Throttle Linkage Dilemma

[jzearfoss]

In the throes of reinstalling engine and throttle linkage on my 1968 280SL (LHD, automatic).

My problem is with the pivot arm mounted on the right-hand side of the block below the intake and exhaust manifolds. The Push Rod (part # 113 300 00 15) from the throttle Control Shaft (part # 113 300 05 20) extends beyond the ball on the upper arm of the pivot.

The socket on the end of the Push Rod does have some adjustability but not enough to connect to the ball on the upper arm of the pivot.  I do not have photo of this connection from when I pulled the engine so I do not know what the connection is supposed to look like.

I have searched through the BBB and the Linkage Tour here on the Pagoda site and have come up empty for any image or diagram for this connection or an answer as to why the Push Rod and pivot arm geometry is off.  I know the mounting plate (part # 127 072 1401) is mounted correctly. My best guess is that there is another linkage piece from the Push Rod back to the pivot arm.  It would have to be a ball on one end and a socket on the other. I can not imagine that I would have lost a part like this but, well you know, sometimes we just screw up.

Would appreciate any help on solving this problem

[mrfatboy]

Here is a pic of my connection.

[Pawel66]

That is the only picture I could find... it is RHD...
The elbow of that lever attached to the cross-shaft seems to be going further backwards, almost under the cross-member. I am not sure if this is helping.

[jzearfoss]

Thanks mrfatboy and Pawel66.  I sure do appreciate the photos.  The one from mrfatboy is exactly like my before picture when I took the motor out. The shaft that the pivot arm rides on is almost directly above the upper right-hand bolt for the engine mount.  So I am sure I have that installed correctly.  It appears then that the Push Rod is to long.  This is the only one I have from disassembly of the car so it has to be what was originally on there.

Does anyone have any specs on what the length of the Push Rod is?

The Throttle Control shaft (also referred to as the accelerator shaft)and the elbow to which the Push Rod connects is a single welded component so there is no adjustability there.

Any other theories or suggestion on what may be my problem will be happily accepted.

[MikeSimon]

I have the cylinder head and manifolds off and should be able to show a picture of the connection. I will take one tomorrow.

[mrfatboy]

The horizontal rod on my car measures approx. 350mm from center to center.  My wife had to help😁 

[DaveB]

Mine seems longer - estimated 380mm center to center. The rear looped end is directly below injector 6 and the front socket end sits approximately where yours (jzearfoss) is now, i.e. near the 4 o'clock bolt on the cover plate. But my rod bracket is attached to the 4 and 6 o'clock bolts on the cover plate whereas your is attached between 6 and 8 o'clock, so the arrangement on my LHD 230SL 4-speed is probably irrelevant for your LHD 280 auto. I guess your cover plate and bracket should look like mrfatboy's, which they do. Also not sure this is helping

[mrfatboy]

In found another picture for you. Maybe it will help.

[mercakungen]

Does these help? The length was 345 mm in my car.

[DaveB]

Is it possible this is not your original rod? Could it have been swapped at the platers? Unlikely I know.

[jzearfoss]

Thanks everyone for the photos and measured lengths of the Push Rod.  I will be doing some disassembly today and check lengths again.

To DaveB.  I did not farm out any plating so this is the original Push Rod that came off my engine. Also DaveB I checked my photo for the mounting plate orientation and if you look you can see that the part # cast into the plate is horizontal, so I am confident that the mounting plate is bolted on correctly.  Good observation though.

I have one thing I need to check.  After looking again at the Linkage Tour I see on p.9 there is a diagram titled Pedal Linkage and in the diagram I see that Item 1 (Pedal lever) has the tang where the gas pedal contacts the pedal lever is facing to the left.  Mine is facing to the right.  If my suspicions are right this may be my fix. It appears that it is possible to install the pedal lever 180 degrees off.   Will confess my sin if this proves to be my salvation.

[MikeSimon]

It looks like you have your answer already, but here are some pictures and measurements from my 1971 280SL, as promised.
Length of rod from rear pivot center to center of ball joint is almost exactly 320mm.
And of course, my engine compartment and the hardware therein doesn't look near as nice as some of these others...

[Mike Hughes]

I am examining the various throttle linkage photos and comparing them to the photo you posted with your original query and am concerned that the problem may not lie with your push rod, but rather with the throttle bar on the firewall to which it is attached.  The end that engages the "loop" in your pushrod seems to be quite a bit farther forward along the side of the block in your photo than in any of the photos posted by others.  Is it just possible that the other end of the throttle bar may be hung up on something behind the foot pedal, such that it is positioned in a "foot to the floor, wide open" condition?

[jzearfoss]

To MikeHuges - I think you have it right.  The regulating shaft is not rotating far enough back towards the fire wall.

I must have not had enough caffeine in my coffee this morning.  The pedal lever is in correctly but I can see that the elliptical hole on the inside of the fire wall under the dash (where the pedal lever enters from the engine compartment) is restricting the travel of the pedal lever and therefore restricting the degree of rotation I can get on the regulating shaft.  I have about 30 mm of travel I can gain before the "loop" (as Mike calls it) hits the firewall.

I am going to get my dremel out and trim the top of that elliptical hole to see if I can get the pedal lever more travel and therefore increase the rotation of the regulating shaft.

[waltklatt]

Why dremel it out? 
It was all in good position before taking the motor out. Right?
Maybe the pas pedal rod itself is in wrong position.
Did you check the two aluminum clips that hold the pedal rod to the firewall? 
Rod should be below the aluminum clips(i.e. the two 8mm bolts should be on top side.
Just imagining, as there is no picture of this.
Walter

[Pawel66]

Actually, as Walter says, feels like you might have fitted, at least the aluminum clip on the driver's side, upside down perhaps...

Bear in mind you also have a grommet there - you need quite a lot of clearance between the gas pedal lever and the edge of the hole in the firewall.

Or: you fitted the gas pedal lever on the shaft at a wrong angle. I do not remember exactly how it looks there now, but perhaps you fitted the gas pedal lever "pointing too high" towards the firewall. The gas pedal lever slides onto the shaft and it is secured by a screw to the lever where return spring is attached. Maybe you had too much play/slack in the screw hole in that spring lever?

Note the upper length of the lever on the passenger side is pretty much "upright" or parallel to cross member at gas pedal idle position.

As per Walter's advise, I would put dremel aside.

[jzearfoss]

Thanks Waltklatt -  You are right, all was in good position and working before removing the engine.  That is why I am so perplexed as to why things are not fitting as I expected.

The two aluminum fittings that hold the regulating shaft are in the correct position. On the passenger side the two phillips head bolts are on the top side of the regulating shaft and on the drivers side the two phillips head bolts are under side of the regulating shaft.  They have to go on this way as it is the only geometry that permits the regulating shaft to pass behind the valve cover.



To all who are responding to my query on this problem I do appreciate any and all ideas and suggestions as to how to get things back to square one.  May I ask one consideration. 

When I describe the parts in this particular situation I am using the terminology in the diagram on p. 9 of the Linkage Tour titled Pedal Linkage.  That diagram comes directly from the BBB at 30-1/1.  I know that it is not uncommon for the same component to be referenced by different names. 

In fact in the diagram on page 48 of the MB Publication 10202 (Mercedes-Benz TYPE 250 SL - 280 SL / Chassis and Body Spare Parts List Edition C/ as per Jan. 1972 / which supersedes Edition B of Jan. 1968), every component has a different reference number than what you see in the diagram in the Linkage Tour p.9, and they appear to be the same diagram but if you look close will see minor differences and different terminology for the same component.

I am pretty sure most everybody knows that MB was constantly making changes to components not only between production years but even during production runs. ( SEE Pagoda Notes Vol.9 No.4 thru Vol. 10 No.4).  So there are ample opportunities for confusion to arise.


Please bear with me as I trudge along on this problem.  I am sure a solution will emerge and all will be right in Pagoda World.

Thanks again.

[Pawel66]

What I was trying to say in my post was that (referring to Technical Manual) you might have got wrong the adjustment on bolt no. 51. Perhaps if you have too much slack there in the hole in the spring lever and the bolt ends up in maximum down position in the spring lever hole, the gas pedal lever may be high enough at the firewall to collide with the edge of the hole in the firewall.

Theory easy to eliminate.

By the way: I have not seen before this "additional" lever with the screw in it... but perhaps I have not seen a lot.

[MikeSimon]

I am examining the various throttle linkage photos and comparing them to the photo you posted with your original query and am concerned that the problem may not lie with your push rod, but rather with the throttle bar on the firewall to which it is attached.  The end that engages the "loop" in your pushrod seems to be quite a bit farther forward along the side of the block in your photo than in any of the photos posted by others. 

That is definitely the reason for the problem. What the cause is, I do not know.

[jzearfoss]

To Pawel66 - I have adjusted bolt #51 (as per Fig. 30-1/1) to both extents of the slotted opening in the tang where the bolt goes through and then threads into the pedal lever.  It does not give me enough additional rotation of the Regulating shaft to make up the distance I need to get the Push rod connected to the pivot.

Looking at MikeSimon's  comment I have to agree with him in that the push rod is not back as far as it should be against the firewall.  That is the reason for the problem, but I am still searching for the cause.

Attached are a couple of new photos of the Regulating shaft: one is of the driver's side and shows everything installed.

Pawel66 - the tang with the screw that you mention is what actuates a micro-switch, which is wired to the fuel shut-off solenoid on the fuel injection Pump (FIP).  My 280 has an automatic transmission and on U.S. imports the FIP has both a starting solenoid (the upper one) and a fuel shut-off solenoid ( the lower one) on the rear of the FIP. There is a good diagram of this configuration in the Haynes Manual (Ch.3) on p.77(Fig. 3.76).  There is also a diagram of the wiring for the micro-switch (Fig. 3.77).

Hey Pawel66 - where is the diagram you posted (control.JPG) from.  The component numbers do not match either the Linkage Tour diagram or the Publication 10202 diagram.  Just wondering?

To all - just as a point of interest.  If you look at the diagram I posted from Publication 10202 you will see in the lower right-hand corner a representation of the Regulating shaft for a right-hand drive vehicle.

[Pawel66]

Tank you - understand what the additional lever is for - I indeed have not seen enough, let's not side track your thread.
Picture - SLS, I just had it at hand. Again, let's not pollute your thread and stick to your picture of the assembly.

I just went to the garrage - my assembly looks like yours.

If you say the issue is that the gas pedal lever gets stuck against the upper edge of the hole in the firewall it goes through - I am afraid I am short of ideas... sorry.

Other than - losen all the screws of the entire assembly, then try to fit it again, then tighten carefully watching for how elements rest in place. Mybe shims under the driver's side aluminium holder will give you some space? I also see paint scratches on top of the lever on passenger's side - maybe somthing is going on there.

Also - sorry for my ignorance - I do not remember the role of part no. 14 on your diagram, the cage nut, (do not remember now how it was on my car when I dissassembled the shaft). Did you look into that?

sorry..

[mbzse]

.../...By the way: I have not seen before this "additional" lever with the screw in it.../...

It is only to be found on US 280 SL:s. Has to do with emission control system (additional relays for shutoff, just as jzearfoss writes)

[Mike Hughes]

Is it possible that the silver bracket on the firewall that holds the electric switch is installed upside down?  If that switch were sitting lower down the shaft could rotate a little more before the screw meets the switch.

[mrfatboy]

Here are some more reference pictures that might help.

[66andBlue]

The switch bracket on my 280SL appears to be a bit different from mrfatboy's the way it is attached to the firewall. If I remember correctly it was right-left adjustable but not up-down. Perhaps Joe A. remembers?
After the engine overhaul he did not reinstall the switch because it provides only a tiny fuel consumption improvement and can cause only problems.