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John Sims

John Sims

PCGB Admin
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I think Beakys LSD is going South - Periodic bad UJ noises coming from the rear that don't seem to be UJs. Slack on drive shaft with a noticeable clunk on as you turn it from one direction to the other. I guess it could be the input splines but difficult to tell without further investigation. Noise is more pronounced when being enthusiastic on roundabouts and produces a speed related knocking noise. I was wondering/hoping it was a loose wheel.

It was obviously going to be the case as I had a spare gearbox with (as far as I'm aware) a perfectly good LSD for years and then recently sold it.

So what are my options?

After market improvements?

Rebuild - is this even possible now?

Try and find another one?

I look forward to your comments.

Another thought, I have had some issues with moments of light or vague handling could it be related? Loose bearing perhaps. There doesn't seem to be any undue movement when the car is on the ground or on the offside wheel (the one I thought was the issue) when I jacked it up.
 
Rebuild is no problem, many places can do it, a few can even do it well. What sort of diff do you want? What sort of driving do you do? If you do many track days then a replacement LSD is probably the best, in which case it may be easiest to re-buld your own along with the box. The aftermarket is now getting lots of options for LSD's including carbon LSD's but not sure if they make one for the turbo, but certainly do for the 968. There are the ATB diffs, arguably better for standard road use and hill climb events, Quaiffe and Guard both make good quality examples for our cars, I think it is this road I will go down for my car. I like the way ATB diffs work, slightly less agressive than a LSD diff, but maybe not quite as full on.

 
I wouldn't bother with the stock Porsche replacement. It'd cost as much to rebuild as an aftermarket item and wouldn't be as good. Pat swears by his LSD and reckons it is well mannered enough for road use. However as Peter says the ATB/Torsen type of diff is just unbeatable for road with odd trackday use. I like the way they send torque to the wheel with the most grip - unlike an LSD, the way they aid steering and reduce understeer as the outside wheel is pushing harder than the inside wheel (unlike an LSD) and with it being geared and not locking you get none of the downsides of LSD's. On the other hand there are advantages to LSD's but they can also work against you and bite you in the backside.

The good thing about a Quaiffe LSD ATB is that they are the same price in US$ as £ so if you can get one shipped over here and avoid import duty then you can bag yourself a bargain.
 
Thanks for your comments guys.

The more I think about it the more I am convinced it must be the diff. It would certainly explain some of the strange handling characteristics I've been experiencing. The M40 in the snow, on the way to Front Runner, was very unpleasant and completely unpredictable.
 
John could you expand on your comment about strange handling characteristics at all?

I only ask as I'm going to get my car set up (corner weights etc) to reduce the understeer I'm getting under power - yes, i know most cars understeer slightly under power, but this is excessive! - and the reverse, severe tightening of line on lifting off. Something tells me that part of this is down to the LSD and its associated effects?[8|]
 
I can't say specifically when, but at various times, and for no apparent reason, I seem to loose feel; as if the steering has gone very light. I wondered if there was something loose at the front but I can't find anything. I also wondered if there was a power steering fault and it was occasionally pumping harder - if that makes sense. Or an issue with the steering rack. The car seems to have stopped talking to me and I don't trust what it is saying. As I said before I wondered if I had a loose wheel. It is actually quite disconcerting. Of course it might be something loose or a steering fault as well.

Aside the periodic lack of feel (and the snow issue) I haven't noticed any lack of grip. It still seems to turn in well and is still nice and neutral in a corner. Perhaps there is a slight tendency to over steer which it hasn't since I had the suspension set up last year.

I did have a strange sideways moment this weekend. I had been driving across dry grass and then turned sharp right onto a service road. The surface of the service road looked fine but the back end came round fairy abruptly - I'm assuming the diff had locked up going across the grass.

 
Powered understeer and lift off oversteer could be associated with a soft back end (or too hard front end), I'm not sure it would be diff related.
 
John,
If your LSD is worn out, its the first one I have heard of. (I refer to clutch plates wearing out)
I would expect its other Diff components that may be on their way out.
The LSD component is just a set of Clutch plates in a housing. They can only wear out , and in wearing they slip more easily so the Limiting of slip has reduced from maximum at day one to where you are now.
The star wheels, or crown wheel and pinion bearings are more likely worn.
You may be surprised to find its inner CV joints. They do dry out, I was surprised how I needed to repack mine recently (140k miles).
I do not like the ATB theory. The idea that it detects slip is OK, but it is also daft. There should be no slip until a consistent loading is achieved. Thats what a LSD provides..

I hope you get to the bottom of the problem without huge costs. Perhaps try a resistance check side to side with the rear wheels in the air - in Neutral. Then check for backlash side to side, do this with the car in gear. Do a comparison with another car, I can check mine if you want a comparison.

George
944t
964
 
John, I'd check what Guards transmissions sell them for in the US as the dollar is very weak against your pound. You should be able to pick up something wonderful for a really good deal and as Scott said, I don't even notice mine on the road for general driving and a boon on the track.
http://www.guardtransmission.com/
Or contact these guys. I'm perhaps doing something else with them and they seem very professional.
http://www.californiamotorsports.net/

 
Thanks for the links. At the moment it seems the best price is still going to be Quaife UK (once shipping and duty is factored in).

Beaky is going to the Doctors in two weeks so we will see what they find. If something has gone the way of the pear and there is a reasonable or equivalent cost upgrade available then it would be rude not to go with the new technology. I'm not saying I hope it is the LSD but now wouldn't be too disappointed if it were. I do take George's point and have every confidence it won't be anything like as easy as slapping in a nice new LSD. Old cars are like that. [8|]
 
As far as I can see replacing a diff is an easy job. The only tricky bit is setting the backlash between the crown wheel and pinion once you put it back together again. Other than that it is a simple job of unbolt the old one out and bolt the new one back in. Assuming, of course, that there are no 'While i'm in there' jobs to do.
 
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