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1975 Plastic fantastic aka Corvette

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  • Originally posted by Bob Holmes View Post
    Sudden and abrupt changes in direction are usually a symptom of either...something is broken, or something is bottoming out or extending to its limit.

    You can also get self-steering if your trailing arm bushings are crap. Not a good thing unless you are setting it up to do that.
    that has to be it...

    so the next question - what heim joints do you like for suspension bits? I may use a johnny joint for the front and then regular heims for the locator arms....

    *guldstrand suspension is next up on the installation list.
    Last edited by SuperBuickGuy; December 24, 2012, 10:16 AM.
    Doing it all wrong since 1966

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    • Have you ever set up the alignment on the rearend? Have you bumped it to check if it is toeing out in compression or extension? Toe out at any point on the rear will cause it to try and pass the front end.
      I'm still learning

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      • it has been aligned (twice, actually)

        yet both issue seemed okay (toe, and camber - which can be set) .... but something has to be wrong, so I'll check it again.
        Last edited by SuperBuickGuy; December 24, 2012, 10:31 PM.
        Doing it all wrong since 1966

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        • This era of vettes were always squirrelly. Easy to get spun around. Not sure what caused it. Heavy front weight bias or rear suspension type.
          BS'er formally known as Rebeldryver

          Resident Instigator

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          • If they're like a Corvair, and I think they are, it might be a good idea to check the bolts that hold the yokes into the diff. If one is loose it can cause some camber changes under load, and affect the loading of the clutch plates in the posi unit. It's a long shot and I would think it would be making noises if that was the case but you never know.

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            • Originally posted by Mr4Speed View Post
              If they're like a Corvair, and I think they are, it might be a good idea to check the bolts that hold the yokes into the diff. If one is loose it can cause some camber changes under load, and affect the loading of the clutch plates in the posi unit. It's a long shot and I would think it would be making noises if that was the case but you never know.
              this got me thinking to a possibility. the internals in the 12 bolt are loose, but the left side. ... part of my near-future plans are to rebuild a differential for the car, I think I'll be doing it sooner rather than later...

              so
              3.08 gears (current), 2.73, or 3.23/3.36? My spreadsheet suggests 3.08 or 2.73 - however, I may be building a 302 for this car, so higher would be better....

              track day car, NOT drag race car

              so two questions:
              what gear/what motor?
              Doing it all wrong since 1966

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              • Originally posted by SuperBuickGuy View Post
                this got me thinking to a possibility. the internals in the 12 bolt are loose, but the left side. ... part of my near-future plans are to rebuild a differential for the car, I think I'll be doing it sooner rather than later...

                so
                3.08 gears (current), 2.73, or 3.23/3.36? My spreadsheet suggests 3.08 or 2.73 - however, I may be building a 302 for this car, so higher would be better....

                track day car, NOT drag race car

                so two questions:
                what gear/what motor?
                Why not split the difference and go 3.31..Transmission makes a difference too...I'm becomming a fan of the th700R4 or 4l60E..both have a lower 1st gear and an O/D4th
                Patrick & Tammy
                - Long Haulin' 2008, 2009, 2010, 2011, 2012, 2014...Addicting isn't it...??

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                • Originally posted by silver_bullet View Post
                  Why not split the difference and go 3.31..Transmission makes a difference too...I'm becomming a fan of the th700R4 or 4l60E..both have a lower 1st gear and an O/D4th
                  you hit on the head why I'm indecisive on the issue.... I already have 4 speeds - rpms at 1:1 4th gear at 3.08 would be the same as .82 at 3.23. Granted, at this point I idle around town in 3rd gear - which is a noisy gear - but other than that detractor....

                  I dunno - it's why I put this out there.... I need input other than mine alone

                  For baseline.

                  350 - it develops its power above 2800 rpm
                  the super t-10 has these ratios 1 - 3.44, 2 - 2.28, 3 - 1.46, 4 - 1.0
                  rear tire size 285/40 ZR 17

                  currently it has 3.08 gears in it..... one thing I hated above the Buick was at 70 mph I was at 3500 rpm (3.73 gears).... and as I really do want to wear this car out - I need it to be able to do prolonged blasts at 80 mph without breathing hard.... I also want it to do cones in 1st or 2nd gear....
                  I've been playing with this
                  Last edited by SuperBuickGuy; December 25, 2012, 01:43 PM.
                  Doing it all wrong since 1966

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                  • That's a wide ratio box. I'd think about something a little tighter, before worrying about rear end ratio.

                    I know that you said its been aligned a couple of times, have you checked its bumpsteer. That's not something that is normally done at "Johnny's house of alignment."
                    I'm still learning

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                    • With that steep first gear, anything steeper than 3.42 in the rear will make 1st gear all but useless. I have 3.06 1st gear and 3.36 rear and shift really darn fast.
                      BS'er formally known as Rebeldryver

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                      • Track day car begs the question - which track - and - do you have any typical lap speed data from guys in a similar class that you could back out to your tire size and gear ratios to optimize your gearing to keep the engine in it's highest torque rpm as much as possible on each lap.
                        There's always something new to learn.

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                        • Have you ever considered a TKO?.........has the four speeds you need and the 5th for overdrive.
                          I've had two TKO 600's.........running a 2.87 1st gear and 3.50 rear.
                          Thom

                          "The object is to keep your balls on the table and knock everybody else's off..."

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                          • Originally posted by Bob Holmes View Post
                            That's a wide ratio box. I'd think about something a little tighter, before worrying about rear end ratio.

                            I know that you said its been aligned a couple of times, have you checked its bumpsteer. That's not something that is normally done at "Johnny's house of alignment."
                            bumpsteer on the rear differential? doesn't bumpsteer come from changes to toe from the suspension cycle? I guess I'm having a hard time understanding how it could be in this case (where the rear toe was set at the factory, and never touched again) - why now?

                            let me ask another question - what would happen to a car that has different camber on each side? say -1* on the right, and one that changes from -1* at rest to +2* at drop....?
                            If the differential yoke on one side has a severely worn retainer, wouldn't the car would literally change the camber on the fly (pun intended).... wouldn't that tend to pull the car in only one direction when it unloads? another, seemingly unrelated/related issue - the posi isn't posi anymore - which suggest the disks in the differential are worn out.....

                            Monk - aren't multiple gears a crutch for a peaky motor? 2.73 gears and a SBC 427 coupled with a 4 speed would have all the pull necessary, right? I'm trying to think package rather than picking shiney bits which, while really cool, don't really do anything for the car.
                            Last edited by SuperBuickGuy; December 25, 2012, 10:03 PM.
                            Doing it all wrong since 1966

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                            • while I'm stewing the answers above.... more progress on another couple issues.
                              1) the clutch is a man's clutch - seriously, a man who can push 400# to disengage the clutch.... the fix is a different master cylinder - for those counting, this is number 3. 1st was 7/8, 2nd 1", now 5/8"... as this thing is beginning to seem like it needs a Randal zipper - I figured I'd help myself out (hard to hold the bolt inside the car while ratcheting on the firewall

                              that was round 1, round 2 came with bolts both the same length

                              out with the new


                              in with the new

                              which looks exactly like the old.... and 5/8" was the right choice..... thus, if you're going hydraulic, 5/8" to the GM pivot point is a good feel. Do not use the short master cylinder because it does not push enough fluid

                              2) carpet work
                              I finally ordered the last major pieces for the inside - so it's time to start buttoning this up
                              before

                              after
                              Doing it all wrong since 1966

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                              • Nice Work...The idea is as you perceived also...the idea of a close ratio gearbox with more gears is to keep the motor in it's powerband...a motor with a nice, fat, torqueband would be optimal with a wide ratio box...less gears...more torque...less shifting...more forgiving...
                                Patrick & Tammy
                                - Long Haulin' 2008, 2009, 2010, 2011, 2012, 2014...Addicting isn't it...??

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