Rattle / Rear disk backplates

[zcacogp]

Chaps,

I have mentioned it in passing on here, but my car had a distinctive rattle at certain engine revs recently. It sounded just like a loose baffle in a silencer, or possibly a loose heat shield somewhere.

I put it up in the air this afternoon and had a look. I found that (as per Paul Smith's suggestion) it was a backplate, behind the O/S rear brake disk. The lowest mouting point had corroded through (yes, it's aluminium but it still corrodes over time) and it was loose. 'Pinging' it with my finger prodcued a sound very like the rattle I heard, so I presume that is the problem.

To solve it, I have removed the plate altogether. Is this a bad thing? I seem to recall on here, a couple of years ago, someone posted that they don't do anything anyway and can be removed with impunity (I think it was Fen who said this.) Is this true? What does the back plate do? Anything? If I remove it, what ill effects will I experience? If it doesn't do anything, why did Porsche pay money to develop and fit the part?

(I do still have the equivalent part fitted on the other side. So the car is unbalanced. If the accepted trend from this thread is that the backplates do nothing then I'll remove that one too.)


Oli.

 

[sawood12]

The backplate serves no function other than to keep brake dust away from the inside of the suspension. In fact if anything it impairs cooling and traps moisture promoting corrosion of the inside face of the disk - OK this is not a problem as such on 944's but is on 996's and Boxsters. I wouldn't loose any sleep over it. If you ever get an opportunity to replace it then you may as well - or simply remove the one from the other side, but I wouldn't go to the trouble or expense to specifically replace it as it involves removal of the rear hub. I have removed the shields from my front brakes with no adverse effects.

 

[zcacogp]

Scott,

Thanks - very helpful. It stays off.

SNAG is that now it has been removed, I just did a 4 or so mile test drive, and it showing symptoms remarkably like those of a loose wheel or duff CV joint. (i.e. Rattle or 'bobbling' noise when moving forward, associated with road speed.) I have re-checked the wheelnuts and I did do them up tight (as I thought). Any idea what else may produce a noise like this? All four CV's were replaced about a year/11,000 miles ago.


Oli.

 

[944psi]

I replaced one of my rear brake disc back plates ...... cost about £48 for a pressed piece of aluminium!

WRT your noise: Could it be loose brake pads, i.e. moving up and down within the confines of the caliper as the disc rotates past?

Just a thought.

Phil

 

[zcacogp]

At £48 it definitely stays off!

Other noise ... I have just had it up in the air again and looked, and there was a noticable 'clonk' within the gearbox when I twisted one wheel with it in gear.

Nasty thoughts of knackered diffs ran through my mind ... I pulled out the top oil plug (fill plug) and it could have been a smidge down on gearbox oil. I filled it right up (level with the plug) and put it all back together and drove it again and it seems to be better. Could be my imagination that it is better tho'. I don't think the problem was imaginary in the first place.

I think I'll drive it next week with the radio off and see whether it happens again. I just don't *quite* trust it yet ...

Thanks for your input tho' chaps. It's appreciated.


Oli.