94 Vette with LT1 w/ LT4 cam rebuilt 20K ago, Trans rebuilt at same time (4l60e) with a "3000" stall converter(supposedly).

3 problems:
1) After I got to work the other day the car was making a bad "rattling" sound underneath. (Doesnt do it when its cold). Sounded like a loose flex plate. Got home checked the torque converter bolts, they were tight. Pulled trans, Flex plate bolts are tight. Checked for cracked flex plate, no cracks and it "rings" when I hit it. WTF?

2) Before I pulled trans I removed the TC cover and let the engine run. It was spraying a small amount of trans fluid off the TC. There was a perfect line of spray on the floor. Bad shaft seal, pump seal? Pressure tested TC and no bubbles present so that rules out bad weld.

3) Before the rattling started the car would surge at exactly 1500 rpm and 45 mph. It wouldn't do it at any other rpm. Was this a sign the TC is going bad, or that the stall speed is not 3000, and is actually closer to 1500?

I just got the car 3 weeks ago and all the work was done by the previous owner. I do have receipts for the rebuilds but no way to tell what stall the TC is. The car shifts great and rides perfectly otherwise.

 

you 100% certain the sound is the trans?

what about cat heat shields, broken cat substrate, loose pipe hangers, fuel filter shield., any other loose tin shield?

From what I recall, a trans that "rattles" won't operate right.

If you can confirm the noise with a stethoscope then the next step would be to drop the pan and look at the chunks.

 

I did drop the pan and its perfect. Could be a heat shield, only does it when its hot

 

The ATF spray is probably the front pump seal. Very easy to replace with the trans out.

The torque converter goes into lockup around 45 MPH. Mine locks at 41 MPH. It feels like a shift. Is that your surge?

 

It feels like maybe its locking and unlocking. Like it can't decide what it wants to do. The tach needle moves slightly and you can feel it in the car and hear it in the exhaust. That's what makes me think its a stock converter. I honestly don't know. If I went with a, say, 2000 stall would that help this?

 

........ The computer commands the clutch lock-up ... it wouldn't matter what stall you have ... what is the diameter of the torque converter ? typically the higher stall versions are smaller in diameter ... 12" stock size is usually 2500 or less ...........

 

It's a 12 inch converter. The guy at the TC shop said it was stock. Not sure how he knows cause there are no markings on it. The guy I bought it from said it was 3000. Not sure if he installed it or the trans shop.

I've never had a performance converter, how do you tell what the stall speed is? What how the car act?

 

if the car has TCC on the trans the lock-up is controlled by the ECM not the converter itself.

Look for the TCC solenoid on the tranny. Check the plug for dirt/looseness.

Also, you have to learn the right way to drive a TCC car... what to expect. If you are driving in 4th OD it lets you drive "soft" with less lock-up. Driving in-town in 3rd is full TCC lock-up and the car drives "tight" like it was a stick. Manual upshift to OD. It can be driven either way without ill effects.

The ONLY cars that benefit from high stall TCs are those that are used on the 1/4 mile track and KNOW exactly where their hp is made in the rpm band. The TC is then designed to capture all that power at the time its made so none slips by and the engine is not wasting it. It takes a built motor then a dyno sheet to know what TC to put in an engine. This guessing and sticking a high stall TC in a semi stock street car is a myth IMO. Especially on a TCC car... I do not know if GM still called the Torque Converter Clutch Control TCC in 1994 but it does the same thing...the ECM controls when it locks. It used to be described as an "electric TC"...not accurate but it describes what is going on.
I believe this can be altered in the "tune" as far as I know...shifts points etc. In earlier C4s there was just the TV cable...later yrs made it an ECM tune feature. More range of adjustment.

If there was nothing in the pan, thats a hint to start looking at the cats or shields. A broken cat will raise hell. Sounds like a rock rolling around in a steel trash can.

BTW
trans shop LIE about what they install. The customer 99 times of 100 has no way of knowing, the shop sells stock parts for aftermarket prices, sells the customer a line of BS a mile long, and everyone is happy after the simple repair turns into $2600 and the customer is made to believe that he got some great upgrades for the screwin he just got. In this case the shop knew there was no need to change anything with an ECM controlled TC lock up. So they floated this BS story. I had a big chain trans shop tell me they went ahead and installed a "shift kit" in my trans. The thing shifted like a mini van no matter how hard you stood in it...Found out later after it was torn down AGAIN that they didn't even use the GM corvette parts...they installed stock servos and valve body parts from the avg GM trans...nothing upgrade about it. Downgrade actually. Not sure if they were too stupid to know the difference or if they assumed ME to be too stupid to notice. Probably the later...

I think these trans shops are close to the top of the pile of thieving lying scam auto repair businesses right along side of dealerships. There are some honest shops out there and there have been some honest guys on here. But many are out there to sell parts and service and if you do not know or understand what you need, they will take advantage of that BIG TIME.

 

That makes a lot of sense. Thanks for the thorough reply. I have the cats off now as well as the rest of the exhaust. I will check those for loose shields and check the cats for loose internals. Thanks!

 

The rattle is coming from the drivers side cat. I shook it real hard and the material inside is loose. With there being an O2 sensor after the cat on the right side, if I gut the cats is that going to cause a problem?