Rattling sound when engine is slowing down, passing 2500rpm

[XPECTD]

Greetings all,

Something Ive noticed recently is my car makes a sort of rattling sound like a heat-shield touching something and vibrating.

Only thing is:
It seems to be coming from the middle of the car
It only happens as I pass 2500rpm, accellerating, or slowing down (engine-braking).

No idea whats causing it, thought I'd see if anybody here had any suggestions :-/

Ive JUST noticed today that its happening at right on 2500rpm, so its quite odd indeed

Cause for concern?

Cheers


Josiah

[SLYDIT]

most common causes of under car attles aer:

* the first heat sheild on the down pipe of the extractors ususally breaks a spot weld.placing a stainless hose clamp around it quiets it down.(my car had the same buzz at a particular revs and this is what it was)
*next is the cat coverter heat sheild casing which is made of two half shells, and often the crimps that hold the seems come a bit loose. re crimping with some pliers is the answer here.
*Busted cat converter....the cat has a honeycomb core in it which can break loose and rattle.


Now heres the biggy....
in older cars there is a drivetrain harmonic which is generated in the driveline and causes a buzzing, particularly on decel..the only cure to this is replacement of the diff first then gearbox,(with newer low mileage units)...
the buzzing can be exagerated by lightweight fly wheels etc.this does not mean that the diff/gearbox are stuffed, its just they are showing there age and has exposed this harmonic.

my car has the decel buzz and is on a replacement gearbox and new exhaust with no heatshields..

[XPECTD]

Flywheel has been lightened.

Major cause for concern? Or just something to keep an eye on?

[jif]

less mass = less damping ... having it a bit noisier - that's just a tradeoff of going lighter m'afraid !
 
even flyinmiata (FM) doesn't get away with it (see the warning):
http://www.flyinmiata.com/index.php?dep ... r=08-26000


[Posted via External Email]

[Carey Hill]

My old 91 with 185000 kms is making the same noise. Has been for a few months. But it is getting worse.
It isnt any shields, I have checked them all. I have had it diagnosed and am told it is most likely ( I have had two expert opinions) a worn thrust washer inside the gearbox, or loose/worn synchro rings. ( I havent opened the box, but it has been drained and there is a fair bit of metal shavings, even though it still changes gears and drives perfectly fine.
They tell me another gearbox ( lower mileage) is the simplest way out, about $350.00
I will be throwing in a new clutch kit at the same time just for the hell of it
By the time we add a new gearbox gaiter at the top of the box, and about $225 labour, some gear oil and sundries and GST, probably be around the $1200 mark all up.
But we dont care, cos we love it
I am going to get one more opinion to see if a transmission repair place is interested enough to take a look... but garage time is money

[MN]

Yes I have had the same thing for about 4 years. It comes in around 2200 revs in any gear and I've also been told its in the gearbox. I've rallied and raced the car for the last 3 years with no problems at all. I'm not going to touch it until the gearbox stops working!

[Carey Hill]

Well, we decided to get the gearbox rattle fixed. took the car (91 fivespeed) to Marshall transmissions in Hamilton.
Good crowd to deal with. Fixed quote- no surprises. The rattle came from a collapsed bearing, worn needle rollers.
They rebuilt the box, and replaced the complete clutch also whilst there and machined the flywheel, included pressure plate, throw out bearing, spigot bearing ete etc for $1500 incl GST.
A little bit dearer than a second hand box and new clutch maybe, but a second hand box is a possible gamble. Second hand boxes are around $450
We think its well worth it, and will now go ahead and tart up the rest of the car.