Renault Trafic: Brake Piston Retreats 4mm on Left Side, Double Press for Resistance, ABS Pump

Back, only one side, left side. Disc clamp with manual self-adjusting mechanism in the piston. And such a thing: the pedal falls to the floor at the first press. Only with the second quick press is there resistance. It turns out that the piston retracts after releasing the brake pedal 4mm from the pad and you need a second quick press of the pedal to compensate for this slack. What causes the piston to pull in? The new master cylinder did not eliminate the problem. No wires swell. The abs pump has been out of order for a long time but the problem was not before.

Since this distance from the piston and quick pumping helps before it can go back completely, it looks like the slack adjustment mechanism is not working properly.
It is true that I do not know the structure well in this vehicle, but the pawl or cloves may wear in the mechanism and this allows the piston to return completely.
It seems to me that you must replace the entire piston.

mrx2000 wrote:

the slack adjustment mechanism is not working properly

I also put the clamp on but now two options remain:
1. Damaged mechanism in the piston which costs PLN 100 together with the piston

2. Damaged mechanism in the clamp. Here comes the replacement of the entire clamp and much higher costs.

I don't understand how this tensioner works. Maybe someone is lurking ...

Replace the entire clamp

Moderated By T5:

3.1.2-3.1.3. Do not use multiple forum accounts. Such action causes confusion for users and incorrect presentation of statistics.

wielecki wrote:

I don't understand how this tensioner works

what tensioner ??
There you have a piston clearance adjustment mechanism, and from what you wrote it does not work. The regulator and push rod of the handbrake mechanism are screwed into this threaded sleeve in the piston
bh.JPG Download (35.82 kB)
In short, it works like this: this adjustment screw does not rotate but moves as I marked in the picture. When you press the brake pedal and the fluid pushes the piston out of the caliper, this sleeve rotates in the piston. That is why the reg. Screw not (excessively) pulled together with the piston. If something blocks the rotation of the sleeve in the piston or the thread in the sleeve or on the screw is damaged, then when the piston extends, the reg. it is pulled by the piston and compresses the pressure spring, which, when pressure drops, the brake fluid draws the piston back into the caliper.

m789 wrote:

If something blocks the rotation of the bushing in the piston

Bingo !!! For me, this sleeve stands as welded. I will try to start it, if it doesn't go, the new piston.

You can try to soak in kerosene, use wd40, or remove the segment and disassemble it completely and clean it properly. I admit that I have forgotten this mechanism myself a bit - recently I had it in a big Fiat, and now drums and it looks like Mate m789 is 100% right about how the mechanism behaves when the sleeve is sealed.

It's over now. I couldn't get the mushroom out, it was baked. I had to drill a hole in the bottom of the plunger and knock it out. Welded hole. everything is fine. Subject to close.