EB Auto versus Manual

[AHarris]

I'ved noticed a significant difference between my old truck (2007. 5 with G56) and my new truck (2010 w/68RFE) when it comes to exhaust brake performance. With my old truck, I could almost use the EB to come to a complete stop. With the new one, once the TC releases, there is no EB assist, especially in regular driving mode. In tow/haul mode, it's a little more pronounced but still not nearly as robust as it felt in my old truck.



I believe the EB only engages when the TC is locked and that probably accounts for the big difference I noticed between the manual and automatic trucks.

 

[Jim W]

I believe the EB is actual controlled by the ECM on the engine. I know with my truck when the RPM is below 1200 the EB will not work. I use the toggle switch to down shift the trans to keep the RPM range above 1200 to keep the EB engaged for as long as possible. I usually toggle between 4, 5 and 6 gears on my truck. I try to maintain a RPM speed range of 1800 at all times and this seems to allow the best fuel economy for me. Then when slowing down, I will down shift when I am under 1200 RPM and then the next gear will place the engine above 1200 RPM again. This seems to keep the EB engaged longer.

Just my $0. 02.

Jim

 

[AH64ID]

You are correct, the EB will only operate when the TC is locked.

 

[Jim W]

You are correct, the EB will only operate when the TC is locked.

I am sorry to call you out: but do you own a 6. 7 equipped truck. Have you read the owners manual?



On page 50 of the supplemental owners manual for 2008. The book states that the exhaust brake will only function. "WHEN THE EXHAUST BRAKE IS IN THE ON POSITION AND THE VEHICLE IS MOVING FASTER THEN 5 MHP ( 8 km/h); --- EXHAUST BRAKING IS MOST EFFECTIVE WHEN THE ENGINE RPM IS HIGHER. --- ON PAGE 51 THE EXHAUST BRAKE CAN BE USED TO WARM UP THE VEHICLE FASTER IF THE FOLLOWING CONDITIONS ARE MET. THE VEHICLE MUST BE MOVING LESS THEN 5 MPH (8 km/h ) , THE EXHAUST BRAKE SWITCH MUST BE IN THE ON POSITION. THE COOLANT TEMPERATURE MUST BE BELOW 180F (82 C ) AND THE AMBIENT TEMPERATURE MUST BE BELOW 60 F (16 C). "

This seems to me that the TC would not be lock-up in these driving conditions.

Jim

 

[AH64ID]

I am sorry to call you out: but do you own a 6. 7 equipped truck. Have you read the owners manual?



On page 50 of the supplemental owners manual for 2008. The book states that the exhaust brake will only function. "WHEN THE EXHAUST BRAKE IS IN THE ON POSITION AND THE VEHICLE IS MOVING FASTER THEN 5 MHP ( 8 km/h); --- EXHAUST BRAKING IS MOST EFFECTIVE WHEN THE ENGINE RPM IS HIGHER. --- ON PAGE 51 THE EXHAUST BRAKE CAN BE USED TO WARM UP THE VEHICLE FASTER IF THE FOLLOWING CONDITIONS ARE MET. THE VEHICLE MUST BE MOVING LESS THEN 5 MPH (8 km/h ) , THE EXHAUST BRAKE SWITCH MUST BE IN THE ON POSITION. THE COOLANT TEMPERATURE MUST BE BELOW 180F (82 C ) AND THE AMBIENT TEMPERATURE MUST BE BELOW 60 F (16 C). "

This seems to me that the TC would not be lock-up in these driving conditions.

Jim

No, and yes.



And that contradicts what I said how? Are you referring to the warm-up feature? That's not exhaust braking, that using the exhaust brake to increase load. Which is not related to the original post in anyway.



On an automatic truck you must meet the above requirements, and be in a profile that allows for TC lockup, then you get exhaust braking. Its a well documented fact. IIRC, the converter will lock in gears 2-6, above 1200 rpms (as you noted). Which as you noted you lose the EB below 1200 rpms, due to TQ converter unlock (but your above 5 mph aren't you).



Not sure what your trying to prove??

 

[rwitt]

On my 09 automatic, the EBrake doesn't work below 20mph, which is where the TC unlocks. Doesn't matter which gear it's in.

Rich

 

[AH64ID]

On my 09 automatic, the EBrake doesn't work below 20mph, which is where the TC unlocks. Doesn't matter which gear it's in.

Rich

Interesting, I didn't realize it unlocked at that high of speed. Is it the same with tow/haul on?



I will say that below about 25mph I can't downshift fast enough, on my NV5600, to keep a decent amount of EB function for decelerating. I can keep the proper rpm for speed control but the service brakes are my primary below about 20-25.

 

[rwitt]

Interesting, I didn't realize it unlocked at that high of speed. Is it the same with tow/haul on?



I will say that below about 25mph I can't downshift fast enough, on my NV5600, to keep a decent amount of EB function for decelerating. I can keep the proper rpm for speed control but the service brakes are my primary below about 20-25.

Yes, the same with tow/haul on.

My previous truck was a G56 truck with PacBrake EBrake, much better control at the lower speeds, especially on twisty steep mountain roads when going less than 25mph. The Ebrake worked all the way down to first gear, hardly ever had to use the brakes to maintain/hold speed. I will say the current auto and ebrake works great down to where it kicks off at 20mph.

Rich

 

[AH64ID]

That's too bad. Like I said I don't use the brake to slow as much below 20 (its on, just not the main stopping source), but I do use it lots to maintain speed on the back-roads, dirt and paved.