mark kibort

I wish. we havent got Scot on the track yet. im trying to get him out for a NcRc race in sept oct.

the mod turned out great. all the clearances are all just like stock, just spaced out. the awesomething here is that you have a 22lb rotor, not some 14lb 10"+ rotor! with race pads, it should be an substantial improvement.

Key to this design was the centering rings! awesome idea. without them, the design doesnt work!

i cant wait to drive it, hard. probably this next weekend.

Mark

pcar928fan

So when can we buy a set of these Mark??? I would LOVE to do this to my EURO85 car!!!

UKenGB

I realise this is an old thread, but I believe it is still relevant, so rather than ask smiffy directly, I thought I'd direct my questions to him here.

1. Did you use the 304 mm 993 discs, or 322 993TT discs?
2. Why not S4 or GTS discs? Would they hit the lower ball joint?
3. The lower offset/width of the 993 discs mean the radial holes are about 5 mm outboard, compared to using the 928 discs. The Cayenne discs even more so. Would using the 928 discs not mean the radial bolt holes, being further inboard would more easily clear the axial mounting lugs of the spindle?
4. How much improvement (in adapter design, not braking) would you get using the larger Cayenne discs, pushing the caliper further from the axial lugs on the spindle?
5. What did you make the adapters from? Steel or Al?
6. How long did they last? Still in use?

One way or another, I want to be able to put S4 calipers on an S and not found any ready made adapters, so looking into making my own and answers to the above would be most helpful.

Thanks.

GregBBRD

The later model 928 rotors will definitely hit the ball joint. The ball joint can be ground down for clearance, but "thinning down" a ball joint that is constantly trying to pull the ball out of the joint ('78-'86 928's) comes with some risk. (I've done this three or four times to cars that already had the rotors and adapters, to keep the rotors from being ruined a second time, without any issues. However, this never gave me a warm fuzzy feeling.)

928 International and 928 Motorsports (no longer in business) used to sell the adapters. Call Mark Anderson (928 International) and see if he still has these.

Moving the caliper a few millimeters is a complex problem, since you will still require a bolt to attach the adapter in the original hole. It's problematic to put a bolt into a new location, where part of that location already requires another bolt.

UKenGB

Oh yes, I understand the problems and cannot find anyone currently supplying such an adapter, but maybe they weren't considering the use of the Cayenne disc which I would think with its larger diameter would ease the 'crowded bolt' problem.

In fact the bolts should cross (at 90°) 1 mm apart, so they don't actually interfere. Just pass quite close. As smiffy has done this (and showed pictures of the installed adapter), I wondered how they held up.

The other option would be to displace the caliper sufficiently to ensure the bolts were well apart, but I'm not sure if that is really necessary.

Hopefully smiffy can respond here, otherwise I'll ask him directly on our UK list.

Wisconsin Joe

928 Motorsports was sold and Carl retired.
The place that bought them is still selling much of the stuff.

UKenGB

Could Xschop explain this. Why are the earlier spindles stronger?

UKenGB

Anyone know how to contact OBehave? He made some adapters and I'd like to ask him about them.

GregBBRD

Are we pretending that late spindles have a tendency to fail or bend, making this important?

Unless the result of a major crash, I've never seem a bent/broken spindle...of any vintage.

Early spindles also have the terrible design issue of the ball joint being constantly pulled out of its' socket....past the "lips.

This was corrected in 1986.5, by inverting the ball joint, allow the load to be transferred to the main body of the ball joint, not on the "lips".

Far superior design!

UKenGB

I had not realised that, but on checking the manual I can see exactly what you mean. What were they thinking. The entire front suspension relying on a ball joint in TENSION. And those first ones were originally the aluminium ones? No wonder they broke.

Do the steel ones actually pull apart? I hate that design choice but in practice do they actually fail?

The only solution then would be to swap the entire front suspension for S4. Are there ANY common parts?

UKenGB

I think xschop is actually referring to the strength of axial to radial adapters required to put S4 calipers onto a pre S4 car. The S spindles/knuckles with their wider caliper mount spacing make it harder for an adapter to be as strong as for the pre S spindles. But he worded it as if the actual spindles are weaker on the S and I hoped he could confirm exactly what he meant.

By S model I mean the cars with the later 'floating' caliper and 104 mm mount spacing as opposed to the first 'sliding' caliper (narrower mount spacing, not sure if 74 or 76 mm), although both axial mount. In UK and US I think the term S was used in different years, so thought I'd clarify that.

belgiumbarry

i swapped the front suspension of a '90 GT to my '82. The arms and of course the spindles are different.They do mount the same way on the chassis.
To me it looked as Porsche changed everything to get it 10 mm more inboard to have that space for the ABS wheel on the hubs which are now longer.

That way we have 1) the better design ball joint and 2) the big brakes without the need of adaptors.
I have the GT steering rack but didn't needed it , the rods must be 10 mm shorter each side and the '82 rods had just enough thread to do so.

UKenGB

Interesting. So are all the little brackety things the same? What about the actual strut (suspension unit)? Can you get away with just arms and spindles (and brakes of course).

So the steering rack ends are shorter on the later cars? I think the ratio did not alter. Thinking of selling your GT rack?

icsamerica

Euro 84's have ABS, same for some USA 85's. all with the old suspension,

I believe Porsche changed everything because of the ball joints, both were redesigned. It was important to remember what's going on at the time. It's late 83 and The C4 corvette just came out and with the help of tire technology was able to pull 1G on the Skid pad, This tire tech was soon going to find it's way to the 928 and suspension changes had to be made to cope with the higher loads and improve handling necessary to compete in the market place. The greater steering axis inclination angle and new ball joint arrangements both serve these purposes.

belgiumbarry

I assume the struts are the same.... sure the shocks, don't know about the spring diameter as i used stiffer "race" springs which have a smaller diameter just as the GT also already had.
Yes, as all comes 10 mm inboard , the steering rods need to be 10 mm shorter. That doesn't do anything on the ratio. Internals stay the same. Now that you mentioned, i don't know if the ratio ever changed over de 928 models ???

Sorry no , as long as i have my 2 running 928's i don't sell parts of my '90 GT parts car .