Hauling safety

[horse7]

A friend recently bought a 2008 Dodge diesel, and apparently they now have the same type of "engine braking" as Ford and GM have had for a few years. The "engine braking" is more like a locked torque converter with controlled exhaust back pressure, the computer controls application and is most noticeable when one takes a foot off the accelerator (no overt braking).

I suggested the Dodge have BrakeSmart, and much to my surprise the local dealer was able to install it in a few days-- I had expected it to be too exotic for these guys. Truck went down to Florida, don't know the owner's impression of the BrakeSmart (I don't have one, they did not make them back when I bought my truck). [BrakeSmart is a brake controller, and has a brake line pressure sensor intended to relieve the driver of having to adjust the controller for differing trailer weights]

 

[jk96]

My 2008 F-250 PowerStroke Diesel has a lot more braking effect then my Cumins 5.9 (when not using exhaust brake on Cumins) but I don't know why. It is especially noticeable when in tow/haul mode mostly, I think, due to aggressive shift pattern when in that mode.

Info on Ford's torqueshift transmission from another site

When in Tow/Haul: The torque converter clutch will lock up at a lower vehicle speed for a given accelerator pedal position to provide improved transmission cooling. It will also stay locked longer on deceleration to provide engine braking. Engine braking is also provided on deceleration through the coast clutch. On the older transmissions EPC would always be minimal with the accelerator in the idle or coast position. This would result in slippage during deceleration on steep down grades, especially with a load. When the Tow/Haul mode is selected on the TorqShift, the computer commands sufficent pressure to the apply components to prevent this slippage.

Finally, to help maintain vehicle speed when desending a grade and help increase brake pad longevity, the transmission will downshift automatically. If the computer senses vehicle speed increase with the accelerator released, it will downshift to the next lowest gear. If vehicle speed continues to increase, the computer will command the transmission to downshift again. The grade braking downshift mode will be deactivated if the Tow/Haul mode is deactivated or the accelerator is depressed.

 

[patrick_g]

jk96, Thanks for digging that up and sharing it. I made a cursory attempt to find the Ford specific info and struck out.

Everything you report sounds right except for something not mentioned. Since there is so little compression braking afforded by a diesel (with no engine break capabilities built in like with a Jake brake or an exhaust brake ) where does the retarding force come from?

I looked into 5-6 makers of exhaust brakes for diesel pickups and motorhomes. Not one lists an application for the 2008 6.4 liter Powerstroke. It isn't enough that it will be an engine only used for 2 years and then abandoned with all the parts and tech knowledge impacts that implies for the outyears but being prematurely obsoleted it will not attract as much aftermarket accessory attention either.

Thanks again for your post. What site did you find with the info?

Pat

 

[bjcsc]

Diesel engines have NO CONTROL to limit intake air. The intake is wide open at all times. When you go to idle with a diesel the engine uses energy to compress the air on the compression stroke but gets most of that energy back on the power stroke (even though there is no extra energy from burning fuel) Then the exhaust valves open and the air is exhausted. There are frictional losses but otherwise there is no net loss of energy and the braking effect is small. The difference in braking effect is the gas engine sucking air in through a restriction when at idle position on the throttle. The diesel's higher compression doesn't really matter as it is getting back most of the energy put into compression at idle throttle setting.

Pat

OK. Now I get it. Thanks for explaining it and it does make sense to me now. So our Ford diesel trucks must be approaching this from the back door, i.e. restricting the exhaust?

 

[patrick_g]

OK. Now I get it. Thanks for explaining it and it does make sense to me now. So our Ford diesel trucks must be approaching this from the back door, i.e. restricting the exhaust?

That is the part that bothers me. You can bet your bippy if Ford had an exhaust brake on there they would be screaming it in their advertisements. The description of how the Ford automagic tranny operates is pretty much how my aftermarket equipment has modified my Dodge/Cumins auto tranny so it will work with an exhaust brake.

Seems like Ford did everything to prep for an exhaust brake but didn't put it on, leaving that as an exercise for the owner (should someone offer that accessory for the 2008.)

I am still troubled as it bothers me to not know where the retarding force is coming from.

I would like an exhaust brake for my 2008 F-250 PowerStroke. There are exhaust brakes that modulate the exhaust restriction so they do not exceed the set pressure. They close off more at low RPM but less at higher RPM to not exceed the max desired back pressure when applied. This way you can adjust the max back pressure so as to not over power your valve springs.

I will have to check the Ford specs but hopefully I won't have to put in HD valve springs to get decent braking. Some Cumins came with HD and some with standard valve springs. Luckily mine came with the HD and I didn't have to change them to be compatible with high performance exhaust brakes. Exhaust brakes can make your regular friction brakes last much much longer and if you keep the vehicle for a long time the savings in brake jobs can pay for the exhaust brake. Safety is enhanced, especially for hilly driving or towing or hauling significant loads.

Pat

 

[Soundguy]

So.. where is the braking force coming from.. can;'t just be torque converter / gearing can it?.. It's quite noticeable..

Soundguy

 

[jk96]

What site did you find with the info?

6.0 PowerStroke Page

 

[bjcsc]

So.. where is the braking force coming from.. can;'t just be torque converter / gearing can it?..

Soundguy

Beats me, but it's not the torque converter because my 450 does the same thing and it's a stick...

 

[JESSE1]

In tow/haul mode the fan clutch is supposed to lock when slowing down. If you're going at a high enough rpm it increases resistance quite a bit. Probably not nearly as much as an exhaust brake but it does help slow down.

 

[patrick_g]

In tow/haul mode the fan clutch is supposed to lock when slowing down. If you're going at a high enough rpm it increases resistance quite a bit. Probably not nearly as much as an exhaust brake but it does help slow down.

I have the Horton electric clutch fan in my '97 Dodge/Cumins 1 ton. The fan freewheels until the temp kicks the T'stat and then you definitely hear the fan as it is quite aggressive compared to OEM. It will contribute to deceleration but not a whole lot (compared to exhaust brake.) Of course it is most effective at high RPM. There is an override switch so you can engage it irrespective of the temp. I suppose it could be wired to a relay and the exhaust brake to run the fan whenever the exhaust brake engages.

SOUNDGUY: bjcsc says not the TC since his manual does it too. I really would like to get the straight info on the 6.4 L 2008 Powerstroke.

jk96: Thanks for the link to 6.0 PS info. Interesting, but I'm not sure how much does or does not apply to the 6.4 L 2008 version.

Braking with friction brakes generates a lot of heat as kinetic energy is transformed to heat which is dissipated to the air flow. Braking by any other means will also generate just as much heat. ("Cap'n, I canno break the laws of physics!") An exhaust brake forces the exhaust stream through an orifice where frictional loses in turbulent flow generate heat. (Compressing the gas with the pistons while working against the exhaust brake heats it but letting it return to normal pressure cools it so that is a wash with no net heating.) If the braking is hydraulic in the auto tranny then the fluid will get all the heat that would have gone to the brakes for the same braking force/duration. On a long downgrade this would put a tremendous heat load on the tranny/oil cooler/whatever and is NOT LIKELY what is happening.

So we have a mystery. What is actually happening?
Can an exhaust brake be used on the 6.4 2008 PS?
Will it help?

Yet another one of those things that make you go hmmmm????

Pat