Braking shudder

[Enchanter]

During normal street driving my (standard) brakes on my ma61 are pefect, no shudering, wobbling or anything, however, on the track under heavy braking the car shakes around quite a bit, not really any fade just alot of shaking.

I cant see how the disks could be warped if its smooth during street driving. Is there somthing more to this or do the disks simply warp or buckle with the heat and return to normal when cooled ?

[PitStop]

im no expert, so anyone feel free to correct me if im wrong here

to the best of my knowledge, usually shuddering under heavy braking can be caused by either wheel allignment, wheel balance, warped discs, or, i would guess faulty ABS as a possiblity too? not sure about that last one.

Generally wheel balance and wheel allignment, under normal smooth driving you will feel it pull in one direction when you brake if this is the issue. If the discs are warped it may not necessarily shudder under light braking under 'normal' braking. depending on the nature of the warp the speed of the spinning disc may not be high enough to transfer the disturbance through the car/steering wheel/suspension.

I could be wrong, but I'm drawing this from a mate who had a '96 Fairmont that was getting the same thing, shuddering (pretty hard shuddering too) under heavy braking.. but when he drove conservatively, you wouldnt even notice. The discs were indeed warped, which he decided to the replace with DBA rotors

As i said though dont take my word for it as im no expert, just my 1.81^recurring cents + GST

[merc-blue]

any worn or missalighned steering suspention or braking component can casue shudder in the brake pedal

[Enchanter]

any worn or missalighned steering suspention or braking component can casue shudder in the brake pedal

This is shudder in the whole front of the car, not just the brake pedal. I should clarify, my heavy braking is what you do when coming up on a hairpin corner at 160kph type heavy (Symmons plains).
I would probably lean towards your explanation Merc-blue, the bushes are my next wallet hurting project as they seem to be original, (although surprisingly good shape considering).

I feel, (although I certainly could be wrong) that the other explanations put forward would show signs of a problem during street use ie wheel alignment, wheel balance, warped discs. The car has no ABS.

Cheers guys

[merc-blue]

i have a theory but want more info,
is it just the peddal or do you get some "shudder" throught the wheel?
im actually thinking it could be a front end suspention/steering setup
look at teh brakes/bushes for any worn components,
Whats the cars "setup" as far as suspention brakes and steering

does the car try to get out of line under hard braking or does it hold steady?

[Enchanter]

The car is completley standard suspension and steering wise apart from the tyres being 235/60/14, they are 225/60/14 stock.
The car feels quite stable and balanced and doesn't veer off at all, just a bloody awfull shudder through the whole front, not just the pedal and steering wheel.

Edit: there is a bit of adrenaline involved here as well, I could have missed an important clue.

[merc-blue]

i think it may be front toe,
im no expert but excessive negative toe could cause shudder like that.
the weight transfer and braking forces casues the wheels to point in even harder, becasue there fighting each other as you go casuses a shudder,

[Kedderz]

I to vote for warped discs, ive had this problem on my old corona, under 80% normal driving no shuddering but soon as you break harder you can notice. Quick trip to my local ABS (brake service) had ther discs machined, was good as new.

[Enchanter]

Well I've got some slotted RDAs sitting here awaiting my attention. If its warped discs I guess I'll find out. I didn't really want to put them on yet though.

[Rodger]

Does it shudder at the first big stop on the first hot lap?

Or does it get worse once everything gets hot?

It could be the shocks and likely front radius bushes.

As everything is standard but the tyre size has increased the tyres would provide much more grip and so there is far more load going into the bushes.

Adding to merc-blue's comments. Under heavy braking with the extra grip the rubber bushed radius rods tend not to hold/stop the forces and would bounce axially causing the front wheels to move forward and backwards. This then causes change in castor and toe which as merc-blue already said vibrates the heck out of everything as the geometry keeps changing.

Hot shocks will only exaserbate the problem, as there is now little control of any vertical movement caused by the wheels shuddering.

Regards

Rodger

[Norbie]

My old MA61 used to do this. If the rotors are slightly warped you won't notice it most of the time, but when the rotors get well hot (eg on the track) the metal expands and the warping gets much worse. This is merely a symptom of the stock MA61 brakes being inadequate - so get busy on that brake upgrade!

[Enchanter]

Does it shudder at the first big stop on the first hot lap?

Or does it get worse once everything gets hot?...

I cant remember noticing a difference from cold to hot but there are a few corners before the hairpin so they could be getting warm on the first half lap. I also tend to push just a touch more each conscutive lap. Its hard to remember when it happens though to be honest.

[Negative Boost]

Its the disc's im afraid. I had the exact same problem. I warped the rotors bad just after i got the car and bought some new ones for it. Just 2000km's later they were warped again due to alot of 'entusiastic' driving. I had them machined for $20 each and that lasted untill i upgraded to R33 GTST brakes but i think they just started to warp again.

If you dont want to use your new slotted ones just yet. Whip the rotors off and take them in to get machined.

[thechuckster]

if the shudder is most obvious thru the brake pedal ->disk needs machining

if the shudder is mostly obvious in the steering and seat-of-pants ->suspension

[oldcorollas]

disk physicall ywarped or uneven resin transfer causing high spots?