On car brake disc machining query

**Grappler** · 14th April 2019, 12:15 PM

Originally Posted by dromader driver

With the cost of discs these days is it cost effective to machine discs. Usually the first pad change doesn't need machining unless overworn or rock damaged.

Oh and min thickness is specified to stop the pistons popping out when both pads and discs are worn . (I've seen some interesting mechanics overseas)

Thoughts?

Yes the rotor discs are the least costly components of a brake overhaul, cheaper than the pads. Replacing the rotors adds to the labour but is an opportunity to clean and regrease the hub bearings, change out the hub seal and properly inspect the calipers/pistons.
Speaking of pistons, during a recent brake overhaul (2012 130) I found the pistons badly pitted. I replaced them with aftermarket stainless steel pistons

**Lionel** · 16th April 2019, 07:46 AM

Thanks to all the replies, people.

Cheers,

Lionel

**Bigbjorn** · 16th April 2019, 09:01 AM

Originally Posted by Blknight.aus

It works well

and minimum thickness, as mentioned, is to keep your calipers and pistons in good order when both the rotor and the pads are at minimums.

I've seen shocking things in this country when it comes to brakes... Including worn pads behind new pads on wafers of rotors.... ON A TRUCK.

I dont even want to think about whats happening in other countries.

In the days of drum brakes with riveted linings it was not unusual for ikey fleet operators and taxi owners to shim up standard brake linings to take up wear in drums rather than pay for the drums to be machined and oversize ground linings fitted. I was the service rep to the Sydney taxi industry briefly in my GM-H days. Taxi owners/operators were the meanest creatures on earth. They pressed for a heavy duty drum brake option as they considered disc brakes unnecessary in urban traffic and discs had a higher cost per mile than drums. A matter of a fraction of a cent per mile. From memory Chrysler did offer a HD drum brake option on Valiants. I am unsure it Ford followed suit.

**goingbush** · 16th April 2019, 10:09 AM

When I was young & stupid (not much has changed) I jacked up my Hybrid one side at a time, took wheels off, started the car up , put in gear & ground the lips off the rotors with an angle grinder as they were spinning under engine power, this was before the days of OHS , common sense & the term 'Darwinism' was not in popular use, hence I survived !!

**LRJim** · 16th April 2019, 11:58 AM

Originally Posted by goingbush

When I was young & stupid (not much has changed) I jacked up my Hybrid one side at a time, took wheels off, started the car up , put in gear & ground the lips off the rotors with an angle grinder as they were spinning under engine power, this was before the days of OHS , common sense & the term 'Darwinism' was not in popular use, hence I survived !!

Hybrid what? Horse + Steam engine 🤣🤣🤣

**goingbush** · 16th April 2019, 05:41 PM

Originally Posted by LRJim

Hybrid what? Horse + Steam engine 🤣🤣🤣

This old thing, I made in mid 1980's , cut down RRC Chassis , Series2 body made to look like a 90 , Ford 302 - C10 , G60 TC , Maxidrives F&R .

**Rick Fischer** · 18th April 2019, 09:38 AM

Miinimum thickness is not specified to stop pistons pistons popping out, rather to ensure there is still enough metal to provide a proper heat sink. (beyond minimum thicknes to "thin" may cause pistons to pop but braking would be severely compromised before that). Braking is a energy conversion process mechanical/momentum to heat. Once the discs are full of HEAT they stop working. However, they dont need to be full, braking degrades ie fades, as the discs heat.

Returning to a Deffie I can highly recommend that standard discs are replaced by good Aussie slotted discs and Aussie manufactured pads. Deffies are underbraked as is. Slotteds give an edge especially when loaded, and excellent pedal feel. (for braking drilled or combined are just as good, but drilled and mud can be a painful excercise)

Also be aware for at least the past 10 years all Euro brakes have had to conform with a EU regulation that essentially states that "if brake booster fails the pedal feel must feel the same as if the system was always unboosted, i.e. no booster/power assistance". Hence the extra soft Euro pads and soft discs, and all the black crap on Euro wheels.............and very short life on Euros. Didn't/ doesn't affect Asian or American built (or Australian built ustawas) cars for their or our market/s.

Cheers

RF

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