Knock when breaking

[Matt99man]

Evening all

After a couple of months in the garage I had a sticky drivers front calliper, there was also a knock when breaking fairly heavily that I put down the the pads slipping, due to heat of the stuck pad. Now I’ve replaced the calliper, and happy days...so I thought! When everything is cool there is no knock, once hot there is a distinct knock I can feel on the break peddle. Everything is tight, no loose calliper, ball joints look good and there is no play on the wheel when jacked up. It feels like something is clicking or slipping, brake performance is good. Any ideas gents?

Edited by Matt99man on Saturday 26th June 23:07

[colin mee]

Warped disc maybe

[Matt99man]

colin mee said:

Warped disc maybe

I thought that, it’s not catching when turned though, looks fine. Plenty of meat on the pads too

[Sir Paolo]

Hi,
Does this ‘knock’ transmit through the steering wheel?

Or does it manifest itself as steering wheel wobble?

Just a thought, I had similar on a Lotus, it turned out to be a worn suspension bush.

Good luck!

[Matt99man]

Sir Paolo said:

Hi,
Does this ‘knock’ transmit through the steering wheel?

Or does it manifest itself as steering wheel wobble?

Just a thought, I had similar on a Lotus, it turned out to be a worn suspension bush.

Good luck!

Nope, just the peddle

[Glosphil]

If the brakes on my car were breaking I won't be surprised if there was some noise.

[s p a c e m a n]

If you can only feel it on the pedal and not on the steering wheel/anywhere else then the issue is probably in the pedal box area. The brake pedal isn't attached to the caliper by anything other than a flexible hose, the steering wheel is 'solid' mounted to the brake calipers so you feel it through there/the rest of the car too. The only way I can think of a knock only happening at the pedal and it not being the pedal box is if fluid was getting trapped somewhere and it releasing quickly ie a sticky piston/expanding brake hose, but then the pedal would drop a bit too and the brake would grab/release/do something else you would feel

In summary: give the pedal a wobble it's probably that.

(I'm going to be miles off )

[phazed]

Glosphil said:

If the brakes on my car were breaking I won't be surprised if there was some noise.

I thought that but didn’t dare put it up!

[Steve_D]

Can we clarify if this is knocking when the brakes are on or a single knock when brakes are applied?

Steve

[Sir Paolo]

Steve_D said:

Can we clarify if this is knocking when the brakes are on or a single knock when brakes are applied?

Steve

Absolutely, if it was a single knock as the brake pedal was applied, I’d guess loose servo mounting, or even loose master cylinder.

[Loubaruch]

Have you had a good look at the brake disks, they do have a habit of failing in between the two outers i.e. the cast iron webs supporting the two outers can crack so that when you brake the disks deform causing a bumping of the brake pedal.

[phazed]

Are you sure it’s not as simple as something loose?

Check swivel joints, track rod ends, anti-rollbar drop links and the actual anti-rollbar rubber mounts to the chassis.

[Matt99man]

Sir Paolo said:

Absolutely, if it was a single knock as the brake pedal was applied, I’d guess loose servo mounting, or even loose master cylinder.

It’s a single knock when the brakes are applied

[Matt99man]

phazed said:

Are you sure it’s not as simple as something loose?

Check swivel joints, track rod ends, anti-rollbar drop links and the actual anti-rollbar rubber mounts to the chassis.

90 % sure, don’t think I checked the roll bar though. Will check tonight if I get chance. If something was loose then surely that would be there from the start, not 10 mins after everything’s warmed up

[Matt99man]

Ok...So I got someone to drive up and down in the Chim and replicate the knock whilst I checked things out. It’s not the brakes, they are a red herring for sure. Having the calliper cease at the same time threw me off the scent, it must be reverberating somehow. I guess it can only be suspension related, there’s nothing obvious but I will have another look this week!

[Steve_D]

So the single knock will be something moving with the torque of the brakes so...
loose caliper, worn bushes in variuos locations, rollbar/droplinks etc.

See if you can produce the noise with someone applying the brakes and someone rocking the car back and forwards. If you can then you need a third person under the front watching or feeling bits.

Steve

[AlexanderV8]

Steve_D said:

See if you can produce the noise with someone applying the brakes and someone rocking the car back and forwards. If you can then you need a third person under the front watching or feeling bits.

After reading that paragraph, I'm having real trouble getting certain images out of my head.

[Adrian@]

Noise travelling from the rear wishbone, ARB bracket broken perhaps. A@

[markcoopers]

If it is a single one off when breaking, but is not brake related (as you say), then I would be looking at ARB drop links, and the mounts where they weld onto the wishbones. It sounds like something is touching when the weight transfer moves the front suspension.

[phazed]

I had a knock manifest itself on my Range Rover P38 recently. Turned out to be nothing more than a damper bolt that was tight but not tight enough to compress the top bush. A little tighten with an 18 inch bar and the noise completely disappeared.