Confused about the "Linkage Tour"...

[teahead]

I'm stuck on part 1 if you can believe it.

I video'd my confusion here:

https://www.youtube.com/watch?v=WBIvJQUm-oI&feature=youtu.be

[ja17]

The "slip joint" is the sliding segment of the linkage rod. Only later USA emission cars with automatics used this additional dash pot and sliding linkage rod to help regulate idle as engine vacuum changes. Engine vacuum variations occur for various reasons at idle (automatic gear selection, use of power steering, ignition timing changes and switching on A/C. The dashpot helped regulate the engine idle during these instances.  The dashpot should be removed, or moved out of the way to set the slip joint. When the engine is off and dashpot is removed, the slip joint should be fully collapsed (linkage rod short).The other linkage adjustments (IP rod length and venturi stop) should also be set with the dashpot off or moved out of the way, on these versions.  Once the dashpot is installed and adjusted correctly (with engine at idle), it will only move the venturi open since the slip joint does not allow the movement of the rest of the linkage.

[teahead]

Great, helps immensely.

So, proper order would be?

1) adjust venturi stop screw with slip joint rod and dash pot removed

2) put rod back on and adjust.  Fully collapsed meaning adjust the length so there is no slop?  Adjust while idling?

3) put dash pot on and adjust while idling in neutral, then pit in gear to see if it moves 1mm?

[ja17]

Sounds like you have a good plan.  Keep us up to date.

[teahead]

Sorry, I'm still confused (dense for sure).

The "Linkage Tour" states:


Disconnect the linkage rod going from the cross over rod to the venturi. If you have a USA version with the vacuum dash pot, you will need to move it out of the way so it does not interfere with the adjustment. The small slotted venturi set screw must be backed off enough to allow the venturi valve to close all the way and then adjusted in just enough to keep the venturi valve from binding in the intake.

USA 280SLs had an "Vacuum throttle control" on the intake venturi linkage. A special linkage with a "slip joint" was also used between the venturi and the cross-over rod on the engine. Adjust the slip joint linkage so it is fully compressed with the engine running and warm at idle in neutral. Adjust the vacuum control/linkage to
zero clearance. Now with the transmission in gear, the throttle lever will open 1.0 mm to 1.5 mm.



After I do (1) above, do I put BACK the dash pot before I adjust the slip joint to be fully compressed (step 2)?

Also, the dashpot...when is it in gear, does the adjusting screw push out or pull in?  I guess I can remove it, but keep the vacuum connected and see how it operates while running/putting it in/out gear.

[teahead]

Okay, from this screenshot, it looks like after I removed the dashpot to do the venturi stop adjustment, I put back everything to adjust the slip joint and dashpot screw:

[ja17]

I think you got it!

[teahead]

What I still don't understand is what do they mean by the slip joint being "fully compressed" at idle.

Should say, "adjust the nuts so that there is no play (as in the video) in the rod."

I did that and now the engine doesn't bog when I step on the gas.

[kampala]

“Compressed” is smaller than its opposite, “expanded”

If slip joint is compressed, the rod is shorter (smaller)
If slip joint is expanded, the rod is longer.

[teahead]

OK, fully compressed at idle.

Dash pot seems to move when put in gear.

Tach moves from ~950 rpm (yes, too high) to around 600 (seems to low).

I adjusted the IP rod to 233mm, but that made it run awful.

Maybe that length is not for USA 280SLs?

[ja17]

233 mm (IP linkage rod) is the base setting for the entire process. If you do not have it correct your other settings are not correct.

[Pawel66]

But the hole in the shaft base works as well, correct?

I assume it should yield the same 233mm, it is just easier with a proper piece of pipe as a tool...

[teahead]

But the hole in the shaft base works as well, correct?

Not sure what you mean.  You got a picture?

[Pawel66]

I think the hole works, a bit silly question from me...
You have it in the Linkage Tour material, position 5 on the drawing "Six Basic Steps...".
Sorry to interfere with your posts.

[ja17]

Not all years had the hole. See "Linkage Tour Post April 6, 2006" in regards to the 233mm  https://www.sl113.org/forums/uploaded/ja17/20061116193824_linkage%201.JPG  If the stop screw or lever location (cinch bolt) on the IP has been tampered with, then the factory setting on the IP lever is lost.

[teahead]

Ya, I don't have that bracket w/the 10mm hole.

1970 280SL USA version.

So the order should be then maybe:

1) set venturi stop screw so barely before binding (dashpot removed).

2) adjust IP rod to 233mm, hoping screw on IP lever has not been tampered with

3) adjust slip joint to zero slack (compressed)

4) put back dashpot and make sure it moves 1mm when put in gear (man, seems like that would barely do anything to change the idle).

5) adjust other rod (??)

6) adjust mixture on IP?

[teahead]

Well...

Did 1-4 again.

That dashpot... that thing seems to make the idle in gear rough.  What's the point of that thing?

I ended up cranking down the dashpot screw so it wouldn't touch the venturi cam whatsoever.  Idles in gear a lot better.

My constant idle solemoid isn't hooked up so guess I'll live with the 600rpm idle in gear.


Now to work on slight hesitation on takeoff and extreme late and harsh shifting.

[ja17]

When the dashpot opens the venture slightly the engine rpms should increase. The slip joint does not allow the IP linkage to move. The IP thumbscrew must be set just slightly rich at idle so the venture opening (additional air) increases idle. If the IP thumbscrew is neutral or too lean the additional air from the venture opening will cause a rough idle situation. This may also cause your hesitation. Try setting the thumbscrew 3 clicks richer.

[teahead]

When the dashpot opens the venture slightly the engine rpms should increase. The slip joint does not allow the IP linkage to move. The IP thumbscrew must be set just slightly rich at idle so the venture opening (additional air) increases idle. If the IP thumbscrew is neutral or too lean the additional air from the venture opening will cause a rough idle situation. This may also cause your hesitation. Try setting the thumbscrew 3 clicks richer.

So if the Dashpot moves the venturi, the slack in the slip joint is such so that the IP rod won't move?  I'll have to check on that.  I'll also check the IP mixture.

This is the thumbscrew, right?

[ja17]

Correct, the dashpot and slip joint work together. Moving the entire linkage system would require more force than the dashpot could produce. The slip joint allows the idle to increase easily without moving the rest of the  linkage.

[teahead]

OK, but in my case, moving the Venturi w/o moving the rods/IP rod results in horrible idle.  I'll tweak the mixture to see if that helps it.

[Benz Dr.]

I would set your idle mixture a bit on the rich side. This will blend with the extra air when the throttle plate opens.

[stickandrudderman]

In some cases I have set the Co with the car in gear. gives a lumpy idle in neutral but smooth one in gear and who spends much time in neutral?

[teahead]

What's interesting is that my idle speed in N, is about 1000RPM.

Wouldn't making it richer increase that or no?

I need to check my timing.

[ja17]

Warm  idle of 1000 in gear is too much. Crank down the intake air screw till it is around 700. Then in gear, the dashpot should maintain around 700.