Wheel vibration under braking - what is it?
 

Ok, so the wheel is vibrating under braking, discs?

However…. I can drive 0-50 and not have any issues under braking, soft, medium or hard.

However at 60 to 70 it is there and persistent even at part braking. Could it be suspension geometry?

I purchased car at 68,000 and was told ‘all new front brakes fitted’ however I can feel a lip on the disc which in reality is probably over 1mm quite easily! So maybe they are the original discs?

I have ordered a set (I am keeping the car anyway so will keep them in my garage if it’s something else).

It’s annoying as I fitted new front pads 5,000 miles ago. I have bought new pads but I got 55k from the last set and they still had lots of life. Is it a real no no to use 5k pads on new discs?

All I can assume is that they are the original discs where I assumed they were replaced on purchase. That said I got 55k from last set with quite a bit of life at replacement so it’s not inconceivable that at 68k when I purchased it the original pads were replaced and the discs have in fact done 120k???

Any thoughts?

It can be caused by weak/split front wishbone bushes.

When you brake, the wishbone moves back, in doing so it effectively shortens he track rod end on that side and pushes the wheel out, this can set up a reciprocating action with is felt on the steering wheel. So I would check your wishbones..

All the good books say don't re-use brake pads but, especially after just 5k, I would. You might want to re-face them using sandpaper on a flat surface if the old discs weren't perfectly even, and carefully bed them in to the new discs.

I would never normally recommend that but knowing you understand your car and will proceed with caution, I can't see a reason as to why not.

I would also check if your wheels are balanced properly. Try the front wheels on the back and see if it still does it. If the disc was warped it should still do it before 60 mph.
If you still believe its brakes am I right in saying you already have new pads to fit. If so I would fit the new pads with the new discs and keep the other set for spare.

I agree with all the above, but my money is on front wishbone bushes, get it in the air with a big bar and you should be able to see the split bush move.

Hope it helps.

Another thing to check is tyres, if one of them has a damaged carcass/bulge, that will get more significant as speed rises...

I'm experiencing this too at the moment, i've had new disks/pads all round (because it needed them) and it's been a while since the wishbones were done even though they pass the MOT. Soft bushes would make sense .... it's on the list to do.

This does sound like warped disks.

This was my first thought, although the other ideas sound like possibilities also.

Don't forget, the XC90 is a beast of a car and takes some stopping. If you sit with your foot on the brake and the rotors are hot, they will warp, and, well....

You can get them skimmed to remove the warping.....
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Speaking from experience with my IS200...

Thank you to all the comments above! My initial thoughts were that the brakes had only had pads. I was informed by Volvo in 2018 when I purchased (all new front brakes) and working on the premise that discs last 2 times as long as pads (finger in the air), and given the last pads had done 60k plus 5k (replaced them due to sequencing slider pins) that the original discs were in place.

However… interestingly I could see damage to the rear braking surface. I can tell with fingernail and visuals it’s considerably in excess of 1mm wear (Clans assertion that most Volvo discs allow 1mm earthed side). Clan makes a very interesting point, because not only did the front look visually ok (Bernie red at 1.13mm wear), but also the disk had stamped on it minimum thickness 27mm and mine was 28mm.

what I can conclude, is that the discs WERE fitted in 2018 as the date code inside said 18. The pads and discs seem to have alasted approximately 60,000 miles.

Now, I was asitonished to get 60k from a pit of pads, I thought it quite amazing!
But I am a little miffed at getting 60k from a pair of discs….

I have found from removing them that the wear is very disproportionately on the rear of the disc (which makes sense as that’s the piston side.

So, lesson of the day here… don’t Vernier measure them and assume all ok as mine verniered at 28mm against mum thickness of 27mm.
Don’t assume that because you have minimul wear on front face that rear is ok.

Do make sure you get properly under the vehicle where you can see the gap in the back plate and inspect. Mine were visually bad on the rear and I would have noted.

I replaced the discs. I think the pads had about 5,000 miles on them and whilst they looked very meaty the rear of the disc have worn in a concave fashion so I reluctantly fitted the new pads.

I did also replace the caliper bracket bolts. And I must say to anyone doing this REPLACE carrier bracket bolts!!! The bolts are torqued to either 140Nm and 60 degrees (yaynes manual) or 200Nm. I did torque them to 200Nm as that’s the Volvo instruction and I felt the bolts bed in and twist so they clearly go through a lot.

Getting them off was a nightmare so do best that in mind. I broke out the 1600nm impact wrench and it did not shift them!!! It simply say there with the socket getting burning hot.

I ended up using half inch breaker bar with 2 foot scaffold pole. Those who know me will know that is absolutly not my style, nor is it my recommendation, but getting beach bolt off from the caliper carrier bracket was very hard work so needs to be born in mind in future!

Thanks all!

............has it sorted the problem though?