Neither. the pedal travel from what I can tell is the same. It's the pivot point in relation to where the pressure (foot) is and the increased psi created. I have some charts of the increased psi created since I initially thought the whole pedal ratio was a bunch of mumbo jumbo. However, it's the leverage created. I hope that makes sense. I will get some pictures shortly. No hole in the floor either. The new pedal arm really only addresses the bends in the brake pedal arm and the relationship of the pushrod and the "U" at the end of the pushrod where it mounts to the pedal arm. One needs a flat area whereas the bends creates a non-flat surface which means the "U" part cannot mount to the pedal arm. Tom is right about changing the diameter of the MC. That's an old hotrodder trick. I think I can go with the OEM master cylinder because the MB design is really interesting. When you take apart the vacuum booster, you realize there's actually 2 pushrods, one on each side of the membrane.

Now, with a manual setup, and the plate, the pushrod actually mounts directly to the MC. The end fits inside a tube about 1" so there's no fear of the pushrod coming lose or disengaged from the MC.

Here are some pics. Not the best, but I think you get the idea. I took my mock up apart when I did a trial run with the OEM ratio plate. The pedal assembly came from Mr. Luna and the firewall was chopped out by another forum member. Even though it took a while to get to this point, there is very little "mod-ing". Overall, a pretty simple project so far.

The thick plate is the 6:1 ratio. I am thinking that the OEM 4+:1 ratio plate could stand another 1/16" so the final product with be that much thicker (slightly less than 1/2). Same exact stud configeration: 4 thru to the pedal assembly and 2 for the MC. The green tape is where the 6:1 ratio would be needed for the pushrod, but you can see there's a few problems with that. As for the last few pictures, it shows the curve or "indent" into the pedal arm. That indent prohibits the push rod from working, so that is why I am getting a new one made out of series 7000 aluminum. Thank goodness for scrapyards because that crap is expensive. All parts are original MB W123 (except the 2 plates and anticipatory pedal arm). Because I am going with the big brake upgrade, SS lines (actually jacketed), I think the OEM plate will be pretty close to what most folks experience now with their current brake set up. With the 5:1, I do believe it will surprass OEM performance. I know my manual steering far exceeds the power steering once I am going at least 15 MPH.

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Last 2 snappies.

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Thanks for those pictures. This is just what I want to do!

I just looked at some w123 and w115 pedal setups in my parts collection. The w115 pedal is straight where the push rod attaches so changing the ratio will be easier.

However, one problem I noticed was the brake pedal stop is integral to the booster. Without a booster attached the return spring pulls the brake pedal back until it fully collapses the brake switch. It moves significantly higher than the clutch pedal. With the booster attached the brake pedal only moves back as much as the clutch pedal.

Since the manual brake pushrod isn't attached to the master cylinder it won't act as a travel limiter. Either the pushrod needs to work with an integral stop in the master cylinder adapter or another type of pedal stop will need to be made.

I took a few pictures of what I mean. It affects the w115 more than the w123.

BTW: The w201 booster I mentioned previously doesn't fit the w115/w123. The pushrod length is the same but the bolt pattern is smaller. Now I really want to try manual brakes.

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__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Hey,

Can you do me a favor ? Can you remove the "C" clip from both pedal assemblies and see if the W115 fits onto the W123? If that is the case, then you just saved me some decent money. The plates are pretty cheap, even the super thick one since I try to always get my aluminum and other metal thru scrap yards. Even aviation aluminum can be found at the scrap yards. BUT the pedal arm is a bundle to make. If it's really just a straight piece of metal, then changing to 5:1 should be EZ Peezy. Also, are the pedals the same length? I think that pedal stop issue would be pretty EZ also to fix by welding a stop or even a piece of angle iron.

Here ya go!

The W115 pedal fits on the W123 bracket. The pivots are the same. But there are significant differences. The W123 pedal is a complex shape and the W115 is straight. The biggest problem is length since the W115 pedal is shorter. I took several pictures and in each I tried to keep the pedal heights or pivot heights the same.

The picture through the booster opening is deceiving. The W115 pedal is offset to the top of the image as would be expected.

If you use the upper portion of the W115 pedal and weld it to the lower part of the W123 pedal you might get what you need.

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__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

One more picture.

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__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

If you change the ratio either by changing the length of the levers or if by changing diameter for hydraulic action the stroke will also change, however it will not be noticeable since once you hit that pressure point it will feel solid.

My old 1965 REO truck was semi tired big but had hydraulic brakes....not sure if it had a booster or not.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The "ratio" is changed at the pivot point, or at least that is what I am talking about. By increasing the ratio from 4:1 to 5:1, you pick up a significant amount of force so that instead of exerting 100 pounds to push the pedal, you're only using 50-ish. Further, the pushrod travel is under 4" which is ideal.

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YES, we are on the same sheet of music. That is the problem with the W123 pedal arm design at least at the pivot point. It does not permit the pushrod being re-located.

I am OK with a shorter pedal at this point, although it does negate the change in pedal ratio. Welding in a 1" or 2" section should be easy. As for the relationship of the pushrod as it exits the firewall, it really doesnt matter if it no longer "matches" the OEM design because the plate can accomodate for any shifting of the MC because the holes can be drilled and taped where you need them. Take a look at the thick plate, and you'll see how the plate had to be made to accomodate the "relocation" of the MC. The problem is I cannot figure out how to get a 6:1 ratio and not grind the housing apart. That is why I abandoned that.

It looks as if the pedals could be spliced. I am looking at picture 4. If I cut the top portion which is flat and then weld the bottom portion of the W123 pedal, that might work.

One other measurement please:

If you attach the W115 brake pedal arm to the W123 assembly, and measuring from the inside of the actual "pedal" part (where the rubber pad or covering goes) of the brake and clutch, what do you get? Right now, there's 2 1/8" between the 2 (that's inside). The pictures look as if it's less than that. I am guessing if the pedal arms could be spliced and the lower portion bent so that there would be the OEM distance of 2 1/8", that would sold the issue. The pushrod exiting at the point of the firewall will not be more than 4" no matter what ... actually, it's around 3" with the 5:1 ratio.

There's a bunch of calculators on the net for manual brake conversions and it looks as if this could be an ideal scenario with that pedal arm. I need to get one now and stop the presses on the aluminum custom deal.

I see what you mean about the plate. You could easily offset the master cylinder to the passenger side and use the upper portion of the W115 pedal as is. The W115 pedal will miss the brake switch but a small tab would take care of that.

I do think you'll need to splice the lower portion of the W123 pedal on since the W115 will end up high and too close to the clutch pedal. If you look at the image "Arms Compared2" it seems to me you could cut the W123 pedal below the indented area where the master cylinder attaches and splice it directly to the upper portion of the W115 part. You should end up with near perfect geometry for your car and a straight section to relocate the pushrod.

I still think the issue of providing a stop needs to be addressed or the pedal will sit too high and the brake switch will take all the punishment. It isn't a huge problem but it will be a factor in determining the thickness of the plate.

__________________
1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K

Once I track down a W115 I can figure out the best place to splice the two -- I think you're 100% correct. As for the stop, are you talking about the pushrod? The push rod travel is limited to around 3+". It's definintely not 4". The MC has a "tube" in which the push rod end enters. Around 1/2" of the pushrod permantently rests in this tube. On the W123, if you fully depress the brake pedal arm, it will eventually hit the assembly housing. However, the rod does not go more than 4". Is that what you mean by a stop?

The plate thickness is driven by the ratio. The 4:1 is around 3/8" whereas the 6:1 is around 2+". The "angle" created by moving the pushrod up the pedal arm creates a down range effect of requiring a thicker plate. So, the 5:1 plate will probably be around 1"+. The MC will be shifted towards the rightside of the car and moved upwards. The pushrod lenght remains the same. I think you solved the issue relative to the pedal arm. It's either splicing one or having a customer one made.