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Old 05-29-2018, 10:45 AM   #1
petiww
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Default Mystery decel rattles in the rear suspension

Hello!

My car developed this strange noise when i swapped in longer wheelstuds and put on 25mm spacers. For the stud swap i just removed the handbrake components and did not pull halfaxles. Axle is a stock 3.54 open diff from '89.
Rattle only happens on engine braking, around and under 50-60kmh. Every susp component is tight...
https://www.youtube.com/watch?v=N6D4NXZlAlY

Any ideas what could it be? I'm a bit lost at it, and its really annoying.
Thanks!
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Old 05-29-2018, 09:23 PM   #2
EivlEvo
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Were you beating on anything back there and maybe shifted a garbage bushing?

On decel the things that come to mind would be your torque rods. Do you see any noticeable scraping or impacts back there (signs of anything)?
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Old 05-30-2018, 06:07 AM   #3
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Originally Posted by EivlEvo View Post
Were you beating on anything back there and maybe shifted a garbage bushing?

On decel the things that come to mind would be your torque rods. Do you see any noticeable scraping or impacts back there (signs of anything)?
I used a bearing puller to push studs out, then used the new studs thread to pull them in. No hammering was needed fortunately.
Also I did not touch torque rods, and they are hourglass shaped massive ones. No signs anywhere to be speak of.
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Old 05-30-2018, 09:20 AM   #4
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I had a resonance similar to what I think I hear in the video. I needed to lengthen my torque rods a wee bit and it stopped the noise on decel. luckily my torque rods were adjustable

The noise was the pinion angle becoming too low during deceleration causing a driveline resonance that was hard to locate where in the car it was coming from. but it did sound more to the rear

How old are your torque rod bushings?
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Old 05-30-2018, 06:13 PM   #5
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Originally Posted by esmth View Post
I had a resonance similar to what I think I hear in the video. I needed to lengthen my torque rods a wee bit and it stopped the noise on decel. luckily my torque rods were adjustable

The noise was the pinion angle becoming too low during deceleration causing a driveline resonance that was hard to locate where in the car it was coming from. but it did sound more to the rear

How old are your torque rod bushings?
Torque rod bushings - as the aftermarket is utter crap - are the original 38 year old ones without any tear. Pretty stiff hourglass shaped style.
Its weird because nothing was changed there, and it just developed this random weird scraping or rattling sound.

I suspect my handbrakes somehow... Dont know what did i do wrong there though.
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Old 05-30-2018, 09:11 PM   #6
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Torque rod bushings - as the aftermarket is utter crap - are the original 38 year old ones without any tear. Pretty stiff hourglass shaped style.
Its weird because nothing was changed there, and it just developed this random weird scraping or rattling sound.

I suspect my handbrakes somehow... Dont know what did i do wrong there though.
you should be able to check if its the handbrake if you drive around with it slightly engaged. the rattle may change or completely stop and then you can say for sure if that is it
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Old 05-31-2018, 04:51 PM   #7
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you should be able to check if its the handbrake if you drive around with it slightly engaged. the rattle may change or completely stop and then you can say for sure if that is it
Tried pulling it when it started doing the noises, but wasnt sure about it. Will try tomorrow how does it behave. I must say that it needs a little "heating" before it starts doing it, probably less than 5min of normal driving.
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Old 06-01-2018, 03:45 AM   #8
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Tried pulling it when it started doing the noises, but wasnt sure about it. Will try tomorrow how does it behave. I must say that it needs a little "heating" before it starts doing it, probably less than 5min of normal driving.
I was wrong, it does it all the time no matter how warm it is.
Tried handbrake properly this morning, and it does not do the weird noises when its pulled a few clicks. Its good that its probably only the handbrake, but also I don't know what did i wrong there.
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Old 06-10-2018, 08:04 AM   #9
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Well, it was a weird one, but its solved!
So i thought its the handbrake... Well, everything was put back together as it was before, its working good. However the noise is not there if its applied a few clicks. I could not imagine what the heck can cause a noise like this and started wondering, how the axle moves and so when the forces twist it.
I checked this cool video again: https://www.youtube.com/watch?v=O3xT5ruClyg and started looking around...
I was probably blind or just ignoring that the stock sway bar with the alu axle cover is so close that they can actually touch when brakes or engine brake is used. 1-1.5mm gap was there only, and with a little beat on the swaybar it could easily touch and bang on the cover bolt...
Strange thing about this that i never heard this noise before, and the sway was at the same place.
34642197_1707800712637206_4964131850780934144_n by Péter Gede, on Flickr
35078664_1707800122637265_1615601074226331648_n by Péter Gede, on Flickr
34857424_1707800112637266_314291735192666112_n by Péter Gede, on Flickr

I should have taken this little clearance more seriously, but i thought it cant be that, it never done that... I was wrong, but at least its solved! No noises with no sway bar. I can run the stiffer V70 springs now and have the same balance.
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