains, to stay OFF cruise
top the hill at the speed you desire for the downhill side



turn on exhaust brake and use your brake not aggressively but firmly to bring your speed down and then get off the brakes



if your rolling at 65 and just plan in exhaust brake to hold you back going down a grade...it will not have enough back pressure HP to do that. it will try, but again it will no downshift into a gear that would overspeed the engine, so it may engage and stay in 4th or 5 th until speed is such that a 3 rd or 2nd gear would let it do its job
it does rely on higher eng rpm to run at peak efficiency



HOWEVER a few tuscanys had the larger 425 hp cummins and it had a real engine brake,

what is your engine?
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Old 09-22-2021, 09:08 PM   #7
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THOR #20989
I have a 450 hp engine and it would have nice for an engine break but do have this. With cruise off and going down a 6 degree hill the RV will not slow down without “riding the brakes” .

I am hoping the exhaust brake can be adjusted and will take it to Cummins BUT any additional advice is welcome
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Old 09-22-2021, 09:18 PM   #8
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THOR #6411
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Originally Posted by Glenn D View Post
I have a 450 hp engine and it would have nice for an engine break but do have this. With cruise off and going down a 6 degree hill the RV will not slow down without “riding the breaks” .

I am hoping the exhaust break can be adjusted and will take it to Cummins BUT any additional advice is welcome
Lets first start off by comparing the key difference between an exhaust brake and an engine brake. An exhaust brake typically mounts down stream of the turbo inline the exhaust system and features a butterfly valve that is operated by an air supply. Based upon various parameters, the valve closes, causing the exhaust gases to pressurize, creating back pressure on the engine. In particular, the VGT exhaust brake found on 6.7L Cummins works by controlling a sliding ring within the turbocharger that moves back and forth. To contrast, an engine brake is mounted to the head of the engine, and creates a similar type of back pressure, but done so by controlling the opening and closing of the exhaust valves. The LoadLeash gives 6.7L owners the best of both worlds. As previously stated, the factory VGT brake does not provide nearly the retarding power as a traditional inline exhaust release brake (Jake Brake), and especially not as much as an engine brake, but by combining an engine brake with a VGT exhaust brake, the results are quite remarkable.
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Old 09-23-2021, 07:22 PM   #9
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THOR #12726
Mine has the 6.7l Cummins and the transmission controller is set to not allow the engine rpms to exceed the redline limit and which shift to a higher gear, and depending on the grade of hill I manually shift to a lower gear and let the engine run till the rpms get to about 1800 and ride the brakes till they get down again.
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Old 09-23-2021, 08:33 PM   #10
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THOR #1469
My VGT on the 6.7 worked just fine going through the hills of South Dakota and Wyoming and I never had to ride the brakes Downshift before starting the descent and let the VGT do the rest.

Same holds true for the hills of Virginia and North Carolina.
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Old 09-24-2021, 01:38 AM   #11
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Quote:
Originally Posted by Glenn D View Post
I have a 450 hp engine and it would have nice for an engine break but do have this. With cruise off and going down a 6 degree hill the RV will not slow down without “riding the brakes” .

I am hoping the exhaust brake can be adjusted and will take it to Cummins BUT any additional advice is welcome
You don't have an exhaust brake

You should have a switch with a high and low setting for the engine brake

450 hp Cummins typically don’t have exhaust brakes on the newer models

You don't have the switch to the left of the steering wheel with the two positions plus off?
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Old 09-24-2021, 02:48 AM   #12
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THOR #22245
[QUOTE=Glenn D;315776]I have a 450 hp engine and it would have nice for an engine break but do have this. With cruise off and going down a 6 degree hill the RV will not slow down without “riding the brakes” .

I am hoping the exhaust brake can be adjusted and will take it to Cummins BUT any additional advice is welcome[/QUOTE

How do you activate your brake? Mine is on the shifting stock. Works great on the Grapevine and the passes in the Pacific Northwest.

Look for a Frieghtliner "Oasis" center. 2VELOCITY TRUCK CENTERS
Oasis NetworkElite Support
12.7 mi away
1230 S. AKIMEL LANE
CHANDLER, AZ, United States

They cater to RV and my experience have been awesome.
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Old 09-24-2021, 12:58 PM   #13
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Where did Glenn go?
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Old 09-24-2021, 05:43 PM   #14
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THOR #1808
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Originally Posted by lwmcguire View Post
Where did Glenn go?
we blew his mind


and thats why i prefaced "A FEW" had engine brakes


most had vgt




i have been to wyoming up to south dakota and it worked OK, but i still had press hard on the brakes at times to bring her back to 65.


the long deadly road in colorado...OMG wholly cow burgers i had to stand on them and pray.. it was not fun. iirc it was 160 2 lane scare the crap out of you road
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Old 09-29-2021, 07:25 PM   #15
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THOR #2228
Always at the crest of the hill make sure your cruise control is off. When you start down the hill begin pumping the brakes slowly in regular smooth intervals. Your transmission or engine brake should bring the load into a more manageable speed and ease the speed between the brakes and the engine.
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Old 09-29-2021, 11:04 PM   #16
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Freightliner in Tucson AZ works on motorhome and on Cummins engines, i have mine services there. It is open at 0700 hrs no reservation first come
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