Jump to content
SAU Community

Brake Disk Machining

siksII
 Share

Recommended Posts

siksII Grand Master

siksII

Posted
Posted

I got my disks machined yesterday due to some vibration caused by some grooves worn into one disk.

Apart from the grooves on one of the disks they were in perfect condition without any shudder etc, and only a few months old.

They machined 0.75mm off one disk, and 0.77mm off the other disk. Since they have 2mm of life this means they have machined off approx 40% of the usable disk.

When you get your disks machined for whatever reason, what is the average amount of material machined off? Is this normal or am i justified in being really pissed off?

Link to comment
https://www.sau.com.au/forums/topic/176881-brake-disk-machining/
Share on other sites
Beer Baron Grand Master

Beer Baron

Posted
Posted

the will machine off whatever is the minimum in order to get a nice true surface. if your grooves were say .35mm thick (which is bugger all) then they would need to machine off double that.

siksII Grand Master

siksII

Posted
  • Author
Posted
the will machine off whatever is the minimum in order to get a nice true surface. if your grooves were say .35mm thick (which is bugger all) then they would need to machine off double that.

Yes of course they do, that is not what i want to know.

To be more specific, assuming there was no visible grooves, just the usual shudder that develops, how much is generally shaved off? And say you have to shave off 0.2mm off one side but only 0.1mm off the other side, would you just shave 0.2mm off each side to make the rotors even thickness, or shave off the minimum off each side and leave the rotors slightly different thicknesses?

B0oStEr Mentor

B0oStEr

Posted
Posted

Grooves don't cause a shudder by themselves.

It's most likely they had a bit of run out due to warping.

I had a pair of discs machined the other day that looked perfect but caused a shudder.

I lost 1mm thickness to clean up the run out but now the brakes pedal is smooth again.

grandmasterb Grand Master

grandmasterb

Posted
Posted
Yes of course they do, that is not what i want to know.

To be more specific, assuming there was no visible grooves, just the usual shudder that develops, how much is generally shaved off? And say you have to shave off 0.2mm off one side but only 0.1mm off the other side, would you just shave 0.2mm off each side to make the rotors even thickness, or shave off the minimum off each side and leave the rotors slightly different thicknesses?

Hang on your first post said that you had grooves in your disks causing vibration hence why they were machined in the first place but that would generally be caused by warping as well...

If thats the case then they will generally machine each disk to the same drop so that you not only get even wear but also lifetime out of the set and not having to replace 1 or 2 at different times.

Did you talk to your mechanic before/after you picked them up and question why they were machined to the levels they were and also what tolerance would be left???

You can be lucky sometimes and have them machined exceeding the minimum thickness but its not really recommended and most places would probably refuse to do so.

If your brakes are set up correctly then you shouldn't have to worry about the rotor for a while so chances are your not even going to own the car by the time they have to be machined again due to wear and tear anyhow :domokun:

siksII Grand Master

siksII

Posted
  • Author
Posted
Hang on your first post said that you had grooves in your disks causing vibration hence why they were machined in the first place but that would generally be caused by warping as well...

If thats the case then they will generally machine each disk to the same drop so that you not only get even wear but also lifetime out of the set and not having to replace 1 or 2 at different times.

Did you talk to your mechanic before/after you picked them up and question why they were machined to the levels they were and also what tolerance would be left???

You can be lucky sometimes and have them machined exceeding the minimum thickness but its not really recommended and most places would probably refuse to do so.

If your brakes are set up correctly then you shouldn't have to worry about the rotor for a while so chances are your not even going to own the car by the time they have to be machined again due to wear and tear anyhow :domokun:

I should probably explain a bit more, they vibration is definitely only cause by the grooves, and not because the disk was warped/runout whatever.. The disks are only a few months old, while i was driving a few weeks ago the pad material tore off the backing plate after which the backing plate came in contact with the disk and created the grooves. As soon as it happened i stopped the car and got it towed home.

Before that incident, the disks were absolutely perfect, no vibration whatsoever, and as i said, nearly brand new.

When i dropped the disks off one was 29.95mm and the other which had the grooves was 29.74 as measured in the grooved area. When i picked them up the good one was 29.18 and the grooved one was 28.99.

So not only did they machine slightly more off the one that was perfect, they are different thicknesses. It seems they just picked approx 0.75mm out of their arse and decided to chop that much off both without any thought.

I specifically told them when i dropped them what happened, and made sure they understood that they should only take the absolute minimum off. When i picked them up i expressed my concerns on why so much had been taken off and they just like well thats how much was required which seems to me complete BS.

I notice the degradation in braking performance as the disk thins out and i go through brakes reasonably quick anyway so it is a concern for me ;)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • PotatoCake
      Has anyone put in brand new full carpet? (not floor mats)

      By PotatoCake · Posted

      Doing a refresh of my 33 and can see a few websites stating they sell the entire main carpet for our cars, but they all have generic photos which is fine, i understand they are custom made to order.  Just seeing if anyone has got it done or had any experience with this, as i would only want to do it if the fit and finish was as good as oem https://carmatsdirect.com.au/products/moulded-carpet-or-vinyl-for-nissan-skyline-r33-1993-1998-coupe https://knoxautocarpets.com.au/moulded-carpets/nissan/skyline/skyline-r-33-1993-1998/
    • MBS206
      R32 update from 1990's spec.

      By MBS206 · Posted

      Any plans for E85? If so, add flex fuel sensor.   I'd probably add in the sensors I mentioned above if the Link will support using them for engine protection. With water pressure, you need to be able to effectively set it that "If temp > X, and pressure = atmospheric, shutdown" as at running temp, you should be able to read pressure in the cooling system. If pressure suddenly disappears, it means the water went some where, and this is a quicker reaction than waiting on water temp to go up (Which, can take a little longer than you'd like, considering it now has to wait for hot air to heat it up) Oil pressure, Oil temp, both would be on my list too if you're looking to add sensors. Wideband O2. And at least one EGT sensor. If you're feeling deluxe, put in individual runner EGTs. Single EGT sensor is more so forget about a specific number, get used to "What is normal EGTs", and then keep an eye on it, if it starts going away from "normal" it's a sign something is wrong (Also, things like the tune can still start going out of spec, but EGTs may not show it, for example one injector starts running leaning, so ECU richens everything up, now 5 out of 6 cylinders are rich, and running cool, with one cylinder lean and running hotter, so it's not perfect) Then there is your other things to look at non sensor related, but you may have already done, or have underway, and that would be things like building a sump for more oil, and better oil control under high G-Forces (Cornering, brakes, acceleration). Basically, the above is worth looking/thinking about, if the ECU can do protective stuff with it, and you continue to use it how you are (Drive it to the track, thrash it, drive home, repeat once every 3 to 4 months)
    • Ty1
      Hicas ball joint install tool

      By Ty1 · Posted

      Can also confirm these work a treat for most balljoints and bushes. If you have access to a big rattle gun, they make the job so much easier and quicker, compared to using a socket wrench or shifter on the c-clamp 👍
    • djr81
      R32 update from 1990's spec.

      By djr81 · Posted

      Its sort of street but got used for circuit sprints on account of I never drive it on the road because I dont have the time to spare. So it usage was sits around for months at a time then gets driven either 50 or 250 kms to the track followed by 20 laps followed by 50 or 250kms home followed by stuck in the shed until next time. So yeah neither fish nor fowl. Just dont want to break it on the track as a preference. Hence the fairly short sensor/mod list. Probably more worried about it pinging itself to destruction more so than anything oil related.
    • MBS206
      R32 update from 1990's spec.

      By MBS206 · Posted

      My thing I'd be doing, is pulling it out, and just getting the tune cleaned up for now. Before that even happens, checking over everything, like vac hoses, fuel hoses, etc. No point dropping thousands on sensors if the moment you start it back up all the oil leaks out, or it has massive vacuum leaks etc.   But really, to know what to do, depends on what your use case is. Hard core track car? Throw most sensors available at it. Street car, I'd probably just run oil pressure, oil temps, water pressure, water temp, probably fuel pressure too. I don't know exactly what the Link can handle and do with those though. And if it's mainly just to cruise the streets, rather than mountain runs, you can probably skip most of the above if you've already got them in as gauges and warning lights.   PS, inb4 "sell it and buy a modern sportscar"
×
×
  • Create New...