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Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

uid 24778's pic
posted by  khanawalt on  Sun Oct 22 18:58 CST 2006
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last visit: Thu Dec 6 21:03 CST 2007
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They are both 1989 models, and my 740 GL (no turbo) had a lock-up torque converter while my 780 Bertone Coupe (turbo B230) doesn't. Seems like they'd put a lock-up TC in their flagship model from that year. Strange, isn't it? Anyone know why?
--
Kenny H Three SUVs, four cars and seven motorcycles








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    Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

    posted by  mapleleafer on  Mon Oct 23 23:30 CST 2006
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    It has nothing to do with flagship or basic model. It also has nothing to do with the converter clutch being able to handle the power of the turbo. That's ridiculous, many higher HP (than B230FT) Toyota Supras use the lockup equiv of the AW71/72 without failure.

    It is all because the drop in engine speed at 49-51 MPH, where the converter would lock (it is speed based, not load based), caused too much of a power loss on the lower compression turbo engine so Volvo chose to omit it. Euro turbos, where highway speeds are 110 km/h (70 MPH) or higher DO get the lockup version. Don't get too upset over it... the feature adds only 1-3% improvement at best, and in this case, possibly less.








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    Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

    posted by  mcduck on  Mon Oct 23 02:48 CST 2006
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    Apparently, the lock-up won't handle the extra power; no turbos had 'em.








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      Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

      posted by  Will740turbo on  Mon Oct 23 19:42 CST 2006
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      That still bothers me. I would think that the turbos would benefit more since they waste fuel at cruising speed anyway (mild turbo rotation, and a little actual boost above ~45). I think the issue is that Volvo expected people with heavy feet would drive the turbos and the lockup might not unlock quickly enough for their liking, hence 1) crimping driving style or 2) functioning poorly at higher miles.

      -Will
      --
      1990 740 Turbo, on its way to stock specs, maybe beyond








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        Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

        posted by  tvpierce on  Mon Oct 23 23:23 CST 2006
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        Some late model '94 and '95 940 turbos came with lockup TC -- I stress the word SOME. It certainly seems to be the exception.
        If you were so inclined, you could find a '93 or later non-turbo 940, that would have the stronger AW-71 (like turbos were always equipped with) but it has a locking TC. I've considered the swap, because I too despise that this car came without a lockup TC. But I have to say, after adding a trailer hitch and towing a trailer with my 945T, the non-locking TC makes this very nice towing rig. But in all other circumstances, I wish it could lock.

        Jeff Pierce







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          Why does my 740 have a lock-up TC, but my 780 doesn't? 700 1989

          posted by  mapleleafer on  Tue Oct 24 02:07 CST 2006
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          Nope! The actual differences between the 70 used on the NA and the 71 used on the turbo have to do with thrust bearings and the OD clutch hub, slightly different yet on the 72. Just as the V-6 AW-71 was valved differently than the B230FT version, the B230F version uses less clutch plates and is valved for softer and earlier shifts than the turbo version. It is functionally an AW-70L with a slightly beefier driveline, but not appropriate for turbo duty.







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