Massive new Vibration at rear or car during decel
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AudiWorld Super User
Joined: Oct 2006
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From: In my Garage
Massive new Vibration at rear or car during decel
Does anyone recognise this symtom ?
car was running fine all winter .. wife cam home yesterday and complained of above synptom
I took it out for a test and all was normal went about 40mph no problem .. as soon as i let off the gas a horrible vibration and shaking from the back of the car .. everything esle was fine... didnt sem to be coming from any side in particular . allmosyt like a wop wop wop sound .. and as you do it from a faste speed it is more violent .. only on decl however.
I did notice something that isnt right .. I checked all the rotors and right rear was 274 degrees and the others were 85. strange thing was it didnt seem to be a gragging caliper at all when i jacked it up . I need to investigate further .. i would somehow love to see what happens if i were able to take the rear calipers off all together if nto to eliminate them . I might pop th pads out for a test as i dont really need the brakes for this test . Any other thoughts .. I wonder if a CV joint failure could do this ?
Any other thoughts ? it does seem to lessen when i put the brakes on but it is hard to tell...
any other thoughts ?
car was running fine all winter .. wife cam home yesterday and complained of above synptom
I took it out for a test and all was normal went about 40mph no problem .. as soon as i let off the gas a horrible vibration and shaking from the back of the car .. everything esle was fine... didnt sem to be coming from any side in particular . allmosyt like a wop wop wop sound .. and as you do it from a faste speed it is more violent .. only on decl however.
I did notice something that isnt right .. I checked all the rotors and right rear was 274 degrees and the others were 85. strange thing was it didnt seem to be a gragging caliper at all when i jacked it up . I need to investigate further .. i would somehow love to see what happens if i were able to take the rear calipers off all together if nto to eliminate them . I might pop th pads out for a test as i dont really need the brakes for this test . Any other thoughts .. I wonder if a CV joint failure could do this ?
Any other thoughts ? it does seem to lessen when i put the brakes on but it is hard to tell...
any other thoughts ?
AudiWorld Super User
Joined: Aug 2004
Posts: 3,277
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From: Toronto
Yes, sometimes the response can be lacking here, unless you put a thread up about timing belt procedures.
Anyhow, if one of the rotors is hot, then it's definitely some sort of friction.
Jack it up, take off the wheel, and see what's going on there. Jiggle each control arm, the driveshaft, etc.
Anyhow, if one of the rotors is hot, then it's definitely some sort of friction.
Jack it up, take off the wheel, and see what's going on there. Jiggle each control arm, the driveshaft, etc.
Tech Guru
Joined: Mar 2003
Posts: 6,006
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that's a mysterious one. Let me mull it over. Random thoughts:...
The germane characteristics in my head are:
1. weight is shifting forward
2. drive line is being reverse loaded
3.
- rear sub-frame hop
- rear diff "funkiness" - drive train lash
- rear control arm slop - coupled with lash in DT
Can you elaborate on what you mean by rotors at X and Y degrees? How measured? relative to what ref?
G
The germane characteristics in my head are:
1. weight is shifting forward
2. drive line is being reverse loaded
3.
- rear sub-frame hop
- rear diff "funkiness" - drive train lash
- rear control arm slop - coupled with lash in DT
Can you elaborate on what you mean by rotors at X and Y degrees? How measured? relative to what ref?
G
AudiWorld Member
Joined: Mar 2001
Posts: 166
Likes: 1
I did notice something that isnt right .. I checked all the rotors and right rear was 274 degrees and the others were 85. strange thing was it didnt seem to be a gragging caliper at all when i jacked it up . I need to investigate further .. i would somehow love to see what happens if i were able to take the rear calipers off all together if nto to eliminate them . I might pop th pads out for a test as i dont really need the brakes for this test . Any other thoughts .. I wonder if a CV joint failure could do this ?
Tech Guru
Joined: Mar 2003
Posts: 6,006
Likes: 2
DOH!!! 274 degrees - as in Fahrenheit! I was thinking of orientation and wondered why it mattered!
I still don't get the connection to decel, yet......but it MUST be a pad or caliper issue.
Cant be a CV - it would not cause a hot rotor.
now, when you say "decel" - you dont mean "lift throttle" do you? You mean "[press brakes" - right?
Now we're closing in. Something is causing ONE caliper to grab or jam. Might a pad be crooked (happened to me)? Might some junk have become wedged?
I would suspect that you have a dragging situation, either a crooked pad or space junk in there, and when you step on the brakes, it does weird things. In fact, it could be grabbing on one wheel, and causing a speed differential to the other wheel,and engaging the ABS... myriad of oddball mechanisms are possible.
Disassemble. Re-assemble clean and true. Check sliding action on caliper. test.
I still don't get the connection to decel, yet......but it MUST be a pad or caliper issue.
Cant be a CV - it would not cause a hot rotor.
now, when you say "decel" - you dont mean "lift throttle" do you? You mean "[press brakes" - right?
Now we're closing in. Something is causing ONE caliper to grab or jam. Might a pad be crooked (happened to me)? Might some junk have become wedged?
I would suspect that you have a dragging situation, either a crooked pad or space junk in there, and when you step on the brakes, it does weird things. In fact, it could be grabbing on one wheel, and causing a speed differential to the other wheel,and engaging the ABS... myriad of oddball mechanisms are possible.
Disassemble. Re-assemble clean and true. Check sliding action on caliper. test.
AudiWorld Super User
Joined: May 2009
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i found out that symtom was an alternate Swedish spelling for
S-Y-M-P-T-O-M
but i never did find out what "synptom", my best guess was synthetic (SYN) protein (P) translocase of the outer membrane (TOM)
all kidding aside, it was just over a day before a response from somebody, a friendly bump would have worked better then the melodrama. we have jobs too ya know
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Tech Guru
Joined: Oct 2002
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From: Olney, MD
DO NOT pop the pads and take it out for a drive...the pistons in the rear caliper will just bang out into the rotor and they might pop out enough to leak brake fluid.
One thing you can do is put the car up on jackstands under the balljoints under the wheel bearing carriers, NOT on the aluminum struts themselves but as far outboard as you can. Bring the wheels up to 30 mph in Drive and let up on the gas. See if you can identify the shaking.
AFter you get the car up on jackstands leave the jack(s) in place on the body jack points.
I've done this lots of times to identify bad wheel bearings...you'll KNOW by the noise if a bearing is bad and you can easily locate it to one wheel.
Have you driven hard over anything lately...like a speed bump?
One thing you can do is put the car up on jackstands under the balljoints under the wheel bearing carriers, NOT on the aluminum struts themselves but as far outboard as you can. Bring the wheels up to 30 mph in Drive and let up on the gas. See if you can identify the shaking.
AFter you get the car up on jackstands leave the jack(s) in place on the body jack points.
I've done this lots of times to identify bad wheel bearings...you'll KNOW by the noise if a bearing is bad and you can easily locate it to one wheel.
Have you driven hard over anything lately...like a speed bump?
Tech Guru
Joined: Mar 2003
Posts: 6,006
Likes: 2
900 degrees will melt every OEM pad on the planet, and most "light race" pads as well.
Read the MOT specs, its nto even close.
My FRONT brakes on the boxster get to about 460 (F) immediately off track, after one cool-down lap, measured at the rotor face (Fluke IR gun)
I think 275 is quite hot for rear rotors.
G
Read the MOT specs, its nto even close.
My FRONT brakes on the boxster get to about 460 (F) immediately off track, after one cool-down lap, measured at the rotor face (Fluke IR gun)
I think 275 is quite hot for rear rotors.
G