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| Vibration or "pulsing" under hard acceleration grant - 7 years ago |
Hi Folks,
I have an annoying vibration [mostly] under hard acceleration. This is in the track car, 2000 986S, 6-sp, PSS9s, stock motor.
It has existed for a while - although memory is never perfect.
Under acceleration i get a vibration through the chassis. My 2.7 street car (5-sp) does not do this, or not nearly as much. It certainly did when my motor mount failed..... As i recall they climb with speed (cant say if its better correlated to speed or engine RPMs, sorry). I have attributed it to several things - all possible, but hard to diagnose:
1. Out of balance or round rear tires - but its more than one set
2. Motor mount can be ruled out since i just replaced it with one from Pedro
3. Transmission mounts felt like this when they were replaced, but a) the trans mounts are only two years old, and b) they show no sign of leaking
4. Driveshaft issues, but i rebuilt them over the winter, they are tight, and slide smoothly in and out. I do suspect that the (normal) extreme angle they are at could contribute
This could all be normal operation in a car with lots of tires that are used very hard and therefore imperfect, ad is OLD (225k and climbing, lots of that track mileage).
If i see no sign of transmission mount leaking, can I rule them out?
If not, how shoudl i test? Apply pressure where and check for how much play?
Any other ideas?? -- especially from those who have chased similar problems on a similar chassis....
TIA,
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
I have an annoying vibration [mostly] under hard acceleration. This is in the track car, 2000 986S, 6-sp, PSS9s, stock motor.
It has existed for a while - although memory is never perfect.
Under acceleration i get a vibration through the chassis. My 2.7 street car (5-sp) does not do this, or not nearly as much. It certainly did when my motor mount failed..... As i recall they climb with speed (cant say if its better correlated to speed or engine RPMs, sorry). I have attributed it to several things - all possible, but hard to diagnose:
1. Out of balance or round rear tires - but its more than one set
2. Motor mount can be ruled out since i just replaced it with one from Pedro
3. Transmission mounts felt like this when they were replaced, but a) the trans mounts are only two years old, and b) they show no sign of leaking
4. Driveshaft issues, but i rebuilt them over the winter, they are tight, and slide smoothly in and out. I do suspect that the (normal) extreme angle they are at could contribute
This could all be normal operation in a car with lots of tires that are used very hard and therefore imperfect, ad is OLD (225k and climbing, lots of that track mileage).
If i see no sign of transmission mount leaking, can I rule them out?
If not, how shoudl i test? Apply pressure where and check for how much play?
Any other ideas?? -- especially from those who have chased similar problems on a similar chassis....
TIA,
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
| Re: Vibration or "pulsing" under hard acceleration MarcW - 7 years ago |
Quote
grant
Hi Folks,
I have an annoying vibration [mostly] under hard acceleration. This is in the track car, 2000 986S, 6-sp, PSS9s, stock motor.
It has existed for a while - although memory is never perfect.
Under acceleration i get a vibration through the chassis. My 2.7 street car (5-sp) does not do this, or not nearly as much. It certainly did when my motor mount failed..... As i recall they climb with speed (cant say if its better correlated to speed or engine RPMs, sorry). I have attributed it to several things - all possible, but hard to diagnose:
1. Out of balance or round rear tires - but its more than one set
2. Motor mount can be ruled out since i just replaced it with one from Pedro
3. Transmission mounts felt like this when they were replaced, but a) the trans mounts are only two years old, and b) they show no sign of leaking
4. Driveshaft issues, but i rebuilt them over the winter, they are tight, and slide smoothly in and out. I do suspect that the (normal) extreme angle they are at could contribute
This could all be normal operation in a car with lots of tires that are used very hard and therefore imperfect, ad is OLD (225k and climbing, lots of that track mileage).
If i see no sign of transmission mount leaking, can I rule them out?
If not, how shoudl i test? Apply pressure where and check for how much play?
Any other ideas?? -- especially from those who have chased similar problems on a similar chassis....
TIA,
Grant
Can a transmission mount fail in such a way a leak is not involved? If so you can't rule out transmission mount failure.
By "rebuilt" the half shafts what exactly did you do? As an aside, when the tech did the half shafts on my Boxster -- due to failed CV boots -- he thoroughly cleaned the bearings and inspected the bearing hardware for any signs of wear. Deeming the hardware OK to reuse he repacked the bearings with grease and assembled the half shaft and then installed the half shafts back the same way they were before.
More on this: I was always taught before removing half shafts (or just a drive shaft) to mark the flanges so I would assemble the hardware in the same orientation it had before. What can happen if this is not done is one can end up with a vibration as the shaft flanges are *not* in the same position.
There are two things to consider with position. There is the rotational position but even if the flanges have the same hole to hole relationship upon reassembly if there is any play then one flange can be shifted slightly off center from where it was before.
Regarding repacking the bearings, one wants to avoid putting in too much grease, or too little grease. One wants to use just the right amount of grease.
If too little grease we know what can possibly happen. With too much grease what can happen is the excess can get slung out but of course is captured by the boot. If this grease doesn't smooth itself out, and being grease it might not, but instead remains kind of in a blob this can cause an imbalance condition until the boot fails from the strain of the extra weight from the grease.
| Thanks Marc - comments below grant - 7 years ago |
Can a transmission mount fail in such a way a leak is not involved? If so you can't rule out transmission mount failure.
--> I wonder the same thing. I have asked and been told " I dont see how", but want to prod it on a lift to see myself.
By "rebuilt" the half shafts what exactly did you do?
--> I did more or less what you said , with better grease. I did not mark the shaft, but FYI only one of the two bearings is removable ( inner). I tested them for smoothness and tightness. If i recall correctly this vibration preceded my rebuild as well. But good thoughts all. Could i haev messed it up the FIRST time I did the driveshafts? Dunno.
Regarding repacking the bearings, one wants to avoid putting in too much grease, or too little grease. One wants to use just the right amount of grease.
--> yes and no. I've been told by all the techs to pack in as much as possible because it thins and goes out the vent hole at temp on a racetrack. I have the mess to prove it. If you look at the end of your splined shaft, it has a hole in it. Guess what it vents :-)
Incidentally i did more testing today. It occurs in the range that the M96 has fundamental vibrations (2800-3600 rpm). It is worst in 3rd gear, but overall worse in hgiher gears where there is less torque multiplication ( therefore more load on the engine). So i more and mroe think the engine is moving. Motor mount? brand new Pedro Mount. Transmission mounts? Weeeeeellll... you and I both suspect it may not be as clear cut as everyone says, reading betwen your lines.
When i find out I'll post back. Don't hold your breath though.
G
Grant
gee-lenahan-at-gee-mail-dot-com
--> I wonder the same thing. I have asked and been told " I dont see how", but want to prod it on a lift to see myself.
By "rebuilt" the half shafts what exactly did you do?
--> I did more or less what you said , with better grease. I did not mark the shaft, but FYI only one of the two bearings is removable ( inner). I tested them for smoothness and tightness. If i recall correctly this vibration preceded my rebuild as well. But good thoughts all. Could i haev messed it up the FIRST time I did the driveshafts? Dunno.
Regarding repacking the bearings, one wants to avoid putting in too much grease, or too little grease. One wants to use just the right amount of grease.
--> yes and no. I've been told by all the techs to pack in as much as possible because it thins and goes out the vent hole at temp on a racetrack. I have the mess to prove it. If you look at the end of your splined shaft, it has a hole in it. Guess what it vents :-)
Incidentally i did more testing today. It occurs in the range that the M96 has fundamental vibrations (2800-3600 rpm). It is worst in 3rd gear, but overall worse in hgiher gears where there is less torque multiplication ( therefore more load on the engine). So i more and mroe think the engine is moving. Motor mount? brand new Pedro Mount. Transmission mounts? Weeeeeellll... you and I both suspect it may not be as clear cut as everyone says, reading betwen your lines.
When i find out I'll post back. Don't hold your breath though.
G
Grant
gee-lenahan-at-gee-mail-dot-com
| FYI- ruled out tires grant - 7 years ago |
Coincidentally, i had my rear street/rain tires replaced yesterday. The new ones are nice, soft, round and quiet.
But the chassis vibration continues. I did some testing on the way over and back. It is present in higher gears, ~ 2800-3600 rpm - right around the M96 resonance. I'm really thinking its related to mounts. Complication is the motor mount is brand new (Pedro) and the transmission mounts were replaced for exactly this problem two years ago, and are bone dry. But i'll be checking the old fashioned way - with a crowbar.
Grant
gee-lenahan-at-gee-mail-dot-com
But the chassis vibration continues. I did some testing on the way over and back. It is present in higher gears, ~ 2800-3600 rpm - right around the M96 resonance. I'm really thinking its related to mounts. Complication is the motor mount is brand new (Pedro) and the transmission mounts were replaced for exactly this problem two years ago, and are bone dry. But i'll be checking the old fashioned way - with a crowbar.
Grant
gee-lenahan-at-gee-mail-dot-com
| Recheck ... Pedro (Odessa, FL) - 7 years ago |
… torque on Front Engine Mount bolts.
Happy Boxstering,
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
Happy Boxstering,
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
| i wondered that too. Gotta get on a lift.... mount to frame or motor to mount? Thanks Pedro *NM* grant - 7 years ago |
Grant
gee-lenahan-at-gee-mail-dot-com
Edited 1 time(s). Last edit at 06/10/2016 07:11PM by grant. (view changes)
gee-lenahan-at-gee-mail-dot-com
Edited 1 time(s). Last edit at 06/10/2016 07:11PM by grant. (view changes)
| So, i did more sleuthing grant - 7 years ago |
Got it on a lift and checked all the motor mount bolts. Tight.
checked the transmission mounts - didnt feel excess play, they are not leaking (oil filled).
I did notice that in the oval-shaped motor mount yoke holes, the bolts have it so the engine/transmission is slightly aft (by what 1/8"?) from center. But from what i see the engine/transmission is located by the transmission mounts, and they seem centered.
I also spun the wheels with car off the ground - nothing loose or binding or noisy.
CVs seem tight and slide side to side. One side (left) seems a little more "metallic" as it slides, but no apparently play. And i just re-packed them with very hgih temp grease (this red gooey stuff the racers use).
No loose suspension bits.
I'm baffled.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
checked the transmission mounts - didnt feel excess play, they are not leaking (oil filled).
I did notice that in the oval-shaped motor mount yoke holes, the bolts have it so the engine/transmission is slightly aft (by what 1/8"?) from center. But from what i see the engine/transmission is located by the transmission mounts, and they seem centered.
I also spun the wheels with car off the ground - nothing loose or binding or noisy.
CVs seem tight and slide side to side. One side (left) seems a little more "metallic" as it slides, but no apparently play. And i just re-packed them with very hgih temp grease (this red gooey stuff the racers use).
No loose suspension bits.
I'm baffled.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
Laz - 7 years ago |
| Another cause could be ... Pedro (Odessa, FL) - 7 years ago |
... the flywheel with a bad (damaged) elastometer.
If the RMS leaked oil onto the flywheel for some time this can happen.
The purpose of the dual mass is precisely to reduce harmonics.
Happy Boxstering
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
If the RMS leaked oil onto the flywheel for some time this can happen.
The purpose of the dual mass is precisely to reduce harmonics.
Happy Boxstering
Pedro
Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
Racecar spelled backwards is Racecar
"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"
"If you wait, all that happens is that you get older"... Mario Andretti
"Being second is to be the first of the ones who lose" ... Ayrton Senna
| Hmmm - that's a plausable idea. Thanks. *NM* grant - 7 years ago |
Boxsterra - 7 years ago |
You could diagnose a problem like this with a vibrometer. Install one of the many phone apps that records vibrations, affix the phone to suspect areas, and reproduce the problem. If you can record sound then you can also tell if the sound happens with the engine speed, the wheel speed, or something else.
Just a thought.
Just a thought.
| Amazing diagnosis grant - 7 years ago |
Misfires.
Yep, misfires.
It also turns out that i have TWO problems - one is the misfires (i'm in the process of fixing) which is also intermittent and goes away after high rpm, hgih temp use.... and the other is some tire/wheel balance or out-of-round condition that is high enough speed to often be missed (begins at 75 mph+, worse under hard accel, which suggests its rear tires).
I HATE doing plugs and coil packs on older S's. Grrrrrrr.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
Yep, misfires.
It also turns out that i have TWO problems - one is the misfires (i'm in the process of fixing) which is also intermittent and goes away after high rpm, hgih temp use.... and the other is some tire/wheel balance or out-of-round condition that is high enough speed to often be missed (begins at 75 mph+, worse under hard accel, which suggests its rear tires).
I HATE doing plugs and coil packs on older S's. Grrrrrrr.
Grant
Grant
gee-lenahan-at-gee-mail-dot-com
Boxsterra - 7 years ago |
Doing it blind, is fairly difficult compare to most cars. But moreover, the "S" is a bit harder than the 2.7 or 2.5 .
I finished to job today. My back still hurts from doing a 1/8 situp and holding it for hours. #4 and #1 are particularly difficult to get at through the diagonal brace, catalytic converter, and wheel well lip. A torque wrench was completely impossible - ok since i'm OK estimating based on lever length and a good feel for how hard i pulled on the other two....
Job, complete with raising the car (not needed on most) took a total of between 3-4 hours. Somewhat uncomfortable hours.
So int he end, yea, its a total PITA. Not complicated, just difficult.
Vastly easier with a lift. No lift today.
Runs great though!
Grant
gee-lenahan-at-gee-mail-dot-com
I finished to job today. My back still hurts from doing a 1/8 situp and holding it for hours. #4 and #1 are particularly difficult to get at through the diagonal brace, catalytic converter, and wheel well lip. A torque wrench was completely impossible - ok since i'm OK estimating based on lever length and a good feel for how hard i pulled on the other two....
Job, complete with raising the car (not needed on most) took a total of between 3-4 hours. Somewhat uncomfortable hours.
So int he end, yea, its a total PITA. Not complicated, just difficult.
Vastly easier with a lift. No lift today.
Runs great though!
Grant
gee-lenahan-at-gee-mail-dot-com
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