GM LT1 Clutch 'On Car' Balancing Instructions
04-26-2014, 08:31 PM
#1
GM LT1 Clutch 'On Car' Balancing Instructions I found this GM Bulletin proceedure for correcting a engine vibration above 3k rpm. Pretty interesting, although it talks about the dual-mass flywheel it should apply to the single mass flywheel. There are 12 holes in the back of the f-body FW for the balance pins. My own FW had 2 balance pins installed.
I was able to reduce the vibes I was getting with my Spec billet FW/ new clutch assy by using this info.
Update: added scanned document to fix broken link to service bulletin.
I was able to reduce the vibes I was getting with my Spec billet FW/ new clutch assy by using this info.
Update: added scanned document to fix broken link to service bulletin.
Last edited by guppymech; 10-29-2015 at 07:17 PM.
04-26-2014, 11:21 PM
#2
the procedure is directed for Dual Mass FW. FWIW I have had "stock" FW neutral balanced at a machine shop which involved grinding off the cast in weight and using "pins" in the outer holes to balance.
The dual mass FW in the LT4 was used as those discs were non sprung. They were heavy & expensive. Most just went to a replacement standard FW with a spring hub disc clutch instead of buying a new Dual Mass FW on clutch swaps. Valeo made the OEM and most auto part store brands were also repackaged Valeos which were balanced to factory specs. Now there are just clones and those PP are not balanced like stock
For stock motors that are still external balanced. This procedure could be used to address vibrations with these "replacement" clutches available today
I have a 383 which is internal balance so I send my FW & clutch to a machine shop for balance (zero) before I install. Otherwise the motor would shake like a dog shiating razor blades
pic of FW with pins to balance
The dual mass FW in the LT4 was used as those discs were non sprung. They were heavy & expensive. Most just went to a replacement standard FW with a spring hub disc clutch instead of buying a new Dual Mass FW on clutch swaps. Valeo made the OEM and most auto part store brands were also repackaged Valeos which were balanced to factory specs. Now there are just clones and those PP are not balanced like stock
For stock motors that are still external balanced. This procedure could be used to address vibrations with these "replacement" clutches available today
I have a 383 which is internal balance so I send my FW & clutch to a machine shop for balance (zero) before I install. Otherwise the motor would shake like a dog shiating razor blades
pic of FW with pins to balance
04-26-2014, 11:35 PM
#3
Interesting information!
What sprung hub disc fit a standard flywheel and the Valeo PP? I haven't seen one; obviously the solid hub would work.
True. It's unfortunate the new PPs aren't getting a quality neutral balance.
For stock motors that are still external balanced. This procedure could be used to address vibrations with these "replacement" clutches available today
04-27-2014, 03:29 PM
#4
The LT4 used the Dual Mass FW. the LT4 clutch disc was solid, no springs
every LT1 clutch regardless of who sells them are LT4 PP which have greater clamp force than the LT1 PP
pic below is sample of clone PP and stock FW after I got them back from machine shop to make them "neutral" aka "zero" balance. Note the shiny pins in the FW on the edge of it. The 3 holes on the "tab" of PP is where machine shop took weight out (26 grms).
My experience with stock motors and various aftermarket clutches is they were all plug & play. The FW has a cast in weight.
My current motor is "internal" balance so I have to get my FW & PP neutral balanced. Even high $ billed "neutral" balanced FW's should be checked...everyone I have had needed balancing even though they were sold as "neutral" FW's
04-27-2014, 06:37 PM
#5
My point was a standard "push" disc (like 10.75" '88 Vette) with rear-facing sprung hub can't clear the Valeo PP in any circumstance.
And the "pull" disc with forward facing hub (93-97 F) requires a "deep" 93-97 F flywheel to clear the bolts to the crank. Which sounds like what you've been using all these years.
And the "pull" disc with forward facing hub (93-97 F) requires a "deep" 93-97 F flywheel to clear the bolts to the crank. Which sounds like what you've been using all these years.
