I couldnt find a thread with this info but I am sure someone will find a thread already started so apologies in advance

Are my brake disks still warped? Can anyone help please.

My 996TT had terrible wobble on braking. I removed the rotors and had them skimmed. The shop took 5 thousands of an inch off and said they were true again.

I refitted everything and gave the pads (EBC yellow stuff) a quick scrub with some sandpaper to remove any glazing and everything felt good. Bedded the brakes in slowly, no wobble.

Now from the left side there is a speed related rubbing noise which goes on to become a rattle. If I touch the brakes it stops but comes back if I let off. Its not all the time, usually once Ive driven a few miles. It sounds like the pad is rattling in the caliper. There is no brake wobble and the brakes pull straight.

I did notice on turning the disk whilst putting the pads back in there was a very slight rub from the pad on the disk at one point as it went round. like a high spot but hardly noticable. Also the caliper was a bugger to get back on.

Could the disk still be warped? Can caliper go on out of true? Or is it a bearing of something.

The machine guy said there is no way his machine would make one disk true and not the other but said he would machine a bit more off if I brought it back which I will do tomorrow but any advice would be hugely aprreciated.

Thanks Guys...and Gals

Carlos

 

The disc is definitely still warped. The machining only made the face true to the pads, but you can't fix a warp. You need to replace them.

 

You cannot machine rotors back into factory condition. I recommend that you buy new rotors.

 

Ooh there seems to be a bit of a consensus building here...thank you for coming back to me....well i just got it back, the guy machined more off it without charge so its going on later whatever and Ill post the result. hope you are wrong but have a nasty feeling I may be bowing to your experience.

As an aside I started the car this morning and the no battery charge warning light came on. It did make a nasty noise for about 3 second when I started the engine which went away...(alternator bearing...?)The main belt is OK and the battery terminals are good. Volt meter inside the car dashboard showing 11 volts. Had a charger on all day and is now at 12 v but warning light still on....happy for suggestions on this too, will open a new thread if I need to...thanks
Carlos

 

Warped rotors are rare, but assuming the rotor is warped...

If the rotor was warped the automotive machinist doing the resurfacing should have seen the rotor wobble and advised you the rotor might not resurface properly.

I've watched brake rotors being resurfaced (heck I've done this -- I am (was) a machinist though I work in another field now) and any wobble is cause enough to have the operator confirm the rotor is mounted correctly -- no burr or something prevented the rotor from being mounted true to the turning machine (brake or engine lathe) spindle -- and if the mounting is ok that there is enough metal to remove the warp and yet have the brake rotor's thickness remain in legal territory.

Afterwards a thorough job would have the worker measure the brake rotor thickness at various points to ensure that at no point is the rotor under its legal thickness.

Then whoever remounts the rotors is responsible for ensuring the job gets the rotors mounted true to the hub face. Someone that has done this before can spin the hub with the rotor in place and visually note the rotor turns without any wobble.

Not sure why the caliper would be a bugger to get back on. Having done brakes on various cars most recently on my Boxster the caliper comes off easy and goes on easy. The pistons are shoved/squeezed back into the caliper to give some room and the caliper then lifts off without any drama.

The caliper is replaced without the pads being installed though.

A wheel bearing could be suspect. With the car in the air and all 4 wheels off the ground you can go around the car and grab each tire in turn at 0 and 180 degrees and see if you can generate any/feel any play; then do the same with your hands grabbing the tire at 90 and 270 degrees. If you want you can also grab the tire and see if there is any play then rotate the tire/wheel some and try again and keep doing this until you have a feel for this wheel's play or lack of it. Do the same to the other 3 remaining wheels and by the time you are finished you should have a good idea if one wheel has more (or several have less) play than others. The ones that have the most play could have a bad bearing, but this is not 100%. There is some play permitted.

But if the one with the worst play is the wheel with the problem brake that bearing becomes more suspect.

Be sure the brake piston dust covers are clean. I like to clean these with brake cleaner (in an aerosol can) thoroughly to remove as much of the grime (dust mainly) that these collect. This is important in at least one way: The dust can weigh down/interfere with the piston's seal and its tendency to help pull the piston back/away from the brake rotor when the brake pedal is released. This slight retraction is important in that the pad is back enough that it no longer makes contact (even if lightly) with the brake rotor.

Between brake jobs I will even 'wash' the brakes to flush away any brake dust that collects and a lot can collect.

Be sure after washing the brakes you take the car out and use the brakes enough to get them hot enough to completely dry them. They'll rust up something fierce in no time if you do not dry them.

At the same time be sure all brake rotor holes are clear of any dust build up. I have seen some cars with brakes with their holes nearly full of an accumulation of dust/rust. (In fact my 03 Turbo when I bought it used had its front brake rotor holes nearly filled with dust.)

The bottom line is whenever one does a 'brake job' on his car he is responsible for ensuring it is done correctly. In the context of your post this means that at least when the rotors are mounted they turn true without any wobble or signs of varying thickness and the pads are the right fit and are properly installed and so on.

You are probably faced with at least removing the brake rotor from the bad wheel and double checking your work and while you are there double checking the rotor's braking surfaces are parallel and that when remounted to the hub and the hub turned the rotor spins without any signs of wobble.

Sincerely,

Rockster.

 

Another possibility is that the calipers may need a rebuild. If the pistons aren't moving freely, that could account for some of your symptoms.

Try removing the pads and seeing how easily you can press the pistons back into the caliper. Put a piece of hard rubber or wood on the rotor and use a screwdriver or long chisel to press them back in. If they don't move easily that could be the cause.

Warped rotors usually get worse as they get hot. Go out and make several hard stops in a row to see if that is the case.

Jon

 

Rockster, good comments, thanks....The left caliper was difficult because the threads on the 2 main bolts into the hub were full of gunk, I cleaned it and bolts went in OK after.

I just noticed I originally put the rotors on the wrong way round. i.e left and right sides got swapped over. The inner vanes are designed, I believe, to turn and draw air inside the disk. so now I am going to remove the rotor on the side without the noise and re assemble them on opposite sides.

---------------------------------------------------
Right all done and back together, I now have the bad disk on the other side so if its a bearing it will stay on the left, if its the rotor it will move and if its cured I am going to be a happy chappy.

Not holding up too much hope as the re skimmed disk still makes a slight brush as it turns, like it has a high spot....

Its too late/beer(after the install!) to go for a test drive now so we will see in the morning.

(Incidentally I took pictures of every stage of the removal so I plan to upload a step by step strip down for anyone who would like to see it but I am not sure how to load pics to this thread, do I need to put links to the pics or can i load them direct to the blog???)

 

I'll guarantee the problem now switches sides. Replace them. I found a front OEM replacement kit off ebay including rotors, high performance pads, and sensors for $500 shipped.

With respect to your battery, if it's not charging at above 13 your battery and/or alternator are (going) bad. How old is the battery?

 

Thanks teflon, you could be right, brakes cant really be tested till I get the charge issue sorted.

Battery is unknown, not marked on it. I have however had the battery on charge for 12 hours and it wont go above 11.9/12 v even though the charger puts out 14v. Drops quite fast when I run the car. Thought it was the voltage regulator and found one for €55 which is a lot cheaper than a new alternator but do you think the batt would show these symptoms?

Going to mechanic tomorrow so hopefully all will be revealed.

 

Just to answer this one Jon, the calipers were re built and the pistons move in and out silky smooth. by now i kind of know its the disks, I just really thought you could grind them true again, still dont really understand why not except when the machine shop re surfaces them the disk is bolted to the lathe via its outer face but the inner face of the disk body is what secures the disk to the hub so if these are not absolutely parralell then I guess the disk is only true with respect to the outer side, not the inner which is what counts...I think Macster actually said this.

Mmm i may go back for a third time and get the guy to fix the disk to the lathe by this inner face but if he grinds off another 2 tousandths of an inch i will be getting a thin thin disk so prob time to bite the bullet and buy 2 new disks.

Anyone have experience of non porsche disks???

 

if i were you, i'd look into either girodisc or brembo's slotted.. or better yet, upgrade to a gt3 setup with the larger calipers..which is my plan when my rotors are toast. i don't think you're gonna be able to bring the one's you've got,back to life though i admire your efforts. GL with it.

 

Hoo hoo, GT· brakes, That would be nice! not heard of girodisc, is that a US brand?? Car on the road again, alternator done now. No probs yet with the brake noise issue but there wasnt last time until I drove it hard which has not happened yet. Have a feeling my next post will be describing my experience of fitting new disks! They are going to be something fairly standard I think, my funds are being set aside for new tyres etc after my very first track day in July.

 

Bad news, put new rotors a nd pads on about 1000 miles ago and now have the same problem on the same side, wobble on braking. Maybe it is the calipers....the car was bought with re built calipers but maybe they were just re painted.

The pistons did seem to slide in ok when I changed everything. Is it possible the movment was actually not freely enough. They felt smooth...

Now looking to rebuild the offending side and see. Canny one point me to the thread on caliper rebuilds?