Traction brake shoes
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Thread: Traction brake shoes

  1. #1
    Fellow Frogger! Greg's Avatar
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    Default Traction brake shoes

    Hi Guys,

    Here's one to test traction owners:

    Traction brake shoes are a fixed pivot arrangement with a short and a long shoe.

    While the manual isn't specific, it shows the short shoe as the trailing shoe, and the long shoe as the leading shoe in its pics.

    This is contrary to any information that I can find on Google, where the have the leading shoe as the short shoe.

    The reason for this is that if the leading shoe is full length, the friction from the drum rotation tries to pull the top of the shoe into the drum, and have a jamming effect.

    DS rear brake shoes are the same.

    I think I've always done traction brake as per the manual, but I believe now that this is wrong?

    Any thoughts?

    Best regards,

    Greg

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  2. #2
    Fellow Frogger!
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    Hi Greg, I think you've been doing the Traction shoes correctly. Pulling of the shoe into the drum will occur whether it's a short or long shoe. My guess as to why it's done as per manual pics is that for any given pedal pressure the force on the lead shoe will be amplified by the wheel rotation but this increased force is divided by the increased lining area gives the same pressure (per square centimetre) as for the lighter loaded trailing shoe with its lesser area. Thus in theory the linings should wear at the same rate. That's my 2 cents worth. :-)


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  3. #3
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    " Jamming effect " is also called "self-servo" in some quarters

    It gives a useful increase in pressure at the linings. It is exploited in mods to cars with crap cable or mechanical brakes where the pull is compromised ( notably Austin seven )

    Manual may be right, especially bearing in mind that Traction was designed when all of these considerations were commonplace

    Andrew

  4. #4
    Fellow Frogger! Greg's Avatar
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    Hi Guys,

    Thanks heaps for your input.............

    There is a lot more science to drum brakes than you think, but anyway, I've learn a bit.

    This all started when I overhauled a Traction front end (silent blocks etc) for a friend. He did the rear brakes himself, and questioned as to whether they shouldn't be around the other way. He finally decided I was right, but in the mean time I decided I was wrong.

    The manual is actually a bit vague. Typical Citroen Manual, they always assume you know what Ur doing, and mostly you don't :-))

    Best regards,

    Greg
    We Have:
    C5 HDI Exclusive 2.7 '09, Pluriel '09, Berlingo 1.6 HDI '10, C4 VTS coupe. C4 Picasso '08, 2CV Charleston '84 Grey, 2CV, '55 Australian delivered. 15/6 H '55, SM '74 BVM, DS21 EFI BVH, DS21 '67 BVH.
    We Had:
    1930C6F, '73 GS1220 wagon X 2, '75 G special, '75 GS panel van, '74 GS Birotor, '82 GSA panel van with factory AC, '85 CX25GTI BVM, 2002 C5 V6, 2006, C5 S2 HDI, '86 BX19GT, '72 DS21 BVM, '55 15/6H, '54 Lt 15,'73 Dyane, '82 Visa Super X, with Chrono Mecs & factory AC, 1972 SM.

  5. #5
    1000+ Posts gerrypro's Avatar
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    Leading shoe is the long lining. It is self energising! The trailing shoe is only about half the length of the shoe and serves mainly to balance the pressure on the leading shoe. Big 6 is twin leading shoes of full length and dual slave cylinders. It is essential in both arrangements to ensure lining concentricity and special tool fixtures are recommended by the manual for use to achieve this condition.
    Concentricity adjustments are made by eccentric cams on the lower fixed pins and on the snail cams either side of the slave cylinder/s in both four and six cylinder cars respectively. Set it up correctly with the correct lining grade ( Bonded linings are generally too hard, riveted are preferred) and you will have the best drum brake system in the business!
    Cheers Gerry

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