780 Intermittent clunking under hard acceleration

I've been getting this intermittent clunk under hard acceleration in the 850 recently. I'm inclined to think it's suspension. The mounts are new (all of them) and I just got under the car today to confirm they were all done up tightly. The drive shafts don't seem to have any side-to-side play.

Anyway it is a very intermittent and mechanical clunk sound, so I don't think it's knock, which is what someone had suggested to me previously. The control arms and ball joints are all fine. I wonder if it could be some play in the strut top causing the wheel to hop or something like that.


  • Transmission mount bushing maybe?
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    Transmission mount bushing maybe?
    You mean the top mount? It seems fine. The bottom one is an ipd mount and tbh that seems fine too.
  • Was thinking the bottom one as had a similar rogue clunk from shagged out rubber
  • Ex850RSnoopy (@Ex850R) Somewhere Over the Rainbow. Melbourne.
    I've seen my bottom trans mount, a blue one, chop out over an unexpected short time due to much boost.
    cancer sucks
  • SpacSpac (@Spac) Canberra-ish.
    Saggy motor mounts can allow the motor to drop, and then even good trans mounts can't stop metal-metal contact.

    Your description is exact how the silver T4 was when I first bought it - if the 850 had the same setup as the S40, I would be 100% confident that this is your problem.
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    The main motor mounts are barely a month old. I looked at them, and they looked okay to me, but that's hardly an expert opinion, and I'll try and be mindful of Occam's razor.

    If I hold the brake and throttle together, the motor rises on the firewall (exhaust) side, maybe a centimetre or two The front (intake) side doesn't seem to move much.
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    I know the spring seats are on the soft side (I think @Philia_Bear saw this and nodded in general agreement) so I've just ordered new seats and strut bearings and misc hardware.

    @Philia_Bear also suggested maybe it IS ignition, so to err on the safe side I've also ordered a new cap and rotor and I've bought a set of OEM spark plugs. I run iridium plugs and have done for ages, so I don't think they're the issue as they've never given me any trouble before, but in the interests of experimental control I'll do it anyway. The cap and rotor are about 2.5 years old so maybe it's time for freshies anyway.
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