On car brake disc machining query

[Lionel]

Hi All,

I'm wondering whether anyone has had Defender brake discs machined on the car. Mine are in very good condition, & measure thick enough, but have wear ridges which need smoothing off prior to pad replacement.

It would be nice not to have to dismantle hubs etc., so can anybody give some feedback on this procedure.

Any information would be appreciated.

Cheers,

Lionel

[Bigbjorn]

I bought an on car disc machine at auction some years ago. I used it on a few vehicles and on sold it. worked very well. Make sure your wheel bearings are to spec. Loose bearings give an untrue result. Main problem with them is that motor mechanics are not machinists and seem unwilling to take a decent depth of cut to get under the hardened skin that develops on cast iron from repeated heating and cooling. You need to be cutting in the soft metal under the hard layer or the insert might be skidding over the hardened skin. This also uses up the inserts early.

[Lionelgee]

Hello Lionel,

Oh no not another one!

Kind regards
Lionel

[weeds]

Just fit the new pads.......if the lip is big I’d be surprise if they would clean up to the minimum thickness

[rrturboD]

No credit for this repair technique, but it did work a treat!

Ensure wheel is spinning, apply angle grinder to lip, inside and outside....

Lip gone.

[jon3950]

Just fit the new pads.......if the lip is big I’d be surprise if they would clean up to the minimum thickness

I’m with Weeds. I don’t think its worth machining discs, rather just let the new pads bed into the grooves. As Weeds said, if the discs are so bad they need machining its unlikely they’ll clean up to the minimum thickness.

Cheers,
Jon

[big harold]

If you leave the lip this gives you a good indication when your pads are worn out without destroying the rotor.
Pads these days do not come with the wear indicator.
Mark

[Bigbjorn]

I only had the on-car machine for a short time. It worked OK but I had bought it for resale and did so. Normally I machined discs and drums in the centre lathe. I was never too fussed about manufacturers specified minimum thickness if the grooves were not bad and cleaned up without taking a big cut. I suspect the makers were a bit conservative about thickness to cover their arse. Badly damaged discs where they had been run metal to metal for instance, I would dump in the bin.

[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?

[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.

[Grappler]

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]

Thanks to all the replies, people.

Cheers,

Lionel

[Bigbjorn]

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]

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]

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]

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 .

https://scontent.fper2-1.fna.fbcdn.net/v/t1.0-9/31646809_1679381662143617_7013619965882269696_n.jp g?_nc_cat=102&_nc_eui2=AeEMeNILN0sQ0Ed_wVnJR-UF47GlVjMPg1tWPkxz55JplJi-4zOxZYa03jnlnZLwNt6ZJ7fW0j0Hqe-0oTBy-y3VkF0lrl69hybD8plqwJr_5w&_nc_ht=scontent.fper2-1.fna&oh=d0fa25ae94da5447898c19f262931c2b&oe=5D4AD8A9

[Rick Fischer]

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