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  • #1

    Vibrations after motor swap...

    Hey everyone,
    I put a 96 LT1 into my 3rd gen earlier this month. I have noticed a vibration that gets progressively worse the faster you go. You start to notice it around 70mph & it just gets worse & worse from there. I know how a out-of-balance tire feels & this is not it. I think its drivetrain related. I also have a squeel coming from my clutch while it slips when I start off. I am wondering if the two are connected. Lastly, I have a energy suspension poly trans mount. I thought these things were unbreakable. But I broke it. The trans is able to move about 2 inches up & down while driving. I bought a new GM rubber mount today to see if that helps with the vibrations, but I just wanted to see what you guys came up with.

    During the swap I...
    Resurfaced the flywheel
    Installed a new pilot bushing
    Installed a new clutch kit
    New wheels & tires


    Thanks in advance,
    Mark B
    No F-Body right now
    Tags: None
  • #2
    How were you able to couple the LT1 to the T5? What flywheel did you use? Did the tranny input shaft fit firmly into the pilot bushing? What driveshaft are you using? Where is the front of the torque arm attached?

    The ES Poly mounts are made so that if the polyurethane breaks, the upper and lower metal parts will be interlocked to prevent the trans from lifting off the cross-member. Have you verified that the mount is actually broken?
    Fred

    381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

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    • #3
      I used the T5 Flywheel & a new T5 Pilot bushing. For some reason getting the input shaft into the pilot bushing was very tough. I really had to force it in. Im running an aluminum 4th gen driveshaft. The torque arm is attached to the tail of the T5 using the stock mounting bracket.

      I havent gotten under the car to check the trans mount, but it feels like a broken trans mount. The shifter moves up & down when I apply throttle to lower gears. However, it doesnt hit the trans tunnel like my stock mount let it do when it broke a few years ago.
      No F-Body right now

      Comment

      • #4
        Since the LT1 has the big balance weight on the LT1 flywheel, did you match the balance of the new flywheel to the LT1 flywheel?
        Fred

        381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

        Comment

        • #5
          I didnt realize I needed to do that. What does the weight do? Does it just balance the flywheel? Or does it counteract some imbalance in the LT1 crank? How can I do this without the stock LT1 flywheel?
          No F-Body right now

          Comment

          • #6
            Originally posted by Mark B
            I didnt realize I needed to do that. What does the weight do? Does it just balance the flywheel? Or does it counteract some imbalance in the LT1 crank? How can I do this without the stock LT1 flywheel?
            There is a mfg specified balance. The LT1 is externally balanced and I don't know if the spec is the same as a SBC in your year. My neighbor balanced mine on a machine that measured the balance and the offset from #1@TDC. The spec was something like 90 grams at 120 degrees. Anybody who has a crank/flywheel balance machine should know the spec. He did not need the crank to balance it. Mine was something like 25 grams off and I could feel it. He put it right on the number and it did cure it.

            However this would be engine RPM related not speed of the car related. If yours is speed of the car related it is after the transmission most likely in the driveshaft.

            As for the trans mount a hard poly bushing will add more vibration to the car.
            2002 Electron Blue Vette, 1SC, FE3/Z51, G92 3.15 gears, 308.9 RWHP 321.7 RWTQ (before any mods), SLP headers, Z06 exhaust, MSD Ignition Wires, AC Delco Iridium Spark Plugs, 160 t-stat, lots of ECM tuning

            1995 Z28, many mods, SOLD

            A proud member of the "F-Body Dirty Dozen"

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            • #7
              Another note: the car will not pull past 110mph. Not that thats a huge deal cause I wont get that fast on a regular basis anyway. But it may diagnois my problem.
              No F-Body right now

              Comment

              • #8
                Originally posted by Mark B
                Another note: the car will not pull past 110mph. Not that thats a huge deal cause I wont get that fast on a regular basis anyway. But it may diagnois my problem.
                Did your custom tune take the speed limiter out?
                2002 Electron Blue Vette, 1SC, FE3/Z51, G92 3.15 gears, 308.9 RWHP 321.7 RWTQ (before any mods), SLP headers, Z06 exhaust, MSD Ignition Wires, AC Delco Iridium Spark Plugs, 160 t-stat, lots of ECM tuning

                1995 Z28, many mods, SOLD

                A proud member of the "F-Body Dirty Dozen"

                Comment

                • #9
                  If it was an unbalanced flywheel, wouldn't it get worse with just rpms, not speed? Just wondering, I know the flywheel is probably the culprit.
                  Greg W. in West Michigan
                  1992 Formula WS6-A/R Rims, Stock L05 swap, Former Abuse Victim
                  1983 Z28-Parts car- *Sold*
                  1984 Z28-305 HO Auto *Sold*
                  1986 Camaro-V-6 5Spd *Sold*
                  1984 Camaro-V-6 Auto *Sold*
                  <Motor out

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                  • #10
                    Well, got some more info...

                    Doesnt vibrate at all in 4th gear @ 80mph
                    Vibrates like crazy in 5th gear @ 80mph


                    Bad trans?
                    No F-Body right now

                    Comment

                    • #11
                      Originally posted by Mark B
                      Well, got some more info...

                      Doesnt vibrate at all in 4th gear @ 80mph
                      Vibrates like crazy in 5th gear @ 80mph


                      Bad trans?
                      Could be. If the vibration were worse in 4th, that would tend to point at the flywheel or engine related imbalence. The fact that it doesn't do it in 4th at 80 yet it does vibrate in 5th could be the trans or the trans mount.

                      Comment

                      • #12
                        I put a stock rubber trans mount on it yesterday & it helped a little bit... But the problem is still there.
                        No F-Body right now

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