What could this be? Brake pedal clunk

[Struggler]

Any ideas what this could be? It's started happening during my rebuild and no idea where to start with it. It seems to happen once after being left a while then not again. Pressing the pedal (while stationary with no servo connected) there is a loud bang and the pedal jolts.

Note that the following has been done:

• ABS removal
• Custom brake make
• Hydraulic handbrake added
• Brake bias valve added
• Rear calliper rebuild
• Refurbished 192 brembos fitted

On this occasion it wouldn't do it again, it might be only once the wheels have moved a little it does it again. Could it be just the pads moving in the calliper? I haven't added any grease to the pads yet.

 

[Struggler]

Ignore the first couple of clicks, that is just the seat creaking a little as I'm pushing quite hard.

 

[Martin_172]

Pad sticking in the caliper then freeing off when enough pressure is applied?
Id strip the front calipers, clean up and grease the sliders and make sure the pads aren't too tight in the caliper

 

[Flob]

I wonder if its a seal in the master cylinder flipping over.

2nd bank looks like pedal hitting bulkhead? Is eveything bled up fully? Doesn't look like it is?

 

[Struggler]

Pad sticking in the caliper then freeing off when enough pressure is applied?
Id strip the front calipers, clean up and grease the sliders and make sure the pads aren't too tight in the caliper

No sliders as they are brembos, but i might try and take the pads out and add some lubricant anywhere there is movement. They were newly refurbed recently.

I wonder if its a seal in the master cylinder flipping over.

2nd bank looks like pedal hitting bulkhead? Is eveything bled up fully? Doesn't look like it is?

How would the seal in the master cylinder flip over?

Should be bled properly, spent a long time putting fluid through. Pedal is not hitting the floor, can't get anywhere near, not sure what you mean by 2nd bank though.

 

[Flob]

Typo, was supposed to be 2nd bang not bank. Hard to judge from your video tbh.

Master cylinder piston and seal, the seal can jump out of its groove or in some cases peel back if the bore is corroded or damaged for whatever reason.

Can you get someone to press on the pedal while you watch everything from the engine bay? Do you still have the servo? How much does it move when you stamp on the pedal.

 

[Struggler]

Ahh gotcha, i assumed that is what you meant. It is only the second bang that is relevant, the first is just the bucket seat flexing a little.

I do still have the servo, though it is not connected to anything at the moment as the engine is not in the car (I've just blocked it off). But good news is i can definitely have someone in the engine bay watching everything as i press the pedal.

When stamping on the pedal, i would say it has a normal amount of travel, when it is not doing this thing. As you can see it normally does this the first time then not again for a while. I am not completely sure what "resets" it so it will do it again. It may be moving the car, but it may be just time. I was trying to get it to do it a second time in the video but it wouldnt.

When it bangs, it feels like it jumps down by a small mount, hard to judge how much it actually does though.