Torque converter failure mode?

Discussion in 'The "Juice Box"' started by techg8, Jul 13, 2022.

  1. techg8

    techg8 The BS GS

    So driving my 73 Century a couple months back I got stranded with no forward or reverse.

    It's a 200-4r built up by yours truly with a 2200 stall converter.

    The trans had worked fine for a year or two. Regular street driving with a few racing.

    It developed a slippy feel. Barely noticeable. Only very occasionally after a hard pull. So I ignored it to make it go away.

    Fast forward to the breakdown. I took the car out cold and got a good hard acceleration on it at which point it slipped like crazy. Eased down the road and it got worse fast until I lost forward and reverse.

    Sitting on the road in D. The engine would rev like I was in neutral but I could lightly hear something sounded like splines slipping or like that. Or loose gears meshing.

    Shut it off dragged it home left it 2 months.

    Finally dropped the trans figuring I broke something hard inside.

    Full disassembly reveals no damage. Clutches, steels, hard parts all good. Air tests fine. Pump is good. Fluid is pristine.

    I need to look at the valve body still but I imagine that will be fine.

    The only thing I can imagine is a bad torque converter.

    Losing both forward and reverse at the same time. Trans internals good. Wtf?

    I have not had a converter failure before. Is this a failure mode?

    Anyone have this happen?
  2. techg8

    techg8 The BS GS

    ...and the converter was kind of a pain to remove. On the edge of abnormal but not quite.

    I inserted the input shaft and it spun ok. I expected to hear and feel lots of metal in there but I didn't. A little scrape is all every rotation.

    Did the same with the pump and it rotated pretty smooth. Nothing abnormal.
  3. TrunkMonkey

    TrunkMonkey Totally bananas

    The pump is the "heart" of the transmission.

    It provides volume (cooling and lubrication), pressure (to properly apply clutches to prevent slipping that can create excessive heat and breakdown of the oil and burning and hot spotting to the frictions and steels in the clutch pack).

    Once low pressure and/or metal are liberated into an auto transmission, the cascading failure is without a doubt.

    Clogged filter. Low pressure. Lack of timely clutch apply (burnt clutches/steels). Rapid oil breakdown. Pump failure from metal/rapid wear of gears and pocket. Rapid wear of hard parts, (planets/sun/ring gears) bushings, bearings and shims, spools and bores in the valve body, accumulators, and failure of torque converter.

    Any and all of these things can happen within seconds in high power application, or within minutes/few miles of "normal driving", once a condition that starts the cascade of failures begins.

    You can never, ever "drive" a transmission out of a "failing" condition. Once it slips or acts up, the damage is done and the "symptoms" are merely indicators of that damage.

    Adding fluid, doing a service, adjusting anything that can be adjusted, is all, too little, too late.

    Best to pull the transmission, start the post mortem, and save the further destruction, rather than "pushing" through, and losing in the end. The longer it is operated in a compromised state, the more damage that will occur to all components.

    (All of these things are why my uncle developed a "racing" transmission that negated all the fluid actuation of an automatic, and relied on the same clutches applying, but with brute force, "manual" apply, and only needed a clutch to launch. Developed almost 50 years ago.)
    techg8 likes this.
  4. sean Buick 76

    sean Buick 76 Buick Nut

    I think if it were me I would go the expensive but safe route and have a pro rebuild it and a new converter.
    techg8 and TrunkMonkey like this.
  5. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Take a close look at the stator splines.

    The next step- toss the 200 in the dumpster and look into a 4l80e. You'll be much happier.
    TrunkMonkey, rmstg2 and techg8 like this.
  6. techg8

    techg8 The BS GS

    bahahaaa! O ye of little faith

    The stator support splines are the hardened ones, and are fine. I will have a look at the converter again.
    Last edited: Jul 14, 2022
  7. techg8

    techg8 The BS GS

    I hear you but I dont spend money on my cars I spend time on them. I enjoy the experience and troubleshooting, even when it makes me crazy.
  8. techg8

    techg8 The BS GS

    I get what youre saying.

    My point is Ive got a trans that lost forward and reverse , but shows no signs of a failure so far, and I am looking for possible causes.
    70skylark350 likes this.
  9. techg8

    techg8 The BS GS

    I am tempted to think maybe I just got low on fluid. But I think I would have heard the pump whining with air in it. Hmmmm
  10. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I am planning on replacing the 200 in the Apollo. It's a stock rebuild with a shift kit, probably around 5k miles. most of which were behind a stock sbb 350. I don't want to hurt the trans with the 430. I'm in northern vt.. PM if you're interested
    techg8 likes this.
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The most common torque converter failure mode is stator problems.
    techg8 likes this.
  12. techg8

    techg8 The BS GS

    UPDATE: I just air checked the valvebody and it is fine. So all the hydraulic circuits check out and I dont see any internal damage. I am not an inexperienced mechanic, nor is this my 1st 200-4r. Does anyone see something I am missing? It just about HAS to be the converter.
    shifter51 and 436'd Skylark like this.
  13. flh73

    flh73 Gold Level Contributor

    Did you ever pull it into gear manually and it worked ok? This would spike the pressure and apply the clutch or band. Usually when they first start going it glazes the band and issues with direct clutch. If TV was set wrong or you were trying to hold shifts out could have stretch converter from over pressure. So that would be a bad converter but still need to address the cause. I'd still start with at least a new band, direct clutch, converter, verify governor and spring. Drive it light to verify and break in band etc. before raging on.
    techg8 likes this.
  14. techg8

    techg8 The BS GS

    I did try every manual valve position and got no movement at all. Like the engine and trans were uncoupled, or a shaft broke.
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Perfect opportunity to get one of Jim’s converters:)
  16. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I'm sure you checked, but is the rear diff ok?
    techg8 likes this.
  17. techg8

    techg8 The BS GS

    Yep. Right as rain.
  18. 12lives

    12lives Control the controllable, let the rest go

    Did you verify the TV cable movement to the valve piston?
    techg8 likes this.
  19. sean Buick 76

    sean Buick 76 Buick Nut

    The issue is if he spends $700 on a new custom converter and the trans has internal issues it will take out both the trans and converter. Use a junk converter till it’s sorted
    TrunkMonkey and techg8 like this.
  20. techg8

    techg8 The BS GS

    yes that is all good.

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