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930 brake rotors, 1978-80

Hi,

I have this brakes on my 1973RSR "LookAlike". When I bought it I was told to tighten up the rotor to hat bolts with rather high torque. The original possibility of floating was removed. They were mounted with only bolts and nuts, any spring, etc. was not used.

I am suffering of heavy unbalance during braking.

Instead of slots on the rotors as the original has, mine unoriginal, have just 6 mm bores, just like the hat. They are building 6 mm together.

Is there any solution to get back the floating disk and if, what hardware should I use?
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Old 07-02-2017, 06:48 AM
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Quote:
Originally Posted by avorkinn View Post
Hi,

I am suffering of heavy unbalance during braking.
Arlid... as to imbalance, will assume all rotors and pads throughout are NOT contaminated and all pistons work freely/evenly. Then, might be piston angle---930 pistons require being at a specific angle...

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Old 07-02-2017, 07:05 AM
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Quote:
Originally Posted by avorkinn View Post
Hi,

I have this brakes on my 1973RSR "LookAlike". When I bought it I was told to tighten up the rotor to hat bolts with rather high torque. The original possibility of floating was removed. They were mounted with only bolts and nuts, any spring, etc. was not used.

I am suffering of heavy unbalance during braking.

Instead of slots on the rotors as the original has, mine unoriginal, have just 6 mm bores, just like the hat. They are building 6 mm together.

Is there any solution to get back the floating disk and if, what hardware should I use?
Depends on what you have on the car now
Here are the 2 main floating components, the rotor annulus + inner ring & hat


the hardware + inner rings


the assembly


the stock 911 hubs + hats
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Old 07-02-2017, 07:15 AM
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DAMN, Bill
That's a toolbox !!

OP should be able to just buy a hat and hardware assuming his rotors are floating compatible already?

Bill K
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Old 07-02-2017, 07:51 AM
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That pictures are from a original setup, mine has just 6 mm holes both in hat and disk, not disk with this slots.
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Old 07-02-2017, 09:01 AM
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Arild, I believe I have the same brakes as you have on my RST. I do remember that the torque setting required was so low that I had to use my small torque wrench presumably to allow for heat expansion.





I'll try to find it for you.
Johan
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Old 07-03-2017, 03:58 AM
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Looks like douglas bray's monster tool collection and I think the picture is from this thread where we helped him sort out his 930 brakes on '87 911 cabrio.

Cleaning/Rebuilding 930 Calipers....

Reason I recall this is because I know he used on his install the Rebel Racing hats from Clint Smith. Rebel also has their own recreation of the floating hat fasteners

brake system components Rebel S Racing Products

The original parts from Porsche are a bit different but the function is the same. Here's a few snapshots from the factory manual. It says the hat bolt number 11 in the picture below is to be tighten to only 10Nm = just over 7 ft-lb (7.375) = around 88 INCH lbs.


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Old 07-03-2017, 07:41 AM
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Nice to see the info straight from the manual, Kevin.
Arild, do let us know how you make out.
Johan
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Old 07-03-2017, 07:35 PM
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Here is mine,



As i understand this setup is a rather common way to do it, disk and hat in a fixed connection. What makes my unbalance I don't know, I can actually see it when I turn the hub and disk around, wheel removed.
I have no reduced the torque on the bolts close to nothing, see if they can find their place 🤔🤔
I am not optimistic 🙄
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Old 07-03-2017, 11:59 PM
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You say "unbalanced during braking".
You mean that the pedal is pulsing?

Hasn't the discs just warped?
Old 07-04-2017, 12:43 AM
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Yes the pedal is pulsing, making the brakes to take unevenly during one turn of the wheel, this again makes heavy vibrations during heavy breaking.

It could be warped, that I have to find out, mounted on the hat and hub, it looks like it is. I have to find out what component causing the problem, disk, hat or hub.
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Old 07-04-2017, 12:59 AM
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Get a dial indicator with a magnetic base, you can find those cheap.
Set it up so you can spin the hub and rotor measure runout.
Remove disc measure hat and so on...
Old 07-04-2017, 01:41 AM
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Quote:
Originally Posted by avorkinn View Post
Yes the pedal is pulsing, making the brakes to take unevenly during one turn of the wheel, this again makes heavy vibrations during heavy breaking.

It could be warped, that I have to find out, mounted on the hat and hub, it looks like it is. I have to find out what component causing the problem, disk, hat or hub.
That can be an issue w/ the rotors but it can also be a bearing or shock issue too

When the Bilstein shock bearings went bad on my C3 there was a terrible brake judder.
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Old 07-04-2017, 04:10 AM
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Hi again,

I have checked the runout of the disks, both disks has the same unlignment of 0,5mm.

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Old 07-05-2017, 03:05 AM
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OK, so either they are warped or they don't sit properly to spinn properly.

I'd disassemble them and lay on glass to check for warping. if OK check strut and bearings.
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Old 07-05-2017, 03:17 AM
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0.5 mm is a lot!

Put the indicator on the hat (the piece between the hub and disc) that could be warped to maybe or at least there could be some crud between hub and hat.
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Old 07-05-2017, 03:24 AM
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Yes, 0,5 is a lot, I tried to measure on the hat, but the measure arm on the dial indicator was to short. I will remove the hub and disassembly, hub, hat and disk to investigate further, I just have to find some spare time. The thread will be followed up as I find out any more. Just some pictures of the car, RSR "LookAlike"😎





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Old 07-05-2017, 04:22 AM
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Nice looking car!
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Old 07-05-2017, 04:30 AM
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indeed it is, wow!
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Old 07-05-2017, 04:40 AM
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Thanks 😊
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Old 07-05-2017, 05:52 AM
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