Knocking under heavy braking (WMS Brakes)

[Kedge]

Right folks, I'm running out of ideas trying to get to the bottom of this.

During normal driving there's no issue but under reasonably heavy braking I'm getting a fast knocking sound as if it's happening whilst something is rotating. I've been all over making sure everything is tight, front and rear, and also the steering. It sounds and feels like it's coming from the front offside. The pads have thick backing tape on them and I can't feel any movement with them either. No steering wobble either to suggest a warped disc.

Anyone got any ideas or experienced something similar?

Cheers
Dave

[chippy1947]

Just a guess track rod end/ball joint

[Duke137]

Just a guess track rod end/ball joint

Everything is new on Dave's car, so it would be unlikely to be "worn"

[jimbom30cab]

Could the calipers be catching the inside of the wheels?

[Sanchez]

If it's only under heavy braking would the fact the front suspension is being more compressed have something to do with it?

[Rav335uk]

Did you install ABS Dave?

[Motorhole]

Could the calipers be catching the inside of the wheels?

Had this before due to very slight play in old wheel bearings. Fine under normal use, but catching when 'hot' - under repeated hard braking.

About 42-secs in!

[DanThe]

I take it you have the double sided 3M anti-rattle tape on the pads Dave?
I had similar but it was only a single clunk at low speed as the pads engaged and this was before I started using the double sided tape

[winx]

Has someone got a link to the tape they use, the rattle on my car drives me insane!

[DanThe]

I got it off ebay Henry, http://www.ebay.co.uk/itm/Brake-Pad-Ant ... 2c8b3bd34c

Works really well, even when charred to a crisp

[Kedge]

I can't remember whether it's double sided or not Dan, it's one you sent me a link for but maybe you've found something better since?

[DanThe]

Your right its not double sided, I was thinking of the clear stuff they send with new regular brake pads. Link above Dave

[winx]

Perfect thanks Dan, just ordered a stock!

[Kedge]

Cheers Dan, ordered a pack of them

Got a short video today so you can hear what it's doing;
[youtube][/youtube]

There's no other noise or vibrations through the steering, brakes or suspension, I've tried pushing it on abit with a good about of steering lock on to see I can an get it to do something, amazing how much better E30s drive when everything is new

[DanThe]

Cant load the video for some reason

[Kedge]

Direct link should work

[Kedge]

Put the new tape on, looks the same as the old stuff, and there's no improvement and I now have a catching sound at around 40mph.

[keri-WMS]

Is it possible that the heat shield is touching the disc? (larger than original steering rod ends might be pushing it, it's pretty tight with the larger/deeper discs as-is, that's part of the compromise to try and avoid wheel spacers....)

Or as the flanges on the WMS discs are thinner (E30 260mm=7mm fl, WMS 280mm=5mm fl, WMS 298.5mm=6mm fl) it's possible the wheel bolts might get close to / touch the ABS cowling?

Or with aftermarket wheels and/or due to the slightly thinnner WMS disc flanges you might find the wheel is hanging on it's chamfer on the middle of the hub's protrusion and not clamping the disc properly (look for marks in the chamfer of the bore of the wheel).

Other possibles are that the calipers are touching the wheel. Or touching any internal wheel balancing weights.

The pads do have more room to move in this type of caliper to make sure that at race temperatures they can't expand enough to seize, if the pads are knocking then bending the split pins "forward" or a bit more open so they grip the inside of the holes in the pad/caliper often helps shut them up.

Which kit have you got, have you got grooved discs and have you got wheel spacers?

There are probably a few more possible sources of a knocking noise to eliminate but I can't think of any at the moment, hope that's some help!

[keri-WMS]

Listening again to the video, it sounds a bit like a slow ABS pulse, but it drops with wheel speed so I expect we can rule that out.

Runout in the disc, or in the hub, or the bearing seats, or dirt/damage on hub/disc mounting faces are another thing to check for.

[Kedge]

Hi Keri, thanks for the input.

I've got the 4P025 kit and I'm running 16" Hartges with the spacer, no ABS. I did find that the dust shield was catching be disc on the position of the bottom ball joint and that looks to be clearing fine and the noise remains, guess it could still be moving under braking? Can you do away with the bottom part of the dust shield or will the heat build up be an issue for the ball joints?

I've not noticed any other sign of unusual wear or marks, wondering whether it could be worth trying spigot rings on the wheels though...

[keri-WMS]

That lower ball joint is close to the disc - the risk of taking the heat shield off is it might overheat/crack the balljoint rubber boot. But then again it might be fine!

Re spigot rings, are the wheels not held concentric?

[Kedge]

Having done a quick Google, yes they are concentric.

Can see me just having to chop up the heat shield some more and hope for the best, can't see anything else that could be causing an issue now.

[keri-WMS]

Only other thing I can suggest is run a dial indicator on the (bolted down) discs to check for total runout?

I take it the wheels are straight? Swapping left>right wheels will eliminate the rims and tyres if the noise doesn't move.

[Kedge]

Swapped the wheels, front to back due to directional tyres, and also cut off the bottom of the heat shield and it's made no difference.

Going to have to cough up and get someone who knows what they're doing to investigate.