Knocking under acceleration 172 Cup

ex-Chinese Dave · Saturday at 3:31 PM

I sometimes get a knocking noise which feels like it’s coming from the right front of the car when accelerating fairly quickly out of a left-hand turn. It’s the same kind of sound and feeling as you get if you lose traction upfront, and the engine revs high i’ve had a similar noise when I was accelerating in second gear on the straight, and the wheels spun up a little.. I’ve had almost all of the suspension components renewed recently, so I am wondering if it could be solved by replacing engine mounts or the gearbox dog bone. The car is on 130k. I’m obviously no expert on this, but just wondered what you guys think.

JamesBryan · Saturday at 3:36 PM

First culprit would be the dogbone.

adamlstr · Saturday at 3:49 PM

Vibra-technics engine mounts and new / poly dog bone, will make a WORLD of difference. No more knocking, barely any wheel hop, and much more positive In everything.

ex-Chinese Dave · Sunday at 6:54 PM

What’s the difference between poly-bushed and OE spec for daily driving a Cup? I’ve read many times that poly-bushed cars are a hard ride although I would only be changing engine mounts/dogbone?

Also, are these jobs a driveway DIY job? (I’ve a few tools and axle stands)

Matt Cup · Sunday at 8:10 PM

You will get more nvh with a polybushed bone mount. I’m pretty sure mines got one one along with the engine mount insert.

JamesBryan · Sunday at 8:34 PM

Matt Cup said:
You will get more nvh with a polybushed bone mount. I’m pretty sure mines got one one along with the engine mount insert.

Engine mount insert is terrible on them.

Polybushed Dogbone isn't too bad.

Matt Cup · Sunday at 8:39 PM

JamesBryan said:
Engine mount insert is terrible on them.

Polybushed Dogbone isn't too bad.

I don’t find it too bad 🤷🏻‍♂️. But then I only drive it once or twice a month.

JamesBryan · Sunday at 9:19 PM

Matt Cup said:
I don’t find it too bad 🤷🏻‍♂️. But then I only drive it once or twice a month.

Caused massive dash vibration on mine.

Had to take it off and fit Vibratechnic mounts instead.

Matt Cup · Sunday at 9:24 PM

JamesBryan said:
Caused massive dash vibration on mine.

Had to take it off and fit Vibratechnic mounts instead.

Yeah true it is a noticeable difference in the cabin. I take it you don’t get that at all with the vibratechnic mounts yet they are more firm than regular engine/gbox mounts?

Brigsy · Sunday at 9:40 PM

Matt Cup said:
Yeah true it is a noticeable difference in the cabin. I take it you don’t get that at all with the vibratechnic mounts yet they are more firm than regular engine/gbox mounts?

Vibratechnic upper engine mount, gearbox mount and poly dogbone are decent for road use. Run them on my trophy no dash rattles etc.

NorthloopCup · Sunday at 9:42 PM

If you press the original dogbone bush out, rotate it 90 degrees and refit it into the dog bone, you get 90% of the benefits of a poly bush with 0% of the NVH.

Matt Cup · Sunday at 9:43 PM

Good to know. Will be on the hunt for some vibratechnic goodies.

Brigsy · Sunday at 9:53 PM

NorthloopCup said:
If you press the original dogbone bush out, rotate it 90 degrees and refit it into the dog bone, you get 90% of the benefits of a poly bush with 0% of the NVH.

Tempted to try that on my dci, engine moves all over on stock dogbone. Tried pu filled dogbone and the nvh on idle was insane.

NorthloopCup · Sunday at 9:54 PM

Brigsy said:
Tempted to try that on my dci, engine moves all over on stock dogbone. Tried pu filled dogbone and the nvh on idle was insane.

Trust me mate, it’s probably the best free modification you can get/make on them.

davo172 · Monday at 7:27 AM

NorthloopCup said:
If you press the original dogbone bush out, rotate it 90 degrees and refit it into the dog bone, you get 90% of the benefits of a poly bush with 0% of the NVH.

Correct

Matt Cup · Monday at 7:35 AM

NorthloopCup said:
If you press the original dogbone bush out, rotate it 90 degrees and refit it into the dog bone, you get 90% of the benefits of a poly bush with 0% of the NVH.

Sorry the the possibly dense question. But which bush gets swapped 90°, the left or right?

NorthloopCup · Monday at 9:23 AM

Matt Cup said:
Sorry the the possibly dense question. But which bush gets swapped 90°, the left or right?

View attachment 1728859

The one circled mate it the one you turn 90 degrees, but that’s not the original dog bone or bush in the image mate. They’re round bushes on the 1*2.

Matt Cup · Monday at 9:26 AM

NorthloopCup said:
The one circled mate it the one you turn 90 degrees, but that’s not the original dog bone or bush in the image mate. They’re round bushes on the 1*2. View attachment 1728868

Nice one fella! Yeah the image was just a quick Google search.

mumpy · Monday at 10:41 AM

On my daily 172 I have powerflex purple series polybushes fitted everywhere, including dog bone and black series for wishbones and steering rack. Also have vibra technics engine + gearbox mounts. Idle is slightly raised I think due to ron 98 map, steering wheel does vibrate quite a bit but doesn't bother me. Car feels great to drive, not too harsh but that's subjective.

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Knocking under acceleration 172 Cup

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