The shudder starts when the vehicles speed exceeds 70kph or only when the brakes are applied at speeds above 70kph?

I'd be pulling the rotors off and checking the mating faces of hubs and discs are all clean and there are no nicks or burrs causing lumps in the mating faces.
Also before undoing anything check all the wheel nuts are correctly tightened and check the calipers are firmly affixed to the stubs.
Check the condition of the Z bar bushes in the lower control arms and the big bushes mounted to the front chassis member.
Check condition of front wheel bearings, ball joints and tie rod ends.

I have a mild shudder in my VZ Holden Cab & Chassis's brakes at the moment, however I know mine is the rotors are worn and need to be machined or replaced.
I don't know if this is just a Holden/Commodore thing but every set of front rotors I put on the wife's VS (exc the last pair) ended up shuddering (incl the original rotors)when worn enough and so far the same deal with my VZ.
One brake shop told me it's because the pads don't sweep right to the edge of the friction surface thus leaving a lip (as the friction surface wears down) that causes the rotor to warp when they heat up during brake application.

Machining the rotors to renew the friction surfaces does eliminate the shudder but as we found out with the VS it wasn't long before I was throwing the original rotors on the scrap heap.
Since then I just buy new rotors, but I only use DBA.

Try PBR T3 rotors.

Sorry, meant DBA not PBR. I’ve had them on my Hilux for about 50,000km so far with Bendix 4x4 pads, and T3 front plus T2 rears on the Lexus RX350 for about 2 years now. Hilux ones are still perfect, still on the same pads. Lexus going in tomorrow for rear pads, will see what the T2’s are like then.
I had the standard size T3’s on the Hilux for a while but took them off as they were overheating, but the originals did too. As I went up a tyre size the original diameter rotors couldn’t handle the increased load. Tyres went from 255/70/15 to 265/65/17.

T3’s are a far better rotor than a T2 in some applications (better metallurgy). However if you screwed a set of T2’s in such low kM either the pads are wrong or the tyres are a bigger diameter than the rotor diameter is designed for or the rears aren’t working properly (eg rear prop valve buggered or not setup right etc). It took a cluey brake shop to point out to me I had a combo of both bigger tyres and sagged front springs (affecting the prop valve) on my Hilux to explain why the Hilux was overheating the rotors. This may be of use to Warren to explain why the rotors have maybe warped? Are the tyres a larger diameter?

Edited by user Monday, 11 March 2019 9:14:19 AM(UTC)  | Reason: Not specified

What mainly happens is what's called out gassing, the gunk from the pads sticks to the rotor surface, you can see it as it gives a dull look to the rotor surface.
What I did when I got this problem was, I just took it up to say 200KM/H and stomped on the brakes as hard as you can and them flatten it back up to say 200 again and repeat this 3 times and bingo problem solved, the gunk can truly be seen to be removed and you have a nice shiny disk surface.
Some times you can see on the rotor that only half the job has been done as the centre of the rotor sill has that mat looking build up and the outer and inner are shining like steel should. so you have to repeat the braking as above. or you have to go down the track of getting new pads and getting the disc machined.

I have never had a warped rotor ever on any car that I have owned and I did no less than 50,000KM a year.

Yours is an easy fix if it is a 2005-2011 (unless it is one of those oddball SR5 dual cab diesels made during 2011 that were the old shape and specs but with stability control):

Buy some new rotors to suit either 120 series Landcruiser (also called a Prado here) or a 2008-2009 TRD Hilux.
Buy some new calipers to suit the same vehicle (or rebuild some old ones as I did but new ones are cheap now).

Both bolt straight on. The harder thing is you need to find some brake backing plates used off a 120 series or TRD Hilux.
Remove the old calipers and rotors, clean up the hub face.
Remove the snap ring and tap the CV shaft with a brass drift to make it slide in the hub, unbolt the 4 x bolts that hold the front hub onto the strut, and swap the old backing plate off for the donor one. Put back together.
Repeat on the other side.
Put new rotors and calipers on and bleed them.

So now you have 100% replicated what a TRD Hilux had so this is 100% legal and self-Engineerable afaik. Only catch is if you have to run 17" rims like a TRD did (or a 2012-15 did), but 265/65/17 tyres will make your speedo accurate. I also replaced the brake booster with a VT Commodore dual diaphragm PBR modified to suit Hilux, as the TRD upgrade and original TRD were slightly spongy on the pedal, still work heaps better than original but pedal feel is not to everyone's liking.

Nah, it's just a work vehicle. I'm not interested in all the expense and hassles of bigger rims, tyres and fitting bigger brakes. When the rotors f**k up I'll just fit new ones. They are cheap as to replace these days.

Yeah I have boiled brake fluid on dirt bikes plenty of times and turned discs blue but never warped one of those. But the Hilux and Prado have both done it. The discs are shined up but they get so worn that there is no way you would get two sets of pads out of them. Plus, neither are capable of doing 200 and I can’t afford the risk of losing my license. I also do 50K a year and all highway driving except for ten k’s of dirt everyday. I reckon that’s where the damage is occurring with the stupid traction control and ABS.

Ah well there you go. It does have 17” wheels. I will keep that in mind if I replace them again.

Thanks for the responses.

It has new bearing and what looks like new rotor. I was changing the rotor with the ones on my wife's car (was disposing of it anyway) when I found a faulty bearing, so replaced that and no fix. (maybe I should not have reversed the rotors back to the way they were)

Will check the rubbers, did not even think of that.

I am not going to do the 200km/h thing, not real safe around here. Might give them a rub down with wet and dry or emery cloth to remove any build up.

Warren