Shake Under Braking Diagnosis mystery

[colwill1]

Hi All,

I recently bought an used A45 AMG and everything was perfect. However 1 month in, I managed to curb it at low speeds. Rather than get the wheel refurbed properly I thought I would give it a go and wait 6-12 months to see if I have any further scrapes. So I jacked the car up Put an axle stand under the front left corner took the wheel off and gave it a go.

Once done, I put the wheel back on and I had a vibration when braking lightly at speeds over 50mph, a slight pull to the left and smallest vibrations over 70mph.

So I got the front left balanced thinking that it was just the weight change due to the filler etc.

This cured the small vibration but I still get a vibration under braking at high speeds.

I have the car booked in for re-alignment on Friday but I am worried that this will not fix the problem and I am baffled what it could be.

Discs and pads are 1000 miles old so doubt they are warped - checked the tyre, that is fine.

Only thing I can think is I placed the axle stand on a tracking rod and this has affected the camber somehow but again not sure if that even makes sense. I did struggle finding a spot to place the axle stand due to all the plastic trim so ended up quite far under the car on the subframe I believe but could have caught something.

 

[Bellow]

First suspicion for braking vibration is disc not seated 'squarely' on hub.

 

[Deletedmember130310]

Hi All,

Only thing I can think is I placed the axle stand on a tracking rod.

Has this resulted in a bent steering arm? The bend could be too small to be visible...

 

[st13phil]

Hi All,

I recently bought an used A45 AMG and everything was perfect. However 1 month in, I managed to curb it at low speeds. Rather than get the wheel refurbed properly I thought I would give it a go and wait 6-12 months to see if I have any further scrapes. So I jacked the car up Put an axle stand under the front left corner took the wheel off and gave it a go.

Once done, I put the wheel back on and I had a vibration when braking lightly at speeds over 50mph, a slight pull to the left and smallest vibrations over 70mph.

Did it pull to the left after you'd kerbed it, but before you jacked up the car?

Where on the car did you put the jack and the axle stand?

 

[colwill1]

First suspicion for braking vibration is disc not seated 'squarely' on hub.

Could that have happened from just taking the wheel off though?

 

[markjay]

Could that have happened from just taking the wheel off though?

Yes. Or rather, from putting it back...

Make sure the mating surfaces on the hub and the rim are clean (use a wire brush).

And that the wheel bolts are torqued correctly.

 

[colwill1]

Did it pull to the left after you'd kerbed it, but before you jacked up the car?

Where on the car did you put the jack and the axle stand?

Circled in photo.

 

[colwill1]

Yes. Or rather, from putting it back...

Make sure the mating surfaces on the hub and the tim are clean (use a wire brush).

And that the wheel bolts are torqued correctly.

I'll ask the garage when they align it tomorrow.

 

[st13phil]

Circled in photo.

OK, that’s good. Just checking because you wouldn’t have been the first person who jacked or supported a car on a suspension arm and bent it.

So presumably the car did pull to the left after you’d kerbed it, but before you jacked it up?

 

[colwill1]

OK, that’s good. Just checking because you wouldn’t have been the first person who jacked or supported a car on a suspension arm and bent it.

So presumably the car did pull to the left after you’d kerbed it, but before you jacked it up?

It pulled after kerbing but before jack yes, which I was pretty shocked by because I kissed the berb reversing at 5mph.

I dont think it vibrated under braking but to be honest I am not 100% on that

 

[st13phil]

OK, in that case it does sound like something was damaged when you kerbed it. Doing that while going backwards could well be relevant.

 

[colwill1]

OK, in that case it does sound like something was damaged when you kerbed it. Doing that while going backwards could well be relevant.

Alignment did not fix the issue as expected. Going to take to Merc indie to see what they say

 

[st13phil]

Was everything within spec, alignment-wise?

Not sure about the W176 chassis, but pretty much every RWD Mercedes chassis will follow road camber to a greater or lesser extent, with a light drift to the left being the effect on UK roads. Are you sure you've not just become sensitised to it as a result of knowing you kerbed the car?

There's a whole thread on the characteristic pull to the left here.

 

[Bellow]

Could that have happened from just taking the wheel off though?

Yes - as MJ has mentioned.
Ultimately, the disc is clamped between the wheel and hub. When the wheel is removed the clamping is also and the disc can move a little allowing dirt or debris in behind. There is a retaining screw but it's such a piddling affair it cannot really be relied on to hold the disc securely with a wheel removed. Often enough, the screw is missing anyway.

The 'pull to the left' - always or just when braking?

 

[colwill1]

Yes - as MJ has mentioned.
Ultimately, the disc is clamped between the wheel and hub. When the wheel is removed the clamping is also and the disc can move a little allowing dirt or debris in behind. There is a retaining screw but it's such a piddling affair it cannot really be relied on to hold the disc securely with a wheel removed. Often enough, the screw is missing anyway.

The 'pull to the left' - always or just when braking?

No it doesnt pull anymore, alignment fixed that. It shakes under light to mid braking at speeds of 50mph +

I dont think the disc is warped because it coincided with the kerbing and painting of alloy

 

[st13phil]

My guess is it’s either wheel or tyre damage then.

Does the A45 run the same wheel width front and rear, or is it a staggered setup? If the former, try swapping the “repaired” front with one of the rears and see if the shudder under braking changes.

 

[Bellow]

Is your car used mainly on motorways?

 

[colwill1]

Is your car used mainly on motorways?

No, mainly urban. Used for around 50 miles per week. Mainly weekends

 

[Deletedmember130310]

7 miles a day?

Swap it for a bus pass...

 

[colwill1]

Yes - as MJ has mentioned.
Ultimately, the disc is clamped between the wheel and hub. When the wheel is removed the clamping is also and the disc can move a little allowing dirt or debris in behind. There is a retaining screw but it's such a piddling affair it cannot really be relied on to hold the disc securely with a wheel removed. Often enough, the screw is missing anyway.

The 'pull to the left' - always or just when braking?

It doesnt pull anymore since alignment was done, just a vibration under light to mid braking over 50mph.

This sounds more feasible, how would I check and remedy? Remove the wheel obviously and then what?