Knocking from front wheel

MartinP · Post by **MartinP** » Wed Jul 18, 2007 12:43 pm

This one is driving me mad, so if anyone can offer some advice I would be extremely grateful

When I got my '67 912, it drove fine at speed, apart from the fact that the tyres were worn to illegal levels. To get it through the MoT, I had the front calipers rebuilt, put new brake pads in (one had seized and worn a pad right down to the metal), and fitted new Vredestein Classic tyres.

Since then, the first time that you get the car up to over 70mph on a journey, after a couple of miles there will be a gentle knocking which seems to be coming from the nearside front wheel.

It slowly gets worse and worse and increases with the revolutions of the wheel. If you slow down to under 50mph, then it will ease off until gone. The odd thing is that 95% of the time you can then take it back up to 70mph for the next couple of hours if you're on a long journey and it will never happen again!

In case it was a tyre out of balance, I swapped the wheels over from front to back, but it's still there. I also trimmed a bit of 'flappy' rubber that was left from the moulding process off of the tyre but that didn't help.

However, there is one other thing that I haven't investigated. When the seized caliper wore the pad down to the metal, it scored the brake disc. This has now resulted in the new pad wearing, but with a ridge through the middle where it meets the indent in the disc and doesn't wear as much.

Is there any possibility that this could be causing some kind of knocking when it first gets up to speed and starts to get really warm, but then easing off and/or braking then causes the pad to seat itself better?

Any thoughts? Please?!

Gary71 · Post by **Gary71** » Wed Jul 18, 2007 12:57 pm

I'd be thinking you've just identified it yourself

Other than that it maybe the front wheel bearing needs nipping up.

MartinP · Post by **MartinP** » Wed Jul 18, 2007 12:58 pm

Looks like a new pair of front discs and more brake pads are needed then. is it worth trying a second hand disc first do you reckon?

Barry · Post by **Barry** » Wed Jul 18, 2007 1:09 pm

Does the sound dissappear (or at least, change) when you dab the brakes?

Might give a clue.

MartinP · Post by **MartinP** » Wed Jul 18, 2007 1:12 pm

Not really, no. When the knocking has built to the extent that it's so bad you think you should be pulling over, putting your foot on the brake to slow can sometimes make the knocking even more noticeable from a feeling point of view, but certainly the sound doesn't change.

Nige · Post by **Nige** » Wed Jul 18, 2007 1:22 pm

warped disks
front wheel bearings
strut mounts/lower ball joint

MartinP · Post by **MartinP** » Wed Jul 18, 2007 1:23 pm

couldn't have anything to do with the front dampers being replaced at the same time could it?

Barry · Post by **Barry** » Wed Jul 18, 2007 1:49 pm

I suspect that if the sound doesn't change upon braking, that probably rules out (or at least reduces the odds) of it being bearing, pads or disks.

Certainly got to be worth double checking those dampers, top mounts and bottom ball are all in and correct: obviously you'll need the weight off of the car to check this.

hot66 · Post by **hot66** » Wed Jul 18, 2007 1:53 pm

this used to happen to my subaru .. the problem was a siezed front calliper. After a bit of driving & when on a motorway at about 70mph I would get a wobbling / knocking coming thru the steering wheel, so bad that I had to stop the car. I'd then start off again & the problem was gone.

Did you replace the brake flexis when you replaced the callipers? If the flexis are damaged internally they might be letting fluid through but not back out again

Have you checked the temp of the front wheels to 100% confirm the brakes are still not sticking?

What kind of noise is the knocking eg is it a deep thudding noise coming thru the body or is it more of a metallic tapping?

MartinP · Post by **MartinP** » Wed Jul 18, 2007 1:55 pm

Didn't replace any of the hoses, but did check that everything was moving in and out as normal. Temperature seems fine although haven't actually stopped the car immediately after the knocking and checked the wheel temp. Knocking is a dull thump - it's almost as if I have a big bolt stuck in the tyre!

Gilbert '71 T · Post by **Gilbert '71 T** » Wed Jul 18, 2007 7:33 pm

As Barry says, have a quick check of the lower ball joints Martin.

Jack the front of the car up so the wheels are about 1.5" off the ground, then put a pry bar underneath the tyre and lever the wheel up slightly, whilst doing that try to eyeball the lower balljoint and see if there's any noticable play.

The uneven pad/disc could possibly cause a slight binding if the pad is rubbing against the ridge, but I wouldnt expect it would cause a knock... but then you never know with these cars, they can be very sensitive to anything that is out of sorts braking & suspension wise.

good luck with it, I know it can be difficult trying to find these things statically