Low whining sound from undercarriage

[ZR11974]

Good morning to all. I hope this email finds everyone well.
I am a new ZR-1 owner and am hoping I can draw on the vast knowledge, here.
The car is a white 1990. It only has 30K on it and is in excellent condition. I love the car. Lifelong goal achieved by getting the legendary LT5 underfoot.
However, I am experiencing a low whining/whirring type sound from under the car. It does not seem to be changing the cars performance. It's just a concerning sound, and it's loud.
It does not appear to be exhaust.
It is not throwing any warnings, and none of the battery, oil pressure/temp, or normal temp gauges are effected by it. Neither is the idle. It sounds like it might be a belt. But, it starts and ends while moving or sitting still, and it never continues once I accelerate. And, as best as I can tell it appears to be coming from the front/center of the car, not the rear.
Steering also doesn't seem to be related.
I keep trying to isolate some consistency with it, but no luck so far.
And, as I've said, it is loud. Almost like a smaller engine is revving, but not the LT5.
Since it comes and goes with clutch release and depression...sometimes...clutch is my gut feeling.
Any troubleshooting suggestions? I have considered buying a code reader, or using a paperclip trick I read about to see what is stored on the ECM.
I absolutely adore the car, and this weird *** sound is the only thing I'm concerned about.
Thanks for taking the time to read all this, and I hope the day treats you all well.

Respectfully,
Geoff

[Paul Workman]

The 90s have straight cut gears in the ZF which produces some gear whine, especially in 1st and 2nd, I find (in my 90 as well). AND, it comes when the clutch is out and goes away when the clutch pedal is engaged. But, if you noise is the opposite, then throw out bearing comes to mind - except seems unlikely with so few miles.

There are many members in your area that might be able to drop by your location and assess the sound with a learned ear. Aside from that, have you changed the transmission fluid yet? Changing the trans and differential fluid - may or may not improve the sound (if coming from the trans), but then you can check that off the list and you'll know that isn't the issue.

Perhaps Mark Horner or one of several other local Texicans can give it a listen. And, given that gear whine is the nature of the beast in the 90 to mid 92s, if that is all it is, the fix is turning up the radio or installing headers w/o cats!;) (kidding ya!)

[Dynomite]

Good morning to all. I hope this email finds everyone well.
I am a new ZR-1 owner and am hoping I can draw on the vast knowledge, here.
The car is a white 1990. It only has 30K on it and is in excellent condition. I love the car. Lifelong goal achieved by getting the legendary LT5 underfoot.
However, I am experiencing a low whining/whirring type sound from under the car. It does not seem to be changing the cars performance. It's just a concerning sound, and it's loud.
It does not appear to be exhaust.
It is not throwing any warnings, and none of the battery, oil pressure/temp, or normal temp gauges are effected by it. Neither is the idle. It sounds like it might be a belt. But, it starts and ends while moving or sitting still, and it never continues once I accelerate. And, as best as I can tell it appears to be coming from the front/center of the car, not the rear.
Steering also doesn't seem to be related.
I keep trying to isolate some consistency with it, but no luck so far.
And, as I've said, it is loud. Almost like a smaller engine is revving, but not the LT5.
Since it comes and goes with clutch release and depression...sometimes...clutch is my gut feeling.
Any troubleshooting suggestions? I have considered buying a code reader, or using a paperclip trick I read about to see what is stored on the ECM.
I absolutely adore the car, and this weird *** sound is the only thing I'm concerned about.
Thanks for taking the time to read all this, and I hope the day treats you all well.

Respectfully,
Geoff

Difficult to understand exactly when you hear this "smaller engine revving".

Seems most likely Serpentine Belt or tensioner but then you associate Clutch operation which is confusing :p

We have the AC, Water Pump, and Power Steering as well as Alternator rotated by Serpentine Belt Also.

[ZR11974]

We can all rest assured I am confused, as well. Haha.
I have not changed the fluids, yet, but considered that. And, I am almost certain it's not the well-documented ZF gear whine. I think I hear that, and I actually love it. Haha.
I'll check out the Serpentine belt, visually and see if anything looks amiss.
And, I'll see about reaching out to some of the Texan locals!
Thank you very much for the ideas, and suggestions.

Geoff

[Mystic ZR-1]

Pilot bushing?

[ZR11974]

Mystic ZR-1,

Certainly could be, but I have no experience with that as an issue. I'll have to look into it. Any ideas on how to identify that as a possible culprit?
Thank you very much.
I'll definitely be doing some research, this weekend!
And, here's a pic of the car:

[DRM500RUBYZR-1]

Pilot bushing?

Great minds think alike hah hah.

How loud is loud?
Is it always there or does it come and go.
Is it loud enough that when it starts, does it get the attention of the car next to you?
Is it a "howling" noise.
30k miles is about the mileage my first ZR-1 had when the pilot bushing went.
It spins around in the crank and can make a variable pitch, variable volume noise that starts on its own and can disappear at times. (at least in the beginning)
My car would scare adults at the corner when it would decide to howl.
Marty

[Mystic ZR-1]

Great minds think alike hah
Marty

Scary...:)

[ZR11974]

DRMRUBY500ZR-1,

I think we may have a winner...it's loud enough to scare the dead. And, loud enough I always try to make it stop, because it makes my beauty sound like a beater!
Definitely comes and goes.
And, it could be described as a howling...not to be confused with the werewolves. This is louder. Haha.
I'm definitely going to do some researching as I think you've nailed it.
Did you do the job yourself, or have someone do it.
The ZF has to come out to get to it, correct?

[ZR11974]

That last question was a dumb one. Let me go with, is it as involved as I imagine to repair?

[oldpro]

Pilot. Bushing mine did the same thing

[Ccmano]

Take it to Crossed Flags Performance in Magnolia if your close enough. There are not many good ZR-1 shops around, he’s the closest to you.

https://www.crossedflagsllc.com/

Steve Schroeder knows what he’s doing on these cars. I agree with the pilot bushing theory based on what I’ve read.
H
:cheers:

[ZR11974]

Old pro and ccmano, thank you for taking the time to respond. It's so great to have a forum like this available to a newbie, like me.
And, magnolia is only a few hours away. Next door, by texas standards.
I will definitely look them up!
Thanks again and take care out there!

[Dynomite]

That last question was a dumb one. Let me go with, is it as involved as I imagine to repair?

The Pilot and Engine both rotate at same speed whenever Flywheel is Engaged with Transmission. It is only when depressing Clutch Pedal and shifting that the Pilot Bearing is spinning within the Flywheel/Crankshaft.

Some links related to the Pilot Bushing and repair.

TRANSMISSION
Post 35 - Pilot Bearing (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581460766)
Post 36 - ZR-1 Transmission Install and Lift Tricks (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581472079)
Post 37 - Vibration Issues Diagnosis (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581472088)
Post 38 - Throwout Bearings and Clutch Forks (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581480710)
Post 39 - C4 Beam Plates and Installation (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581480716)

[TX '90 ZR1]

I believe everyone is on the right diagnosis track.
There is also Corey Henderson in New Braunfels (Henderson Performance) that is well versed in the ZR-1/LT5.
That being said, Steve @ Crossed Flags is very highly regarded also.
Good Luck and hope to see you next year @ the BBQ??
:cheers:

[ZR11974]

Kenny,
Thanks for the input. I've already had the car to see Corey, but of course it wasn't making this sound when he did the initial once over for me. Corey is great, and I'll be reaching out to him first to get his thoughts. Really helpful, genuine guy.
I would love to come out to the bbq! Where it's the best place to get info about it?
Thanks again and take care.

Geoff
'90 #2591

[ZR11974]

The Pilot and Engine both rotate at same speed whenever Flywheel is Engaged with Transmission. It is only when depressing Clutch Pedal and shifting that the Pilot Bearing is spinning within the Flywheel/Crankshaft.

Some links related to the Pilot Bushing and repair.

TRANSMISSION
Post 35 - Pilot Bearing (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581460766)
Post 36 - ZR-1 Transmission Install and Lift Tricks (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581472079)
Post 37 - Vibration Issues Diagnosis (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581472088)
Post 38 - Throwout Bearings and Clutch Forks (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581480710)
Post 39 - C4 Beam Plates and Installation (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-2.html#post1581480716)

Dynomite,
Thanks so much for helping me start my research. I love learning more about these cars!
I appreciate your efforts, my friend.

Geoff
'90 #2591

[XfireZ51]

DRMRUBY500ZR-1,

I think we may have a winner...it's loud enough to scare the dead. And, loud enough I always try to make it stop, because it makes my beauty sound like a beater!
Definitely comes and goes.
And, it could be described as a howling...not to be confused with the werewolves. This is louder. Haha.
I'm definitely going to do some researching as I think you've nailed it.
Did you do the job yourself, or have someone do it.
The ZF has to come out to get to it, correct?

I think its fun at times when u pull up to some late model “fast car”, and there u are with the motor rumbling and the ZF w SM flywheel is making noise like all ur rod bearings are failing.
And then the light turns green. 🤣🤣🤣

[TX '90 ZR1]

Geoff,
The BBQ is normally in the spring. Have not seen any details about next year's yet, but the info will be posted here on the forum when they set it up.
I went this past spring and saw a bunch of neat cars and met a bunch of really nice people!
My understanding it is always at Joe Cagianut's place in Cibolo. Not far at all for you.
:cheers:

[dredgeguy]

I think its fun at times when u pull up to some late model “fast car”, and there u are with the motor rumbling and the ZF w SM flywheel is making noise like all ur rod bearings are failing.
And then the light turns green. 🤣🤣🤣

You just made me burst out laughing...........great one!

[Hib Halverson]

The 90s have straight cut gears in the ZF which produces some gear whine, especially in 1st and 2nd, I find (in my 90 as well). (snip)


There are no "straight cut" gears in any version of the ZF S6-40.

Gears in the early 6-40s have a slightly smaller helix angle and that's why the early transmissions are a little more noisy and have a little higher input torque rating.

[Paul Workman]

(snip)


There are no "straight cut" gears in any version of the ZF S6-40.

Gears in the early 6-40s have a slightly smaller helix angle and that's why the early transmissions are a little more noisy and have a little higher input torque rating.

A picayune distinction, to be sure, Hib. :rolleyes:

[Dynomite]

(snip)

There are no "straight cut" gears in any version of the ZF S6-40.

Gears in the early 6-40s have a slightly smaller helix angle and that's why the early transmissions are a little more noisy and have a little higher input torque rating.

https://upload.wikimedia.org/wikipedia/commons/e/e5/Helix_angle.jpg

I find that information very interesting....thanks Hib :thumbsup:

[Hib Halverson]

A picayune distinction, to be sure, Hib. :rolleyes:

Granted, you've got me beat on the vocabulary front. I had to look up the meaning of "picayune".:rolleyes:

Nevertheless, Paul, if you knew a bit more about manual transmissions you'd not say that.

I'd like to suggest that when you're making statements about subjects on which you lack accurate information, maybe you should think twice about commenting.

[Paul Workman]

Granted, you've got me beat on the vocabulary front. I had to look up the meaning of "picayune".:rolleyes:

Nevertheless, Paul, if you knew a bit more about manual transmissions you'd not say that.

I'd like to suggest that when you're making statements about subjects on which you lack accurate information, maybe you should think twice about commenting.

Oh... THIS certainly went off the rails! It isn't going the way I intended! I meant no disrespect, Hib. OK, I'll admit in jest I was just "pokin' the bear" a little, but thought you'd "get that" - that I was really giving you a sort of a "left-handed" compliment.

(edit): Everyone...should think twice before saying stupid, derogatory, and unfounded chit on an open forum. Especially the two of us.

Sorry for the misunderstanding, Hib. (Shoulda taken my meds first.)

[Dynomite]

(edited)

Gears in the early ZF S6-40s have a slightly smaller helix angle and that's why the early transmissions are a little more noisy and have a little higher input torque rating.

Regarding the ZF S6-40 ZR-1 Transmission.......I find that that the smaller helix angle (of the gear teath) attributing to a little more noise and higher input torque rating is of technical interest and worth documenting........something not described before :thumbsup:

https://upload.wikimedia.org/wikipedia/commons/e/e5/Helix_angle.jpg

[grahambehan]

The change made to helix angle as mentioned by Hib was a significant change to radiated gear mesh frequency because it increased contact ratio, ie the number of teeth in mesh. There are detail changes to tooth profile and flexibility that affect the load progression across the teeth and thereby reduce the noise generated as the gears mesh also.

Graham

[WARP TEN]

The change made to helix angle as mentioned by Hib was a significant change to radiated gear mesh frequency because it increased contact ratio, ie the number of teeth in mesh. There are detail changes to tooth profile and flexibility that affect the load progression across the teeth and thereby reduce the noise generated as the gears mesh also.

Graham

As usual, the voice of knowledge and reason. Thanks Graham --Bob

[Hib Halverson]

Oh... THIS certainly went off the rails! It isn't going the way I intended! I meant no disrespect, Hib. OK, I'll admit in jest I was just "pokin' the bear" a little, but thought you'd "get that" - that I was really giving you a sort of a "left-handed" compliment.

(edit): Everyone...should think twice before saying stupid, derogatory, and unfounded chit on an open forum. Especially the two of us.

Sorry for the misunderstanding, Hib. (Shoulda taken my meds first.)

Ok. I did misunderstand the context. Sometimes, that happens when we can't see or hear each other, but I'm still smarting from having to go to my dictionary to look up "picayune".

[Hib Halverson]

(snip)something not described before :thumbsup:

https://upload.wikimedia.org/wikipedia/commons/e/e5/Helix_angle.jpg

The change was made mid-year 1993, as I recall. Without trying to find some of my old S6-40 articles I can't say for sure. Graham remembers more about that change than I, so maybe he can confirm the time line.

The early S6-40s were designed when GM was still considering a turbocharged LT5 for the future and it wanted some extra torque capacity. After it became obvious there never would be an LT5TT, GM decided to address customer complaints about noise and decided to increase the helix angle as well as the other changes Graham details. The decision resulted in the later transmissions which were quieter and made less noise.