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  #1  
Old 01-13-2004, 04:13 PM
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not just wind... loose a lot of speed when off the throttle

Hi,

I brought my 83 300D in for service, and the loner my indy gave me was another 83 300D. It wasnt as nice as mine, but the performance difference was noticable.
What struck me the most was the ability to coast and not loose speed.

When I am going down the highway, or even down a steep bridge, and let off of the throttle at say, 55, Ill be at 50 in a second, and keep slowing from there at a very fast rate. 65-60 is the same, more or less anytime I let off of the throttle, Ill loose speed at 5+mph per second, even on a steep decline!

The loner 300D didnt do this at all. It did more as I would expect, I let off of the throttle, and it very gradually slowed. Not more than 1/2 mph per second at 55 mph.

So, my question is, why would my car do this? I always attributed it to my car having the aerodynamics of a brick, but obviously thats not it.

What really gets me is the economy of my car. A suggestion for the quick loss of speed miught be a slightly siezed calpier or partially releasing parking brake, something like this. But it definitely isnt, because for as long as Ive had this car, now over 50k, its done this. And, its done this while constantly getting me between 27.5 and 30 mpg! Its not the tires either, as I have the same ones (dunlop sp sport A2) on my fathers van and my girlfriends car, and they dont have a whole lot of rolling resistance, and they are aired up properly.

SO, any comments? Could wheel bearings do this? Any other suggestions?
Thanks,

JMH
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Current Diesels:
1981 240D (73K)
1982 300CD (162k)
1991 350SD (113k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #2  
Old 01-13-2004, 04:21 PM
HGV HGV is offline
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Boils down to one or two thing assuming you car runs well and has no other woes.

COMPRESSION

Your car has it and the loner does not. The loner tranny is bad. You car does what mine does even thought it is a different diesel.

henry
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  #3  
Old 01-13-2004, 04:45 PM
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27.5-30mpg = don't complain!
am sure that what henry said is right on. if there is no stuck calipers or ebrake in your car then just drive and enjoy!
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Old 01-13-2004, 08:59 PM
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Thanks for the replies... The problem is, the compression might be lower, if you say thats a telltale sign, and the transmission in the loner might suck (I noticed that), but the loner's performance feels much stronger than mine. Ill be creating another post about that...
The other thing I noted though was that I believe the idle was perhaps a little faster than mine (the tach was broken so I dont know for sure), and I sure had to hold the brake harder to keep it from rolling at idle. So it seemed more powerful from off-idle until whenever (EGR valve looked brand new, maybe mine is stuck open?).

Thanks,

JMH

P.S. Both cars have identical mileage (215k vs 225k), both start easily at freezing temps with just the glow plugs, etc. I have to wonder if maybe my injection could be screwed up somehow? I have 3.5 degrees chain stretch according to the marks on the harmonic balancer.
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Current Diesels:
1981 240D (73K)
1982 300CD (162k)
1991 350SD (113k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)
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  #5  
Old 01-13-2004, 10:37 PM
ForcedInduction
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What are the idle speeds of the two? Higher idle means more fuel is being injected when coasting resulting in less speed loss.

I have my idle set at 850-900rpm for winter time and better off the line performance. When I let go of the throttle, it will coast with the same 1/2mph per second as your loaner did. I have no transmission problems. Shifts smooth, fast, at the right rpms, no slipage, and no odd sounds. My compression was all in the 325-370 range.

The only thing I can think of is that they are worn-in differently.
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Old 01-14-2004, 12:56 AM
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JH,

If you have not done it already, I suggest getting the car up in the air and spinning the wheels by hand to see if anything is dragging. When all is right, these cars are easy to push by hand and therefore should coast easily.
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  #7  
Old 01-14-2004, 07:30 AM
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Diesel Duality Observation

My two OM617.95X-equipped vehicles are as different as night and day. These differences are a never-ending source of amusement, confusion and frustration in my life. I claim that "it is the best of things; the worst of things...having TWO Mercedes-Benz diesels to compare to each other.

Lilly (84 300D 260,000+ mi) has great pickup and responsiveness to throttle changes and gets a consistent 24-25 mpg regardless of driving. In comparison, Marlene (83 300TD 230,000+ mi) is a dog off the line but with economy ranging anywhere from 21 to 27mpg.

Both are making about 9-10 psi boost at full chat and are sporting 3.07:1 final drives. The biggest difference in these cars is that Lilly is indicating about 7-8 of timing chain elongation and Marlene's timing has been adjusted to spec with an offset woodruff key (which BTW, improved performance significantly but nothing approaching Lilly's). Doesn't make any sense, does it?

I'm beginning to think that differences in the transmission and, particularly, the torque converter may have a lot to do with the way these two cars behave coming off idle because Lilly just seems to pick up revs faster than Marlene.
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