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W123 Benz recurring problem

DrEntropy

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In the diesel cars before 1986 the accelerator pedal is connected to a pivot point on the firewall, secured with a "bobbin" in a bracket. The material of the bobbin is some sort of plastic and the part is now Unobtanium or NOS if available, and sold at outrageous prices. Yesterday for the second time the bobbin in Diesela disintegrated and the car would only slowly get to 30MPH. After the first one failed in about '98 I substituted one of Mitsy's wood beads for the part 'till the replacement was bought, available then for around $20. Yesterday I MacGyver'd another two wood beads to serve until we can make a better part from nylon or some other long lasting material. At least for now the car accelerates as well as it's supposed to.

What was left of the second OEM replacement part.
SS5_1366sc.JPG


The wood beads in place as replacement:
SS5_1364sc.JPG
 
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DrEntropy

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That's th' thing. Outrageously overpriced for a part that turns into crumbs in a few years. The one I put in when the first wood bead got worn down only lasted a decade... the bead went just as long. I'm good until I can't procrastinate any more. 😏

EDIT: And that one advertised is a USED one, "out of stock"!
 

NutmegCT

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JPSmit

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If it just the bushing perhaps someone even on this forum could turn you a couple out of nylon or some such thing
 
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DrEntropy

DrEntropy

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These (also used) are a tad more affordable:


Wrong part, Tom. This is what it looks like:
Firewall bushing

If it just the bushing perhaps someone even on this forum could turn you a couple out of nylon or some such thing
I've got "friends in th' business" and there are a few YouTube videos with various "fixes" as well. For the immediate future the bead solution will serve. I have the old bracket ~someplace~ and will find that to make a more permanent piece.

There's no way I will replace it with OEM again.
 

JHaydon

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I wonder if you could punch the ball out of a spherical bearing or rod end joint and make that work, perhaps with an oilite insert to let the linkage rotate. Depending on the size the price could be anywhere from expensive ($20) to you-gotta-be-kidding-me ($100), but the ball would be hard chrome plated alloy steel, so it would be a permanent fix!

BTW, those prices would be for a racing-quality bearing from my place of employment. You should be able to find cheaper ones from other sources.

OR... modify a bracket (or make a new one) to hold a complete spherical bearing including the race? Then the ball could rotate inside the bearing. Use a PTFE-lined bearing for lifetime lubrication.
 
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DrEntropy

DrEntropy

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I wonder if you could punch the ball out of a spherical bearing or rod end joint and make that work, perhaps with an oilite insert to let the linkage rotate. Depending on the size the price could be anywhere from expensive ($20) to you-gotta-be-kidding-me ($100), but the ball would be hard chrome plated alloy steel, so it would be a permanent fix!

BTW, those prices would be for a racing-quality bearing from my place of employment. You should be able to find cheaper ones from other sources.

OR... modify a bracket (or make a new one) to hold a complete spherical bearing including the race? Then the ball could rotate inside the bearing. Use a PTFE-lined bearing for lifetime lubrication.
Love the oilite and PTFE ideas! But with this dingus-thingus, outlasting the wood beads or a nylon replacement would be over-engineering the solution... but maybe there's a market for a reasonable solution? These cars are slowly becoming dinosaurs, so it'd be unlikely other than a satisfying exercise in engineering.

Or OVER-engineering. A shame (and embarrassing) Benz didn't step up and issue some better upgraded replacement. The vehicles themselves were likely never intended to live as long as they have.
 

JHaydon

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I'd be surprised if Kent (MercedesSource) wouldn't be interested if you came up with something better.

As someone once remarked about a Packard at a car show, "they made them to last a million miles, they just didn't know it yet." I think M-B was aiming for a million but either underestimated their abilities or overestimated the lasting power of nylon.
 
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DrEntropy

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Thinking I could whack the threaded rod from a Heim joint of large enuff O.D. and epoxy the outer housing into the retainer. When I find the old bracket I may give that a try.
 

LarryK

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My old Jags have multi-ball bearings in the pivot of the throttle. Looks like two washers concaved with the bearings inside then sealed enough to hold (bb size balls) but still can be oiled. Car is 65 yrs old and joint still works.
 
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DrEntropy

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My old Jags have multi-ball bearings in the pivot of the throttle. Looks like two washers concaved with the bearings inside then sealed enough to hold (bb size balls) but still can be oiled. Car is 65 yrs old and joint still works.
The Jag linkage is what gave me the Heim joint idea.
 
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Maybe get a chunk of Delrin and turn it in a lathe? Or possibly 3D print something - I understand some of the 3D printer materials are rather robust?
 
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DrEntropy

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teh really good 3D printers can print titanium :cool: (seriously though, F1 teams R 3D printing titanium parts these days! )
Only problem there is it would cost enough to buy a few hundred more of the same W123 car.
 

Gliderman8

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Can you cast one from epoxy or sand-cast one in aluminum?
 
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DrEntropy

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Others have used JB Weld and potted the steel bushings from the deteriorated one into the bracket, it may be easy enough to do that. For now, the wood bead solution will work in the near-term.
 

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