Problem with Green Stuff brake pads

[roy4matra]

I will try to perform the operation tomorrow, but just hod much pressure is needed?

Sometimes it can be quite considerable at the beginning.  I have a special Facom tool made for this particular job!  It's like a large pliers but it operates in reverse - as you squeeze the handles the jaws are pushed further apart not together.  The jaws are made with a section that fits the groove in the piston.  The other jaw pushes against the inside of the frame opposite the piston.  So you can squeeze the handles to push the piston inward and at the same time you can rotate the piston using the pliers as the lever!  I'm not sure if it is still available but I think it was D60A

I am considering concocting a special tool from an old ratchet wrench and a spring. Since the piston housing is still attached to the frame, I cannot apply pressure directly. But if I can wedge a spring between the frame and the wrench, perhaps it will be a simple mater...

No sorry, I doubt a spring will be strong enough, since it would have to be very strong and start compressed to try and apply enough force.

However, if you don't wish to separate it from the car and take it to a bench and vice, then you really need two people, one to hold the caliper whilst the other works on the piston.  You need a piece of square bar that fits well in the groove in the piston.  Then you need a piece of wood that almost fits the space between that square bar and the opposite frame.  Finally you need a wedge to push between the square bar and wood, a chisel is often ideal.  Tap the wedge into the gap between the wood and bar applying pressure to the piston, and then rotate the bar 90 degrees to rotate the piston.  Tap the wedge a bit more, then rotate the bar, keep doing this alternately.  It should start to wind back down and once you have it started, you can probably dispense with the wood and wedge and just keep rotating the piston with a bit of hand pressure.

Roy

[Jon Weywadt]

Sometimes it can be quite considerable at the beginning.  I have a special Facom tool made for this particular job!  It's like a large pliers but it operates in reverse - as you squeeze the handles the jaws are pushed further apart not together.  The jaws are made with a section that fits the groove in the piston.  The other jaw pushes against the inside of the frame opposite the piston.  So you can squeeze the handles to push the piston inward and at the same time you can rotate the piston using the pliers as the lever!  I'm not sure if it is still available but I think it was D60A

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Roy

Thanks Roy.

That is an excellent idea for a tool. If I can't find it I will definitely make a similar one myself. 

[Jon Weywadt]

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When you wish to push the pistons back in to fit new pads, you cannot, since it is held in position by this one way mechanism.  However, you can rotate the piston to wind it back down the spiral, but you must apply pressure as you rotate the piston, and since the frame stops you using a conventional wind-back tool it is a little more difficult, particularly when on the car.
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Roy

I finally had to do this work on the rear calipers. The reason being that it would fail the biannual MOT (Syn, in Danish), because the hand brake was unable to hold the car to the point of stalling the engine. That is about the braking power it needs to hold a car on an 18 degree sope as the law calls for in Denmark.

Part of the work consisted of replacing the outer hand brake cables from the caliper to the chassis. Last year I replaced the inner cable with a stainless one. (Still looking for stainless outer cables) the old ones were so rusted that they compressed when pulling the hand brake.

The rest of the work, and the hard part, was to screw the pistons back in, to fit the Green Stuff pads I skipped last time. With help from Jesper, who held the caliper with a huge pipe wrench and applied pressure to the piston with a long 19mm wrench, I was able to turn the piston and it actually retracted. The left one took a lot of pressure and many tries, while the right one moved fairly easy, using the same tecnique. I naturally had the dust seals removed while doing this.

With the new pads installed and the brake applied to seat the piston, I could adjust the hand brake to the correct tension. It now can stall the engine, if you try to start in 1st gear with the brake pulled tight.

It has never worked this well.  

[Oskar]

ive manage to screw it up. I thought it just had to be turned 45degres and then pushed in and after that turn it another 45degres so it would sit. 

[Jon Weywadt]

Success  

The car just passed the MOT (bilsyn) with flying colors.

Releasing the clutch, with the car in first gear and the hand brake pulled, will stall the engine.

If I try to drive, with the hand brake pulled, the rear end will settle down about 3"-4".  

[RazorbackNOR]

Congrats Jon!!