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I have an '81 competition package five speed. When I bought the car, I was told it has been upgraded to S4 brakes. I am in the process of replacing the rotors. I ordered S4 rotors but they were much smaller than what I have. So I thought maybe I have GTS calipers and rotors, so I measured what I have, which are right at 13", which is slightly larger than the GTS rotors. Turns out I have S4 calipers with brackets that have been sized for bigger than GTS rotors. Since the GTS rotors were slightly smaller than what I had, I reduced the size of the spacers that were on top of the brackets to fit the slightly smaller rotors. However, the old rotors have a seriously thick rotor hat, about a quarter inch thicker than the new rotors. So, no I have two problems: the calipers bolts don't line up with the holes on the brackets. The rotor is 1/4 inch more inboard now. The rotors also now contact the tie-rod. I'm assuming that the caliper brackets were specific to the old, thicker rotor hats. I also discovered that I still have the old style aluminum tie-rods. I'm thinking I could add a spacer to the back (inside) of the rotor hat to solve both problems. Or, after I update the tie-rods, I'm assuming there is some adjustability and I can move them more inboard. But then I would have to purchase different caliper brackets which should line up, since my new rotors are probably what most people are running with upgraded rotors. I'm not sure how much spacers would cost to get machined but probably at least as much as new caliper brackets. Also, since I have an '81 car but with upgraded brakes, do I purchase the tie-rods for an '81 or newer model? I'm not sure what changed between the older and later model car's tie-rods.
I think by 'tie-rods' you mean bottom ball joint carriers? You should swap the alloy units for steel ASAP, and as these are thinner than the alloy ones this problem MAY go away - no guarantees though ! Very odd mixture of parts, shame you cant identify where the rotors came from.
jp 83 Euro S AT 57k
You should contact thePO to verify the parts that were used
Otherwise you need to chat with a brake system company to identify the rotors you have
I would not try to use spacers to move the wrong rotors to fit
replace any aluminum lower. Ball joints before the car is put back into service as already suggested
The rotors might have come from another Porsche model so with the originals you should be able figure this out
It looks like you've got an S hub and a brake caliper fitting so you can pass an S4 caliper on the S hub. So there's no way you can fit the S4 brake discs. What should be found is the origin of your rotors, by far like that, I'll say you should have AP racing brake discs and that's what you may buy.
Can anyone comment on how much adjustment there is for the ball joint carriers? I can only assume there is some adjustment there, I only need 3/16 to a quarter of an inch, so when I upgrade to the steel ball joints, I should be able to fit rotors that almost every other 928 is running. The PO had this car for twenty years and doesn't remember exactly what is on there. But I shouldn't have to replace with the exact rotors to get everything to fit. I will definitely follow up when I figure it out. I'm just looking for any insight if anyone has seen or experienced anything like what I have.
I would contact Carl and 928 Motorsports. They make kits to put S4 calipers on all early 928. I kinda doubt they made this particular kit, but I could be wrong. In any case they can sell you adapters and rotors that will work with your setup.
As someone who survived an aluminum ball joint coming apart while under way, I strongly suggest you replace those sooner rather than later.
If you bought 928 S4 rotors it will be the wrong offset. You need 993 rotors instead, possibly from a 993TT if they are indeed that large. The ones you took off were probably a custom offset.
The 993 rotors wont contact the ball joint if it has been upgraded to the later steel ones. Yours look to be the earlier alloy ones.
From what I have seen all 81 in the US, competition package or not, came with the standard brakes. I would change out the adapters for ones from one of our vendors and use 993 brake rotors.
Let me know if I can help. I agree its time for the aluminum ball joint carriers to go and get replaced. The steel carriers are not only safer, but they are smaller at that outer point and will provide greater clearance to the rotor.
Also: Blake is right (above) and this is a common misunderstanding. When upgrading to S4 brakes on an early car, you cannot use the S4 rotors and a caliper adapter and call it good. Doesn't work. The 993TT rotors have more offset, what you need to clear the lower ball joint with the spindle you have.
Jeanie at 928 Specialists, informed me that I needed 993 rotors and gave me the part number. She said all the aftermarket brackets designed for upgraded brakes were designed for 993 offsets. I am ordering steel ball-joint carriers, and 993 rotors. I'm confident this will work and will post up results regardless. I think the rotors I have are some sort of older racing rotors that are 13" in diameter and the spacers on my brackets accounted for the bigger size rotors. I'm assuming they were the same offset as 993 rotors. Jeanie gave me part #993.351.043/044.01 which are 304 mm, basically the same diameter as S4 rotors. I am going to ask before ordering, but I think 993 turbo rotors which are 322mm, should fit as well. I just may have to adjust to size of my current spacers smaller, since these rotors would still be slightly smaller than what I currently have. If I use the 304 mm, I shouldn't need the space at all.
06-04-2019, 12:58 AM
Brake issue/Questions
