coaster car - PeachParts Mercedes-Benz Forum

crash9 · #1 11-18-2003, 11:51 AM

Hi:
Bought a 79- 240D about a month ago and I’m just getting used to the car. The car is in fine shape, and the further I get into it, the better it seems. The clutch may need a little adjusting with 165k, grinds a little going into reverse, if I’m not careful. I’ve had gassers before - so I’m generally familiar with Mercs.
My question is the weight of the flywheel, or I should say the way the engine responds when I get out of the throttle. RPM’s stay up between shifts and there is not a great deal of engine braking. The linkage is tight and everything seems right. My only concern is that this could be a problem on downhill grades – at least in third it would seem the engine might spin to easily. The compression seems fine; at least it shuts right down, starts easy, blowby OK.
Just seems like it’s got a very heavy flywheel and can explain how it sails along so well. Does this all seem proper.
Thanks,
Chan

Rick Miley · #2 11-18-2003, 01:52 PM

It should not act that way. Mine does that when the idle adjustment is up too high after the engine is warm.

crash9 · #3 11-20-2003, 08:44 AM

Thanks for the feedback – I may really be nit-pickin here. I’m just used to getting a quick drop in the revs and more engine braking. If the idle adjustment is turned up it really exacerbates what I’m talking about, and brings up another Q. The only manual I have is the Haynes, and it really doesn’t go into how the mechanical governor works. When the idle adjust is turned up, and the engine has warmed, when I back out of the throttle the revs hang for a couple of counts before slowly dropping to the higher idle speed. This is in the carport, under no load, and say from about 2500 rpm. When the adjustment is turned back to normal it drops right off – just not as quickly as I would expect. I suspect this has something to do with the governor, or maybe the difference in the way FI works vs. a carb. The change in adjusted idle speed from fast to normal seems only about 500, and I can’t understand why it would cause this effect.
The weight of the flywheel just seems like the logical answer – it would also seem that the turbo motors should have a lighter wheel in order to get a quicker turbo response, but I am only speculating
Chan

Rick Miley · #4 11-20-2003, 10:14 AM

No, it's not acting right. When my engine is warm and the idle adjustment knob is set properly, the revs drop like a stone. Get the engine warm, open the hood and play with the linkage while it is running to see what is going on in there. Sounds like it is hanging up on something.

crash9 · #5 11-20-2003, 02:27 PM

Thanks guys – I don’t think there’s really anything the matter here. Under no load it revs up and backs off equally and that would make sense with what “Dude” said. I’m just having fun playing with, and getting to know my new toy. Maybe I can find out about the flywheel on the tech discussion.

P.E.Haiges · #6 11-20-2003, 05:31 PM

As soon as the throttle as released, the fuel is cut off until the engine returns to idle speed and then the fuel necessary to maintain speed is applied.

If this doesn't happen, your throttle linkage may be binding. You can check this from under the hood. Rev up the engine manually and see if it quickly drops to idling speed before you hear the Diesel idle sound again.

P E H

Maxwell · #7 11-21-2003, 01:18 AM

actually a diesel with an EGR system does have throttle, it has a lot less effect than the throttle on a gasser, but it has one, i removed mine an got rid of my EGR, and it definitely got rid of most the engine braking.

william rogers · #8 11-21-2003, 02:46 AM

My 240 was hard to get into reverse and ground going into second if not shifted very slow .A new clucth master cylinder and slave cylinder made it feel like new............
William Rogers.......

crash9 · #9 11-21-2003, 01:53 PM

P.E – I think it’s OK – just a little different than I’m used to – still can’t get any feed back on the flywheel weight issue, which I think explains the response
I think Max may be pulling my leg
William – I’m thinking the syncro might be tired – If I hold the clutch in for a second and don’t jamb, but just gently feel for reverse, it ‘s no problem – one of those things that you know isn’t quite perfect but that you get used to, and doesn’t hurt anything. When I was first trying the car out -- I didn’t know to lift up on the shifter, and thought I found the real reason she wanted to sell - and the PO didn't act like she knew. When I finally lifted up after trying everything else – the PO got a look of shocked amazement, so God only knows what she had been doing. Thankfully she took the car in for every little thing, but I’m still wondering why she didn’t know how to shift it, or never asked anybody. Maybe it’s a testament to MB’s durability, cause this is really a tight very good car, with 165K – at least showing – tested comp at 290 – 310 . BTW she got a good deal on a 300TD

Rick Miley · #10 11-21-2003, 03:10 PM

Alright, since this thread is still going I'm going to chime back in. Engine braking comes from compression, not from the engine being throttled. It takes energy to compress air to 1/21 its original volume, and with your foot off the accelerator the engine doesn't get any fuel to provide that energy. PEH, I'm surprised you didn't explain this in more detail when you posted earlier.

All three of my diesels have plenty of engine braking, probably even more than similarly sized gasoline engines. And as I posted earlier the revs drop like a stone in the 1980 240D. Although probably not dangerous, crash9's car is not acting as it should. crash9 - is the hood pad falling down? It could be interfering with movement of the stop lever.

Rick Miley · #11 11-21-2003, 03:14 PM

On shifting into reverse - there is no syncromesh on the reverse gear in this transmission. If it's already sitting still in neutral, press the clutch and shift into any forward gear. They all have syncros, so any will do to stop the transmission input shaft from spinning. Then shift into reverse. Nothing is spinning, so no grinding.

Habanero · #12 11-21-2003, 03:47 PM

One of the selling points of the Allison automatic transmission in my 03 Chevy/Duramax is that it provides "grade braking", which means it shifts down as you are coming to a stop to save your brakes. When it shifts down, you definitely notice the engine braking of a diesel.

crash9 · #13 11-21-2003, 03:55 PM

Rick – your starting to get me worried – Ah so the tranny – I frequently start the car in neutral –
Compression, on even a bad Diesel, is so high that it would stop dead quick without a properly heavy flywheel – I don’t know, but there may be variations from year to year – I’m manufactured in 78 – sold as Feb 79. As soon as the market closes I’m gonna go ring her out real good.

william rogers · #14 11-21-2003, 04:44 PM

A diesel engine is very different from a gas engine as far as breaking power no matter the weight of the flywheel. Try typing "how a diesel engine works" into google it's nice to know how they differ.........

william Rogers..........

240Demon · #15 11-21-2003, 05:34 PM

Ok guys...I have a manual transmission 240D and what you feel as engine braking in a 240D is really the drop to idle speed and the incredibly heavy flywheel that 240's have. They are huge, trust me...So...low idle speed (characteristic Diesel thing) + heavy flywheel= lots of resistance=slows the car down