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LT4 Just bought an LT4 CE and it has some problems...

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1996 LT4 Topic
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Skant

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I just purchased an LT4 CE from a GM dealership in Colma, CA on Friday. It's my first Corvette, and I'm quite excited about it.

The car seems to be in very good shape except for two things. The simple one is that the cruise control does not operate.

The one I'm more concerned about, however, is that the transmission makes a whirring/whining noise when you let the clutch out in neutral. When you push the clutch in, the sound slows to a stop in 2-3 seconds.

It's not extremely loud or anything, but it is noticable. To my understanding, this would mean that the input or thrust bearing is near death.

However, I've never owned anything quite like this 6 speed before. And I've heard lots of tell that it's just plain noisy. Searching through the forums and reading the FAQ on that rebuilder guy's website seems to indicate that this particular noise is not supposed to happen?

Drivingwise, it all 'feels' perfect to me. It's not having problem getting into any gears or anything like that (other than the annoying forced 1st->4th thing... I must purchase the bypass for that immediately).

Is this a problem I need to worry about? If it's just noise, I'm really not too concerned about it. But if it means that the input bearing is going to spill its guts into the transmission, that's concerning...


It is a GM certified 'pre-owned' car. It has a 1 month/1000 mile power train warranty on it (no deductable). Plus I purchased a 4 year/36000 extended power train warranty for it ($200 deductable).

I want to know what I'm talking about before I talk to them about it. Because I envision talking to a brick wall about a noise the car is making that hasn't affected its operation at all yet.

I guess what I'm most concerned about is having the tranny self destruct in a few months and then having them refuse to fix it under my 4 year warranty because they claim I abused it or something. I don't know if that's a realistic concern though.

I wish I had figured out about that noise during the test drive before I purchased it... but there's just so many sights and sounds and gadgets in this thing, I was just overwhelmed.

Anyway, thanks in advance for any advice!

- Skant
 
Skant,

Welcome to the Corvette Action Center. It's a little hard to make a proper diagnosis regarding the sound you describe, however, based upon your description here, it sounds like it's normal. When you let the clutch out in neutral, you should hear the transmission....."whir" a little bit more than when the clutch is pushed in. The helical cut gears are more noisy by nature.

For more of an explanation, please see the last paragraph here:

http://www.corvetteactioncenter.com/kb/answers.php?sp=0&order=sdate&select_list=11&ownertopic_id=72

As for your cruise control problem, I'll let another more knowledgeable member try and help you with that. Keep us posted!
 
Skant said:
The simple one is that the cruise control does not operate.

- Skant

Skant :upthumbs Congrads on your 1st Vette & Welcome to :CAC

As far as the cruise control not working, there's a black vacuum valve under the passenger side fuel rail cover that goes bad quite often. It's a little black critter with 3 small vacuum hoses connected to it. They sell them at most auto stores for a few bucks.

I know you'll enjoy your LT4 !

Later . . . . . .
6 Shooter
 
Welcome to the CACC Skant.

Check out www.ZFdoc.com. They are pretty reliable when it comes to information/diagnosis on our trannies.

And congrats on the new ride. I'm sure you will have a lot of fun with it.:D

Jason
 
Wow! Thanks for the warm welcome!

It's a great relief to hear that this sound is normal. Though the Q/A link says that this 1st gear growl existed in the 93 and older 6 speeds and they quieted it down in the newer ones? It would still be there in the 96 LT4, but just not as loud?

It doesn't sound like a mechanically 'bad' sound, per say. Just a whirr. And it's not so loud that I could hear it while the stereo is playing. Just most manual transmissions don't make additional noise with the clutch out in neutral.

I guess the Corvette would just rather be moving... *smirk*

- Skant
 
The FAQ on ZFdoc.com would seem to indicate that this sound is not normal? It seems to say that the input bearing is 'compromised' if it makes a sound like that. Or maybe I'm misreading it.

If other 96 LT4 owners hear this sound and haven't had a problem with the transmission, then I'm not too worried about it. The sound itself doesn't really concern me. It's not that loud. Impending doom of the transmission is my only concern.

- Skant
 
Sounds like the typical ZF6 noise... everyone I've heard has it.
 
Sounds like I don't need to worry about the transmission then.

I took a look under the hood for the cruise control. My vacuum valves look externally okay. Then I found the culprit. There is a break in part of the vacuum line which has become brittle.

The break is located to the left and low underneath the cruise control unit. It's broken just before it enters a trunk which routes it to the boss right side of the engine (presumably where it's drawing the vacuum from). I don't think it will be possible to replace this hose easily without digging out the trunk. Unless I reroute a seperate hose another way.

Since I just bought it as a certified pre-owned car, I guess I should see if the dealer will fix it under warranty first.

Makes me wonder if any of the other vacuum hoses are about done, too... hmmm...

I wonder if the dealer would dig out the trunk and replace the whole line, or if they would just reroute the hose a different way, too?

- Skant
 
Hi Skant, welcome to CAC. I joined last month after getting a 96 LT4 conv.( 44K on it) I had the same concerns you have. My cruise control didn't work, but before I called the dealer to scream, I checked the fuse. It was blown. Hopefully that is it for you. The tranny and clutch noise sounds identical to yours. From all the things I have read from this forum, it seems that it is somewhat normal, although a little disappointing that these high $ sports cars can sometimes sound like a 1950 farm truck. o.k. maybe not that bad. The 1 to 4 shift drives me nuts, but I'm getting used to it. I don't know if there are any cons to disconnecting it. I've also learned to take curbs and speed bumps at a slight angle so I'm not scraping the bottom at all anymore. I've owned a 77 and 74 several years ago, and I can tell you, the 96 is head and shoulders above them as far as reliability, speed, and fun to drive, ( I'm not slamming sharks, I do miss them!) let me know if you find out any more info on your tranny or clutch. Sounds like we are both going through our "honeymoons" with our LT4's. You'll also find this forum to be a great resource. Kind of like a "crisis hot line" for vette lovers.
 
I purchased my Lt4 last April (23,000 miles) The car had two problems with it. 1. The transmission has the same sound you described. 2. The cruise control didn't work. I took the car to the best vette mechanic in the area where I live. "He said the transmission sounded better than most,the noise comes from the input shaft. " The cruise control didn't work due to chaffed wires under the right
side of the dash. After 3500 miles of driving the transmission noise hasn't changed. Good Luck with your LT4!
 
Whoa...a warm welcome to all you new folks in here......and take your vette/cruise to the dealer and ..........make him fix it.....that's what certification was all about...........stuff working
:w :w :w :w
 
Vettelt193 said:
Mine whines so bad when I have the clutch out, it sounds like i have a supercharger....

yes, yes, and doncha just love it..............you Gotta like the way the ford guy looks at ya..............on those warm summer nights at the stop lite............heck.....I do.........it's a boost......(pun)
 
nobody wants to play with me... some think I am supercharged, some think it is a ZR1, some think it is a Z06, and some know it is an LT4.... :)
 
Welcome Skant, the sound you are describing sounds like the norm for these trannies. There have been posts about this before and it seems they all do it. Enjoy the LT4, I know you will, Guy
 
Thanks for the info about the cruise control, guys! While it didn't turn out to be the check valve, your information did help me repair it... since I would have had no idea where the other end of that vacuum line went to without your descriptions. (The line goes into a trunk that runs behind the engine... it would have been impossible to guess where it came back out).

I rerouted a new vacuum line to do the job rather than trying to dig out the trunk it went through. I decided that for such a simple job I could do myself it wasn't going to be worthwhile to deal with taking it to the dealer. And now the cruise control vacuum line in my vette is much easier to get at.

Works great! Thanks again!

- Skant
 
Skant, Congrats on the LT4... you'll love it.

I have been confused with an ZR-1 once, it must be my wheels. When i told the guy, "no no, LT4 - the grand sport motor" he looked at me like i was talking about brain surgery. The LT4's are just not well known outside of real Corvette people.

Have fun,
John
 
Wow. Lot's of new LT4 owners. I have had my 96 convert one week and it just gets better and better. I too have a blown cruise control. My [great] mechanic went right to the vacuum hoses [initial visit] and they are in terrible shape [he says they just do not last long] but not the cuplrit. I checked all fuses and they are ok. I will have him try that diaphram thingy next. I have the 6 speed with 40k miles and get a very mild whir in neutral. Getting ready for tires. Firestone Firehawk SZ50EP seem to lead the field as I research. Any suggestions? I love this forum!!! Denny Nelson
 

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