Brake rotor upgrade ideas for O.B.'s
09-27-2009, 04:36 PM
#31
Road Warrior
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I think you totally missed my point. I could be wrong, but let me explain again.
OB or "S" systems use the same spindles, so I was refering to the inner diameter of the brake rotor from a hub-centric perspective. Lets talk "S" brakes.
1. The S brakes have a rotor with a 154mm inner, hubcentric rotor diameter. the part that fits on the hub.
2. The S4 brakes and that entire family of the same hubcentric rotor inner diameters (GTS, 993TT, 964T, S4, etc) have a inner diameter of 157mm.
3. IF we want to increase the rotor size as far as diameter by using S4, GTS or 993TT rotors, OF COURSE we need to move the calipers out to take advantage of the greater leverage. The reason that this mod can be so easy (as it is on the radially mounted S4 brakes going to 322mm GTS) is that instead of using spacers to push out the calipers radially, with the S, we can do BOTH, with the axially mounted calipers. We would do this with a simple plate the width of the two mounting holes axially on the "S" models. use bolts and bolt the plate to the brake caliper mounts . THEN, there would be two more drilled holes spaced radally outward about 1" or so, (whatever the diameter difference of the S brakes and the rotors you want to install). BECAUSE you are using a spacer of some thickness, you make that thickness equal the offset difference. (hopefully greater than .5") Now you have the calipers moved inboard by .5" via the space made of a strong steel or aluminum, and radially outward by the diameter difference of the old and now new , say 322mm rotors)
The only question is how thick that material should be, probably made of stainless steel. the rest is pretty simple. the only hard part is threading only 2 of the 4 holes on the adapter plate. on my post, remember, I said things need to be moved, "in and out". This meant, the spacer moves the caliper inward and outward, radially.
Is that a little more clear?
Mk
OB or "S" systems use the same spindles, so I was refering to the inner diameter of the brake rotor from a hub-centric perspective. Lets talk "S" brakes.
1. The S brakes have a rotor with a 154mm inner, hubcentric rotor diameter. the part that fits on the hub.
2. The S4 brakes and that entire family of the same hubcentric rotor inner diameters (GTS, 993TT, 964T, S4, etc) have a inner diameter of 157mm.
3. IF we want to increase the rotor size as far as diameter by using S4, GTS or 993TT rotors, OF COURSE we need to move the calipers out to take advantage of the greater leverage. The reason that this mod can be so easy (as it is on the radially mounted S4 brakes going to 322mm GTS) is that instead of using spacers to push out the calipers radially, with the S, we can do BOTH, with the axially mounted calipers. We would do this with a simple plate the width of the two mounting holes axially on the "S" models. use bolts and bolt the plate to the brake caliper mounts . THEN, there would be two more drilled holes spaced radally outward about 1" or so, (whatever the diameter difference of the S brakes and the rotors you want to install). BECAUSE you are using a spacer of some thickness, you make that thickness equal the offset difference. (hopefully greater than .5") Now you have the calipers moved inboard by .5" via the space made of a strong steel or aluminum, and radially outward by the diameter difference of the old and now new , say 322mm rotors)
The only question is how thick that material should be, probably made of stainless steel. the rest is pretty simple. the only hard part is threading only 2 of the 4 holes on the adapter plate. on my post, remember, I said things need to be moved, "in and out". This meant, the spacer moves the caliper inward and outward, radially.
Is that a little more clear?
Mk
S and early OB DO NOT have the same spindles. that's why I had to change mine for the big red upgrade which uses the 993 rotors.
DR or any of the other big 3 might have the specific differences, but I think it's an offset issue...
09-27-2009, 04:40 PM
#32
Nordschleife Master
Gotcha.
My confusion is that True OBs don't have the same spindles/knuckles as S cars. The calipers don't mount the same way.
Your description of the way the caliper would mount makes good sense. Just need the hat to be 1/2" deeper and then the plate would be easily fabbed: ya cut a piece of plate, drill four holes, tap two of those and it's done.
09-27-2009, 05:32 PM
#33
Road Warrior
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the adapter plate that 928 SP sells is just like that: https://www.928gt.com/default1.htm
but they anodized it
seems that you could use one of them for the template, then slice as needed for the proper thickness, or just ask DR to make up another set w/your specs. prolly in a CNC system already, so that would be super easy to do.
but they anodized it
seems that you could use one of them for the template, then slice as needed for the proper thickness, or just ask DR to make up another set w/your specs. prolly in a CNC system already, so that would be super easy to do.
09-28-2009, 12:29 PM
#34
Rennlist Member
Thread Starter
Im not talking about OBs really, just the hub inner hubcentric diameters. I know the spindles are different, as they bolt different calipers with different bolt patterns too. we are talking offset and hubcentric measurements.
I want a big offset with the "S" brakes, as it allows for a thicker spacer. a thicker spacer would adjust for the offset and then you could choose any diameter rotor outward and still use the original "S" brakes, but on 13" rotors! 322mm
mk
I want a big offset with the "S" brakes, as it allows for a thicker spacer. a thicker spacer would adjust for the offset and then you could choose any diameter rotor outward and still use the original "S" brakes, but on 13" rotors! 322mm
mk
09-28-2009, 12:35 PM
#35
Rennlist Member
Thread Starter
Yep, you got it. the question is, what is the clearance of the ball joint.
Here are the 3 rotors in question. S4, '84 "S" rotors, and a suspected 993 rotor.
I dont know if the 5mm difference of "S" to 993would be thick enough. but the S4 to " S" would allow 18mm of a plate.
I also included a picture of the hubcentric part. notice the difference for the S vs S4 or GTS rotors. 154mm vs 157mm. I used a pencil for size reference.
mk
Here are the 3 rotors in question. S4, '84 "S" rotors, and a suspected 993 rotor.
I dont know if the 5mm difference of "S" to 993would be thick enough. but the S4 to " S" would allow 18mm of a plate.
I also included a picture of the hubcentric part. notice the difference for the S vs S4 or GTS rotors. 154mm vs 157mm. I used a pencil for size reference.
mk
Mark,
Gotcha.
My confusion is that True OBs don't have the same spindles/knuckles as S cars. The calipers don't mount the same way.
Your description of the way the caliper would mount makes good sense. Just need the hat to be 1/2" deeper and then the plate would be easily fabbed: ya cut a piece of plate, drill four holes, tap two of those and it's done.
Gotcha.
My confusion is that True OBs don't have the same spindles/knuckles as S cars. The calipers don't mount the same way.
Your description of the way the caliper would mount makes good sense. Just need the hat to be 1/2" deeper and then the plate would be easily fabbed: ya cut a piece of plate, drill four holes, tap two of those and it's done.
09-28-2009, 12:50 PM
#37
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Glen, no they don't use the small diameter around the bearing cap- they use outside diameter of the hub.The ends of Marks pencil point to the contact area.. That's what makes a swap such a pain in the ***. I don't know if you can put S-4 hubs on an S spindle, maybe Mark has enough parts to try it- depends on the bearings and the spacing between them....
09-28-2009, 12:57 PM
#38
Road Warrior
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Im not talking about OBs really, just the hub inner hubcentric diameters. I know the spindles are different, as they bolt different calipers with different bolt patterns too. we are talking offset and hubcentric measurements.
I want a big offset with the "S" brakes, as it allows for a thicker spacer. a thicker spacer would adjust for the offset and then you could choose any diameter rotor outward and still use the original "S" brakes, but on 13" rotors! 322mm
mk
I want a big offset with the "S" brakes, as it allows for a thicker spacer. a thicker spacer would adjust for the offset and then you could choose any diameter rotor outward and still use the original "S" brakes, but on 13" rotors! 322mm
mk
I thought one of the advantages of the bigger caliper was more surface area contact for the pads, and more pistons too... won't the pads heat up/fade the same even with a bigger rotor?
09-28-2009, 02:10 PM
#39
Rennlist Member
Thread Starter
Yes, that is only part of it, but MOST of the advantages are in the diameter of the rotor. Racing pads can handle the heat, with NO issues. In fact, most top racing brakes have Less contact area than the S brakes which are not that far off the size of an S4 pad, which in turn, is not that far off the area of a Ferrari f50 pad and IDENTICAL to the Stoptech ST40 system (big racing set up for 13" rotors). you never see pads as thick as the GTS big reds on real race cars. the inner diameter has no leverage and just generates usless heat. better to have a larger diameter rotors and a smaller pad. sure, 4 -6 piston calipers are better, but for different reasons.
In the club ranks, there are plenty of single piston caliper racers running spectacular times, with large diameter rotors. (none running a rotor diameter as tiny as the S brakes, primarly designed due to the little wheels the older 928s came with.
make a 13" S brake system and you get almost all the advantages without the bling factor. think about cost! just larger rotors when you replace them and the adapter plate can be home made almost.
In the club ranks, there are plenty of single piston caliper racers running spectacular times, with large diameter rotors. (none running a rotor diameter as tiny as the S brakes, primarly designed due to the little wheels the older 928s came with.
make a 13" S brake system and you get almost all the advantages without the bling factor. think about cost! just larger rotors when you replace them and the adapter plate can be home made almost.
09-28-2009, 02:23 PM
#40
Rennlist Member
Thread Starter
I think the bearings are different, so the question really is, are the spindle shafts identical, so that you could use the S4 bearings inside and outside with dust cover if you could use S4 hubs. however, is the clearance of the ball joints less than .5"? if so, can the 993 rotors work with a 5mm plate adapter? that seems very thin, and would only give a few threads of engagement for the caliper bolts. I like the S4 offset better, giving a 17mm thickness of the proposed adapter plate, but I think folks have said, we will then hit the ball joint.
mk
mk
Glen, no they don't use the small diameter around the bearing cap- they use outside diameter of the hub.The ends of Marks pencil point to the contact area.. That's what makes a swap such a pain in the ***. I don't know if you can put S-4 hubs on an S spindle, maybe Mark has enough parts to try it- depends on the bearings and the spacing between them....
