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Topic: 91 ZR1 Trans rattle

in Forum: C4 ZR1 & Grand Sport Discussion

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91 ZR1 Trans rattle (1/3)
 6/25/20 6:01pm
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Joined: 6/25/2020
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1991 ZR-1 Vette had new flywheel, Dual clutch disc and pressure plate with new hydraulic throw out bearing installed, now the car rattles like marbles bouncing around in the bell housing.  It gets very loud when the car is idling in neutral and when you leave in 1st gear.  This was done by a corvette shop and I was told that this is normal for that car.  It rattles so loud it sounds like someone is hitting it with a hammer.  Any suggestions on what happened?


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Re: 91 ZR1 Trans rattle (2/3)
 6/25/20 7:53pm
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1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.

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The ZF units DO have a high degree of "gear roll-over" at idle that can get loud. It's a by-product of the clearance between the gear teeth, and the engine pulses that create a noise. The dual-mass flywheels were developed to combat the noise, and they DO help make it quieter, but they do not eliminate the source of the noise. I would guess that the shop either screwed up the install, changed the dual-mass flywheel to a solid flywheel with solid center discs meant for a dual mass(a definite noise maker), or something along that line, assuming the noise was not as loud before.


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Re: 91 ZR1 Trans rattle (3/3)
 6/30/20 4:14pm
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I would be very surprised if the flywheel was replaced with a dual mass unit. I had to do mine a number of years ago and it was hard to find. I have followed things along since and basically they are no longer available. Your shop should be able to tell you exactly what they did. I do note that some suppliers are providing single mass upgrades that apparently do not cause excessive noise.

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