Semi-Girling brakes

[Ian Williams]

I think you may have the wrong cams fitted, they are handed and different at front and rear so specific for each corner. Original's are stamped FR, FL, RR and RL

[falcott]

I have just had a set of rear shoes relined by Saftek(posted Monday back Thursday).
I asked for 5mm thick material as the drums are 7.1 internal diameter. Assembly is almost done with new bearings and cams with new springs.
Just need to adjust the cables.
Over many years I have used a variety of lubricants and pastes on the plungers and adjusters with poor results,this time I am using ceramic grease .results to follow,

Looking at the cams looks as though you may have a front and rear,the ones from A7components are clearly marked.

Mine are from Seven Workshop, with no markings at all. They are a pair, supposedly front.

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Hi

I am still puzzled by this.

The advantage of semi-girling is that the smaller cams and longer levers give more leverage, so that for a given cable tension more force is applied to the shoes for more braking force.  The downside is that lining wear has a more pronounced effect on pedal travel, so there had to be an easy way to re-adjust at each wheel without messing about with cable lengths as used to be the case. Hence the square headed adjusters.

With shoes adjusted for minimal running clearance and brakes off, the flat cams will be at their minimum position and will sit vertically between the steel plungers.  The lever should then be more or less vertical, and the machined cotter pin slot more or less horizontal, so the slot will be at right angles to the cam.  Presumably one has to factor in the need for the levers to actually be slightly ahead of vertical when off, so that with their (small) travel they are truly vertical when on. Also, one has to allow for the small taper angle of the cotter pin. The cam on the left of your photo is therefore what I would expect to see. The cams are handed left and right, and don't forget that rear cams are also different to fronts.  The heads used to be stamped with letters to identify them.

Lining thickness shouldn't upset the above, provided you can still adjust for the correct running clearance ( which you can - just ).  Clearly, if you had thinner linings and deliberately mis-adjusted them for a large running clearance you could make the levers travel more between the brakes off and brakes on states, so that they would be vertical with the brakes on.  But this isn't how they are supposed to work and would give you a very long pedal travel.

The photo below is of my own setup, the levers are from Seven Workshop but I cannot remember the source of the cams. The handbrake is on (which fully applies the rear brakes and lightly applies the front brakes) but the travel from off to on is pretty small.  As you can see, the lever sits more or less vertically and the cotter nut is to the rear.

You're not the only one who is puzzled. The only thing I can think of, is that the cams are wrong. As you rightly said, the thickness of the linings shouldn't make any difference to the operation of the brakes. If this wasn't my first A7 brake rebuild I would have notice the error straight away. Ah well, we live and learn. Now I need to get new cams to replace the new cams...

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Thank you, Geoffrey.

You have the cotters correctly orientated for a Girling system and although the levers are forward and down, the ends are sitting up higher than I would expect.

This is one of my own cars, with handbrake fully applied (note, I prefer to set up the system up so that front brakes are fully on with the rear just starting to come on).



I have measured several NOS linings that I have here and they all measure exactly 4mm.



The lack of top adjustment on your car can only really be attributed to the linings being too thick, even with new I can normally still get a couple of clicks using second hand drums.

The lever position is down to the cotter slot in the cams and, looking carefully at yours, I do wonder if you have a pair intended for the rear brakes.

I am away from my workshop but I may have some spare cams in the car and if that is the case I will post a photo later for you to use as a comparison.

Thanks for helping, Ruairidh. Much appreciated.

[Ruairidh Dunford]

Hi Geoffrey,

I only have one spare set of cams with me just now, comparing them to the ones on the car I am fairly sure they front ones.

Hope this helps you to compare.

Ruairidh

   

   

[Ruairidh Dunford]

  4CABABE9-F8B9-4623-A25F-47A214BF3FC0.jpeg (Size: 657 KB / Downloads: 181)

[John Cornforth]

Hi

These look more like rear cams to me. As far as I know the shaft of the rear levers should be to the rear of the backplate, slightly below the centreline with the lever facing more or less down and the cable passing underneath the axle. This places the levers roughly at right angles to the cam, so the the cotter slots will be roughly parallel to the cam. As with the fronts, the Left and Right cams will then have a different small offset from parallel.

The front cams have cotter slots roughly at right angles to the cam, again with different Left and Right offsets, as I described in a previous post.

The situation isn't helped by some confusing published drawings. The top left section of the Austin drawing shows this, but looks odd presumably of the drawing convention: https://archive.a7ca.org/collections/tec.../td0010-2/ Woodrow's drawings H12 and H13 show the adjuster at the top, which is incorrect. On top of this, the backplate is held on with 4 bolts which has allowed owners to reposition them over the years !

[Ruairidh Dunford]

I attach further photos of the cams above, along with an Austin arm, the only one I have with me.

They show the position of the cam and arm at rest and also fully on - I hope this helps.


   

   

[Ruairidh Dunford]

On a standard factory car, the rear backplates should be orientated so that the adjuster is at the front, the brake arms should face down and backwards and the cotter nuts should be towards the centre of the car, as shown in the factory drawings above.

[falcott]

In a fit of frustration (heh!) I emailed Seven Workshop. They admitted that the manufacturer has mixed up the batches, so they are sending me out some proper front ones. I guess that now I have spare cams for the rear. Thanks everyone for your help. There was only one logical conclusion in the end.

[Ruairidh Dunford]

Good news.

[falcott]

The correct brake cams have now arrived and have been fitted -- and things are looking good. Thanks for all your help here.
Next question: How much slack may be allowed in the cable on the initial setup? Or should it be taut? Thanks.