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Location: Terrigal
Registered: May 2002
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Vibrations when under deceleration
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Tue, 30 March 2004 01:36
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Hi all, just wanted to start up a discussion and get some ideas about what can cause a rather harsh vibration in a car when under deceleration.
I find if I floor the 3T its quite smooth all the way up to redline, though if say at 4000 + rpm I back off there is a vibration that feels like coming from the engine. Though cannot be sure as hard to tell. I don't have to be completely off the gas either for it to happen, occurs when you change from engine RPM accelerating to when it planes out so to say.
It makes anything that is slightly loose in the car vibrate and rattle around.
Under 3500rpm or so this problem isn't apparent at all.
The engine was fully balanced when rebuilt.
Any ideas?
Cheers
Joel
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Location: Northwestern Sydney
Registered: August 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 01:49

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Flywheel/clutch/gearbox out of balance? bearings warn.
Had the same problem but mine was self created
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I supported Toymods
Location: Australia
Registered: November 2003
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 02:11

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Driveshaft uni's maybe
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Location: Terrigal
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 02:17

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The clutch/flywheel is possible, though this was balanced along with the crank, rods, pistons, pulley etc. Unless the machine shop made a mistake while balancing??
The driveshaft uni's is a good suggestion also thanks. Mine is 2 piece and there is a rubber type thing in the center that looks pretty worn.
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Location: HORNSBY
Registered: October 2002
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Location: Terrigal
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 02:44

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Was the middle section upside down or the alignment of the uni's wrong?
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Location: Madrid - Spain
Registered: August 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 03:16

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Just to trouble shoot things a little, does it only occur at these RPM or is it at different speeds???
Thinking along different lines to the previous suggestions. I know that your not using a blow off valve and that you do have fairly obvious wastegate flutter. Maybe this is just the turbo compressor blades stalling after the throttle is closed. Does it only happen when measurable boost occurs??
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Location: Terrigal
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 04:13

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I probably need to do some more testing, cannot be positive if its RPM or speed dependant.
It usually is when in 2nd or 3rd and engine revs are up high (so also going quite fast) and then when you ease off the peddle. Not usually doing 5000rpm in 4th or 5th so cannot be sure if it happens there.
If cruising along the freeway at 110km/h in 5th at 3000rpm its fine.
It doesn't seem to be boost dependant at all. Often happens with no boost, and little load.
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Location: Madrid - Spain
Registered: August 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 04:26

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It could also be your exhaust rubbing on something. I have had worn engine mounts create phantom vibrations like that. Similarly my brothers Escort does that with the gear stick housing rubbing on the transmission tunnel under acceleration.
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Club Member
Location: sydney
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 06:34

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2 most obvious would be a driveshaft that hasnt been rematched to either center bolt point or the diff or the mounting bolts are loose somewhere ( you should mark them before removal to ensure they will balance the same again), or the the rubber bushes to either of the following is worn/degraded ... engine mounts, gearbox mounts , uni centre ring.
Id start with the tailshaft, as it seems from your replies you may have allready tinkered with that
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Location: Terrigal
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 06:55

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Yeah does sound like it could be a tailshaft issue.
I don't really know the history of it as was pulled from a RA28 being wrecked awhile ago.
The rubber around the center bearing doesn't seem too good, you can move the tailshaft up and down a lot in the center section.
Is it meant to be a snug fit at the center?
I tried Toyota and they don't carry the center bearing/rubber anymore.
Auto one carry the bearing but not the rubber section. Which is odd as I thought the bearing was sorta moulded in.
Even if this isn't the problem I'd feel better about replacing it. Any ideas where I might be able to get a new part from?
Thanks
Joel
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I supported Toymods
Location: Australia
Registered: November 2003
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 06:59

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Give the driveshaft too a driveshaft balancing place (look in the Yellow Pages)
Tell them to have a look at it, and call you with whats wrong with it.
Then get them to repair it.
Driving the car after having a driveshaft rebuilt/rebalanced is like driving a new car, and, in theory, its something you only have to ever do once
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Club Member
Location: sydney
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 08:31

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Try asking for one for an AE86 , I believe they are idenetical, perhaps they carry that kit, im sure repco do.. I think Mos might have replaced one of his not too long ago, maybe find out where he got his from.
id try rotating the driveshaft to different spots first and see if that fixes it start at the diff ( assuming you havent removed the centre section ) and put a mark on both the diff flange and the drive shaft.. roatate it one bolt at a time till it comes smooth and mark it permanatly with a stamp or chisel mark
if the middle section has been unbolted.. well thats a big PITA... best is to pull the shaft right out and have a good look at the uni joint for any possible markings ( while youre there look at the bolts to see if theyve been touched by a spanner etc), or in many cases just the build up of dirt and crap can be a good indicator of the proper orientation.
In my experience it is rare ( but does happen ) that the tail shaft as a whole and the diff orientation causes a problem, its more likely the two tail shaft sections have been unbolted and missmatched when they reassembled it.
basically what it comes down to is a 4^4 adjustment test fitting, i.e 16 possible combinations to try to get the balance right.. after the first 4 or 5 is when the cursing starts
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Location: Melbourne
Registered: May 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 10:01

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I had a driveshaft issue recently after mine was strengthend, problem was solved, turns out it was a worn centre bearing (the rubber bit), mine waw fairly worn and what it did was shake the shit out of the whole car when the engine was under load at first, then it ended up just doing it most of the time before i had it replaced. If that seems like what your car is doin it is most likely the case, also check things like engine mounts and g/box mounths, they could be susspect also.
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Location: tas
Registered: June 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 11:18

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hmmm i wonder if this issue is the same problem i'm having.
I have an Auto and when i put it in 'R' the whole car shakes real bad. I can hear the gear engage and then with a small delay i hear a clunk in the rear of the car (diff area).
I put it up on ramps today to check it out, the shaft has abit of play in it, the uni joint looks good, possibly the CV's are worn at the back. But that's all i checked.
Also i had my friend get in the car and stick it into reverse so i could see from underneath what was going on.
i nearly lost my life! the wheels spun up really quick which made the ramps shoot out from under the car! luckily i had such good refelxes to get outa there before being dead! My stupid friend actually put it into 'D' with the break on and the fuckin accelerator on, either he wanted to kill me or he is just really dumb with auto's.
any of you had a simular problem that could help me out?
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Location: adelaide
Registered: April 2003
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Location: Finland
Registered: November 2002
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Re: Vibrations when under deceleration
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Tue, 30 March 2004 14:41
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I'll put my balls stake on that it's your unijoints and/or the center bearing rubber thing. Both causes shake while accelerating or decelerating. Center bearing makes noise not shake. Tailshaft out of balance causes vibration at steady regular speed. Mine started to shake badly at speed of 90kmh and shaking eased off at 130kmh. Shake frequency changed that it started to occur as a humming noise. You can affect on the balance by turning tailshaft from the fastening flange one position at a time which means 90degrees. Mark original position and try different positions. If you have really badly balanced tailshaft and some DIY spirit, you will balance your tailshaft yourself. It can be done and I did it, worked nice. You just need two hose-clamps, piece of chalk, and tripods.
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