Rattle Underneath

[Twinmags]

I'm getting a rattle from underneath my '91 Z, it has 28,000 miles and I'm stumped. The rattle goes away when I press in the clutch. Any thoughts?

Hmm yep everyone has hit the nail on the head but look at the heat shields for the Cats as well. Might be a combination of noise.

[marc.madmax]

typically that is the throw out bearing on a clutch. some wait but I think you may damage the input shaft on the transmission if you do. look at replacing the clutch when you do it since you have to pull the tranny to replace it.

[tomtom72]

I would humbly suggest also remembering that we use dual mass flywheels and that they are prone or can make some strange noises with the trans in neutral and the motor at idle speed.....some make an occasional thud or thunk or sound kind of like a diesel motor...you know that rattle that diesel's make at idle. Also sometimes due to the nature of the cut of the trans gears in 1 thru 4(?) the trans makes rattling noises. Our gears are straight cut in 1 thru 4 like the old M22's & can make a bit of a racket in neutral....that is also what makes the gear noise we hear at low speeds in 1st especially.

Over at zfdoc.com there is a great Q & A section on the throw out bearing and some of the noises that it can make and some "do it yourself" tests to use. Also the Q & A section is generally devoted to our trans & it's associated parts with great tips for some simple trouble shooting.


Tom

[WB9MCW]

TRANNY SYNCRO RATTLE SAME SOUND I GET SINCE I HAVE AN ALUM FLYWHEEL AND NO DUAL MASS STOCK UNIT--THE REASON FOR THE DUAL MASS IS TO QUIET THIS EXACT THING---
TOMTOM WAS ON THE MONEY WITH THE GEAR ANSWER--PROLY UR DM FW IS SHOT!

[rkreigh]

listen closely when you shut the car down. often a bad dual mass will rattle and bang a bit as the car turns off.

a "mechanics stethescope" which is nothing more than a rod attached to some tubine is great for trouble shooting rattles. get the car up on a lift and listen with the "scope" and I'm sure you'll figure out where it's coming from.

the single mass flywheels give the "rattle all the time" at idle with the the clutch out and give the zr1 a bit of a diesel truck clatter type sound from the gears in the ZF banging around. it doensn't hurt anything though.

I love the light flywheel, but the noise is annoying.

hope this helps.

[xxxscimitarxxx]

Hi to All

Ive been trawling the threads for dual mass flywheel issues and this one seems relavant to me

just got my 92 shipped into UK, and while l havent driven it (seen it)yet, the guy who picked it up for me says there is a definate knock at idle.(he hasnt driven it either , just started it and let it warm up)

discounting crankshaft bearing related problems lm hoping its at worst the flywheel. I havent discounted it may have been replaced already with a single plate fidanza type and therefore it seems knocks and rattles go with those, but thats only a guess

Anyway, l will get to see car soon and work out where noise is coming from.

In the meantime (in the absence of manuals to hand) and taking it for a run, my main questions are

1)If it is stock dual mass flywheel problem, can l carry on driving it as normal(ish) without doing any harm.

2) does a problem flywheel cause regular spaced sounds or irregular

3) can a worn out harmonic balancer cause knocking

4) could it be a bad injector

are there any uploaded sound files of engine faults?

[tomtom72]

I'll speak up till Jeff or one of the other more experienced guys see your Q's.

#4 = yes if the injector's coil or/and spray pattern is causing a miss in that cylinder; then the irregular cylinder power output causes the D/M to knock. Same to applies to an issue with the plugs and/or coils if they are causing a miss.

#3 = that's a good Q as our balancers can have slippage with the rubber between the inner & outer rings. I just can't figure out how it would cause a knocking noise unless some part of the balancer was actually hitting something, but I don't think that would sound like the kind of deep thunking or knocking sound at odd intervals that is characteristic of a "miss" induced knock from the D/M flywheel.

#2 = if it's miss induced yes. If the D/M is actually bad I would guess that it would knock at shut down. I do not know for sure what it would sound like at idle if the springs &/or diaphram were bad....maybe it would be regular even timmed knocking.

#1 = Well if it were bad I wouldn't do any 6800 rpm run-ups... I would guess it might fall apart????

as an aside. I listen when I shut down to hear any thunks or knocks from the trans tunnel/firewall area. I know for sure that when my injectors went out my car sounded like there was a boulder rattling around in my bellhousing. I also have observed that when my std ACDelco plugs get past the sweet spot, my idle quality starts to suffer & I get the oddly spaced "knock" from the D/M. Just one "knock" and no real regularity to it either and it's not all that pronounced.

Sorry I don't have more...


Tom

[xxxscimitarxxx]

That was plenty.....thanks very much for taking the time to tell me all that

I also read that injectors or misfire can cause the D/M to knock....but having not been shown, you wouldnt think such a small thing would have such an effect.....l will get that checked out

at least my fears of bottom end, crankshaft bearing failure, seem at this stage to be receeding

However, lve got a wtb thread for a serviceable engine going, but its something l would rather not need right now.....my cars only a baby with 110,000 miles on it

[rhipsher]

It could also be a cat failing. All you have to do to check it is get under the car with a rubber mallet and tap on your kats. And if it rattles like there's a bunch of loose rocks in there then thats it. And if it is! Been there done that. And if your lucky you have a 93 and up because the cats are just bolted on. If your unlucky and have a 90-92 they are welded on. And you have to remove the entire manifold as one piece.

[xxxscimitarxxx]

Thank you for that.....

Its good to know that the worst possible thought you can have about a problem is probably just that......the worst ''possible''..... and not neccessarily the worst ''probable''

Ive got a good list of things to check when l get home

Thanks again

Dave