shadejo

Clutch fork failure

121 posts in this topic

Well, its all back together and with the actuator cleaned and lubed with fresh white lithium, and the rod to shift fork lubed with a drop of moly grease it shifts more smoothly then it has any time since I have owned it. Need to get it in to Mercedes to have the clutch set up properly on the Star machine next week to complete things.For the curious, total effort was about 6 hours. Took the time to clean the EGR valve up (truth be told my son got that job !) while I had it off. I will say the job is not for the faint hearted, especially as you must cut most of the tie wraps on hoses and harnesses then move many of these to get at things, and finally reinstall them all later on. I had quite a pile of parts and loose cables at the height of the repair !John

Edited by shadejo

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Setting bite point on a Star machine only needs to be done once. All I do when servicing clutch actuator is just to set it right mechanically. Fitted position of clutch actuator is not really that critical. Too much preload results in clutch connecting late and could cause clutch to slip. Too little or no preload at all results in clutch connecting early.

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Mechanical adjustment is done using a spring balance.

Actuator is preloaded by applying 50 Newtons (not Nm as stated in above workshop instruction) on the spring balance. Preload is reduced to 11 Newtons and bolts tighened.

ClutchActuatorFittingInstructions.pdf

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In Canada they try to teach us french :D No deutsch for us!

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We need some kind of solution that doesn't involve a $1,000 shop bill!

I've discovered that my car has this problem too. Wondering if there is some kind of friction-reducing cup or cap that can be placed between the actuator and the fork socket?

Or how about epoxying a section of rod to the fork and then use a small bored universal joint coupling between there and a cut-short actuator rod to allow for angular movement? Posted Image Basically do away with the current metal-on-metal friction that kills the fork? This could theoretically be done without removing anything but the actuator.

Bil - thinking caps: ON! :scratch:

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Wondering if there is some kind of friction-reducing cup or cap that can be placed between the actuator and the fork socket?

My fix to thi problem:

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Clutch actuator rod and a piece of 1/2" marine bronze solid rod. Note that I've painted actuator rod in special black actuator rod enamel. Rust forming in centre reduced diameter area of rod allows water to penetrate into clutch actuatator housing. Paint protects steel so less chance of rust and water ingress.

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Modified clutch actuator rod. Contact area with fork socket has been increased by 61%. There is much less friction between steel and bronze so should reduce wear rate significantly. Additionally, I centre bored the rod and drilled a radial grease point. Grease can then be injected directly to the contact point using an Oregon chain saw bar grease gun or similar. Note that above modified rod needs painting before fitting.

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Clever idea, TK! My fork failure is imminent. A temporary "get you home" ad-hoc solution devised by FastEddy yesterday may last me 6 months or six days, or fail the next time I get in the car! You have PM.Bil :sun:

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[How did you know he's going to break soon?I would like to know mine? :P If it is not to hard to see...

Edited by smart142

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When Eddy attempted to perform a Star clutch drag-point teach-in, the actuator push-rod got a little bit stuck in the fork cup and would not retract properly. Visual inspection of the fork through the hole in the bell housing where the rod inserts revealed significant wear of the fork cup where the actuator rod presses. Is was clear from this that the fork cup's thickness has diminished such that prolonged wear will inevitably result in a hole appearing in the cup resulting in complete failure. In my case, this will happen unpredictably soon unless we devise a remediation of some kind.

You can inspect yours by removing the actuator and peering into the same hole with a strong light to see the condition of the clutch fork's cup. While you've got this apart, you can add a dab of heavy grease to the end of the actuator push-rod before reassembly to help reduce friction, rust and wear.

Bil :sun:

P.S. mostly city-driven cars in dusty or corrosive environments appear to be more at risk than others. Eddy estimates the thickness of this stamped metal part has been worn away and/or deformed by perhaps a little over 1mm.

Edited by bilgladstone

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The swivel joint as described won't work. Imagine pressing down on a pencil. If you don't allow your hand to move sideways the pencil takes the straight force, and quite a bit of it. Now put a swivel in the middle of the pencil...

One of these rigidly attached to the fork would work, but requires the engine and tranny to be separated.

If you can get an old fork somewhere for fitting purposes a larger ball or even a shell in suitable material to fit over the existing rod could be made, like Tolsen showed.

Boy, am I ever glad now that mine has been regularly lubed!

Edited by Alex

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Hmm.... wondering if a brass "acorn" or cap nut could be threaded onto the end of the rod! Cut the rod appropriately short, cut threads with a die, then screw on a suitable size of cap nut. In order to fit through the hole in the housing, the flat hex profiles can be filed away. What do you think?? I'm trying to think of a mod that is cheap, effective, and can be done fairly easily with simple tools.

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B :sun: Edited by bilgladstone

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Given that it is only a straight push rod, threads aren't needed. A snug fit and epoxy would work great. The difficult part is matching the shape of the fork indentation, wear would be greatly accelerated if it doesn't have a reasonable contact area to spread the load. You really need an old fork! Hello? Anyone listening?

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Not sure about needing to exactly match the fork indentation (socket or cup) radius. Note that TK's working solution appears to gave a larger diameter than the OEM rod end. I can probably get hold of an old, damaged fork (with a hole in the indentation) in a week or two. Maybe Tolsen can tell us more about the socket's radius? Oh, and what is diameter of the push-rod?Does this part get really hot? Would a nylon or teflon cap melt in the application? On maniacs, we're exploring something called Tufnyl. Ever heard of it? I'll have to stop in at Industrial Plastics and see what's available!B :sun:

Edited by bilgladstone

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....I'm sure glad Uncle Glenn and Matt decided I needed a new fork when I had my clutch replaced!Check with smart142; I'm sure he's got at least one old clutch fork laying around because it used to be in my car. :D

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Not sure about needing to exactly match the fork indentation (socket or cup) radius.

You don't have to be exactly right on the radius, but you do need to be reasonably close so just a little seating-in wear will spread the load out. I wouldn't worry about extreme heat, but if plastic a fairly high temperature rating would be required.

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I believe main reason for punch through is a rattle fit of clutch actuator rod, i.e. fitted without any preload.

Sachs has issued revised instructions for the adjustment. Basically same as the old instruction, see post 27 but now in English and less ambiguous.

http://www.zf.com/media/media/document/bra...or_11861_EN.pdf

SI_SX_Kupplungsaktuator_11861_EN.pdf

In case of a punched through fork, one can do a lasting repair by reshaping an M10 hex bolt into a new socket. The hex head need be reshaped such that it will fit into the existing socket. Shank of the M10 bolt will "lock" onto the hole of the fork. Obviously shank need be cut to right length when you are happy with its shape. One also has to drill and shape a socket into the head to accommodate actuator rod. A fairly easy job that can be done using an electric drill, drill bits, files, patience, Dremel or equivalent tool with grinding bits and some elbow grease, the latter often on special offer at your nearest Canadian Tire.

Diameter of actuator rod is 10 mm.

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Diameter of actuator rod is 10 mm.

Thanks for that, sir. Also, what is diameter of your modified (larger) brass end please?Bil :sun:

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[1/2" or 12.7 mm. Anything larger will touch hole through bell housing unless you make hole larger.

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So what would you do? Drill out the threads of the brass acorn nut an epoxy it to the end of the push rod?

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For the curious, the broken fork. 5 minutes to change - after the transmission is out that is.....!

Looking at this fork, it appears as though there is similar cup wear on the other end at a pivot point. No way to get at that without dropping the engine and taking apart the housing, What a failure this stamped part is!B :sun:

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This type of fork is not just limited to the 450 Smart but is very common on smaller engines.

The fixed pivot point has a larger socket and is better protected from the elements.

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Could you explain what temporary repair you have done to keep you mobile?

PS. Cheapest Sachs fork complete with release bearing is currently £ 32,43 inclusive of UK delivery. Wonder what inflated price you have to "fork out" in Canada?

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The socket in my car's clutch fork is not holed, and is only very slightly depressed beyond normal. Slightly, but enough that recent re-teach of the drag point revealed a tendency for the rod end to get "sticky" and not consistently retract properly every time.

For the temporary repair, we scoured Eddy's repair shop parts bins for - I don't know how to properly describe this - a kind of washer that is about 1mm thick around the outer edge and is minutely larger in diameter than the end of the push rod. Instead of having a circular hole in the middle, it has a kind of "tabbed" center of thinner, flexible metal (stainless, I think) that allows the flat washer to readily deform to the convex shape of the rod end.

With proper pre-load and STAR adjustment, and with dabs of heavy synthetic grease on both sides of this washer-thingy, it is working perfectly so far. It may last for months or years, or... not.

For the time being, I think I will leave well enough alone and not tempt fate by tinkering with something that is working just fine. Reading here of clever repairs that can be done even if the rod pushes right through the socket gives me encouragement that all will not be lost, even up to full failure.

A new fork is a fairly inexpensive part here as well. But shop labour rate to drop the engine and pull everything apart to replace that simple component is estimated to run as much as $1,000. Basically, any time the engine must be dropped out, the cost starts at $500 and then add whatever additional work and parts that need doing after that, plus 12% taxes on top or everything.

With this kind of cost incentive, a cheap D-I-Y repair is highly sought-after.

Bil :sun:

Edited by bilgladstone

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Then try an M8 brass dome nut that is 13 or 14 mm between the flats. Bore nut out with a 10 mm drill bit. Use epoxy or super glue when assembling.I am not convinced your problem is caused by rod sticking in socket. Impossible unless rod has punched through socket.

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