01ws666

As the title says I'm having a bad vibration when driving and in park/neutral... The latter of which could only come from the flexplate/torque convertor area.

I have a fairly new yank stall and a "Hughes" brand sfi flexplate, The flexplat seems to have like 1/8" runout and about the same amount of wobble (moving front to back at ring gear) Now my trans shop ordered and installed the plate about a year ago so i'm trying to find the specs online but Which one do i need for a stock internal 01 ls1 when buying a flexplate Zero / internal / or externally balanced? Thanks

01ws666

No one knows? Next question would it be okay to put a short bolt with a nut in one or more of the empty holes in the flexplate to try to get some balance out of the one thats in the car now?

12secSS

iTrader: (30)

There shouldn't be options to balancing of an LSx flexplate. That is for older SBC applications, the LSx uses a neutral balance. As for using a bolt in one of the extra holes, sure if it is determined that is where the imbalance is at. If not it will make it worse. Have a professional shop balance the flexplate, don't jimmy rig it.

382ssz28

iTrader: (24)

You should have NO runnout. You will end up taking out the converter bushing in the pump. Remember, the converter bolts to the flywheel and "floats" on the bushing, so to speak, on .003"-.005" of atf. Make sure the flywheel is flush against the crank and no burs or dirt between them. I've seen a case where the pads of the converter weren't the same height and caused the flexplate to wobble. SFI wheels are pretty true so unfortunatly, you will have to pull the trans to check some of these things out. Keep us posted. Good Luck.
PS, NEVER add weight to a flywheel to find the problem! You could have a grenade on your hands.

01ws666

Okay thanks for the replies guys! So any flexplate I order designed for an LS motor should not need any balancing at all correct?

Mine deffinently has some run out to it, So i'm assuming the shop messed up the install somehow. I'll be getting a new flexplate and switching my prothane trans mount back to rubber oem here in the next week or two, will post back if and when that fixes my vibration issue

01ws666

F**K prothane tranny mounts!!!

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Like the title says WOW they really REALLY suck! (cant stress that enough!)

For the last year now I've been trying to trace vibrations/ changing pinion angles/ having my driveshaft balanced, even bought a second driveshaft! / replaced U-joint's/ replaced convertor (well that one just wanted to go bigger) but it didnt help with the vibes! And have been to the transmission shop numerous times trying to get them to figure it out. Not to mention the hours I've spent under the car myself ... and finally FINALLY! thanks to advice off LS1Tech just switched back to a stock rubber mount I picked up at napa for $21 ******* dollars and that just fixed 95% of my vibrations!

Holly **** are you kidding me!? I'm so happy right now I can drive on the freeway again, and at the same time SOOO pissed at prothane and the jackass who designed their poly trans mount I wish I could kick him square in the nuts so ******* hard for all the money and headach that mount has caused me!
Anyone with an automatic who is thinking of using prothane or any poly trans mount for that matter DONT DO IT! Its not worth it I'd much rather have to replace a torn rubber mount occasionally than ever go back to poly!

And btw the napa mount i got is only listed for 94-97 firebirds but it works great on LS1's trust me! End Rant! I think I'm going to go for a drive and actually enjoy it for the first time in forever... THANK YOU LS1tech!!!