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Knocking Noise, When Decelerating


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#1 Adam101

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Posted 20 December 2009 - 12:49 AM

Mayfair
1989
When ever i take my Mini for long drives e.g. 22 mile trip to work experience, i get a knocking noise, it usually begins about 8 miles before i get there, and only happens when i take my foot of the accelerator, the noise is like a loud thud, and it sounds like its coming from the engine bay, but it has had new engine mounts recently.
Most of the trip is down the A38, with mostly 50 and 40 limits.

I never get this problem when going to college or work, which has 30/40 limits.

John ( Guessworks ) said my strap is missing from my exhaust attaching to the gearbox, so could this cause the exhaust to hit the floor pans?
If so, why does it only do it on long journeys?


Cheers Adam

Edited by Adam101, 20 December 2009 - 12:50 AM.


#2 Ethel

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Posted 20 December 2009 - 12:59 AM

Is it linked to road or engine speed? I wouldn't expect the exhaust to knock more than once or twice as you come off the power.

#3 Adam101

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Posted 20 December 2009 - 01:03 AM

Sorry if i misunderstand you Ethel.

But it happens when i change down in all gears, and does not get faster when the revs go up.
It sounds like its happening when the actuall car is slowing, even at lights etc, the noice happens, but not as much as when first decelerating

#4 Ethel

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Posted 20 December 2009 - 01:10 AM

I guess that fairly rules out engine issues, but are you sure it's not a bit of a misfire that would explain the engine needing to be warm?

I know it's hard to describe a thud :angel: but you should get a sense of whether it's something engine or gearbox/driveshaft related or a more random loose mounting.

#5 Adam101

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Posted 20 December 2009 - 01:17 AM

It could be, when in heavy rain a few weeks ago, the mini just died, a bit of WD-40 sorted it, but the knocking noise was there, i thought it wasnt running on all 4 cylinders.

I know have a Marygold around the Dizzy, and it hasnt been raining when travelling there.

#6 jkjaxor

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Posted 20 December 2009 - 09:49 AM

sounds like a mounting point somwhere, or as said before the exhaust,
can you tell what side it comes from? if it sounds like its to the right it could be exhaust or maybe a damper?
if it comes from infront or to the right check the damper or top engine steady, the top steadys sometimes wears the mounting plate into a notch and slides backwards and forwards, if this has happened a spare exhaust washer fits perfectly in it and weld it on, one last idea it may be a tierod is loose, but not likely
jack

#7 my_first_mini

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Posted 20 December 2009 - 11:26 AM

i had this before, was exhaust knocking against the floor!

#8 Tomar2

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Posted 20 December 2009 - 02:21 PM

Yeah is the noise coming from your feet? or from the dash? I had a few knocking noises. One was where the engine steady bracket broke and the engine was bouncing off the dash haha and the other was an exhaust bracket below the footwells went. Both were easily sorted. I'd check these areas. The fact the noise only happens when you decelerate is not familiar with me but check these points anyway

#9 Adam101

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Posted 20 December 2009 - 05:12 PM

Cheers for the responses guys.

It sounds like the noise is coming from the front left of the car, i usually listen to music, so cant be certain.

But it only ever begins, near the end of my journey, the car still accelerates fine, and drives normal.

#10 newdawn1st

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Posted 20 December 2009 - 05:49 PM

You said you had new engine mounts but what abouit the steadies? Gearbox steady may of come loose or adrift completly. Mine did this and caused a knocking noise in that area, worth a check

#11 THE STIG

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Posted 20 December 2009 - 06:02 PM

i refitted the engine lin the car after gearbox rebuild last week

the engine mounts , top engine steady and lower front gearbox steady are all in good order

as you said there i no gearbox to exhaust bracket the lcb and system dont look that old so dont know who fitted it and why they did not fit bracket

could be exhaust hitting floor

have you sorted out the left hand tower bolt ? if not that could be the cuase the subframe could be moving and hitting the bulkhead/ cross member

#12 Adam101

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Posted 20 December 2009 - 07:12 PM

No we havent sorted it yet, we are looking into it more.

But will definetly get it done.

P.S car is much smoother through gears and much more of a pleasure to drive. Great job guys! :cry:




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