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Brake vibration

petefm10

Trainee
Joined
27 Oct 2008
Messages
86
Hi Folks Re 1996 993
When brakes are applied at above 65mph vibration occurs through the car. Seems not to be through the steering wheel and the front and rear discs have been replaced recently. Could this be due to ABS component?

Car also has a lowered suspension so could this cause wear on the CV joint and cause the vibration? Car has done 62k miles.
Any help appreciated - thanks

ps I placed a thread here about 2 months ago re car not starting when hot and it was suggested to replace battery earth lead. Done and it's been fine ever since!!! So thanks
 
As one newbie to another I have to be prepared to be shot down in flames but my guess would be whoever replaced your discs did not clean up the mating surfaces thoroughly so you have excess disc runout. Typically everything seems OK for about the first thousand miles or so then you get the judddering. Often attributed to 'warped discs' but really it is a slight change to the surface of the disc in certain patches. I'd be looking at taking it back to the garage that changed the discs (unless you did it yourself of course).
 
Hi and welcome from the shadows.

Certainly worth checking the run out on the discs, and even having them resurfaced whilst on the car to ensure all run out is completely eliminated. I believe the brand name for this device is pro cut. Many Specialists have them, my local one certainly does.

Before doing that, I would inspect the from lower arm rubbers for wear, as these can cause wobbles under braking if soggy.

Do you use the car a lot? My car always drives like the tyres are 50 pence shaped for about 5 miles as they end up not quite round from the car sitting in the garage for weeks on end. It's gets bad at 60-65mph and feels a lot like bad wheel balancing. Totally clears once the tyres are warm and re-rounded. Is your wobble definitely only under braking? If so do the above
 
I had that brake wobble on my 993 that I never really got to the bottom of before I sold it. Most noticed when exiting onto a motorway slip and applying the brakes coming down from 70-30mph.

I didn't use my car much and the discs/pads were less than 1.5k miles of use but some corrosion to the inside face (common through incorrect bleeding). I believe skimming the discs would have sorted it - which was recommended.
 
Do you go for a quick run post washing? Surface rust between pad and disc can sometimes build up after a wash and cause the wobble feeling on the next outing. Try a couple of high speed stops to clean the discs up.

Also, have you had your wheels refurbed recently? I recently had mine done and despite the wheel bolts being fully torqued to manual spec, loosened off due to the wheel paint being chewed through in the area where they seat. A quick retorque sorted it.
 
Hi

It can be quite difficult to get the discs on and running within spec when changing them. Porsche do allow you to rotate the disc 180 degrees and use just one retaining screw if it helps. You have to use a dial gauge and check once all the nuts are properly torqued up

Getting the run out to be within spec is key. Having them skimmed on the car is a very good idea, but I have never found anywhere that still does it these days, but maybe I did not look hard enough. I used to have a CRX which juddered and are notoriously difficult in that respect.

Berni
 
To test run out properly I bought some open ended steel wheel nuts. These allowed me to torque the disc down tight without fitting a wheel.

This is the pro cut machine in action

http://youtu.be/qAOFErcUMoE
 
kerb scraper said:

Good write up but nothing has been mansion in here about calipers itself.
If the pistons are sticking and you get pressure to the discs only from one side of the caliper you're more likely have a vibration through your pedal and steering wheel.

Did you check if the plates are not lifted as they will trap the pads as well and prevent them from moving.

From what i see 95% of any calipers from a car of 40K on the clock and more will need new fluid seals.
 
I've had vibration on and off for years. When I had new discs and plate lift sorted in 2010 the problem was cured but it only lasted a year or two. Your symptoms sound identical to mine. Not an actual judder, more of a sound that comes from the rear of the car. When I refurbished my rear callipers I noticed that I had plate lift again and as a result the inner pads had not been fully contacting the disc. This has left a 1 inch rim of rust on the outer lip of the inside faces of the disc. Repeated hard stops has not cleared the rust off. A friend suggested helping the rust on its way by breaking down the bulk of it with some emery cloth. Next time the car is up in the air I'll try this.
Have you looked at the insides of your discs? Use a mirror, you can do it without even jacking the car up. I would check the simple things before busting out the dial indicator and open ended nuts.

Stuart
 

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