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Growling/Clunking noise in rear while accelerating hard in 1st or 2nd ??


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No offense, trabbic... but where? :confused:

 

No offense taken, mccorry... It just seems to me like we are going in circles (or beating a dead horse).

 

People keep repeating the same thing over and over again. Or not reading the whole thread, and asking questions that have already been answered several times. (my biggest pet peeve on forums :( )

 

I think we pretty much have this thing narrowed down. It will be hard or impossible to get more specific than we have without more evidence, or trial and error.

 

I REALLY like the camera idea, it will help us to maybe prove (without actually replacing bushings) what is causing it.

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Keefe may chime in here today....but he thinks it has to do with the engine pulling timing....common issue for most. (currently TDC st.2 93, had same issue with Cobb 1.15 st.2 93) He could feel the vibration in the floor board while in the passenger seat. The noise in the rear could be just the side effect of the engine pulling timing...causing the vibration. We found no suspension issues, car handles fine, no odd noises. No drive train issues either. After about 15-20 minutes the noise became harder and harder to reproduce and eventually we couldn't get it to do it at all. Next step...data log.

 

BTW...drove Keefes car:icon_mrgr

 

Thing sounds mean with that single straight pipe. Handles great!

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Keefe may chime in here today....but he thinks it has to do with the engine pulling timing....common issue for most. (currently TDC st.2 93, had same issue with Cobb 1.15 st.2 93) He could feel the vibration in the floor board while in the passenger seat. The noise in the rear could be just the side effect of the engine pulling timing...causing the vibration. We found no suspension issues, car handles fine, no odd noises. No drive train issues either. After about 15-20 minutes the noise became harder and harder to reproduce and eventually we couldn't get it to do it at all. Next step...data log.

 

BTW...drove Keefes car:icon_mrgr

 

Thing sounds mean with that single straight pipe. Handles great!

 

I don't think it is from pulled timing. I have logged runs where I am no where near pulling timing (so has Casopolis), and we both had the growling still (TDC tunes).

 

My car has NEVER pulled timing in the low rpms, where I get this growling, the only pulled timing I have ever recorded was @ high rpms. And the only logs I have recorded with pulled timing were Cobb's maps; with my TDC maps (and 94 octane ;)) I don't' get pulled timing.

 

Also I am curious how pulled timing would vibrate a floor board. :icon_conf

 

Please log, I doubt you will find any correlation.

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It isn't in ANY WAY the engine pulling timing. :rolleyes: Sorry... I'm just not buying it.

I have worked on cars most of my life and I can tell you that this isn't an engine issue. It is a driveline issue.

 

 

This a harmonic vibration that is being passed into the car from the driveline... due to cold HARD bushings. When the bushings get cold, they are less compressible and less flexible.

 

Our cars are probably squatting under hard acceleration and that is compounding this issue.

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It isn't in ANY WAY the engine pulling timing. :rolleyes: Sorry... I'm just not buying it.

I have worked on cars most of my life and I can tell you that this isn't an engine issue. It is a driveline issue.

 

 

This a harmonic vibration that is being passed into the car from the driveline... due to cold HARD bushings. When the bushings get cold, they are less compressible and less flexible.

 

Our cars are probably squatting under hard acceleration and that is compounding this issue.

 

 

+400

 

It is a mechanical issue of some sort, NOT PULLED TIMING!

 

As far as the car squating, I just thought of something: Have you ever seen pictures of thr OEM suspension squat under a hard launch, I think it squats more then my car does, even though mine is lowered.

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This a harmonic vibration that is being passed into the car from the driveline... due to cold HARD bushings. When the bushings get cold, they are less compressible and less flexible.
So we don't really want somebody to come out with a stiffer polyurethane bushing then. Otherwise it would happen when it's warm out too.
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So we don't really want somebody to come out with a stiffer polyurethane bushing then. Otherwise it would happen when it's warm out too.

 

I don't think so. When I am driving the car in real cold weather the noise sounds like it is metal vibrating against metal. I can stop it and start it when I want by the throttle. I believe some clearance on two metal pieces gets smaller when it is colder thus allowing the contact. I do not believe it is a harmonic vibration!

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OK.. maybe not harmonic vibration... but it is vibration. It is being transfered into the cabin via the bushings or a metal/metal contact point.... maybe the bumpstops.

 

Metal on metal contact or some conatct that is a hard material on a hard material.

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Just got this again MUCH worse that I had before yesterday.

Going around a fairly tight right hand turn, floored it after the apex and it really did sound like something smacking against the underneath of the car.

 

In the past all I had heard was a mild growl, noticeable, but not bad. This time it sounded like I was ripping my car apart

 

Tried again on a similar left hand turn, nothing.

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