Page 1 of 5 123 ... LastLast
Results 1 to 10 of 46

Thread: Opened up my gearbox after hardcore road racing on 800ft/lb tq engine.

  1. #1
    Banned Feedback Score 11 (100%) J. Fast's Avatar
    Join Date
    Sep 2010
    Owner Since
    - O - SIX -

    Location
    Colorado, USA
    Posts
    2,755
    Thanks
    412
    Thanked 203 Times in 143 Posts

    Opened up my gearbox after hardcore road racing on 800ft/lb tq engine.

    This is the third gearbox I’ve seen with expelled shift forkroll pins. I think when they get hot and vibrate the pins work themselves loose. I road course this gearbox and lean on it REALLY REALLY hard with no lift shifting and full on driving to the limit. I slowly started losing 3rd gear last week while making large left hand sweeping turns registering in the 1-lateral-G range. After about 120 consecutive laps third gear began to sneak some grinding. After about 140 laps I was consistently grinding and then suddenly I was blocked outof gear entirely and 3rd gear disappeared altogether. I opened up the gearbox and these were my observations.










    Shift fork roll pin is expelled on one fork (it snapped inhalf when I tried to pull it): gahh: The roll pin worked itself out it allowed the shift fork to slide toward the end cover about 5mm. I observed the fork resting on 4th gear entirely. It was locked below the hub/slider keeper step and consequently didn’t have enough reach to grab third because of how far it slid down the shift fork rail. At first I thought I rounded all the teeth on third gear because I ground it at least 20 times at 7500 rpms and then I finally whizzed the gear and it hummed for a second or two and blocked me out. After further inspection the gear/hub slider teeth are in good shape and it appears I just need to replace the synchro. I also discovered I melted the oil splash pan at the mount. Also appears the adjacent shift fork roll pin is starting to work itself out also (it’s projecting about 3mm).

    Surprisingly, I didn’t observe any metal flakes or chunks in the gearbox or in the fluid I drained. Just before I hit the road course I drained my Mitsubishi OEM Diamond Gear Lube and swapped in Royal Purple 75w-90 Full Synthetic Hypod Gear Oil. Can't say wether or not the full synthetic was a contributing factor. For the most part everything else in the gearbox is good to go. The synchromesh looks good on 3/4 but I’m going to swap in new synchros for my own sanity.
    Last edited by Alan92RTTT; 07-05-2013 at 03:21 AM.

  2. #2
    There will be Blood! verified Feedback Score 4 (100%) CoopKill's Avatar
    Join Date
    Sep 2010
    Owner Since
    1997

    Location
    In Sane!
    Posts
    4,757
    Thanks
    1,095
    Thanked 451 Times in 332 Posts
    Weak, old roll pins, or metal is just being flexed enough with extreme use they move out of place?

    Help them, for they know not that which they do not know!
    CoopKill's Mistress Makeover Thread!
    "Punk, Nutswinging, Small Time, Asshat, Monkey, Jerkoff, Loser that rides on other peoples accomplishments!" . .

  3. #3
    One day....it will be on 4 wheels. supporter Feedback Score 2 (100%)
    Join Date
    Sep 2010
    Owner Since
    2004

    Posts
    1,822
    Thanks
    154
    Thanked 37 Times in 30 Posts
    You got lucky... Taz popped the box when his DID engage both gears at once

    guess it's time for upgraded pins
    Building a House, Car Mods on hold!
    1996 GTO, Owner since 2003.

  4. #4
    Banned Feedback Score 11 (100%) J. Fast's Avatar
    Join Date
    Sep 2010
    Owner Since
    - O - SIX -

    Location
    Colorado, USA
    Posts
    2,755
    Thanks
    412
    Thanked 203 Times in 143 Posts
    If you look at the first picture, you can see the roll pin is starting to work itself out on the 1/2 shift fork. You can also see that the 2nd shift rail over is projecting a little bit higher than the others. Thats the fork binding on 4th gear.

  5. #5
    Banned Feedback Score 11 (100%) J. Fast's Avatar
    Join Date
    Sep 2010
    Owner Since
    - O - SIX -

    Location
    Colorado, USA
    Posts
    2,755
    Thanks
    412
    Thanked 203 Times in 143 Posts
    These are the original shift forks. They have never been disassembled or modified. What I was most surprised about was how brittle the roll pins are. When I tried to pinch them with vice grips they snapped and when I tried to punch them out they chipped. I'm going to have to add opening my transmission and checking the roll pins to my nut and bolt list.

  6. #6
    Forum User Not Verified Feedback Score 2 (100%) RealMcCoy's Avatar
    Join Date
    Sep 2010
    Owner Since
    2001

    Location
    Medford OR
    Posts
    1,426
    Thanks
    5
    Thanked 603 Times in 303 Posts
    I would assume it is the usage that contributed... That is not a real common failure. I have seen it happen on the selector shaft a few times, and I do feel the pins are a little bit suspect in their construction. My fix for the selector shaft is some thick wall spring steel 1/4" roll pins. You have to ream the hole slightly to use them as the factory ones are 6mm, but I've yet to see one move... I guess maybe it's time to consider the same treatment for the forks.

    The thick wall single wrap pins also allow you to drive a second smaller pin through the middle if you need make them even tougher...

    I don't remember where we sourced them, we've had them on the shelf for years, be they appear to be very similar to these: 1/4" x 1" Plain Finish Steel Slotted Spring Pin | Fastenal


    Real Performance Automotive (541)816-4500 www.FB.com/RealPerformanceAuto

  7. #7
    Member Not Verified Feedback Score 2 (100%) Erron Spalsbury's Avatar
    Join Date
    Sep 2010
    Owner Since
    1995

    Posts
    429
    Thanks
    45
    Thanked 85 Times in 50 Posts
    Good info, Jer! Glad it's something fairly easy to fix.
    www.stickyvinylgraphics.com
    Custom Stickers & Graphics

    www.chumpcar.com
    Regional Series Promoter for the ChumpCar World Series

  8. #8
    Member Not Verified Feedback Score 2 (100%)
    Join Date
    Nov 2010
    Owner Since
    2003

    Posts
    2,082
    Thanks
    113
    Thanked 276 Times in 210 Posts
    Seen it several times on cars that are drag raced. Bang the gears an that is a possibility, also broken select forks.

  9. #9
    Banned Feedback Score 11 (100%) J. Fast's Avatar
    Join Date
    Sep 2010
    Owner Since
    - O - SIX -

    Location
    Colorado, USA
    Posts
    2,755
    Thanks
    412
    Thanked 203 Times in 143 Posts
    It would appear the spring pins have undergone some type of annealing process but when heated they relax? I'm thinking maybe solid pins would be siffice to aid in keeping them from walking out? What about swapping the spring pins out for a tapered dowel and inserting a cotter pin? I was actually having a conversation with my dad about the issue this evening over dinner. He metioned in old muscle cars they used to drill holes and use tie wires on pins, dowels, and any bolt they didn't want to back out. I think that's a good idea but we're talking about potentional interference due to close proximity to gears... I would like to use something that won't temper and become brittle and snap later on. Any ideas on a fix for this? I don't think new pins are the answer...but? Open to discussion. What works?
    Last edited by J. Fast; 07-06-2013 at 01:20 AM.

  10. #10
    Member Not Verified Feedback Score 2 (100%)
    Join Date
    Nov 2010
    Owner Since
    2003

    Posts
    2,082
    Thanks
    113
    Thanked 276 Times in 210 Posts
    safety wire and bolt if enough room, or maybe a clevis pin....I'll have to take a look and see if there is enough room there. 100 ways to skin a cat...

Page 1 of 5 123 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
The 3000GT/Stealth/GTO Web History Project
3000gt.com
3000GT / Stealth International WWWboard Archive
Jim's (RED3KGT) Reststop
3000GT/Stealth/GTO Information and Resources
Team 3S
3000GT / Stealth / GTO Information
daveblack.net
3000GT/Stealth/GTO Clubs and Groups
Michigan 3S
MInnesota 3S
Wisconsin 3S
Iowa, Nebraska, Kansas 3S
North California 3000GT/Stealth
United Society of 3S Owners
3000GT/Stealth/GTO Forums
3000GT/Stealth International
3000GT/Stealth/GTO Event Pages
3S National Gathering
East Coast Gathering
Upper Mid-West Gathering
Blue Ridge Gathering