A Jake Brake is not an exhaust brake. There are 4 basic types of exhaust/engine/driveline braking systems available.
- Exhaust brake – Dodge and aftermarket
- Engine braking – Ford and & GM type
- Jake Brake – typically big rig but available aftermarket on the Dodge. A Jacobs (AKA Jake) brake works but opening the exhaust valves at the top of the compression stroke.
With the valves open there is no power stroke. The engine not having a power stroke is being forced to only compress air, slowing the engine down (here are other factors involved too). What you here on big rigs when they are rapping away on decell is a jake brake working with a poor or modified exhaust system. Those vehicles are responsible for the signs you see “No Engine Braking”.
- Telma retarder – IMO, this is the best. Telma’s work with electricity, rotors, stators and on the driveline, typically the drive shaft.
All the above can be disengaged, Exhaust, Jake and Telma – just turned off. The Ford/Gm – don’t use tow haul mode.
Aggressive engine or exhaust braking can be undesirable without a load or in less then ideal road conditions. As mentioned above it can cause the rear wheels to lock momentarily. But in theory, in less then ideal conditions you are driving slower anyway and don’t need the full affect of exhaust engine braking.
An exhaust brake can be full time or typically turned on/off electrically with a switch.
Turned on, no user input is required, which is one of the reasons the Dodge came out ahead in braking in the above article (sorry Dodge boys, about the only lead Dodge had).
Dodge
Take your foot off the throttle and the E-brake closes a butterfly in the exhaust system, either right at the turbo discharge (factory setup) or somewhere downstream in the exhaust pipe (aftermarket). I don’t know if the Dodge manipulates the transmission to assist in engine braking, and is a moot point with Dodge offering a manual transmission.
Ford/Gm
Only in tow/haul mode.
GM called their braking, “Cruise Grade Braking” prior to the current system as it did not manipulate the turbo.
So, when in tow/haul and you let off the throttle the first thing to happen is the torque converter stays locked up. This will start to give you some engine braking.
When not in tow/haul and in 5th or 6th gear traveling down the road the converter is locked up, soon as you take your foot off the throttle the converter is unlocked, this gives you smoothest, jerk free ride, but does nothing to slow you down, especially in a diesel vehicle.
So off throttle, you have a locked converter, the transmission shift points are kept higher and the programming will typically let the engine run over 3000 rpm, as high as red line if necessary. Although the noise is undesirable, maximum braking is done at higher RPMS.
Tapping the brake pedal will initiate engine braking. The power control module will start to close the vanes in the turbo, doing almost the same as a down stream exhaust brake.
Each tap of the brake pedal is supposed to increase the vane closing, increasing the amount of engine braking.
Cruise grade braking without turbo vane control was fairly effective with my GMC. Haven’t driven either of the new Fords or GMs with a trailer to see how well they work.
BTW, the Banks “electronic” exhaust brake works by manipulating the turbo vanes and transmission. The control is user adjustable and ranges from mild to aggressive. The Banks warns that when in the aggressive mode it can be harsh with no load. I had a Banks Brake on my GMC, and I can attest to the fact it is very aggressive in “max”. It would “brake” the rear tires loose whenever I backed off without a load on the truck.
Of the four systems mentioned above, I would take a Telma retarder over them all. It is silent and does an amazing job in slowing the vehicle.
In my job I drive 25-28000 fire engines to 70-75000 pound aerial trucks.
The best stopping vehicle we have is my normal ride, a 70000 pound ladder truck equipped with a Telma retarder. Of every vehicle we have this truck is by far the best stopping vehicle we have. I will not even drive it if the Telma is not working.
BTW, all of the above systems are either turned off or ineffective below 15—20 mph, depending on the programming. You certainly would not want aggressive braking in stop and go traffic.
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