Well, I modified my wheel sets and was able to pull one more car with the Bachmann HHP8 engine.  I have 7 Amfleet cars and could only pull two with the HHP8, but after modifying them, I can pull three.  I had really hoped to be able to pull more - for a more prototypical length - but I just don't see how that's possible.  My layout is a flat dog bone with 11 inch curves at each end, but there isn't enough traction (even on clean rails) to pull more than three coaches.  I'm seriously thinking about taking all the electric pickups out of the trucks, just to see if that solves the problem.  That would be too bad since Bachmann did such a great job with the coach lighting on these cars.  I guess if I want to pull a seven cars, I'll have to invest in another engine to gain tractive effort.  If I put four cars on the HHP8, there's too much wheel slippage, the engine just can't overcome all the friction.  Just to see how much power it would take...before I modified the Amfleet's trucks and pickup tabs, I modified a ConCor Budd Amtrak car with a rapido coupler at one end to couple with the Bmann Amfleet cars.  It took two Kato P42's to pull the seven Bmann Amfleet coaches (plus the one Concor baggage car).  One Kato just couldn't pull the unmodified Amfleet cars without slipping.  I would guess that since I modified all the Bmann Amfleets that I could pull all seven plus the hybred coupler baggage car with only one Kato P42.  The friction has been reduced, but not enough for the little HHP8 to pull more than three coaches.

As a side note...I widened the area the wheel axle has inside the wheel truck assembly.  I very carefully used a file to open up the inside diameter where the wheel is held by the truck, being careful to not increase the opening that prevents the axle from falling out.  That seemed to help decrease the friction on the axles.  I also added a small amount of graphite where the axle touches the metal pickup and truck.  This helped reduce the overall friction on the axles as well.

Those are two GREAT tutorials!  Thank you for taking the time to post them.  I will try both as soon as I can.  I agree with you about changing out only the one end of the AmFleet coupler.  With the rapido couplers, I never have a derailment on my 11in curves, and the cars are closer together than if I used a MT anyway.  But I would like to change out the rapido on the HHP8 engine and the last AmFleet car just for appearance sake.  Also, I too have real problems with the binding on the wheel pickups...I can only pull two cars with my HHP8.  I've tried several "fixes" but think yours might do the trick.  Thanks again!

Same for me...I was first told the engine would arrive in Dec 08.  Although I'm sure there was a good reason for this delay, it is frustrating.  It seems like almost every manufacturer these days are missing stock and release dates by months.  It's gotten to the point where whatever date a manufacturer gives, I add four to six months.  I have no idea how complicated it is to make a product like this, go through the production process, and around the world shipping to finally get one into the customer's hands.  Hopefully, this engine will be released soon.  It looks like Bachmann did a great job modeling this one, and hopefully it will run well with the onboard DCC.

Just wondering when the DD40AX will find itself on store shelves and when the pre-orders will be filled?  Any latest word Mr Bachmann?

Update!

Thanks for your idea about adding resistance Tim - It worked!

I didn't have a 1000 ohm resistor lying around, but I did have a Bachmann lighted Amtrak passenger car.  So I added length to the programming track and placed both the car and engine on it, went through the reprogramming steps, and successfully changed the engine's cv 03 address number to the engine's road number on the first try!  Thank you very much for that suggestion...your idea fixed a problem!   

Again - I sincerely appreciate the info - thanks!  Unfortunately, Digitrax sent me two Zephyr Starter Manuals and omitted to send the Decoder Manual, so whatever decoder knowledge I'm gaining is coming from the internet and the more knowledgable people like yourself on the forums.  I just downloaded the Decoder Manual from the Digitrax website so I'll read it and see if there's anything regarding this error in programming a decoder.  I'm hoping to get a "fix" for this, so I'll make the trip to Radio Shack for that resistor and try Tim's idea out.  Hopefully, the Bmann DD40AAX I've got on order with "DCC Installed" won't have this problem...but I'm not betting on that.

Thank you Tim for the quick reply..........just wondering when the Bach Man might shed some light on this as well. 

Forgive my electical ignorance, but let me make sure I get this; I need to place a resistor (one lead touching each track) to add resistance to the overall decoder/resistor/track programming track so that the Zephyr's electrical signal will be "stepped down" enough to actually realize the decoder is there?  Well...then how does the Zephyr "see" the HHP8's decoder when it's on the layout now?  As it is now, I can run the HHP8 on cv03 and everything works just fine.  It is also recognized by a seperate "jump" cab.  Why wouldn't the programming track discover the decoder when the layout does?  I understand the programming track doesn't carry the same electrical load to make the train move - just read the decoder.  (As a side note, when I was first trying to change the decoder address, the engine started moving when I entered the "programming" program.  It did that maybe three times, and each time I powered everything off while the engine tried to move down the 10 inch flex track programming track.  It hasn't tried that since...but I can't understand why it tried doing this or why it hasn't since.  Additionally, I've successfully programmed two other decoders (a Lenz and Digitrax)...so at least I've proven to myself that I can follow the directions in the manual.)

This is probably an obvious answer to anyone in DCC for a while...but I've got a total of 16 hours experience and haven't found the answer in any written material (either in the manual or online). 

Thanks again Tim for a "fix" for this.  Are there other Bachmann decoders that have this problem too?

I just set up my Digitrax Zephyr DCC system last night.  When I tried to either "read" or "overwrite" the factory set 03 address on the HHP8, the system couldn't do it.  I consistently received an error message that said there was a problem "reading" the address.  I was trying to change the decoder address to the engine's 4-digit road number, but wasn't successful.  No matter what programming track I used (just in case it was a track issue) I couldn't read the decoder.  I continually received an error that said there was an electrical problem with the programming track/decoder/engine.  But using the 03 address, I could use the engine on the layout and all functions (speed, direction, lights) worked fine. 

I really need to change this engine's address because I'd like to buy another one with a different road number.  I can't have two engines with the factory set 03 address.  Has anyone else had this problem and what was the fix? 

WOW!  Thanks for the info.  And this is for Nscale Amfleet cars - because every website I've visited except one indicates the Nscale Amfleet cars have rapido couplers and not a knuckle coupler.  And the Bachmann website shows knuckle couplers on the cars but rapido couplers on the engine.  So I'm confused.       (Only one retailer's website listed the HHP8 and Amfleet cars as having knuckle couplers - but the listing looked like a "cut-and-paste" from their HO ad for the same items.)   If the Nscale cars have the knuckle couplers, is it possible to switch out the rapido style couplers for the new knuckles?  And even on the HHP8?  Or am I stuck with the rapido's forever?  And have the trucks of the Amfleet cars been improved to roll easier?  Or is there a fix to improve them?

I'm confused...

You mean there's Amfleet cars out there right now with dummy knuckle couplers on them?  That's good news.  But I travel the entire country and haven't seen them yet anywhere, and everytime my local hobby store orders me a car (I now have seven), they come with the rapido coupler.  When and where were these released?  Will there be a conversion coupler released or available to remove the rapido-style coupler of the older cars?  What about a dummy knuckle coupler for the matching HHP8?

But maybe more importantly, have the trucks been improved to allow the cars to move easier?  (As reflected in other past threads), these are great looking cars, but the friction of the metal lighting kit pickups do not allow more than two cars to be pulled by an HHP8 on a level - zero grade layout.  Three cars will make the engine wheels slip, and four cars is impossible to move.  I hate to remove the metal lighting pickups since the lighting is a really great feature.

I used a very small metal file (standard kind you could buy in a set at a Radio Shack for electrical work/repair).  I removed each wheel and filed out the plastic holding the wheel set in place - being careful to not file away the opening of the truck so the wheels wouldn't fall out.

(My apologies for not answering sooner - just got back on line.)

Believe me - no malarky intended!  I had a consist of 4 Amfleets and two Concor Amtrak cars and with one P42 there was just too much slippage, so I added another P42 and it ran fine.  Granted, the Concor couplers aren't very good so I had quite a few derailments between the Kato P42 and Concor baggage car with their fixed position knuckle coupler.  But with the HHP-8 - the engine I really wanted to pull 4 or 5 Amfleet cars with - there's no chance till I work more on the wheel sets.  Thanks very much for all the good ideas though - I'm going to get to work trying to reduce the friction from the car weight and obstructions from the truck plastic and pickup metal and get these things running better.  I'm going to try to file the pick up tabs tomorrow and see how that goes.  Where did you find your pick up tabs needed filing by the way?  Mine seem ok - but I'm really going to look hard at them tomorrow with a magnifying glass to see if they're part of the problem.  But how did you notice yours were causing a problem?

Thanks for all the great ideas.  I just got back from work so I'll get started figuring out how to improve these trucks tomorrow.  I will definitely check out the pick up tabs and widen the areas as suggested and let you know how it goes.  I added some fine graphite power but it didn't seem to work too well...or at least...I couldn't see a noticable improvement.

Has anyone had success running more than three Amfleet cars behind a single HHP-8 engine?  (It takes two Kato P42's to pull four Amfleet's and two Concor Amtrak coaches on my flat layout.)

Well, I tried some graphite and was unable to tell if it improved the axle/truck condition or not.  There still must be some way to improve the roll capability - and I guess widening the axle space of the truck is the only way to decrease the friction.  Still trying ideas.............stay tuned.

Many many thanks for the ideas and replys.  I'm not going to let this die and I'll try to figure out a solution - using the existing trucks.  Don't hold your breath of course, it might take me a while, but I'm going to get a solution to this because I really want these cars to run better.

Thanks again for the ideas!