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Author
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Topic: weird vibration/humming when in gear?
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SydeWaySix
CAFords OG
Member # 3596
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posted
 
 
I have a 98 cobra and I noticed today that when I'm cruising at freeway speeds and in gear, theres a constant humming/slight vibration. The sound is very consistent (on, off, on, off, etc) and only occurs when my foot is on the throttle and in gear. If I release the throttle it does not occur. It sounds like its coming from the rear of the car but its kind of hard to say. The only thing I have changed recently is my clutch cable, quadrant, and adjuster.
I initially thought something was rubbing my wheels but when I let off the throttle the sound/vibration goes away. Also, as I speed up, the sound doesnt get any faster but it does get a little louder.
Does anyone know what this could be?
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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50DADDY
CAFords OG
Member # 3076
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posted
Sounds like gear whine.Your rear end gears might be getting sloppy.
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"Im not stupid,i just act that way so i dont make you dummies uncomfortable."
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Posts: 4827 | From: Suckramento | Registered: Jul 2003
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by 50DADDY:
Sounds like gear whine.Your rear end gears might be getting sloppy.
Would it occur in all gears if it were the rearend whine? I can really only hear it when Im cruising in 5th.
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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66_5.0
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Member # 9974
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posted
Well I have that same noise.. Sounds excactly how mine is. I just got my car back and they told me my rear end needs to be rebuilt asap. I can't tell u if it's gears or not but def rear end.
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1966 Mustang
Posts: 1967 | Registered: Apr 2010
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sigsagg650
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Member # 8368
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posted
I have the same noise coming from my 2001 Gt. I had new gears put in, but the noise is still there.
Posts: 158 | From: Mountain View | Registered: Apr 2008
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SydeWaySix
CAFords OG
Member # 3596
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posted
The noise is more like a humming noise that's on-off-on-off at a consistent pace. I'm doubtful that it's the reserve because I'd think as I speed up the sound would speed UO as well, bit it doesn't. Could it be exhaust related maybe??
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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BIGBALLFACTOR
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Member # 7277
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posted
sounds like the rearend gears or the the bearings are going out.was the pinion seal changed in the last couple months
Posts: 6908 | From: okc | Registered: Dec 2006
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Luke87GT
Lay'n more stripes
than Caltrans
Member # 21
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posted
Ian, few questions:
1.) Does it do it at a specific RPM window or at a specific speed? Does it only occur in 5th gear? Can you reproduce it in 4th?
2.) The on-off-on-off sequence... what frequency would you estimate? About 1 Hertz?
3.) I assume you can feel it in the shifter?
4.) You mentioned that as you speed up the sound gets a little louder. Does it go away after you pass a certain RPM or speed?
The reason I ask these questions is because I have very similar symptom in my 96 Cobra. It's an extremely subtle thing, so I never paid too much attention to it nor have I ever been able to narrow it down. I've never even had any passenger notice it before. Here is what mine does:
The humming that you are describing has about 1 second between hums: hum -> 1sec pause -> hum -> 1 sec pause -> hum (just like you described on, off, on, off, etc).
- It only happens in 5th gear (never does it in any other gear - I tried to reproduce it many times in 4th but cannot).
- It only happens between 2100-2500RPM. Outside of this window it never does it.
- It only happens when I am on the throttle in the 400 RPM window described above. If I am off the throttle, I never hear any humming.
- If I am parked and rev the engine between 2100-2500RPM, I don't hear anything... it's silky smooth.
Since it does not do it when I rev the engine in neutral, I don't think it has anything to do with engine harmonics.
Since it only does it in 5th gear at a specific RPM window, it's not the wheel balance. I also find it hard to believe that it is rearend related. If it were rear-end related, I would expect to feel it in 4th gear too (if I matched the vehicle speed where I normally feel it in 5th gear). It's possible that it is related to the rear, but i am not 100% convinced.
Now I notice that we both have 4.30 gears and aluminum shafts. Wonder if that may have something to do with it? I'm also curious if you have your "dogbone" removed from the underside of the pumpkin? Might be worth bolting that back on and giving it a whirl. Mine's long gone too.
It's puzzling, and I have just ignored it for the past year, lol.
Maybe we could post this on corral or svtperformance and see what people say?
[ July 12, 2010, 01:43 AM: Message edited by: Luke87GT ]
Posts: 7802 | From: San Mateo | Registered: Jul 2000
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by Luke87GT:
Ian, few questions:
1.) Does it do it at a specific RPM window or at a specific speed? Does it only occur in 5th gear? Can you reproduce it in 4th?
2.) The on-off-on-off sequence... what frequency would you estimate? About 1 Hertz?
3.) I assume you can feel it in the shifter?
4.) You mentioned that as you speed up the sound gets a little louder. Does it go away after you pass a certain RPM or speed?
The reason I ask these questions is because I have very similar symptom in my 96 Cobra. It's an extremely subtle thing, so I never paid too much attention to it nor have I ever been able to narrow it down. I've never even had any passenger notice it before. Here is what mine does:
The humming that you are describing has about 1 second between hums: hum -> 1sec pause -> hum -> 1 sec pause -> hum (just like you described on, off, on, off, etc).
- It only happens in 5th gear (never does it in any other gear - I tried to reproduce it many times in 4th but cannot).
- It only happens between 2100-2500RPM. Outside of this window it never does it.
- It only happens when I am on the throttle in the 400 RPM window described above. If I am off the throttle, I never hear any humming.
- If I am parked and rev the engine between 2100-2500RPM, I don't hear anything... it's silky smooth.
Since it does not do it when I rev the engine in neutral, I don't think it has anything to do with engine harmonics.
Since it only does it in 5th gear at a specific RPM window, it's not the wheel balance. I also find it hard to believe that it is rearend related. If it were rear-end related, I would expect to feel it in 4th gear too (if I matched the vehicle speed where I normally feel it in 5th gear). It's possible that it is related to the rear, but i am not 100% convinced.
Now I notice that we both have 4.30 gears and aluminum shafts. Wonder if that may have something to do with it? I'm also curious if you have your "dogbone" removed from the underside of the pumpkin? Might be worth bolting that back on and giving it a whirl. Mine's long gone too.
It's puzzling, and I have just ignored it for the past year, lol.
Maybe we could post this on corral or svtperformance and see what people say?
Luke, sounds like we have the same issue. My cousin was in the car today and culdn't hear it until I pointed it out to him. Like you, I can only hear it in 5th gear. I tried 4th gear and I couldnt hear anything. The only difference is that I can hear it in any RPM range, not just 2100-2500 like you. I'm not sure if I have the dogbone or not, but if you can describe what that part is then I can check. I posted this on svtp so hopefully we can get more input on it there.
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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JohnB
Tech Moderator
Member # 969
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posted
That "dogbone" that everyone insists on pulling off is actually there for a purpose. It is a mass dampener, deadening the harmonics of the rear end. When you remove it, you are effectively throwing the weight of the rear end snout off considerably. Now throw a numerically higher ratio in the rear, you're compounding the problem. What you are hearing is the pinion/DS yoke area vibrating under load. Mass in rotation will always generate a harmonic...doesn't matter how well it was built/assembled/etc.
If the car has a TQ arm/Panhard bar on it...check all angles/mount points/ bushings/welds/etc...something is wrong.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by JohnB:
That "dogbone" that everyone insists on pulling off is actually there for a purpose. It is a mass dampener, deadening the harmonics of the rear end. When you remove it, you are effectively throwing the weight of the rear end snout off considerably. Now throw a numerically higher ratio in the rear, you're compounding the problem. What you are hearing is the pinion/DS yoke area vibrating under load. Mass in rotation will always generate a harmonic...doesn't matter how well it was built/assembled/etc.
If the car has a TQ arm/Panhard bar on it...check all angles/mount points/ bushings/welds/etc...something is wrong.
John, thanks for the input! I do have a phb/ta setup but I actually heard the noise before it was all installed on saturday. What does the "dogbone" piece look like and where exactly would it be located? I want to see if I actually have it still on my car. Is there anything you'd recommend doing as far as replacing parts, etc?
Thanks ![[patriot]](graemlins/patriot.gif)
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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JohnB
Tech Moderator
Member # 969
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posted
If the car has a TQ/P-bar setup...it's not there anymore. Check to see if there is anything loose/broken/etc...also check with the installer to see if they set it up correctly, taking the pinion angle into consideration.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by JohnB:
If the car has a TQ/P-bar setup...it's not there anymore. Check to see if there is anything loose/broken/etc...also check with the installer to see if they set it up correctly, taking the pinion angle into consideration.
I'll throw it on a rack and check for anything loose or broken. Hopefully nothing is broken since all new hardware and bushings were used when I got the phb/ta installed. As for the pinion angle, shouldn't the angle be fine if the torque arm was installed correctly? I know there are mounting points and if T/A is where it's supposed to be, can the angle still be off?
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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JohnB
Tech Moderator
Member # 969
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posted
quote:
Originally posted by SydeWaySix:
quote:
Originally posted by JohnB:
If the car has a TQ/P-bar setup...it's not there anymore. Check to see if there is anything loose/broken/etc...also check with the installer to see if they set it up correctly, taking the pinion angle into consideration.
I'll throw it on a rack and check for anything loose or broken. Hopefully nothing is broken since all new hardware and bushings were used when I got the phb/ta installed. As for the pinion angle, shouldn't the angle be fine if the torque arm was installed correctly? I know there are mounting points and if T/A is where it's supposed to be, can the angle still be off?
Key word is "should be". Doesn't hurt to check it.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by JohnB:
quote:
Originally posted by SydeWaySix:
quote:
Originally posted by JohnB:
If the car has a TQ/P-bar setup...it's not there anymore. Check to see if there is anything loose/broken/etc...also check with the installer to see if they set it up correctly, taking the pinion angle into consideration.
I'll throw it on a rack and check for anything loose or broken. Hopefully nothing is broken since all new hardware and bushings were used when I got the phb/ta installed. As for the pinion angle, shouldn't the angle be fine if the torque arm was installed correctly? I know there are mounting points and if T/A is where it's supposed to be, can the angle still be off?
Key word is "should be". Doesn't hurt to check it.
Tnanks for the input John...btw, WE NEED YOU BACK! I'd just bring it over to your house if you still lived out here
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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BIGBALLFACTOR
¯
Member # 7277
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posted
if you realy want to find the noise out 2 words chassis ears
Posts: 6908 | From: okc | Registered: Dec 2006
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Luke87GT
Lay'n more stripes
than Caltrans
Member # 21
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posted
The dogbone is a 6lb weight that gets bolted under the rear differential, directly below the pumpkin.
Since your problems appears to be in the entire RPM range, I would be interested to see you bolt it back on (assuming it is gone) and see if it eliminates the symptoms. Unfortunately it does not sound possible if your TA is already on.
You can see the "dogbone" bolted just underneath the snout of this differential in the pic below.
I may try bolting mine back on to see if it makes a difference.
[ July 12, 2010, 06:08 PM: Message edited by: Luke87GT ]
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Stangless
Posts: 7802 | From: San Mateo | Registered: Jul 2000
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Luke87GT
Lay'n more stripes
than Caltrans
Member # 21
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posted
Got a line on a spare dogbone... I'll have it on the car in the next 2 weeks and let you know if it makes any difference.
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Stangless
Posts: 7802 | From: San Mateo | Registered: Jul 2000
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Secnd2nun64
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Member # 1431
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posted
Check your u joints for wear.
Posts: 1460 | From: CA | Registered: Jun 2002
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SydeWaySix
CAFords OG
Member # 3596
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posted
quote:
Originally posted by Luke87GT:
Got a line on a spare dogbone... I'll have it on the car in the next 2 weeks and let you know if it makes any difference.
Cool, let me know how that goes. I doubt thats whats causing my issue though. I didnt have this problem a few weeks back and I didnt have the dogbone in. Hopefully I can find some time to get under the car this weekend to check it out. I'm hoping something is just loose ![[Frown]](frown.gif)
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2013 Boss 302 #356. Performance White. Stock.
1965 Fastback GT Restored to stock spec.
Posts: 9882 | From: Bay Area | Registered: Dec 2002
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Luke87GT
Lay'n more stripes
than Caltrans
Member # 21
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posted
Ian, I installed the dogbone and it made very little difference. I checked my DS bolts and they were tight. The aluminum shaft and U-joints are nearly brand new so it is very unlikely that it has to do with that. The control arm bushings are great and the torque boxes look spectacular.
I am not sure how serious your issue is, but this might be somewhat intrinsic to having very steep gears (4.30 or 4.56 or more).
Since my symptoms are very subtle, I am not going to pay much attention to this, but I would be interested to know what you discover.
Last thing I might try is putting a slightly heavier oil in the rear 85W-140 instead of 75W-140, but I doubt that would make a difference.
Best of luck!
[ July 18, 2010, 06:46 PM: Message edited by: Luke87GT ]
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Stangless
Posts: 7802 | From: San Mateo | Registered: Jul 2000
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Sydewayz_Stan
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Member # 10217
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posted
+1 on the driveshaft try turning 180 degrees that was my problem i didnt mark it before and it made noise i turned it around and problem solved!
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Posts: 3432 | From: 707 vallejo/richmond 510 | Registered: Aug 2010
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Luke87GT
Lay'n more stripes
than Caltrans
Member # 21
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posted
I agree that it would probably be wise to spend the few bucks to rebalance the shaft to rule that out before tearing into it and spending bigger bucks with no guarantees.
What we are hearing is a "beat" frequency. Two or more higher frequency signals are interfering and causing us to hearing a slower frequency combined signal.
(we are hearing the bottom one)
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Stangless
Posts: 7802 | From: San Mateo | Registered: Jul 2000
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