Clutch Release Fork: Wear at the Pivots

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Written by Loz Scott

Written by Loz Scott | 16 April 2013

Sometimes clutch release problems are not caused by the hydraulics but by wear in the mechanical parts. The clutch release fork is carried on a pivot bolt that moves in bronze bushes, so after many thousands of miles, it is not surprising that it can become loose, causing lost motion in the release process. If the first part of your pedal movement is just to take up the wear in the pivot, it means you may not have enough left to operate the hydraulics fully.

Long-time Magnette owner Loz Scott in Australia, has been doing some work on this and has contributed the following piece: 

Later MG Magnette Z type Clutch Throw Out Lever - Refurbishment

A comment about my ZB's clutch throw-out lever being very worn proved accurate. Inspection showed 50 plus years had worn the pivot bolt and excessively worn its bushes. Gear box pictured is the later  type that uses a shouldered 1/2 inch bolt. Whereas the earlier   Magnette gearbox uses a standard 5/16 inch bolt. (NB.See MG Magnette Parts Book. AKD 688; pages 59 and 60 for details.)

  

Above. Picture No.1 shows the internals  of the bell housing and, unique to the Magnette,                                   its top mounted slave cylinder.     Inset is view of installed  pivot bolt.

Wear and Replacement

 

 Picture No.2 above compares worn and replacement parts.

New bolt was fabricated from a standard 1/2 inch [12.7mm] high tensile bolt. Specifications:
- 44.26mm plain shaft[3/4inch AF spanner]
- 17.7mm stepped end with 24tpi; taking a
9/16th inch nylock nut.

New bushes [phosphor bronze] cut and machined from tube length. Specifications:
- O/D = 16.1mm
- I/D =12.8mm and
- Length =3/8th inch

Bush Bashing [ not really just a pressing need]

 

 

Above. Picture No.3 Displays all the parts associated with the Clutch throw out lever.

Preparation:

ü  Remove the old bushes from lever [Typically weaken them with a saw cut and tap out with a suitable drift]

ü  Check and clean[damage, dirt, grease & rust] the lever's bore so it is suitably prepared

ü  Make sure the new bushes are relieved at the ends to aid pressing in

Installation:

• Press in a bush each side of the lever using a press [or carefully in a vice].
• trial a bolt into the bushes. Test for jams or binding. Usually a light polish of the bolt will solve the difficulty.
• The pivot bolt and the bore of the pivot must be lubricated with grease; making sure the internal gap, between the two bushes, is filled.
• Install the items shown at picture 3 into the supporting lugs of the bell housing [Picture 1]

Comments:

v  Bushes were coated with a medium loctite retaining compound prior to pressing in

v  All measurements given in this text should be used as a guide only; As basic home garage instruments were used.

v  Remember this is a later Z Magnette gearbox. Compatibility of parts such as the throw out lever and splining of the tail shaft should be considered if gear boxes or parts are to be interchanged.

v  Plain washer for pivot bolt is 1/8th inch thick; It's a closer fit than a normal washer.

v  Machining a worn pivot bolt necessitates: [1]Bushes with a smaller I/D; and [2]reducing the bore of bell housing's location lugs with cylindrical shims.

by Laurence [Loz] Scott   25th Jan 2013

Warped Wisdom - Look! No synchromesh on 1st and no 5th gear. Can concours standards save the original ZA & ZB gearbox? Remember the Bilby or suffer the loss.