Brake shudder

steveoz32 · Apr 16, 2011

Point one sounds like warped / worn front discs as it only happens when breaking, if it was wheel balancing you would get vibration at a certain speed range, breaking from said range would stop the wobble. 1st to 2nd is normally notchy on most 996's I hear these days until warmed up, but point 2 and 3 sound related to your tranny issue, is the vibration in your drive train? (if you take it out of gear and coast does it still vibrate?). If while in gear or under acceleration could be flywheel / clutch.

Paul James · Apr 16, 2011

ORIGINAL: steveoz32 Point one sounds like warped / worn front discs as it only happens when breaking, if it was wheel balancing you would get vibration at a certain speed range, breaking from said range would stop the wobble. 1st to 2nd is normally notchy on most 996's I hear these days until warmed up, but point 2 and 3 sound related to your tranny issue, is the vibration in your drive train? (if you take it out of gear and coast does it still vibrate?). If while in gear or under acceleration could be flywheel / clutch.

Hi steveoz, I do get a vibration through the steering wheel at 60+mph, Chris Franklin at CoG also commented that they were imbalanced. I was wondering if this could also be the cause of the braking shudder? Also I must emphasize that point two has never happened before - it was only after a medium/heavy braking session from high speed, it sounded like it was coming from the front end of the car. It has never before and hasn't since made the noise. Thanks for your reply

steveoz32 · Apr 17, 2011

No problem. I've had warped discs happen on other cars and the vibration / shudder under breaking worsens and really shakes the car the more you apply them. If I have ever had a tyre fitted poorly and the wheel not balanced correctly in the past, the wheel vibrates and front end shudders for around 5mph range give or take from anywhere around 60mph upward. Normally you can go through it by accelerating and the speed balances out the wheel again. We had a tyre place here who did great deals and wouldn't sell tyres without fitting them, so I used to have to take his service then drive to get them re-fitted lol. I can't recall having an unbalanced wheel shake the car under breaking though it's no doubt possible. The sound / vibration is odd, it's coming from the front and it's a C2 so that rules out tranny issues then, not sure what that could be sorry. You can feel warped discs through the wheel though even when not breaking if they are bad, as the pads rest against the discs all of the time anyway. Always best to eliminate the simple things first anyway so it sounds like you have the right plan of action

Paul James · Apr 17, 2011

As many of you might know, I picked up my 996 C2 at the start of this year. Having had the car for a few months, I've noticed a few things;

From around 60mph plus, the car shudders under braking. The steering wheel vibrates and a sound can be heard - the problem is accentuated when braking from three figure speeds, the higher the speed the more serious it sounds and feels. My wheels are not balanced properly (having them done next week), could this be the problem?

Thanks in advance for your help

Paul

Richard_Hamilton · Apr 17, 2011

I don't think the vibration is wheel imbalance, because it would wobble under normal cruising, not just when braking. I agree with Steve - disks and/or wheel bearing. As for the gearbox, again as Steve says, they can be notchy 1st to 2nd when cold, but this should disappear after a couple of miles. If it does it when hot, it sounds like it might be a lazy 2nd gear synchro to me.

Paul James · Apr 17, 2011

Thanks for the comments. Today I performed the bedding in process on the brakes, two sets of 10 runs from 80mph to 10mph, one after the other in quick succession. This reduced the vibration when braking from speed greatly, any thoughts as to why that could be?

ashley · Apr 17, 2011

Have you changed any of the components, i.e discs and pads? if not, not sure why you would carry out the bedding in procedure. Like others have said likely to be a warped disc, same symptoms appeared on my Boxster and was cured with a disc change.

gezr · Apr 17, 2011

ORIGINAL: Paul James Thanks for the comments. Today I performed the bedding in process on the brakes, two sets of 10 runs from 80mph to 10mph, one after the other in quick succession. This reduced the vibration when braking from speed greatly, any thoughts as to why that could be?

The reduction could be because there was uneven build-up of pad material on the discs prior to you performing the bedding process. This can happen if you come to a complete stop after a heavy session on the brakes and sit with your foot on the brake. It effectively leaves an imprint of the pad on the disc. I would recommend finding a place near you that can skim your discs on your vehicle. This is assuming the discs aren't worn out. Do you know when they were last changed? I have a small issue with my front discs similar to yours. It's a long story so I wont go into it here but I had two new front wheel bearings last week and the shudder has reduced by a lot. My car has 50k miles on it.

NXI20 · Apr 18, 2011

ORIGINAL: Paul James Thanks for the comments. Today I performed the bedding in process on the brakes, two sets of 10 runs from 80mph to 10mph, one after the other in quick succession. This reduced the vibration when braking from speed greatly, any thoughts as to why that could be?

'The "Warped" Brake Disc and Other Myths of the Braking System' - a very worthwhile read [

] http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

steveoz32 · Apr 18, 2011

Interesting, but we know pads wear and groove discs, if uneven material can be transfered then surely the disc can wear unevenly. Either way, I've had two cases of what I believed to be 'warped discs' on previous cars, and in both cases rotating the wheel while elevated returned more resistence at certain parts of the disc. Renewing the front discs cured the issue in both cases. It is worth noting that I normally change pads with new discs to let them bed in and wear correctly on a new disc as well, eliminating issues with the pads.

NXI20 · Apr 18, 2011

But isn't that the point he's making? Yes, there can be more resistance at certain points on the disc, but this isn't because the disc has warped (a pretty difficult thing to do with cast iron over an inch thick). It's either due to a buildup of transferred pad material (usually caused by applying the pads to a stationary hot disc) or the formation of cementite, which is much harder than the surrounding cast iron of the disc & so as the disc wears, these areas are left standing proud. As more heat is introduced into these areas, the cementite spreads & deepens, which is why discs that are too badly affected have to be changed as a skim will not remove the cementite completely & the process will start again.

steveoz32 · Apr 18, 2011

Didn't read the full article as I was busy sorry

Richard_Hamilton · Apr 18, 2011

Have we any idea how old the disks are, or what the condition of the inside faces are? Could be that they are rusted badly. I'm sure you have seen how horrendous the inside faces can be, yet the outsides look perfectly OK.

Paul James · Apr 25, 2011

I recently had my wheels balanced, and it turns out both of my rear wheels are buckled. 911V were great about it, they said they would replace them straight away (they didn't argue in any way). Now the wheels are balanced, the brake shudder from speed has been reduced massively - I'm hoping the new rear wheels will eliminate it completely. I should think it was a combination of both build up of pad material on the disc, and imbalanced/buckled wheels. Thanks for all suggestions.