'96 Surf Brake Shudder

[solitaire]

Hi All,

I am pretty sure where to go with this but I would apreciate it if you good people could sanity check my next step.

Problem: Heavy shudder felt in the front when braking going down a hill (sort of speed maintenance braking - trying to prevent acceleration)

- I have tried the same hill preventing acceleration using the handbrake and it does not shudder - that eliminates the rear brakes from the equation right?
- Previously we had a garage skim the disks and it went away a little bit for a while, but its now as bad as ever.
- I am wondering if the fact that the garage undoubtedly did the wheel nuts up with a rattle gun has caused warpage?

My next step is to buy new disks and pads and replace the brake fluid while i am at it.

Is there anything else i should try before this?

Thanks in advance

[Bling]

How thin are the discs compared to standard specs? There are minimum thicknesses, could be worth looking into. Have never had discs skimmed due to that problem so can't really offer much more. Doing wheel nuts up tight I don't imagine would warp anything.

If the discs are low, then it's a good time to replace the whole lot. Has always eliminated problems for me. Have never bothered with skimming. Haven't had shuddering before, only squeaking which indicated to me something wasn't true and straight.

[solitaire]

How thin are the discs compared to standard specs? There are minimum thicknesses, could be worth looking into. Have never had discs skimmed due to that problem so can't really offer much more. Doing wheel nuts up tight I don't imagine would warp anything.

If the discs are low, then it's a good time to replace the whole lot. Has always eliminated problems for me. Have never bothered with skimming. Haven't had shuddering before, only squeaking which indicated to me something wasn't true and straight.

Yeah, i'm thinking I should just replace them...

[sergei]

Skimmed disks sometimes (most of times if they are very close to minimum), will warp again (imagine skimming warped disk: it will create even disk with uneven thickness, which will cause warping under temperature).

I never bother with skimming, if disks are shuddering I throw them away and put new ones. Skimming is 25 to $50 per disk, why bother when you can get for $100-150 new disk?

TL; DR; Get new rotors.

[STR]

+1 for getting new rotors. Just replaced them in my sisters Isuzu to solve the same problem. $160+gst to machine them, or $100 for 2 new rotors from NZ Brake Company in Te Pai Place, Henderson.

[rollaholic]

yikes, who was charging that much for a skim?

we have a mobile guy that does em for $50 a pair or something, on car.

anyway, as mentioned new discs are pretty affordable. bit more labour intensive to install than corolla discs though

[Scottie]

Take the wheel off and check with a dti. I can't imagine that it would be anything other than the discs though, like you have mentioned.

[Lloyd]

Surf discs warp easy, and skimming them is only a temporary fix. New ones, and use the box more

[allencr]

Check the hub to disk mounting surface, Extra hole/s in the disk can cause a small small raised bit of rust on the hub that MUST match a corresponding hole when remounted, else it is bending the disk when it gets tightened down.
I have no idea why so many disks are replaced rather then machined. One asshole that tried to tell me a freshly machined disk's runout was within specs rather then a worn out and/or incompetent setup.
****
Here's a racing guy/author that says 'I have never seen a warped disk'.
http://www.stoptech.com/technical-suppo ... ther-myths
Lost a lot of respect for him!!!

[solitaire]

Check the hub to disk mounting surface, Extra hole/s in the disk can cause a small small raised bit of rust on the hub that MUST match a corresponding hole when remounted, else it is bending the disk when it gets tightened down.
I have no idea why so many disks are replaced rather then machined. One asshole that tried to tell me a freshly machined disk's runout was within specs rather then a worn out and/or incompetent setup.
****
Here's a racing guy/author that says 'I have never seen a warped disk'.
http://www.stoptech.com/technical-suppo ... ther-myths
Lost a lot of respect for him!!!

Sorry it might be a bit late, but are you saying a warped disk is possible or not possible? I'm a bit confused.

[Lloyd]

He is saying that on some brake discs there is an extra hole that isn't used. From regular use etc a small amount of rust can form on the flange that the disc mounts on to. If you don't put the disc back on in the same place then that rust can cause a high spot and the disc wont sit flat. We used to skim heaps of these at the car yard, the Surfs are shocking for warping rotors. Usually all auto as people would simply ride the brakes rather than pull it down a gear on hills. They aren't a light vehicle and that kill discs

[Mr Ree]

I agree with the stoptech article and I dont believe rotors warp, rather they wear unevenly and cause high and low spots and this is what leads to the shudder.

That or micro deposits of pad material on the face of the rotor.

Either can be remedied with a rotor skim, just be sure to have it done while the rotor is on the car, and the hub and corresponding inner face of the rotor has first been cleaned immaculately to get rid of said rust deposits

[allencr]

I disagree with that article, it's completeBS about no warping.
Any variation in thickness, either wear or deposits will show its symptoms at any speed, any amount of braking force, with pulsing through the pedal, car jerking to a stop.
That isn't the case with runout, that will have no low speed or low braking force problems when the caliper slides have relatively little pressure on them or the fluid moves between the pistons on fixed calipers. [/b]

[sergei]

I agree with the stoptech article and I dont believe rotors warp, rather they wear unevenly and cause high and low spots and this is what leads to the shudder.

That or micro deposits of pad material on the face of the rotor.

Either can be remedied with a rotor skim, just be sure to have it done while the rotor is on the car, and the hub and corresponding inner face of the rotor has first been cleaned immaculately to get rid of said rust deposits

What happens to metal which is of uneven shape, when it is heated? It warps - different parts have different temperatures and expand differently. Additionally there are initial stresses since casting, which are released through heating, which cause further warping. If you add that brakes apply substantial force, many times uneven due to seized sliders, you have brake shudder as effect.