Whump, whump, whump?
08-22-2012, 03:53 PM
#1
Burning Brakes
Thread Starter
Whump, whump, whump?
I was coming back from the east Bay (about 60 miles away) in my '89 5 spd on a very hot (90s) day last week. I was on the freeway running at 70-80 when I started to notice an occasional thumping type noise coming from the rear of the car - especially when I backed off the accelerator.
At first it sounded to me like I had broken an exhaust hanger and the exhaust system was flopping up and down. As I got closer to home, the noise became more frequent and started to sound more like a rotational whump, whump, whump noise - especially when coming to a stop.
Put the back end up in the air the next day and took a look underneath - exhaust system is solid - no broken hangers and nothing else obviously wrong.
I drove it over to a fellow 928er's house (about 25 miles) the next day to see if he could help me diagnose the noise. The noise did not start happening again until I was within a mile of his house, so the car has to be hot to make the noise. The noise is now definitely rotational and is most noticeable on deceleration. It seems to go away if the clutch is depressed while the noise is occuring. From the driver's seat the noise seems to be coming from the passenger's side. From the passenger's seat, Paul seemed to think it was coming from the driver's side. The car had a rebuilt torque tube from 928 Int ~15k miles ago (before I bought it).
We are leaning towards it being a bad half shaft (axle). Anyone BTDT or have any suggestion. Thanks.
James
At first it sounded to me like I had broken an exhaust hanger and the exhaust system was flopping up and down. As I got closer to home, the noise became more frequent and started to sound more like a rotational whump, whump, whump noise - especially when coming to a stop.
Put the back end up in the air the next day and took a look underneath - exhaust system is solid - no broken hangers and nothing else obviously wrong.
I drove it over to a fellow 928er's house (about 25 miles) the next day to see if he could help me diagnose the noise. The noise did not start happening again until I was within a mile of his house, so the car has to be hot to make the noise. The noise is now definitely rotational and is most noticeable on deceleration. It seems to go away if the clutch is depressed while the noise is occuring. From the driver's seat the noise seems to be coming from the passenger's side. From the passenger's seat, Paul seemed to think it was coming from the driver's side. The car had a rebuilt torque tube from 928 Int ~15k miles ago (before I bought it).
We are leaning towards it being a bad half shaft (axle). Anyone BTDT or have any suggestion. Thanks.
James
08-22-2012, 05:24 PM
#2
Supercharged
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It's not clear...
Is the wump wump wump there while the car is in motion with the clutch peddle depressed? Does it matter if it's in gear or not? RPM or speed dependent?
If it goes away when you disengage the clutch, but the car is moving and in gear, it's likely engine or clutch related.
If you are in neutral (car moving) and the sound goes away, then possible TT.
If the sound is completely speed dependent then maybe half-shaft.
The heat thing is a curve ball for me and may be unrelated unless it's a TT going south.
Is the wump wump wump there while the car is in motion with the clutch peddle depressed? Does it matter if it's in gear or not? RPM or speed dependent?
If it goes away when you disengage the clutch, but the car is moving and in gear, it's likely engine or clutch related.
If you are in neutral (car moving) and the sound goes away, then possible TT.
If the sound is completely speed dependent then maybe half-shaft.
The heat thing is a curve ball for me and may be unrelated unless it's a TT going south.
08-22-2012, 10:33 PM
#3
Burning Brakes
Thread Starter
The "whump, whump, whump" noise is on deceleration - if the clutch pedal is depressed while it is making the noise, the noise seems to go away (although I haven't played with it enough to be absolutely certain).
The noise is definitely coming from the rear end of the car - which side seems to depend upon which seat you're sitting in ... From the driver's seat I thought it was coming from the passenger's side. With Paul in the passenger's seat, he thought it was coming from the driver's side.
Anyone have a trick for removing the rear axle nut. We have access to a "parts car." I tried using a 6' piece of pipe as an extension over a half inch drive "breaker bar" and sheared the square drive off of the breaker bar - but the axle nut didn't budge. It's torqued to something like 330 ft/lbs.
James
The noise is definitely coming from the rear end of the car - which side seems to depend upon which seat you're sitting in ... From the driver's seat I thought it was coming from the passenger's side. With Paul in the passenger's seat, he thought it was coming from the driver's side.
Anyone have a trick for removing the rear axle nut. We have access to a "parts car." I tried using a 6' piece of pipe as an extension over a half inch drive "breaker bar" and sheared the square drive off of the breaker bar - but the axle nut didn't budge. It's torqued to something like 330 ft/lbs.
James
08-23-2012, 04:34 AM
#6
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Impact.
If it's not off yet, a trick to check and see if it's the half shafts/cv is to run the car in reverse and do a couple opposite circles going backwards. Do this after its making the noise. If this maneuver make the sound go away temporarily, it is most certainly a half shaft. I had a 944 in my youth that had a bad cv... I did the back up trick to make the sound go away over a course a full summer... (kids never have spare cash). I would often back the car up before picking up a date... Eventually, the trick quit working and I had to replace the cv... When it first started making the noise, it was a whump, whump, whump. Towards the end it turned into a whump clack, whump clack, whump clack...
Good luck
If it's not off yet, a trick to check and see if it's the half shafts/cv is to run the car in reverse and do a couple opposite circles going backwards. Do this after its making the noise. If this maneuver make the sound go away temporarily, it is most certainly a half shaft. I had a 944 in my youth that had a bad cv... I did the back up trick to make the sound go away over a course a full summer... (kids never have spare cash). I would often back the car up before picking up a date... Eventually, the trick quit working and I had to replace the cv... When it first started making the noise, it was a whump, whump, whump. Towards the end it turned into a whump clack, whump clack, whump clack...
Good luck
08-23-2012, 08:56 AM
#7
Undoing rear axle nut? Decent socket. Short extension. Longest bar you can find. Friend in car with brakes on. Attach tools. Get trolley jack. Jack up end of bar. Nut unwinds. No effort, no hurt back, etc..
To retorque to 400 ft/lbs add bathroom scales between end of bar (4 feet long) and jack till scales show 100 lbs. Adjust weight 'target' so bar length x scale weight equals required torque..
To retorque to 400 ft/lbs add bathroom scales between end of bar (4 feet long) and jack till scales show 100 lbs. Adjust weight 'target' so bar length x scale weight equals required torque..
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08-23-2012, 09:01 AM
#8
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08-23-2012, 01:44 PM
#9
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08-23-2012, 10:16 PM
#11
Ha Jon,
Note: John D did not say "I" was ingenious, but that "that's" (ie the process) is ingenious. So, mate, technically you're wrong. And therefore you owe me a beer or three. :-)
But no, I hadn't read it on rennlist, I'd done it in my garage when doing my CV joints, using the bathroom scales while my (ex) wife was not at home!! But certainly someone may well of thought of this beforehand - it's so obvious when you think about it - ie the fundamental definition of 'foot pounds' that I'd be surprised if I was the first to think of it.
Cheers all
Note: John D did not say "I" was ingenious, but that "that's" (ie the process) is ingenious. So, mate, technically you're wrong. And therefore you owe me a beer or three. :-)
But no, I hadn't read it on rennlist, I'd done it in my garage when doing my CV joints, using the bathroom scales while my (ex) wife was not at home!! But certainly someone may well of thought of this beforehand - it's so obvious when you think about it - ie the fundamental definition of 'foot pounds' that I'd be surprised if I was the first to think of it.
Cheers all
11-17-2016, 11:35 AM
#13
Burning Brakes
Thread Starter
Just stumbled on to this post again while searching for something else.
For future reference, the whump, whump, whump noise turned out to be a bad rear wheel bearing.
James
For future reference, the whump, whump, whump noise turned out to be a bad rear wheel bearing.
James
