FredR

Whereas I am reasonably competent at analysing technical problems in general, I have a mystery noise that is irking me somewhat. The issue only occurs on one specific left hand bend I commonly drive around with enthusiasm if and when no other vehicles are present. The bend is question is at the bottom of a short but sharp drop and is off camber with a double apex. At normal road speeds the bend is nothing special but when pushed along it is a challenging bend. With wide rubber front and rear I can easily generate over 1g lateral acceleration and when I push the 928 hard around this bend I experience a strange noise on the left hand [driver's side] of the car. As best I can tell the noise emanates from the front left hand suspension. The noise is not continuous, rather it is a sudden short "creak". Such issue may well present itself elsewhere but this is the only bend I regularly challenge on my way home.

Initially I thought it was the upper ball joint as that was a bit suspect so I replaced that arm and fitted urethane bushes whilst in there [did both sides] but the sound persisted. I also had a squeal going over speed bumps and eventually tracked that down to drag on the roll bar bushes that I treated with a cover of PTFE tape on the roll bar mating surface and some silicon. The Devek bar has Rose joints on the drop links and they are greased and seem ok and I wondered if they may be prone to such moaning and groaning. The sway bar mounts are reinforced and visually appear to be solid.

My prime suspect at the moment is the lower control arm bushes given they are original rubber but I am struggling to relate the sound I hear with such an issue. I hate changing anything to cure a problem only to find it makes no difference.

Any thoughts?

Rgds

Fred

Mrmerlin

FredR

That is an interesting suggestion but I have little clue as to what I would be looking for.

I have come across the term "fingers" being used in threads but I do not know what they are or look like- if you happen to have a pic handy that exemplifies that would be appreciated. FYI the current mounts are the Volvo type ones and were fitted about 5 or so years ago and will have about 10k or so miles on them. I got them when I was earning big bucks so bottled out of trying to fit them myself [as I would today now that I am retired and semi skint after purchasing a luxury villa by the sea to live in].

I take it the logic behind your suggestion is that if the mounts are in a state of partial degradation then under extreme lateral loading condition some kind of metal to metal contact may be occurring?

crushingday

following

Kaplan69

As I am assembling my 928 to race, and spent several hours removing the lower rubber bushes on the lower arm; could it be, on this loading AND bump, you're getting a rotation (along with associated growl or squeal) of one or both of the larger bottom bushes? The factory ones are supposed to be "bonded" somehow, maybe you've tweaked one loose? You've already put urethane up top- the lower arm (and bushing) are the heavily loaded ones... Ken

Speedtoys

The upper mount block (at the top of the image), and lower mount plate (#4), have fingers that lock to each other if the mount collapses.

FredR

Jeff,

Thanks for the sketch- at least I now understand the term "fingers". No idea what I should be looking for though. I have no strange vibrations- indeed the motor is running very smoothly at the moment.

Speedtoys

See if they ave touching or rubbing...indicating the motor is rolling over under the hood a lot causing them to...grab and arrest the movement.

FredR

Ken,
My primary suspicion still lies with the lower arm bushes and for some time I have been contemplating fitting the Powerflex solution as I can get the bushes sent over and fit them here irrespective of whether that is the root cause of what I am hearing. I have pulled the bushes from a spare earlier model arm just to prove I could get them apart and I saw no signs of any bonding material being used on what I pulled out.

Mrmerlin

Fred, when fitting Volvo mounts the finger plate should be adjusted.

Read (slightly bent), to prevent the fingers from being too close to each other, they will be close with the Volvo mounts.

NOTE as the mounts wear in or sag this distance becomes greater so less of a chance they can touch.

To adjust these fingers use a 17MM socket on a 8 inch 1/2 inch extension and put the other end on a floor jack,

put the socket on the 17mm motor mount bolt thats closest to the finger pad and jack the bolt up.
NOTE go very slow as you dont need much to bend the finger.

I had a noise similar to what you describe after fitting new Volvo mounts,
and it would only happen when making a hi G turn.

NOTE make sure the finger is parallel to the opposite finger this will give the max clearance,
it can be adjusted sideways with a long screwdriver and hammer

FredR

Fascinating- I hope to be under the car tomorrow or the day after- hopefully will be able to make some sense of your note as I view the thing directly- well past my bedtime at the moment but I am trying to stay aware so I can watch a UK motoring programme involving the rebuild of a Triumph GT6 that is about to start!

Mrmerlin

to see the fingers well you need a good flashlight and a inspection mirror

FredR

Driver side front

Passenger side front

Passenger side rear
Stan,

I was in there this morning and found something of a surprise that may even exceed the nonsense Paul found on his mounts shown in his current thread! It seems as though the plate that fits under the mount is just not present and the external bracket seems to be mounted in the wrong bolt position as it is not on the centre line of the mount. This is the same both sides but at least the hooks seem to be fitted on the correct side for what little that is worth.

Now I am left wondering why they were omitted. These are Volvo mounts and whereas I do not want to say who fitted them it was not me and it was someone who should well know what to do! Thus my squeak is not being caused by the brackets coming into contact but of course the obvious question is whether this form of installation has caused some issue that generates that squeak?

.

merchauser

fred, can you give a little more explanation about this orientation? not understanding about wrong bolt position, and center line. obviously, I am very interested in your findings.

while I am no expert, I believe the lower plate is not critical for proper function; an important safety feature, the hooks/fingers will prevent the engine from dropping in the event of collision. I have heard many leave these lower plate off to help compensate for the taller volvo mounts

FredR

Paul,

I have a feeling that is exactly what the agent did and perhaps why. Whether this design feature is present for a collision or a bit of insurance if and when the mount fails remains to be seen. The externally mounted bracket needs to be aligned to the mount centre line if it is to do what it was designed for- that bracket is mounted on the bolt that is off centre so could not catch the lug on the piece that is supposed to sit between the mount and the cross member.