Sluggish off the line
 

Hello all,

My 300SD is pretty slow off the line. It takes 5 - 6 seconds to get the car up to 20 mph, but once the RPMs get to 2300 the turbo spools and the car runs good. It shifts 3 times when this occurs and my transmission is a 722.303.

I keep reading about injection pump timing, camshaft offset keys, and throttle linkage adjustment. Is there a certain order to perform these checks?

Maintenance I just performed:
Diesel purge and filter change (expect tank strainer)
valve adjustment
oil change + filter
transmission filter and fluid
Air filter
Banjo bolt and line cleaned

None of this has made much difference in the off idle performance of the car.

Is this off the line performance typical of these 300SDs?

Any help is greatly appreciated.

Thanks,

Keith

None of the items noted will affect offline performance.

And, no, offline performance of the 300SD is excellent when it is setup properly. It has a very low first gear and it scoots.

So, for your issue, you have two things that need to be done:

1) IP timing. If late (likely), the performance suffers across the entire spectrum. You believe the performance is adequate once the turbo spools..........but, your belief is incorrect.

2) ALDA adjustment. As they age, the IP's gradually put out less fuel. Off boost, the ALDA limit will tend to reduce performance below what is required to limit smoke.

The ALDA can be adjusted............carefully so you don't snap the adjustment screw and destroy the unit...........

The screw is turned counterclockwise to increase fuel. See if you can get one complete turn and drive the vehicle again. DON'T BREAK THE SCREW.

You also have the option of removing the ALDA completely. However, smoke control is now governed by your right foot............and...........you have no overboost protection.

I'm going to go out on a limb, and ask if your bowden cable is connected...
the shifting 3 times makes me think not.
it sounds like the car just goes right into 2nd gear, then rapidly jumps to 4th as you get moving.

From a stop, the three shifts should properly be 2-1-2-3.

You need to let that go..............;)

Although it's perfectly accurate, you'll just derail the thread.

If the cable was disconnected............he'd get two shifts.............2-3 and 3-4. That's it.

hmm. my SD starts in 1st, then bangs into 2nd, then pulls into 3rd, then drops into 4th around 60...
from his description it sounds like he's starting moving slowly, then the transmission is quickly shifting through the gears before he really has power built up from the turbo...

We've had this discussion before.

The SD starts in second. Period.

When you press on the pedal, the first 1/4" of travel moves the Bowden cable but does not open the rack. The transmission very quietly does a 2-1 shift. It's almost imperceptible.

You can prove it to yourself, however. Get the vehicle coasting at about four MPH with your foot off the pedal. Lightly press the pedal about 1/4"...........not enough to open the rack. The engine will climb in revs ever so slightly and the vehicle will SLOW DOWN. It has done a 2-1 shift. The first time you try it, it's rather disconcerting.

Sorry guys, I will clarify the shifting.

I meant that it shifts 3 times as it accelerates up to 65 mph. So WOT from a stop 1-2 (20mph) 2-3 (~40mph) 3-4 (~55-60mph). I cannot exactly remember the mph at each shift, but they are not stacked on top of each other.

Should I feel that drop from 2-1 off the line? I am assuming that it is doing it without noticing it since I am counting 3 shifts total.

The cable is connected and it looks like it was unscrewed counter clockwise quite a bit. There are a lot of threads between the bracket and plastic adjustment nut. It doesn't look like there is much more adjustment to tighten the nut up, but since it seems to shift pretty good and revs out when WOT it moves pretty good.

BTW - what do these cars rev to? I have had mine shift at 4700 rpm before at WOT?

After the valve adjustment I believe I noticed better mid-range power.

I just checked the throttle linkage to ensure it was moving all the way to the stop on the IP, but it misses it by about 1/8" or so. If someone depresses the pedal, it is close to the stop, and I can move it a bit further with my hand?

Should I check the cam timing before the IP timing? I am just trying to prevent adjust and then re-adjustment, but maybe it doesn't matter? Also are any special tools needed for IP timing adjustment? I read somewhere to remove the #1 line and while rotating the engine at the point where it starts to fill the delivery valve mark the damper and that is your timing, sound correct?

Thanks for any help. I didn't think that MD would make a car this slow off the line. You definitely have to be sure you have enough time when turning left!

ah, sorry. I've not had this discussion before that I can remember. next time I'm in my SD, I'll have to play with it a little, and feel the shifts.

any car out of tune will be very slow off the line. MB did not make it that way for sure! My SD pulls VERY hard from the line all the way to the end of 4th gear. (waaaay faster than I want to drive)

with BC and TF of the case, I'm sure we'll have your car acting normally again.

could this explain why my 82 SD holds a hill but my 83 does not??? the transmission was rebuilt in my 82, and lots of pistons and parts were replaced, perhaps it sits in 1st at the light? it's also the fastest to 60 diesel I've got, less than 10 seconds... any possibility that's the issue? I can't drive the car for another month or so to see if it's doing the 2nd-1st-2nd... thing

If you are referring to "holding a hill" at idle, you might be correct.

It should not sit in 1st at a light. It sits in 2nd until you just barely press on the pedal...........then it goes 2-1.

I have found that the SD can hold just about any hill in second...........idling at about 750 rpm. I cannot recall any hill whereby it rolled backward............then again, we don't have any serious hills here.

You also might have the Bowden cable too tight on the '82. If so, the trans thinks that you've already pressed the pedal slightly and will give you first gear. Check under the hood and look at the linkage. Push the linkage ever so slightly. The Bowden cable will move but the linkage to the IP will not. It's very interesting.

None of this has any effect on the 0-60 time.

Fascinating thread. I have had my 81 300SD for thirty years and never heard about the 2-1 shifting. I continue to be amazed by the old time MB engineers.

That said - could his problem be the switchover valve?

Also - he might try comparing performance with the AC compressor turned on and then turned off. Not sure if this will tell you anything but I have considerably more oomph off the line when running the AC system in Econ.

Brian - you are a wealth of info.

You bet. Cleaning the banjo bolt at the intake manifold won't help if the switchover valve isn't open. Or if there is a leak in the associated plumbing.Brian got a free scholarship on the 2-1 shift issue. He was a stubborn student, but when the light bulb finally came on, it burned brightly.