[928uk] FW: [Fwd: Re: PSD operation] & Tyre pressures

[David Morgan]

Hi Mark,

I've run the RDK system to the recommended tyre pressures for many years
now, and there doesn't seem to be any untoward wearing in the middle. It was
a bit of a pain though to see the warning continually light up on the dash
when the pressure dropped just a couple of psi. 

About a year ago I purchased a second set of D90s and got them refurbished.
While the tyres were off, I replaced all the tyre pressure o-ring seals and
most of the back nuts, as these are a bit difficult to remove, even though I
have the correct Porsche tool, so you have to use a hammer and chisel:-(
Since replacing these, I have not had any problems with leaking sensors, and
the tyres now correctly hold their pressures.

If you want to do this, you are welcome to borrow the special tool, but the
back nuts are about £22 each, and from memory, the seals are about £2.00
each, and as you are probably aware, you need eight of each. I got mine
through Dick Lovett in Cardiff.

Hope this helps.

Regards,

Dave Morgan

Guards Red GT


-----Original Message-----
From: 928uk-bounces at lists.928.org.uk [mailto:928uk-bounces at lists.928.org.uk]
On Behalf Of Mark Nichols
Sent: 09 February 2012 10:25
To: 928uk at lists.928.org.uk
Subject: [928uk] FW: [Fwd: Re: PSD operation] & Tyre pressures

Thanks Smiffy,
I am pleased the function appears correct. You are right, I need to gain
more experience. First car I have driven with an LSD and last night was
unintended. Just poor driving. Cold night, cold tyres and poor road surface
all conspired. I run standard wheels and T1R tyres at handbook pressures of
44psi rear and 36psi front. My TPS system works and nags readily if
pressures drop by more than about 2psi. 44 Seems quite high for the rear. Do
any 928'rs run at reduced pressures at all or is the 44psi considered
optimum? I havn't run these tyres far enough to see if they are wearing in
the middle yet.

Regards
Mark N
90GT



---------------------------- Original Message ----------------------------
Subject: Re: [928uk] PSD operation
From:    "Paul R. Smith" <smiffypr at clear.net.nz>
Date:    Thu, February 9, 2012 9:57 am
To:      928uk at lists.928.org.uk
--------------------------------------------------------------------------

That all sounds like it is working correctly. The PSD does back off the
locking gradually.

In a cornering situation, with an open diff, the inside wheel would loose
grip, limiting the torque to the outside wheel, allowing it to keep the rear
end in line. With the PSD preventing the inside wheel spinning, it allows
you to apply more throttle in the same situation, so when both wheels loose
grip the back end goes more sideways. So, if you are using the extra grip
that the PSD gives you, you need to be extra careful. Lifting off the
throttle sharply makes it worse.

You really ought to practice in a safe place rather than on a sharp country
bend.

Smiffy

On 09/02/2012 22:23, Mark Nichols wrote:
> Hi,
> My PSD appears to be working fine. Question is one of how it should 
> work in use. I have a steep drive (tarmac) and have to turn sharp left 
> into it from a narrow road, so no way I can enter square on. Can't 
> reverse on because front scrapes on the road. So what happens is, no 
> matter how careful I am, the inside rear wheel has sufficient weight 
> lifted off it so the PSD operates. I get onto the drive and the PSD 
> disengages and the light goes out, but it doesn't release immediately, 
> I can feel it engaged for a few seconds as I ease up the drive (about 
> 20 ft). All good. So I thought. Last night I was a little too 
> exuberant on a sharp country bend and the back broke away. Fun I 
> thought for a moment, but I wasn't able to correct as quickly as I 
> expected. Felt a bit strange which I could only put down to the fact 
> that the PSD locked the diff up once I started snaking. Of course if 
> the weight was being transferred left to right to left, then I might 
> expect that. I had lifted off the throttle as it was quite low speed, 
> but it got me thinking. How quickly should the PSD activate and 
> de-activate when it engages? Is what I am experiencing normal? (I 
> know, I should drive better!). Thanks for experience shared.
> Regards
> Mark N
> 90GT
>
>
>
>
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