Help with '79 930 Floating Rotors

spsfiend · 01-31-2009, 08:03 AM

Hello, I was hoping someone could give me some tips on how to "quiet down" the chatter from the floating rotors. I bought new spring washers in an attempt to quiet down the noise a tad but before i go in there to replace I figured I pulse the savvy pelican community. Are there any other mods to help with the noise factor? I use this car now as my daily driver.

Here's a pic:

NY65912 · 01-31-2009, 08:14 AM

Nature of the beast. A typical complaint of the floating design.

I do not think there is a solution. But the plus side is they are a great track setup.

Dennis Kalma · Dennis Kalma's Garage

I have the floating rotors and they have driven me nuts from time to time. I did actually take one apart and apply a thin skim of high temperature silicone to the dogs, idea was to take up the slack and still allow the expansion afforded by the floating design.

So far (only 2 years) there have been no issues and they are a lot quieter....

Dennis

Jack Olsen · 01-31-2009, 10:50 AM

I've read that Steve Weiner has a hat/rotor alternative that makes them essentially 'one piece' and also cheaper to replace.

RoninLB · 01-31-2009, 11:42 AM

"thread tool" to "subscribe to this thread" ng

also I read recently that 930 floating rotors can be rebuilt to lower noise

spsfiend · 02-01-2009, 11:35 AM

Anyone else? I thought I read somewhere about "Mclaren bobies" or something? i tried searching again and could not find...

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by spsfiend

Anyone else? I thought I read somewhere about "Mclaren bobies" or something? i tried searching again and could not find...

The 930 dogs are just a loose fit in their slots, Mclaren added a spring clip to reduce the noise, never heard of them being fittrd to 930 rotors.

Dennis Kalma · Dennis Kalma's Garage

Not sure if that would work on the Turbo rotors. If I recall there are slots in the hub made up of the dog assembly and a ring that forms the other side, as per the picture of my rotors when they were new and the floating assembly was fresh from the machine shop....

Hence my idea of the film of silicone....

Dennis

FPB111 · 02-01-2009, 08:29 PM

SPSFIEND,
I worked with floating rotors for 17 years on my 1972 "RS". Springs like those in Bill Verburg's post may help more with low speed braking chatter but not much with the clunk-thump of the rotor "falling" into place radially as the wheels turn at slow speeds, ~35mph and below.
Your rotor carriers do not look like stock 917 carriers. Dennis Kalma's pic does look stock. (2 major pieces- carrier with 12 square dogs machined into it and retaining ring)

Do yours have 12 individual "T" shaped dogs bolted to the carrier? (VCI http://www.vehiclecraft.com/Brakes/rot_ques.htm) If so you can loosen the 12 dog mounting bolts and turn the, slightly elongated, dogs to contact the rotor slots to reduce float and make them quieter. This will last longer if your rotors are running true, less time if they have run-out.
You could replace three of the dogs with cylindrical brass bushings machined for a snug fit in the slot. Space them evenly around the rotor, IE every 4th slot. This will still allow some axial and radial float but reduce play and help keep the rotor on center reducing "clunk" as the wheel turns. This also has the advantage of many “faces” that can be turned to present new wear surfaces to the rotor slots.

You could replace the floating setup with 2 piece non-floater carrier and rotors. There are some members of this forum who offer options. I think Steve Weiner [porsche@rennsportsystems.com] is one.

If you use stock Porsche floaters, shown in Dennis's picture. The square aluminum engaging dogs present a larger wear surface to the rotor slot but are softer and wear about as quickly. With them you can, file/machine the height of the dogs to reduce the clearance between the retaining collar and rotor carrier. This will create some friction on the rotor that is pinched between them. This will wear and could cause some vibration if you have rotor runout.
Heliarc the worn sides of the dogs and machine them for a little tighter fit in the rotor slots.

You can also buy new Porsche carriers every few thousand miles.
I found that the individual dog type were noisy from the beginning.

The 930 calipers mated with a 23mm master cylinder and the 1.25" thick rotors are a great no fade combination on early cars.

Dennis Kalma · Dennis Kalma's Garage

Quote:

Originally Posted by FPB111

SPSFIEND,

If you use stock Porsche floaters, shown in Dennis's picture. The square aluminum engaging dogs present a larger wear surface to the rotor slot but are softer and wear about as quickly. With them you can, file/machine the height of the dogs to reduce the clearance between the retaining collar and rotor carrier. This will create some friction on the rotor that is pinched between them. This will wear and could cause some vibration if you have rotor runout.
Heliarc the worn sides of the dogs and machine them for a little tighter fit in the rotor slots.

Just FYI, my floaters are a copy of the stock ones and they were steel, I correspondingly had mine machined out of steel - not aluminium. I can see how aluminium would wear quickly but the steel ones seem to be OK, or at least mine were fine at 30,000 km.

Dennis

spsfiend · 02-02-2009, 08:29 PM

Thanks for the input guys! Really appreciate it. I will look into these options. I bought my car with the current set up so I am not sure what I exactly have. I will take them apart and see what i am really dealing with.

Cheers!

FPB111 · 02-03-2009, 06:48 PM

Dennis,
They did look more like zinc chromate then one of the aluminum anodizing processes. Did the machine shop write a CNC program for the pieces? Did you get/consider getting a batch made? I bet some folks on this site would be interested in them. I sold that car so not me.
I am investigating building a 996 coup track car this time. The 99s are so reasonable now and with Jake Raby, L&N engineering and others addressing the engine weaknesses one could build a potent car for reasonable $$.

Dennis Kalma · Dennis Kalma's Garage

The originals were some sort of silvery plating, I think it was straight zinc or perhaps even paint as it got scratched in the process. Mine were machined by hand, cost was $550 Can. for the pair, but I did not consider more than my own. I had them zinc dichromated and so far it is holding up well.

The machine shop that did it told me they did lots for the motorcycle crowd so it wasn't a big deal for them.

Dennis

FPB111 · 02-04-2009, 11:49 AM

Dennis,
You copied Porsche ORIGINALS that were STEEL? I bought Porsche carriers twice over the years and both sets were anodized aluminum. Steel would defiantly last longer.

Dennis Kalma · Dennis Kalma's Garage

I did not test them with a magnet, but they most definitely were the weight of steel...and straight from the dealer. I ordered one new from the dealer, then returned it after machining the new ones and paid the restocking charge....

Dennis

FPB111 · 02-04-2009, 01:15 PM

The aluminum carriers were very light. You would have noticed.
I wonder if they went to steel because of "The$e Damn Thing$$ wear too fast!" Complaints??