diesel truck help can't decide what to get

[CJDave]

[img]/forums/images/icons/tongue.gif[/img] Pretty good diesel synopsis, Pat.......lots of good info in there. Do they not have the Jacobs Brake available for the Cummins that is used in the pickups? The Jacobs principle is also used on Detroit two-cycle diesels as well, it works the very same way.....delaying the exhaust valve opening. On the Detroits, you can actually idle and start the engine with the Jake brake in "on" position, whereas you cannot on the Cummins unless you have the foot throttle above the idle setting all the time. [img]/forums/images/icons/crazy.gif[/img] I'm not much of a fan of automatics-as-a-puller application, EXCEPT for the Allison. [img]/forums/images/icons/tongue.gif[/img]

[Pat]

tbolt, I haven't a clue about transmission braking. I suppose the tranny could pump fluid through an orifice to dissipate energy but you'd think it would heat the heck out of the fluid. Maybe someone a lot smarter on this than me will chime in.

I didn't set out to buy a Dodge. I went to buy a Ford but they didn't make what I wanted in '97 so I bought a Cummins engine and it came wrapped up in a Dodge truck. I have low miles on this unit (about 70K) and am on my second tranny. I twisted the input shaft off of the original one. This one is an after market HD modified unit built by BD to take a lot more HP and Torque than I can produce so I don't think I will have a repeat failure.

I also had my aux tranny (over/under drive) fail but the maker gave me a real good deal on an exchange for the new improved version. Their aux tranny survived well in Duromax and PowerJoke applications but there was something about the torque pulses coming out of the Cummiins that did the units in. I got more miles on mine than most owners. They changed alloys and hardening processes and I don't expect to have a problem with that again either.

My '97 isn't even begining to be up there with the BIG DOGS running their propane boosted torque monsters. I changed out the injectors and injector pump and get more HP and more torque than stock and a small increease in milleage while doing it. The pump produces a lot more pressure and the injectors have smaler holes and together they spray a little less fuel but in a finer mist that burns more efficiently. I have an EGT so I can avoid overheating problems which could happen if you just put the pedal to the metal and left it there on a long grade while towing real heavy. No over heating if you don't try to show off.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[StanleyinMd]

What I'd like to see is a Cummins powered pickup with an allison 6 speed auto tranny.


Now that would be a winner!!!!!!!!!!!! Can you imagine?

[Pat]

Dave, I have no clue what the current situation is with Dodge. When I was shopping, Dodge was selling an exhaust brake by Jacobs but would not authorize it for an automatic. I got mine from BD and had it installed at a Cummins shop. I had the HD exhaust valves installed (Cummins option) so I cold get real efective braking. I had some trick s--t put on the tranny by BD so it would work OK with the exhaust brake. The Dodge tranny freewheeled in 4th (OD) so it was useless for braking. The hydraulic pressure that held the converter in lockup bleeds off while coasting. A mod fixed that and I could use the exhaust brake in any gear but not in the half gears provided by the Over/Under drive because the way the gears were cut to have torque help lock it up. It makes you think a bit to do everything right but it was no problem for me.

My slide in camper, largest unit Lance made in '97, is about as aerodymanic as a brick. Coming down the grape vine in California in 4th gear with no throttle applied I would make 85 MPH. After getting the exhaust brake I could do it at 70 without using the service brakes. I tried it in 3rd gear with the exhaust brake and it held me back to 50-55. The kinetic energy is dissapated in heating the air the engine compresses. The engine does not overheat doing this. I'm not sure I would want to put all that heat into an auto tranny and expect to safely dissapate it with the stock trany cooler.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[hudr]

"That is why diesels do not hold you back worth snot when coasting."
I may be stepping in it here, but when I step off the footfeed in my 95 Chevy 6.5TD, I immediately get some engine braking. Some of that I will attribute to the manual tranny since I notice my BIL's auto equipped truck (same motor) doesn't do it as much. But, I thought this had a lot to do w/ engine compression ratios.
Example: We have 2 tractors of roughly the same hp rating, same approx. weight, (both 2 cyl JDs). One is diesel and one is LP Gas. The LP Gas model will always "out coast" the diesel. i.e. the diesel slows at a greater rate. I always assumed this was due to the greater compression in the diesel engine. Thoughts? Comments?

[egon]

The new Dodge CTD can be ordered with a factory installed exhaust brake.

Egon

[Pat]

I was thinking of typical diesel powered pickup trucks, not tractors. Anyway the diesel typically has no control over the intake configuration. It is wide open all the time and power output is changed with fueling, spraying more or less fuel.

The diesel has higher compression. OK, so what? It makes it harder to take the piston to TDC on the compression stroke but then the compressed air pushes the piston back down and ignoring friction as a simplification, you get the effort back again. In a gas (oline or propane) rig when you let up on the throtle less air gets into the cylinder because you are pulling a vacuum against the restricted intake. (Carb's butterflly or throttle body is closed.) This is what causes engine braking in a typical gas engine, doing the work of pulling that vacuum.

Find someone with a diesel pickup and coast it down a grade and you'll soon see just how little engine braking there is. This is why there are numerous after market suppliers of exhaust brakes for diesels. Ever hear of an exhaust brake on a gas pickup?

Have no clue regarding your observations with tractors, I'd have to be there. Of course when yo take your foot off the accelerator of your diesel pickup the friction of spining all those parts holds you back a little but precious little compared to a gas rig.

Side note: the Toyota folk have biased the regenerative braking of the Prius to simulate engine braking so the car feels like a standard gas car when coasting. Otherwise it woiuld coast too good and make folks nervous.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Pat]

Egon, With automatic tranny?

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[egon]

Thought I saw it somewhere but now I can't find it.

Egon [img]/forums/images/icons/confused.gif[/img]

[hudr]

I understand the diesel having no intake control. Hence the vacuum pump (no buterfly valve, no vacuum) on a lot of diesels. Here is my hypothesis, I may be wrong, but hey [img]/forums/images/icons/grin.gif[/img]
Foot comes off throttle, pump goes to idle as far as fuel delivery, piston comes up against compression, no fuel to support increased burn so lots smaller fire, no acceleration. next piston comes up against compression, and so on and so on.
Just seem from my experience w/ diesel p/u (I started w/ a 5.7 chevy) that they slow down faster than their gas powered counterparts. Just an observation from having driven both engine types. Like I said in my earlier post, my P/U (6.5TD manual) slows down faster than my Brother In Law's P/U (6.5TD automatic) and I am sure it has something to do w/ the manual vs. auto BUT my P/U also coasts LESS than my gas powered suburban (auto) and less than my gas powered Bronco (manual). Maybe there are other forces at work here, but like I said that is just my seat of the pants, non-scientific observation/opinion. And you know what they say about opinions [img]/forums/images/icons/grin.gif[/img]