LT4 Manual Transmission in LT4

[Nick S]

I test drove an LT4 Corvette and I was wondering is the manual transmission in this car louder than other manual transmissions. I have driven various Camaros with automatic transmissions for the past 15 years, and I don't have a point of reference for the noise that a manual transmission makes. So, I guess my question is, is the amount of noise that this transmission makes normal for a manual transmission in a sports car?

Thank you for your replies.

Nick

 

[LT4man]

When is transmission noisy? When cruising or at idle?

 

[Nick S]

It doesn't make any noise that I can tell at idle. It seems to me that it makes more noise when accelerating going through the gears than my Camaro with the 4L60E automatic transmission. In general, it seems noisier than the automatic transmissions that I have had.

 

[froggy47]

There should be some gear whine in 1st & 2nd, they're big strong gears. It should go into gear smooth & maybe a little stiff or firm. When I first got mine I wondered about the whine, it's normal.


This is not a Honda or Toyota gearbox

 

[Nick S]

The transmission seems to transition from gear to gear rather smoothly. Other than the stupid skip shift feature, which I never totally understood until I actually drove a manual transmission, the transmission seems easy to operate. Like I said before, since the last time I drove a manual transmission was when I was learning to drive like 17 years ago, I just wondered if all manuals were a little noisy.

 

[LT4man]

The only admitted noise in the ZF trans is at idle. Being a racing transmission, the gears are straight cut, not bevel cut. That causes a distinct gear "rattle" while at idle in neutral. The noise is annoying but not damaging in any way. If you are hearing that, you can eliminate that noise quite easily. Instead of running petroleum oil in the trans, you can run synthetic oil and the noise will leave immediately. I believe the synthetic oil also helps with the shifting of my trans. But, that is just my opinion.

 

[Aurora40]

Being a racing transmission, the gears are straight cut, not bevel cut. That causes a distinct gear "rattle" while at idle in neutral.

Um, is this true? Straight-cut gears would result in a ton of noise while driving. I'm not sure it would affect idle sound, as the gears wouldn't be engaging and turning. I can't imagine a street car having straight-cut gears no matter how "race-tuned" it was supposed to be.

 

[MMM]

I agree with Aurora, if the gears in the ZF used straight cut gears it would be noisiest while in motion, not during idle. The Muncie M-22 "Rock Crusher" was so named becauce of the the noise it made in operation, and it used gears with reduced helix angle, not straight cut (I forget the difference between the "standard Muncie gear helix angle and the M22).
However, all that being said, you cannot compare the noise of a manual trans to an automatic. The only gearing in an automatic is planetary and all are helixed and much smaller. An automatic will always make less noise. If you are concerned about the noise, it should be checked out by a knowledgible mechanic to determine if a bearing is failing.
Mike

 

[6 Shooter]

1996 LT4 Corvette Transmissions

ZF 6-Speed Manual

A ZF 6-speed manual transmission is standard on all 1996 Corvette models equipped with a 5.7 Liter LT4 engine -- Grand Sport, Collector Edition, Coupe and Convertible. (The 6-speed is not available with the 5.7 Liter LT1 engine for 1996.)
Introduced in 1989, the 6-speed gearbox was designed specifically for the Corvette by Zahradfabrik Friedshafen A.G. (ZF), a German transmission manufacturer known worldwide for its transmission expertise.

The 6-speed's 2.68:1 ratio in first gear provides high torque multiplication, for quick initial acceleration; two overdrive gears (0.75:1 fifth and 0.50:1 sixth) produce quiet, economical highway cruising. All speed-equipped Corvettes have a 3.45:1 rear axle ratio.

The 6-speed incorporates a Computer-Aided Gear Selection (CAGS) system. The CAGS system is designed to improve fuel economy during normal driving situations by directing the driver from first gear to fourth gear under light acceleration from a dead stop. Rapid acceleration automatically cancels the one-to-four shift.

One of the first cars sold in America with a six-speed was the '89 Corvette. Designed by Chevrolet and Zahnradfabrik Friedrichshafen (ZF) and built by ZF in Germany, this tough-as-nails six-speed was available in the Corvette up to the conclusion of the '96 model year. Today, the Corvette uses a Tremec T56 six-speed mounted at the back of the car.

Gear Ratios
1st 2.64
2nd 1.78
3rd 1.30
4th 1.00
5th 0.74
6th 0.49

 

[jcs44]

No argument with anything stated so far. The ZF 6 speed is a no kidding race car transmission so some gear noise is normal but it seems to vary from example to example. My 95 LT1 would whine in 1st and 2nd and then was quiet. My current LT4 is quiet in all gears. Iy does make some noise at idle in neutral though. The CAGS skip shift is annoying and there are after-market devices you can plug into the wiring harness to disable it.

John 96 LT4 Vert, Blk/Blk

 

[LT4man]

I have talked to many transmission rebuilders over the years. In a previous life (for eighteen years) I owned an auto and truck repair shop. The info I received about the straight cut gears came from those rebuilders and some of the Corvette experts I have talked to over the years. Even tho there are synchros in all the gears (including reverse, believe it or not!) the hydraulic clutch system is of UTMOST importance in the shifting of the trans. The zfdoc.com has a lot of very useful information about this incredibly durable and bulletproof trans. But as in any situation, the weakest link always needs to be addressed. The other interesting tidbit of info that I know: the ZF trans was used in conjunction with the ZR-1 because of the high horsepower and torque that the engine made. Being able to use that same trans in all the other Corvettes was just the icing on the cake!

 

[froggy47]

The transmission seems to transition from gear to gear rather smoothly. Other than the stupid skip shift feature, which I never totally understood until I actually drove a manual transmission, the transmission seems easy to operate. Like I said before, since the last time I drove a manual transmission was when I was learning to drive like 17 years ago, I just wondered if all manuals were a little noisy.

On my 96 I just unplugged the cags, did NOT get ANY codes. The 1st to 4th light does still illuminate, however. I ignore it.

 

[Skyguy007]

Nick,

Get a CAGS adaptor for your ZF. They're inexpensive and will keep the connections clean in case some fool wants to reconnect this feature in the future. I'm not sure if this really matters, but adaptor also contains a resistor that makes the computer think the CAGS is still connected. It won't affect whether the idiot light comes on or not. If you're seeing that light often, just accelerate faster!

As for noise, the noisiest part of my transmission is the clutch throwout bearing when the car's in neutral at idle. Even this is not very loud. Remember to swap out the transmission fluid for the Red Line stuff Hib Halverson recommends.

 

[redvette6spd]

my 91 and my 96 make all sorts of noise boath sounded the same it's normal it's the way thay are

 

[LT4BUD]

What kind of noise???

Mine has always been pretty quiet, but there is "some" whine in first & second, normal

The Castrol oil at about 30k miles really smoothed out the shifting..


www.zfdoc.com

 

[JAGSFAN]

i dont know about the tranny noise. all i can hear is the bora exhaust and the rumble of the engine as i shift thru the gears.

P.S. I found out that the radar detector I have works absolutely great.
Cruising at 125 going to cincinnati on I71 and it went LASER ALERT LASER ALERT
When I hit the brakes there he was. I drove by and waved at 65 MPH