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Discussion Starter #1
I deliver high profile ‘fire safety’ trailers. Traded the GMC Duramax/Allison I’ve used for over two years on a Dodge Cummins/6 speed. Just returned from my first tow with the new Cummins. The run was PA. to Texas and back. Five days and 3,200 miles later here’s my comparison of the trucks.

Both trucks are 2500 models, extended cab and crew with standard beds. The Dodge is a heavier truck. Its hitch receiver sits about 5 inches higher than the GMC and its suspension seems to have more heavy-duty spring assemblies. The Dodge also uses 17 inch 265/70 tires with more load capacity than the 16 inch 245’s used by GM.

It’s hard for me to compare two engines with different transmissions. The Allison automatic with the Duramax engine has pulled many trailers for me all over the country. This combination seemed more than adequate in power but always suffered the maddening ‘downshifts’ on hills and into headwinds. This immediately raises engine speeds into the 2,800-rpm range. Upon downshifting I usually slowed the truck down to the low 50 mph range to limit engine speed and noise. Much of my driving involved attention to throttle positions that would minimize these downshifts. With the hill and headwinds I experienced on this tow, my guess is there would have been hundreds of downshifts with lots of attention, fatigue and stress trying to avoid them.

After leaving Pennsylvania for West Virginia my astonishment with the Cummins was just getting under control. Pulling a hill out of Wheeling I did my first downshift to 5<SUP>th</SUP> gear. I’m not sure it was needed but the truck only had 300 miles on it and I didn’t want to lug the motor. All the way to Texas and I downshifted just one other time coming up a hill out of Cincinnati. Think about this. For the first time I could sit back, turn on the cruise control, hold my speed and just pull hard all the way. I am still in disbelief. Man, the Cummins just pulls the hills flat in 6<SUP>th</SUP> gear. There is almost no sound from the engine or turbo on even the longest hills and overall speed drops very little. I am guessing my average speeds all day are 5 to 10 mph faster while towing with the Cummins than with the Duramax.

Towing comfort and safety involve many issues. More power makes for easier towing but ride issues must also be considered. The GMC truck was easily moved around when big trucks passed. . You had to always be alert because the sway wanted to move you into the passing trucks. Not with this Dodge. There is almost no sway. At times I got scared seeing a big truck so close, not feeling the sway and not really hearing it as I used to. The higher speeds on hills also reduced the number of times a big rig was able to pass me. Chalk one major win up to the Dodge in the area of stability and this was also true in strong cross winds.
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Sounds like that combination is well suited to the open road.


I've never heard how the Dmax/6spd compares to the Dmax/Allison. It would be interesting to see. I'd think the Allison would be a bit more lossy than the 6 spd, but it's well known that many towing power modules remove most towing application complaints of excess shifting.


I went down the hand shaker path and swore off the monotony for the comfort of a reliable 5 speed auto. Each person has different needs and my lazy butt says the Allison is the only game in town.
 

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When I went from my 5-speed ford to my 6-speed Duramax, the thing that struck me on my first tow was how much less downshifting I had to do for hills. Highway towing became largely a process of sitting there with the cruise control set, it took a hell of a hill to necessitate a downshift. And since I've chipped it, the need to downshift at all has basically gone away. My biggest problem on hills is the people in cars who either can't climb it at freeway speed because they have some underpowered dippy little foreign thing, or people who subconcsously slow down on hills rather than apply more throttle.
 

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Discussion Starter #4
ZFMzx,


You are the first report I ever read on how the Duramax works with the 6 speed. Thanks. I've never even seen a 6 speed Duramax as everyone is in love with the Allison. Between your comments and my experience with the Allison my conclusion is that the manual transmission is the way to go if you use the truck for towing.


Another nice thing about the manual is that you do not have to deal with all those crazy computer systems that default the transmission and engine into limp mode. My thoughts are that is another weak point for Duramax/Allison reliability. I also know that dealers just are not comfortable or maybe even competent diagnosing problems in that area.


"KISS"......simple stupid.
 

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The diesel trucks from the "Big Three" are all expensive. They don't seem to be able to make a profit on cars, so they are concentrating on trucks and SUV's. With this focus comes faster change in a competitive market. If everyone looks back 5 or 6 years you can see tremendous change in the diesel pickup offerings. This will continue in the future, driven by the higher profit margins these vehicles offer the manufacture.


The Duramax we can buy today has not been changed in four years. The other two manufactures have made engine updates in this time to stay competitive with the Duramax (which raised the bar when it was introduced). In a few months we will see GM introduce the "LLY" version of the DMAX, with a corresponding increase in HP/TQ. So quite possibly the above comparison will be different. Time will tell!


I have enjoyed reading your posts Captainmal. I am certain everyone here will be interested in reading your posts as you roll the miles up on you new truck. I suspect the Cummins engine will perform well. The rest of the vehicle is a bigger question mark in my mind (from my past personal experiences with that manufacture, but times change).Edited by: OC_DMAX
 

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Discussion Starter #7
OC_DMAX,


Interesting comment you wrote. This has occurred to me but I have not chosen to voice that issue. Tact is a virtue but can also be an indicator of dishonesty and weakness.


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"The Duramax we can buy today has not been changed in four years. The other two manufactures have made engine updates in this time to stay competitive with the Duramax (which raised the bar when it was introduced). In a few months we will see GM introduce the "LLY" version of the DMAX, with a corresponding increase in HP/TQ. So quite possibly the above comparison will be different. Time will tell!"


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Back in '01 I was coming off a good, high mileage experience with the 6.5 diesel. One injector pump under warranty and 150,000+ miles. Ford had given me trouble in the past so my choices were another GM with the 'new' Duramax engine or the Dodge/Cummins of that time.


A friend bought the Dodge back then. I towed with it and it has less power than the Duramax, rides rough (huge springs on the back), gets less fuel mileage, is loud as all heck and had a reputation for a weak automatic transmission. Today that guy has the same truck. It looks good, has never had repairs except for maintainance, is used every day with plans to use it for a couple more years. Oh, it also has over 120,000 miles on it.


I bought the Duramax because of my good GM experience, powerful motor, Allison transmission and quiet operation. What went with it were seriously defective Bosch fuel parts, labor intensive engine/fuel design, inadequate fuel filtration, overly complicated computer controls, poor dealer service capabilities, a drivetrain with high maintainance requirements, an Allison not programmed to handle the engine properly with a host of expensive parts prone to break.


Today, years later, the current Duramax/Allison is no better. I just left a "famous' dealer and watched another infamous engine teardown for fuel problems on a nearly new model. It's the same old thing.


Today I have NEVER met anyone or heard of anyone who did not have major problems and expense trying to put high mileage on a Duramax. Forget Brokers. Everyone who likes them has something like 50 to 80 thousand miles or less. That's hardly 'break-in' mileage in my book. The two I know of with high mileage, other than mine, also had major repairs, downtime and major expense. To like a Duramax you have to run it hard and get rid of it before the warranty runs out.


If I could have seen the future the best bet would have been in the past. The old Cummins would have probably still been running and I would not have been skinned for multiple thousands of dollars trying in vain to keep a defective design going. Unless the LLY motor addresses the issues of reliability, all the power in the world will not make this loser worth it. It will take years and mileage to find out if things are right with the LLY. Is it worth the money and risk to find out?


"Time will tell"!
 

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So captain..... why were you all ready to buy another one?
 

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Discussion Starter #9
Hoot,


Thanks for letting me answer that good question.


My wife is not perfect. She was crippled 10 years ago and is quite grouchy most of the time. I think I stay with her because I'm just 'used' to her and hope she will get better.


I have the same kind of feelings toward GM. I am just comfortable with their products and hoped another newer one would be better. In retrospect I guess those are both failures on my part as I yielded to emotion rather than objectivity.


Other issues that had me trying to buy another Duramax were my initial comfort level with the saleswoman I often bought from. We dated 35-40 years ago and go "way back". The fact that GM was getting me a $3,000 loyalty bonus over and above all other rebates and incentives factored in. Then there is the influence of Eric Merchant.


Eric was so competent that I actually wanted to buy from his dealership. Heck, I drove nearly a 1,000 miles to buy there but they just did not have a basic truck on the lot that would fit me needs.


I also knew how to add extra filteration, change filters, service transmissions and rear ends, do normal maintainance etc. Like my wife, flawed or not, I was familiar with the product and lived on the hope it would be better.


The Dodge truck scared me. I believed the rumors and reputation. Never did find anyone to prove them true, but I "felt" all the bad talk about Dodge must have some credence. On the other hand, talking to people all over the country had repeatedly proven to me the Cummins was a true "high mileage' engine. Many an evening I had dinner at truck stops with Cummins transporters and both saw the trucks and heard the stories. Their only factual horrors involved lift pump pressures below 8 psi and the attendant $250 every 150 to 200,000 miles to change the pump. I wish I had it so good.


After failing to buy at Eric's dealership, I returned to Pittsburgh and had another problem with my local dealership (mostly GM temporarily refusing to honor their own incentive) I could take it no more.


Over 20 serious breakdowns in a couple weeks, a wasted $1,000 replacement of a pressure regulator, the quote of them wanting as much as $7,000 MORE to try fixing an injector pump/transmission/computer and the fact I had already spent over $6,000 in recent repairs just flipped me out. Also in the back of my mind was a nearly new Duramax I saw with the motor torn down for 'the same old thing'.


Outraged and smoking one cigar after another, I went home, got on the phone, called Dodge dealers I never heard of and took a "pig in a poke".


Never had I heard of this dealer before. Just happened to see a small ad for them in the newspaper. Went there, did a deal, they got the truck, I got lost, they gave me a better deal (long story) and I took delivery. That's it!


It became an impetuous act based on frustration with the whole situation. In retrospect, time will tell, it may have been the best thing to do. Cost me more money for the Dodge than the GM because I lost my discounts. In the long run it just might be a whole lot cheaper.


Now ..... should I stay with my wife and endure her abviously flawed condition?
 

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You might not have a choice if she reads this!
 

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Stay with your Wife.....

I hope the Dodge with the same injection system does better.

That's my real question... you had terrible luck with your Bosch HPCR that you said that's it.... I'm getting a Dodge with Bosch HPCR.

Looks like you're happy with a lot of other things though. Keep cheering us on
 

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As Hoot mentions above, the new Dodge/Cummins models (2003 and later) have a very similar Bosch HPCR fuel system (injectors and pump) to what the DMAX has. So the reliability of the fuel system on previous Cummins engines (prior to 2003) is no indication of future performance of the fuel system your 2004 engine. If Dodge/Cummins did their design correctly, they hopefully provided a robust fuel filtration system instead of the marginal unit we have on our DMAX's. You may want to inquire on the various Dodge Forums to see if anyone has made measurements of fuel filtration performance and whether an additional supplemental filter is recommended.


One big advantage you have with the Cummins engine is that once you exceed your Dodge engine warranty (5yr/100k miles I assume), you'll be able to have the engine worked on by any Cummins repair location. Should any service be required, you'll most likely find a service tech that understands the engine. You may want to inquire whether the Dodge engine warranty is honored at authorized Cummins repair stations since you spend so much time on the road (a real bonus if it is).


Happy motoring with your new truck. Keep us posted in the months ahead.
 

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I would think replacing the wife would cost more that fixing the D-Max many times. But a younger model may give you better performance for a longer time.
 

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Discussion Starter #14
Blue Max,


Stealer wanted an additional $7,000 in an attempt to fix my Duramax. My wife would want a whole lot more. A younger model might have problems (like Bosch HPCR?) that surface in the future.


I like your attitude.
 

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The Cummins does have a better fuel filter system .....


"The lift/supply pump is located on the side of the motor right next to the fuel filter and is an all new design supplied by Federal-Mogul."





In addition there are running a different injector then on the Duramax ...Cummins has been using this paticular set-up over seas long before the Duramax went the way of Bosch HPCR ...





Like it or not boys ...





Mac
 

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What kind of injector? Is it Bosch? What is so different about the actual nozzle design? We know the body has to be different and we know it's fed through a port in the head instead of lines.
 

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hoot said:
What kind of injector? Is it Bosch? What is so different about the actual nozzle design? We know the body has to be different and we know it's fed through a port in the head instead of lines.
It's a Bosch but I was told it's different from the boys on the TDR .... I don't recall exactly (I know I should have been prepared) but I'll go back and find out ....
I received some info way back when I was doing some research on their fuel filter rating .....

Mac
 

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Discussion Starter #18
Mack,


Keep it up. I'm fascinated as these are answers Hoot asked me in private e-mails and I had no details, only suspicion. I asked these questions at a Cummins repair station today and got mostly blank answers.


You and others here are a better source than the experts on the big and famous Cummins sites. There is quality and character in Duramax people...excluding me of course.
 

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Gettin warm...



 

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I hope the Cummins fuel filter is finer than the 10 um filter shown in the schematic above ! Possibly an error with the schematic?
 
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