Light rattle over small road irregularities?

[zcacogp]

Chaps, 

Quickie. I have the usual musical suspension problems on my 987.1C. It rattles slightly over small road irregularities; typically the sort of slightly broken road surfaces that we see so often these days. It's a light rattle but the handling is otherwise very good. 

Am I right in thinking this is usually ARB drop links? (Annoying if so as I changed them 18 months ago for some Meyle ones.)

Thanks. 

[½cwt]

Drop links, or could be a tuning fork starting to rattle a bit.  Problem is these can't easily be tested in situ and even off the car it is difficult to feel the wear in the spherical joint.

[zcacogp]

Thanks. The tuning forks are even more recent and from Spyder Performance. 

I think the answer will be to get underneath it and give the drop links a wobble and see what's what. 

Thanks for your help!

[Ninesomething]

Heat shield?

[½cwt]

32 minutes ago, JonSta said:

Heat shield?

^^ Good call!

[zcacogp]

Good call but I don't quite think so. It's a bit too mechanical and happens regardless of speed. 

 

It's also front near side, and I don't think that there are many heat shields there. 

[½cwt]

47 minutes ago, zcacogp said:

Good call but I don't quite think so. It's a bit too mechanical and happens regardless of speed. 

 

It's also front near side, and I don't think that there are many heat shields there. 

OK, front - most likely drop link or maybe a hardened ARB rubber?

[zcacogp]

Hardened ARB rubber .... I'd not thought about that. Let me have a look. Thanks for the suggestion. 

[Menoporsche]

Heat shield is always possible, but discussions on here mentioned that while the 986 frequently has problems with rattly heat shields, the 987 has a lot less as they changed the design/materials. IIRC.

[Paul676]

Have a look at the metal shield behind the brake disc... 

[zcacogp]

Update: I've swapped the near side ARB's, front to back and vice-versa. And tightened up the bolts on the saddle cover on the N/S/F ARB mount (they weren't loose, but weren't done up as tightly as they could have been). And now that I've taken it for a brief run 'round the block I can tell that the noise could be different but isn't gone. 

So .... any more ideas? The difference could be my imagination, of course! 

On 4/23/2022 at 7:58 PM, Paul676 said:

Have a look at the metal shield behind the brake disc... 

Now that is a GOOD idea, but there aren't any heat shields there any more as I've removed them. 

[Paul676]

have you looked at the ones behind the brake disc ? I removed the ones from the exhaust...

[gardenkirrie]

A long time ago I had a similar rattle. Took car to OPC who said there was nothing wrong. A couple of months later it failed MOT at a local garage; short section of a front spring had broken off, and was rattling around in the pan. There was still enough of the spring left to support the suspension. and there was no effect on the handling. Found myself a reliable indy after that.

 

[zcacogp]

Guys, 

Thanks for the replies. And thanks for the prompt to update this thread gardenkirrie; I've had the car up in the air in the last few days and the news is good. 

The problem turned out to be the big bolt between the end of the tuning fork and the middle of the coffin arm. It was not as tight as it should be on the N/S/F and tightening it solved most of the problem. I therefore tightened up the other three corners and the problem has entirely gone away, which is very good news. How those bolts weren't as tight as they should have been I don't know; I fitted the new arms about 9 months ago and it's been in to an indie for a fitting and geo check twice since then. I'm glad that it is now OK and hope that this is the end of the story. 

The only downside is that the car seems to creak more than before, but that's probably due to having polybushed arms. Ho hum; it's a price I'm happy to pay as the handling is so precise. 

FWIW, while it was up I removed the heat shields from behind the rear brake disks, and I had removed the ones from behind the front disks about 18 months ago. What are these for? My 944 had them as well, and I removed them as they started to rattle and never suffered any ill-effects so I am curious as to why Porsche carried on fitting them to later models. Can anyone shed any light? 

Thanks for your help chaps. 

Edited May 23, 2022 by zcacogp

[½cwt]

@zcacogp not so critical on the coffin arm to tuning fork bolts, but did you torque them up (160Nm/118lbft) with the suspension at the normally loaded position (Z=0) i.e. not on full droop when jacked up.  This is essential for the coffin arm to subframe bolts otherwise you'll damage the rubber bushes between the inner metal bush and the arms by preloading them.

[zcacogp]

5 minutes ago, ½cwt said:

@zcacogp not so critical on the coffin arm to tuning fork bolts, but did you torque them up (160Nm/118lbft) with the suspension at the normally loaded position (Z=0) i.e. not on full droop when jacked up.  This is essential for the coffin arm to subframe bolts otherwise you'll damage the rubber bushes between the inner metal bush and the arms by preloading them.

Good Q and I didn't know that this was a requirement. No, I didn't! 

How do you do this for any of the bolts without a pit (or hoist that lifts the car on it's wheels)? If it's sitting on it's wheels there there isn't space to get in to the do the job, is there? 

[½cwt]

1 hour ago, zcacogp said:

Good Q and I didn't know that this was a requirement. No, I didn't! 

How do you do this for any of the bolts without a pit (or hoist that lifts the car on it's wheels)? If it's sitting on it's wheels there there isn't space to get in to the do the job, is there? 

When the car is on axle stands, use the jack to raise the hub protect the bottom of the coffin arm,  until the weight just comes off the stsnd, you are then near if not exactly at z=0.

[zcacogp]

2 hours ago, ½cwt said:

When the car is on axle stands, use the jack to raise the hub protect the bottom of the coffin arm,  until the weight just comes off the stsnd, you are then near if not exactly at z=0.

Thanks. I'll put this on my list of things to do this week. 

[Paul P]

12 hours ago, zcacogp said:

Guys, 

Thanks for the replies. And thanks for the prompt to update this thread gardenkirrie; I've had the car up in the air in the last few days and the news is good. 

The problem turned out to be the big bolt between the end of the tuning fork and the middle of the coffin arm. It was not as tight as it should be on the N/S/F and tightening it solved most of the problem. I therefore tightened up the other three corners and the problem has entirely gone away, which is very good news. How those bolts weren't as tight as they should have been I don't know; I fitted the new arms about 9 months ago and it's been in to an indie for a fitting and geo check twice since then. I'm glad that it is now OK and hope that this is the end of the story. 

The only downside is that the car seems to creak more than before, but that's probably due to having polybushed arms. Ho hum; it's a price I'm happy to pay as the handling is so precise. 

FWIW, while it was up I removed the heat shields from behind the rear brake disks, and I had removed the ones from behind the front disks about 18 months ago. What are these for? My 944 had them as well, and I removed them as they started to rattle and never suffered any ill-effects so I am curious as to why Porsche carried on fitting them to later models. Can anyone shed any light? 

Thanks for your help chaps. 

Not just porsche - pretty much every car I have ever had with disc brakes has had them - as far as I know - they are to help stop heat transfer to the suspension, help stop brake dust getting all over the show, and help stop general crud and grime from building up on the disks - my thinking is they put them there for a reason - otherwise they would save themselves 50p per corner.

If their function is to help prevent earlier failure of other components - not sure if you would necessarily "notice" a difference - if you took them off a 8 year old car, and the shocks failed a year later - who knows - might have nothing to do with it, or they may have lasted another 3 years if they hadn't been cooked for example.

[gillbe]

From an internet search, they are designed to keep water off discs

I was at a Tech Session with the local PCA at HighTec this weekend, and this specific question was raised. The answer was that it would be appropriate to remove them for a track only car, but not for a street car. The mechanic had removed them from his car and then moved to seattle and very nearly got in a serious accident because of the vastly increased wet braking distance. Those things are safety features. If brake cooling is your goal get the ducts.

[zcacogp]

Thanks PaulP and gillbe, both of those are really interesting answers. I fully understand the logic that the plates do something and are worth the money that Porsche spent on fitting them. The question of whether that benefit is applicable to me or not is the relevant one; for instance I will never use the ISOFIX child seat mounting points on any car as I have no kids but they have been installed on a number of cars I have owned. 

The notion that they help keeping water off disks is very interesting and I'd not argue the point with Porsche. Thanks for the info gillbe. 

[Jon61]

I'm sure they are there for a reason, but I'm not convinced that it's to keep water off the discs. I think centrifugal force is quite enough to disperse most water off discs once a car is in motion, with the action of the pads on the discs (and cross-drilling if applicable) once braking starts doing the rest. Personally I think their purpose is more likely to be one of those that @Paul P mentions above.

[gillbe]

seemingly for both reasons, from https://www.sciencedirect.com/topics/engineering/disk-brake

 

Basic Principles

The modern automotive disc brake is an ‘open’ type of ‘spot’ disc brake, i.e. the friction surfaces are not enclosed for protection (a ‘dust’ shield may be fitted to prevent the ingress of road debris and water spray, but does not enclose the brake)