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Computer Controlled Exhaust Brake Operation??

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Would someone with a new '08 Ram tell me how the exhaust brake is factory programmed to operate?



My '06 with OEM Jacobs Exhaust Brake, 48RE, and 4. 10 gears is controlled by the ECM. When I lift my foot at highway speed the exhaust brake is activated and remains closed down to 40 mph. At 40 the exhaust brake opens momentarily, the ECM blips the rpm, the 48RE downshifts to 3rd direct, and the exhaust brake is again closed and remains closed down to 20 mph. At 20 mph the 48RE torque convertor unlocks and the exhaust brake is deactivated.



Today, just out of curiousity I drove an '08 Ram pickup with 68RFE and 4. 10 gears. At highway speed when I lifted my foot the exhaust brake engaged just like on my '06 but at around 40 mph the exhaust brake disengaged and remained off as the truck continued to slow. The transmission did not downshift as road speed declined whether in normal mode or "tow/haul mode. " I expected the exhaust brake to turn off momentarily while the transmission downshifted then close again and remain on down to 20 mph or so like my '06. I was surprised and frankly disappointed.



I've recently driven a couple of 4500 and 3500 cab and chassis trucks with the Aisin automatic. Each of those trucks activated the exhaust brake and kept it closed all the way down to 20 mph or less as it downshifted through the gears.



Was the operation of the Ram pickup I drove today out of the ordinary or is that the way they are programmed?



How about a cab and chassis owner? Does the ECM on the c & c trucks keep the exhaust brake engaged and downshift through the gears all the way down to 20 mph or below as I was thinking the trucks I drove did?



I'm confused by what I experienced today and now questioning what I thought I knew or understood about the new Rams.



Harvey



On edit: After posting this thread I had a thought that may answer my own question. Before I slowed the first time and observed the exhaust brake operation described above I had been experimenting with the thumb shifter. I shifted down a couple of gears then back up to sixth. I didn't know at the time but after shifting back up to 6th gear it is apparently necessary to flip the thumb shifter one more time to return the transmission to full automatic operation. I didn't notice until later in the test drive that "6" was displayed in the instrument panel. I realized then that I had locked it in 6th gear and had not returned the transmission to computer control. I think that may have been the reason why the transmission did not downshift and did not keep the exhaust brake activated. I think I made a mistake but the computer knew better. I guess I was outsmarted by the computer.
 
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In Tow/Haul and ex brake on my 08 Automatic will down shift until 25 MPH. The brake cuts out on rpm (1100) not mph. It seems to work better with a heavy load.

Mark
 
1100 Rpm Is The Key

The exhaust brake on the pickup truck releases at 1100 rpm no mater what

gear you are in, so just use the gear selector ( plus or minus) on the paddle

shifter on the auto 6-speed and you can control your speed just as you

would if gearing down with a stick shift... . I leave my exhaust brake "ON" all

the time. Just be sure to bump your brake pedal when using it to stop in

city traffic so your tailgating buddies won't dent your Tailgate GOAT.
 
HBarlow..... any chance the transmission fluid temperature may not have been up to the optimal operating temperature ?



Greg
 
If the "Tow Haul" light is off the Turbo Brake doesn't really work under 4th gear, converter isn't locked. If you want the full break effect I believe your brakes need to be slightly applied.
 
HBarlow..... any chance the transmission fluid temperature may not have been up to the optimal operating temperature ?



Greg



Greg,



That's possible. It was just a dealer test drive so I was completely unfamiliar with the truck.



I did notice that when we left the dealership and reached about 60 mph the transmission did not shift up into sixth gear for a while. That may have been due to low transmission fluid temp as you suggested or engine coolant temp.





Thanks to each of you who replied.



Harvey
 
Greg,



That's possible. It was just a dealer test drive so I was completely unfamiliar with the truck.



I did notice that when we left the dealership and reached about 60 mph the transmission did not shift up into sixth gear for a while. That may have been due to low transmission fluid temp as you suggested or engine coolant temp.





Thanks to each of you who replied.



Harvey



Depending on the outside temp in the winter it takes mine 2 or 3 miles before it will shift into 6th.
 
I have noticed in operation that a heavy load / towing with T/H and Exh Brake really works well, until 1100. Sometimes a bit of brake helps the downshift procedure too.



As someone else said, use the shift paddle to manually downshift using the exh. brake is good too. Personally I don't care for the operation of the T/H and Exh Brake together when unloaded, it is hard to judge when the downshift will occur. Also - use care on wet and slippery roads as the combo could cause a spin out.



Other than getting used to the truck - it is great! I use exh brake 95% of the time, loaded and unloaded. It does have a slightly different sound at idle when exh brake is on / versus off.



Has anyone noted any mileage difference in unloaded ops with exh brake on versus off?



Thanks, Luke
 
The brake cut out must be st differently on different trucks...

Our new 08 5500 with the auto works below 25 MPH but I can't tell you how low... it was coming on yesteday at 20 MPH for sure... but I didn't pay attention when it shut down. .
 
Personally I don't care for the operation of the T/H and Exh Brake together when unloaded



I second that, I'm not sure I really like it lightly loaded either. Some serious braking starts happening when you have the 'Tow/Haul' and 'Exhaust Brake' both on and you touch the foot brake, the transmission downshifts very aggressively and when combined with the exhaust brake it can be pretty jarring. It definitely does the job but for light loads or light towing I dont know that the 'Tow/Haul' is necessary with the EB on.
 
The brake cut out must be st differently on different trucks...



Our new 08 5500 with the auto works below 25 MPH but I can't tell you how low... it was coming on yesteday at 20 MPH for sure... but I didn't pay attention when it shut down. .







I bet it has something to do with 4:88 gears and the Aisin transmission. ;)
 
Just picked up my 3500 dually 4X2 and the exhaust brake only works when I push the button for it. It will then work even sitting at idle. It helps the engine warm up when cold according to the book and according to the last three mornings (cool). The owners manual says nothing about the exhaust brake cutting out at any RPM. The owners manual does state that after market exhaust brakes are NOT recommended. Why it says that I don't know, because it is standard on the 6. 7 . Well guess Dodge knows best. :rolleyes:
 
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