Intermittent growling and harsh vibrations in neutral

[1991 Corvette ZR-1]

Hello all. Recently, I have noticed an extra prominent growling, chatter or vibration while in neutral. I can feel it through the gearshift lever pretty well when it happens. Does not seem to happen all the time and does not occur when coasting in neutral from speed. I have mainly noticed it 20 seconds or so after startup and it lasts for about 5 seconds. Just came back from a drive and was waiting for the garage door to come up with clutch in and it did it again. Happens if using the clutch for neutral or leaving the gearshift in neutral gate and idling. Does not appear to be a thing that happens when in gear and at speed.

If I had to guess, it is dual mass related. 1991 with almost 93K miles. I am wondering if anyone else has experienced this? I am aware of the normal growling from black tags but this is not the normal frequency. I am planning a fluid flush of the trans next week and now I am considering replacing the clutch hydraulics just for safe measure. I committed a cardinal sin and only replaced a failing clutch master two years ago and left an aftermarket cast iron slave in place.

[1991 Corvette ZR-1]

Ugh just realized I put this in the wrong section. Mods, if you can move to the appropriate tech section.

[GOLDCYLON]

Moved

[Great White]

Possibly a bad pilot bushing/bearing or throw-out bearing.

Sent from my BBF100-2 using ZR-1 Net Registry mobile app

[1991 Corvette ZR-1]

I see Corvette Central has the fluted pilot bearings. That is one piece of the puzzle. As far as a replacement clutch fork stud, because I know it will be worn and they are hard to come by. The fork, the TO bearing, these items will be tricky to find?and expensive. The dual mass is probably close to being toast. I was looking at an aluminum flywheel RAM clutch kit with hydraulic TO bearing on Jerry?s website not long ago. Sounds so much more hassle free to order that than try to wrangle all these rare parts together.

Anyone installed this kit?

https://www.jerrysgaskets.com/clutch...sc-89-92-28d1/

[tccrab]

Be forewarned, the lightweight aluminum flywheel can cause a very loud gear rattle that I've heard referred to as the box of rocks syndrome.
Just so that you're aware of it, and it doesn't come as a surprise.
I've read that there are certain tweaks to the idle speed that can help......a little.
The good news is that the lightweight flywheel will cause an immediate improvement on how quickly the motor will rev up, the bad news is that you'll be buying rear tires much more often.

Crabs

[A26B]

FYI
Not all single mass flywheels are featherweight (13~14lb).

Jerrys Gaskets had Ram Clutches make custom, aluminum billet flywheels in 18# & 22#. There are 2 principal reasons for these flywheels.

1. The heavier flywheel will mitigate/dampen engine impulse, the cause of transmission rattle. Not as effective as the DMF flywheel, but more than the 13~14# SM units. The 18# & 24# units are dimensionally identical to the OE DMF, maintaining the same clutch geometry, with the OE pull-release clutch.

2. The SM lightweight flywheels do rev quicker but do not develop the same level of kenetic energy as heavier units. More weight translates into easier launches during street driving as well as drag racing.

We do have some OE clutch components (fork & ball studs).

The push-release clutch can be used on all flywheels offered by Jerrys Gaskets.

[1991 Corvette ZR-1]

Thanks for the input, guys. Crabs, I have heard all about the rattle one can expect with the 13lb flywheel. I am wondering if one of ZF doc?s countershaft shims would help. I have one collecting dust unopened. I have also read some have applied brake quiet on the crank mating surface before bolting the flywheel on, but I do not think I would do that. I think the goal would be to go for the most free revving option, while I am in there but I would probably be happy with the 18lb version as well.

Jerry, on the RAM kit that includes the hydraulic TO bearing, are there any additional pieces that need to be picked up, such as shims or any other bits? Just trying to do my homework. Also, blue loctite: is there a specific formula number to use on the pressure plate bolts and flywheel to crank bolts?

[A26B]

Originally Posted by 1991 Corvette ZR-1

.......... Jerry, on the RAM kit that includes the hydraulic TO bearing, are there any additional pieces that need to be picked up, such as shims or any other bits? Just trying to do my homework. Also, blue loctite: is there a specific formula number to use on the pressure plate bolts and flywheel to crank bolts?

Use RED Loctite 262 (high strength), not Blue/medium strength on all Flywheel & clutch bolts.

Read the full description for the RAM kit you are interested in. What is included and any other needed parts which are not included are specified.

[1991 Corvette ZR-1]

Originally Posted by A26B

Use RED Loctite 262 (high strength), not Blue/medium strength on all Flywheel & clutch bolts.

Read the full description for the RAM kit you are interested in. What is included and any other needed parts which are not included are specified.

Red 262 works. So after some browsing, I believe I will stay with the pull clutch setup. I see throw out bearings are still available for the black tag and I have a fluted pilot bushing ordered.

A dilemma I am running into now is making all the other parts work. I would like to use an aluminum flywheel, 13lb version. Some pictures of Fidanza brand appear to show the flywheel not designed to accept a sprung hub clutch. For those who have gone the aluminum flywheel route: what sprung hub disk did you use and what brand pressure plate? Just trying to avoid sending parts back because that is never fun.

Aftermarket pressure plates require longer bolts but is there a particular brand or pack to purchase?