Ive got a noise, that I originally thought was in the tranny. I get a shuddering or grinding noise when I accelerate, it doesn't happen when idling, and it doesn't happen every time you accelerate. It will do it when you are in park revving it up quickly, letting off and revving it again etc at say 3000 + rpm. It also makes the noise when you first start it up, most of the time. I have narrowed it down to a cracked flywheel, but any suggestions would be appreciated. I figured it wasn't the bottom end of the engine because it is perfectly normal at idling, and even sometimes during acceleration. I eliminated the tranny, because it will still make the noise in park when you rev it up, and when it starts. It definitely "feels" like it's coming from the tranny tunnel area where the bell housing is, at least when I am driving it, it feels like that. Anyways, any input is greatly appreciated. Thanks!


By the way, it is a '91 GTA 5.0 700R4.

 

shift,

I also have a 700r4 and when my flexplate went out it would make a ticking noise. Sounded like an exhaust leak. It would only make the noise when it was in gear though. The last time I changed it The flexplate was actually hitting the starter gear. So maybe this could be your grinding noise but its all speculation until you get under there and check it out.

Rabi C.

 

I've seen cracked flexplates sound like a grinding, ticking, or knocking making you think the problem was elsewhere. but when I showed customers the problem they were in disbelief.

 

Common issue with 3rd gens is the 3 bolts for the torque converter backing out and rattling

Drop the dust cover and check if they are tight

 

I checked the bolts, they are all tight, I tried to look for cracks but saw nothing. It is reeeally hard to pinpoint this noise with the engine running because of all the other noise haha. Any other suggestions? Could it be bottom end even though it doesnt make noise at idle?

 

ive got the same problem....when i get around to it...im gonna try to get in there and retorque the flexplate bolts...hopefully i can get to them without having to drop the trans..

 

Yeah you will be able to, you can access them by removing the dust cover and turning the engine over.

 

I've seen cracked flexplates 'self clearance' the block, so check it out and don't let it go... its only going to make things worse if it is indeed broken.

 

How do you check it? woohoo, I solved part of the problem, the vibration is now gone. My timing was way retarded. When I set it I disconnected the wrong connecter, not the brown and tan one by the accumulator. Anyways the rattle noise is still there, and I stillt hink it is a flexplate. I saw a post about how to check for cracks once but I canyt find it anywhere. Does anyone know how? I remember them saying something about prying the flexplate away from the crank with a screwdriver or something?

 

Bump. I really need to solve this problem, anyone?

 

first check your exhaust... CATS

then have you checked your tranny fluid?

 

Tranny fluid is a bit browny like said above. Does that mean there is internal damage? or just that I should change the old fluid? Also, the Cats are fine, not clogged or anything. I dont get why it makes the noise in park or neutral when you rev it up, that would suggest to me that it isn't the tranny.

 

no it would cast doubt on it being the tranny itself... but also the fact that it doesnt do it all the time... sorta leads me to believe it isnt the flexplate....

that is why i said exhaust

BTW whats you OIL pressure at idle? with the car warm?

 

Almost 0, but I was under the impression that my gauge was screwed, it never read right before i rebuilt it and still reads weird. And if I really had 0 oil pressure I am sure I would know it in a hurry.

 

Brown trans fluid is burnt up

That trans doesnt have much time left, run it until it dies but get a spare ready

A bad cat will also rattle as well as loose heat shields around it

You do know the difference between a rattle and a bottom end knock dont you?

 

my 700r4, was making the same clunking, ticking, rattling.... sound, from around the distributor area...... i had the trans completely rebuilt....and the sound is still there.... i looked under the car while it was running....and the flexplate/TC, was wobbling, and the clunking matched the wobble.....

is it possible to get in there and change/tighten the flexplate, without removing transmission?

 

Yes, as stated above, you simply drop the dust cover and tighten them

Since you can see the parts moving then the cover is missing and you simply need to tighten them

The Flex/crank bolts are inaccessible without removing the trans thou. These only work out when proper locktite was no applied

 

totally sucks...i just got it back from the mechanic, i dont think they would leave those bolts loose, and yea, i was refering to the crank ones in the center of the flexplate.....how much do new plates go for? and where do you get em? kragans?

 

if you were getting enough wobble to make noise the tranny needs to be taken out and inspected ... i would also inspect the rear main and the thrust bearing

 

If you were to ask me what I thought originally, I would say it sounds like a bottom end noise. But I dont know why it's doesnt do it at idle. AND I already went through this dilemna once before. I rebuilt the motor, ended up putting standard bearings in by accident, and the crank was turned down previously. Stupid mistake I know. So I pulled the oil pan and put in new bearings (connecting rod AND mains, I put .010"s in. I measured my clearances and I got .018" smaller than the stock size. .020's wouldnt work, so .010's with .005" oil clearance seemed logical to me. Even though that leaves another 3 thousandths. I torqued everything down and triple checked them all. I even plastigauged it and it seemed ok.) Anyways, I wish I had a sound clip that was of good quality, so I could let you all listen. But I cant imagine it being bottom end, even though it sounds like it to me. The sound occurs on start up, it makes a quick rattle. It occurs at 3500+ when accelerating, it does it in park when revving up to like 3500+, and sometimes it vibrates when accelerating at virtually all RPM's, but the vibration part doesnt happen ALL the time.

 

Ive come to the conclusion of this noise being in the bottom end. I can now hear it at idle, knocking. I don't know how in the hell, but I am sure.

 

i can tell you it is from the .005 clearance on the rod/mains must have hammered the **** out of them

 

What was I to do, I was told I couldn't get bearings in .015's. Is my crank screwed probably? Its been like this for like 4000 - 5000kms

 

when you say measured your clearances do you mean with a mic? .018 might be .020 and you did a poor job measuring... it is hard to measure a round surface accuratly with flat anvils... verniers, you would be able to get a measurement but then i wouldnt trust the accuracy of them... as they tend to be most accurate as close to the body as possible...

do you still have the old bearings... from before you did the rebuild... they would have the undersize marked on the backs

but you understand how with that much clearance this was garaunteed to happen right? when the engine isnt running you might see only .005 of oil clearance around the crank... however once it starts you will find that the combustion forces the crank into the main caps causing a .010 clearance on top... where the main is supposed to be getting oiled there is no pressure so the oil never reaches the bottom of the bearing

 

I used a a digital vernier and measured it multiple times from different sides. Anyways, crank. Think it's probably screwed or should it be alright if I just replace the bearings again? And no I dont have the old bearings anymore. I believe it was just the mains that were off sized.

 

well, those verniers... they are 0-6" right? the jaws are probably to small to measure a 2.25 main journal... what is the smallest unit of meassure with them .001,.0005? basically who makes them...

as for the crank... i would play games with it any more... then again i wouldnt have bothered with undersized bearings in the first place when a new crank is pretty damn cheap

 

Ok, determine once and for all if its engine or trans

Drop the dust cover, remove the torque converter bolts
Push the torque converter away from the flex plate, it will slide a little over an inch

This will let you you crank the engine and not have the flex plate beat the crap out of the torque converter

Let us know if the rattle is still there