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1996 Subaru Outback with 164,000 miles. Front brake pads, rotors, calipers just done, rear brakes are just fine. Mechanic says this thud-thud-thud when applying brakes is NOT a brake problem because when he tested it, it doesn't react like a brake problem. He says it is something else and not to worry about it being unsafe. Have appt Monday for him to check it out. BTW, I drive mountain roads and don't like to drive an unsafe car...either for me or for anyone I could potentally injure.
This car is a bit older than I usually drive. I'm having maintenance work done on it every month or so in order to get it up to my personal auto code
More about the thudding...although I hope I'm describing it in automotive terms It occurs primarily when driving above 30-40 mph and apply the brakes. It jerks the car a wee bit, more so as the speed increases.
Does anyone have any ideas? I like to go to my mechanic with my own education, even though I think their shop is extremely honest. I've gone to them for at least 7 years.
Sounds like a warped rotor in the brake system some where. Do you feel this in the steering, or does the rear view mirror shake. In general if you feel this in the steering and because apx 78% braking is done with the ft brakes it is typically ft rotors.
In the work were the rotors machined? Chances are they should have been.
Sounds like a warped rotor in the brake system some where. Do you feel this in the steering, or does the rear view mirror shake. In general if you feel this in the steering and because apx 78% braking is done with the ft brakes it is typically ft rotors.
In the work were the rotors machined? Chances are they should have been.
Mac , Don't feel it in the steering...will check the front mirror ASAP.
My mechanic just did my entire front brakes: pads, rotors, calipers...I will see what he says on Monday. Thank you for the suggestions...I would never have thought to re-check the front...but I'm sure on Monday, Scott will do so. If not, I will certainly mention it.
Machining rotors should be a standard part of doing brake work. It adds to the costs some. At times if the rotors run true enough this can be skipped too.
If you bought and had installed new rotors the hubs they mount to must be spotell clean, as any debris will hold the rotor off it's true straigh plane.
With either a magnet or vise grip mounted dial indicator this should be a easy find true/ false. No rotor is perfect so there will be some run out, but you have too much.
In the case of a over heated warped rotor, machining only works a limited time. The stress tends to return. The only soulution then is new rotors.
The juddering you feel is caused by the warp and the pad following that warp.
It also might be that if the rotors were not machined, that there is inner and outter rust ridges on the rotors, and the new pads are in some contact with them. A fairly true rotor can still cause this juddering if these rust ridges are in contact with he pads.
If the rotors are other wise sound, what I do is start the engine on a ft wheel drive vehical and with a big bastard file cut off the rust ridges with the rotors spinning. That is the proper name for that type of file. I am not swearing.
I modify the file, but taking it to a grinding wheel, and true up the front end it it, to be dead on 90 degrees square. This is easy to do. You somply square the file on the front end. This file better havd a good handle grip on it then and for the chore that comes next.
Other wise there is a high risk of driving the files own tang into the workers wrist, which is going to end baddy.
With the front end of the file squared, you can cut the inner rust away. The caliper must be removed and hung on a sturdy cord, and be out of the way of the turning rotor, or all hell will break loose if that caliper contacts the moving rotor.
Cut away all the rust ridges inner inside and out, outter egdes inside and out and the top edge of the rotor at it's max diameter. Taking care for any lumps that may be cast into the rotors on purpose.
Then last a tech wearing a face mask can chamfer the pad to be away from any remaining rough rust surfaces, by grinding a bit off the pads, as a chamfer.
The mirror and steering tricks are just to help ID which set of brakes cause the pedal to judder. The fact the pedal judders is all I need to know at least one rotor is way out of spec. I just can't help ID which one that is.
Another trick is to let go of the steering wheel. I don;t mean to pray, or mess around texting with both hands. I mean you get up to around 40 let go of the wheel and hit the brakes like you mean to slow down briskly, as if you misjudged entery speed to a tighter curve in the road. Not a blind panic stop, not engaging ABS, but not creeping up to a red light 1/4 miles away either.
If everything is correct the car will still track straight. If the car pulls to a side something is wrong. Be ready for the car to pull to one side. Do not crash.
Chances then are that steering wheel will jiggle side to side or rotate some. Which ever way the car goes left/right, will be the side to start looking at rotors.
This pulling to the side can be other things wrong as well, so this isn't the end all for pulling. This is a test to tell where to start looking for the warped rotor.
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Other things that cause pulling can be, and this bit is just to say so, not to really look into deeply are uneven tire psi, bad suspention and track arm bushings, bad tie rod ends, drag links, and relay rods, bad shocks, bad ball joints, bad king pins (your car has no king pins) Bad tower fittings on McPhearson struts, and bad wheel alignment front or back, if back applies which it can on any car.
Even a rear wheel drive car can have bad rear axel alignment. Usually it takes a fairly bad accident to get that to be, but it can happen. Certainly you have seen other cars moving that, don't seem to sit straight on the road. You can bank on one pair of wheels are out of alignment then.
Mac , Don't feel it in the steering...will check the front mirror ASAP.
My mechanic just did my entire front brakes: pads, rotors, calipers...I will see what he says on Monday. Thank you for the suggestions...I would never have thought to re-check the front...but I'm sure on Monday, Scott will do so. If not, I will certainly mention it.
More to the point I guess, your tech needs to pull off the rotors and clean the hubs they bolt up on. If he left grit, rust and sand between the hubs and the new rotors then the rotors are going to wobble on the plane of axis.
If you do any carpentry work, and know what a daddo blade is for a table saw, it is a lot like that. Not as extreme, but similar.
More to the point I guess, your tech needs to pull off the rotors and clean the hubs they bolt up on. If he left grit, rust and sand between the hubs and the new rotors then the rotors are going to wobble on the plane of axis.
If you do any carpentry work, and know what a daddo blade is for a table saw, it is a lot like that. Not as extreme, but similar.
Mac, thanks for all the time you took to explain Now I'll know how to communicate with my mechanic... BTW...the rear view mirror does not shake. Also, do new rotors need to be machined? or just existing rotors?
ANOTHER QUESTION: It's been about a month since the new pads, new rotors, and calipers were installed....do you think in the past 4 weeks damage has been done to the new rotors and/or pads?
New rotors are good to go out of the box, other than need to be de greased. They are usually coated in cosmolene. I am almost willing to bet there is crud under the rotors and between the hubs. So no I don't see any real way to cause damage at this point.
I know if it were me and mine, i would set up a dial indicator and turn the rotor by hand. The new rotor is in spec at 0.006" run out, that adds up to 0.003" each way. More than that is out of spec.
If your guy hasn't got that tool, he has 0 bee's wax doing brakes.
The only way new rotor can be out of spec is if someone dropped a crate of them too hard and they all got trashed at once.
Here's the scoobie...took my car in Monday...rear brakes needed pads/rotors...had this done and my car drives like a dream No more thuds at all. Thanks for all your input/ suggestions! Emily
AHHH HA! Glad you started this thread. I test drove a VW Jetta yesterday and the car did exactly what you described. I mentioned to the sales guy and he told me that cars will make that sound when they sit on a lot for a few days without being driven. Whatever. I didn't believe him.
You braked too late. The 'thud-thud-thud' was Larry, Moe and Curly. RIP stooges. :-(
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, Don't feel it in the steering...will check the front mirror ASAP.
Whatever. I didn't believe him.
