Any way of setting first gear run-out?
 

1983 300SD....Engine pulls well in all gears but first gear duration is not long enough. First gear changes out at about 3,000 rpm or so. Second and third shifts occur higher in the rpm band (4,000 & 4,700). But first shifting out so soon gets you back to not much power rpm. Zero to 60 would be quicker if I could get it to hang on to first gear longer. Any ideas?

Regards,

Run-Em

You can try adjusting your bowden cable.

Danny

I've noticed the SD also shifts somewhat early out of first. Probably about 3500 or so.

However, if the 2-3 and 3-4 are close to spec, adjusting the cable probably won't get you much.

If it really bothers you, then manually shift to second. You can hold first as long as you like.

If you find yourself needing these rpm's on a regular basis..........either the vehicle is not in good operating condition..........or you're the type of fellow that needs a 250 hp gasser and not an old diesel.

This SD stays with the traffic by allowing the 1-2 at 2200, the 2-3 at 2200 and the 3-4 at 2800 rpm. If I exceed these numbers, I'll be the leader of the pack unless a gasser decides to race.

Ok, you'll have to do a search on transmission vacuum adjustments for the actual tutorial, since I don't have time. But in a nutshell: The more vacuum the transmission receives, the earlier and softer the shifts are.. So, less vacuum means later and harder shifts. The bowden cable adjusts the shift points relative to pedal position. So if you shorten it, you will have to let further up on the pedal before it shifts, lengthen it and it will shift while you still deep in the pedal.

Vacuum affects only the characteristic of the shift not the rpm at which the shift occurs.

We're speaking of the 1981-1985 617's.

I'll beg to differ with you Brian. I'll have to dig out my FSM, but at least on 122.xx transmissions, less vacuum from the IP mounted regulator results in later harder shifts, more vacuum results in earlier softer shifts. This is why the IP mounted transmission vacuum regulator is tied into the throttle linkage. If you are deep into the power, you don't want an early gentle shift, but a higher rpm harder shift, so the deeper into it you are, the more vacuum is bled off from the regulator. All you have to do is disconnect the vacuum from that regulator to find out exactly what the effect is, (the rpm will go very high before a tire-chirping shift into second). The Bowden cable reflects shifting in relation to the pedal position, not rpm directly. Believe me, I've done some exhaustive transmission adjustments on a few of these. They are very tuneable, but only when one understands the relationships the different adjustments have. Now the vacuum modulator down on the transmission, that's a different story.

On every one of these, I've operated them without any vaccum to the modulator at various times during testing. In no case did the shift points change relative to engine speed. The speed of the shift and the harshness of the shift is dramatically affected by the application of or elimination of vaccum to the modulator.

My suspicion is that you are conveying information based upon testing of an older vehicle........maybe your '79.........that does not have a Bowden cable. The vacuum system was utilized for throttle pressure modulation on those vehicles and the results on them would be as you indicated.

Be careful in extrapolating that data and applying it to the later vehicles with independent throttle pressure modulation via the Bowden cable.

Brian is correct, the vacuum only dictates the harshness of the shift, not the rpm/shiftpoints. I have also driven with the vac line disconnected, it shifted at the same rpms, but harder than the hammer of Thor! :eek: :D

"Harder than Thor's hammer".. :D That's actually a good description. Well, none of my observation is from the '79, since it has no vacuum modulator on the transmission. All my transmission time has been spent on the 722.xxx series alongside a MB master technician. So anyway... Here's a link to a well written procedure for your transmission adjustment. I stand by my original assertments as to the effects of vacuum, based on my experience.

http://articles.mbz.org/transmission/adjust/

i think all of the SD do it, mine does.
If it comes down to it and your really in a bind to step on it, just mash the pedal and make sure your on the kickdown switc in order to keep high rpm shifts
or, u could add propane and a dumptruck turbo....;)

while on the subject of rpm shift points in low gears
I note my 83 300sd has no RED LINE on the tack
and I donot think it just fell off
so what is the max safe rpm?
and at what point does the HP and or tork drop off
so you may as well shift anyway?

The peak torque is at 2800 rpm and the peak HP is at 4400 rpm.