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Thread: 451 diesel gearbox update

  1. #101
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    Have concluded the roller wedge mechanism will hold by friction only so there won't be any multiple position grooves inside female part of rod.

    Minimum required coefficient of friction is tangent to half the wedge angle. Judging by the photos I have estimated the wedge angle to be 5 degrees. Minimum coefficient of friction becomes thus 0.044. Even when wetted in grease the actual coefficient of friction will be much higher so there is no chance the rollers will slip. Such a small angle means very high load being applied to inside walls of female rod which could lead to fractures. Perhaps worth while to look for cracks and splits. Is wall of female plastic rod reinforced by metal?
    Last edited by tolsen; 15-12-2016 at 08:58 AM.
    Drives a Smart Cdi - 65 to 85 MPG

  2. #102
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    I concur. No grooves, just plain hardened steel plates. However there are certainly signs of slipping and wear on the one that was in the car. That part was actually under the seat from the old one and was in much better condition than the one in the new actuator so I fitted that. Tested it in and out lots of times and it is certainly not slipping now. What a complete ball ache it is engaging and disengaging the clutch with star, one requires it to be in 1st gear, the other requires neutral and by the time I had climbed down from engaging the correct gear the clutch had finished doing what it needed to, it really is a three man job, one to watch, one to operate gear and one to operate the computer. I think Renault must have had a hand in designing this it is so illogical.

    Anyway, all back together again, I didn't take any more pictures after I saw your link, good find that. I had searched on that site but didn't find those pictures.

    What I do have now is a consistent CAN bus error between the gearbox ECU and the ESP unit. I have seen this error before a few times along with a few other CAN bus errors that were not really consistent enough to blame but this one I can now reproduce reliably by operating the gear lever so I am back to buzzing out CAN bus completely in search for the problem.

  3. #103
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    Check all the earths. Had can issues on one after Halfords fitted a battery, earth strap not connected to anything!

  4. #104
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    More thoughts on how 451 clutch actuator rod wedge roller mechanism works:


    1) The white plastic "buffers" and square section tab sticking out facing us in above photo and identical tab out of view opposite side are free to slide axially relative to main part of male push rod.
    2) These two tabs rest against lands inside aluminium housing of actuator body when actuator is retracted.
    3) When actuator is retracted, the white buffers keep rollers slightly away from wedge allowing full travel of spring loaded female part of push rod.
    4) At start of actuator extension stroke, main part of male push rod moves wedge in contact with rollers and mechanism locks by friction to female push rod.

    Had to knock my brain windings into highest gear to figure above out. Would have been much easier with an actuator in hand.
    Drives a Smart Cdi - 65 to 85 MPG

  5. #105
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    If you had one you would have explained it slightly differently too.

    When the "push" is fully retracted the rollers are allowed away from the out box part of the push rod. This allows the weaker spring inside to fully extend the push rod thus auto adjusting the length. As soon as the clutch mechanism pushes that length is fixed with the friction of the rollers.

  6. #106
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    More thoughts:

    1) Purpose of spring inside female part of clutch actuator push rod is to preload the whole clutch operating system to eliminate slack and prevent rattle and wear.
    2) Below is procedure for fitting clutch actuator, complements of Smart and Smart of America. Spring inside female part of clutch actuator is preloaded by moving clutch actuator 3 graduation marks in way of its bolt fixings. This is from initial contact of push rod with clutch release arm.


    3) I assume the clutch itself on 451 Smarts has no built in cam ring mechanism to automatically compensate for clutch wear. Such a mechanism is not required on the 451 since built into the clutch actuator.
    4) As clutch wears, the fingers that operate clutch diaphragm move further out pushing clutch release arm nearer towards clutch actuator.
    5) When clutch actuator is retracted, the female part of push rod can move freely only restrained by the tension of its preload spring.
    6) Clutch wear therefore only results in an increase in preload. Clutch release and bite point remains unaffected since required stroke of release bearing does not change much with normal wear of clutch linings, pressure plate and flywheel contact surfaces.
    7) Summary: The mechanism adjusts itself automatically. Sets itself to zero position each time clutch actuator is retracted. This is similar to the auto adjuster mechanism in hand brake lever which also sets itself to zero each time hand brake lever is lowered to its rest position.
    Last edited by tolsen; 08-02-2017 at 11:42 PM.
    Drives a Smart Cdi - 65 to 85 MPG

  7. #107
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    The spring inside the female part is also strong enough to make sure that the thrust bearing is up against the pressure plate. I think that is really the only reason for the preload.

  8. #108
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    Wedge is pulled slightly out of engagement with rollers when clutch actuator is fully retracted. Rollers stay where they are. I can clearly see there will be problems with proper function of this actuator if ball at end of male part of push rod is not fully seated in its socket in sector gear.
    Drives a Smart Cdi - 65 to 85 MPG

  9. #109
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    Which truly all adds up to a over complicated piece of crap design whose total purpose for existing is to remove the need for maybe 2 or 3 adjustments at the most throughout the expected life of a clutch.

    Or to put it another way it is ridiculous.

  10. #110
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    Most clutch actuators have the auto adjuster similar to your 451. Here is one for Peogeots and Citroens:
    Drives a Smart Cdi - 65 to 85 MPG

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