Torque Converter Identification

Transmissions and Rear Ends

  1. Bruceynz

    Bruceynz Well-Known Member

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    Hi Guys,

    I have a 904 trans that came with my engine, I am sort of kicking myself for not using it now, its a non lock up unit. But the guy I bought it off said it had a small stall, he also told me the engine had a small cam as well! 9 inch of vacuum, small hmmm me thinks not! So his definition and my definition of small were quite different! So I suspect the converter that I have is a higher stall than stock but how do you tell what it is, does the color give it away? I can't find any markings on it, the ring gear looks like its new, its got balance weights on it. Can anyone offer any suggestion to what it maybe?

    IMG-20160808-WA0002.jpeg


    IMG-20160808-WA0004.jpeg
    Thanks
    Bruce
     
  2. Aspen500

    Aspen500 Well-Known Member

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    The color has nothing to do with stall speed, just whatever color the company uses.

    It appears that's a standard, low stall converter. You can tell by the ring gear being only slightly larger than the converter itself. Higher stall would have a wider ring gear.

    This is a pic of a stock Chrysler high stall off a '73 340 Challenger Rallye that I had EON'S ago (and wish I could have kept.......)
    Notice the ring gear. Higher stall converters are generally smaller diameter.

    What a converter actually "stalls" at depends a great deal on the engine in front of it. A low compression 250 ft lb torque engine may stall at 1,700 rpm, same converter behind a high compression engine with 500 ft lbs of torque may stall at 2,500.

    The weight in your pic is a balancing weight for the converter. If it was for a 360 (or '73 340 as they were cast crank also), it would have weights like the 2nd photo below (in the 1 and 2 o'clock positions). Of course an aftermarket converter wouldn't have the external balance weights and you'd need a special flex plate with the weights instead.


    DSCF0012.JPG
    DSCF0001.JPG
     
    Last edited: Aug 8, 2016
  3. BudW

    BudW Moderator Staff Member

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    One thing not mentioned is what transmission type are you using?

    The torque converter (pic below) appears to be a 727 style converter (appears to have the larger hub).
    The 904/998/999 converter has a smaller hub and will not interchange with 727 converters (see red arrows on first picture).
    I don’t have hub measurements to give – but a 904 hub will fit inside of a 727 hub with a lot of wiggle room.
    IMG-20160808-WA0002.jpeg


    All 904/998/999 torque converters all use a 10¾” flexplate (see blue arrows on second picture).
    727 High Stall converters also use the 10¾” flexplate.
    727 Low Stall converters use a larger 11¾” flexplate.
    DSCF0001.JPG

    Another issue is non-lock up vs lock up converters are not interchangeable.
    All lock-up converters DO NOT have a drain plug (see second picture – pink circle – generally opposite side of the weights, if equipped).
    Many non-lock up converters do have a drain plug – but not all. In the Mid ‘70’s Chrysler stopped adding them. IF you have a torque converter with a drain plug – it will be a non-lock up version.


    Still not sure what you have? Time to count splines (inside of the hub).
    ’67 up 727 non-lockup has 24 splines
    ’78 up 727/518 lockup’s have 23 splines
    ’68 up 904 non lockup has 27 splines
    ’78 up 904/998/999/500 lockup’s have 26 splines.

    ’78 was the changeover year to lockup converters – but a good number of vehicles built after that date were set up from factory for towing and special orders, come with non-lockup converters.


    Non-lockup transmissions are preferred for a performance application and have been for a long time – but I disagree somewhat.

    There are a lot more aftermarket performance torque converters out there for non-lockup’s - but more and more, the lockups are gaining ground. One type is not “stronger” or “weaker” than the other.

    For racing a non-lockup might be preferred.

    For mostly street usage or daily driver – the lockup converter will give you 10-15% better fuel mileage. My F/M big block conversions will be lock-up, for my intention is to drive them - a lot.
     
  4. Bruceynz

    Bruceynz Well-Known Member

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    Its off a 904 trans early 1974 model from memory, has balance weights on converter for a 360
     
  5. Aspen500

    Aspen500 Well-Known Member

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    Just to add a little to the lock-up converters. On anything but light accel from a speed where the converter is locked, the clutch will disengage so it never really has to hold all that much torque. Diesel pickups have lock up converters and the newer ones have what, 700, 800 ft lbs of torque or more with very few, if any, converter clutch failures. Heard the 2016 RAM Cummins has 900 ft lbs of torque (holy..........)
    One way so many newer vehicles are rockets out of the hole. They use relatively high stall speed converters but then at cruise the TCC locks or modulates and you're in mpg mode. Kind of the best of both worlds.
     
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  6. Bruceynz

    Bruceynz Well-Known Member

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    Its quite interesting, I have changed the rear end from 2.2 to 3.21, so now the trans goes 1 2 3 and instant lock up. I think I need to get myself a lockup stall converter if there is such a thing for a 904? Oh I was looking at the build sheet and it says my car has an A999 installed, I dunno why but always thought it was a 998 :confused:

    I am going to change the lock up spring to a heavier one I have bought later on.
     
  7. BudW

    BudW Moderator Staff Member

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    My ’97 Dodge diesel pickup 5 speed makes 215 HP / 440 foot pounds of torque (peak torque is at 1600 RPM !) and that is moving my 9,000 pound truck (yes, 4½ tons) – and it scoots along pretty good for a twenty year old truck with 240k miles. Also, for being stock, I also get about 24 MPG on the freeway (as long as I keep my foot out of it).

    The ’17 Ram pickup diesel is reported to have 385 HP / 900 foot pounds of torque (MPG and vehicle weight is not yet known).
     
  8. BudW

    BudW Moderator Staff Member

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    904, 998 and 999 transmission are the same basic transmission - but do have some minor differences to differentiate them. For all practical purposes, calling any one of them a 904 is good enough for me. The only person who is concerned will be the parts guy, if you need to get a specific replacement part - and for that, he will use the number on the side of case (so again, not a biggie).

    Note: Bruceynz, your first (green) converter still looks like a 727, to me.
    Also, Aspen500’s converter looks like a 904, to me.
    Without measurements, I could be wrong on both accounts. My eyes don’t work as well as they did 30 years ago.
     
  9. Bruceynz

    Bruceynz Well-Known Member

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    its a 904 converter, I have a 727 one on the floor as well and its bigger, It came with a 904, its slips into the 904.

    Umm 998 4 clutch packs, 999 5 clutch packs is as much as I know the differences were. In the lates 70s the 999 went behind 360s
     
  10. BudW

    BudW Moderator Staff Member

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    Smiles,
    I'm still going to call them, a 904.
     
  11. Bruceynz

    Bruceynz Well-Known Member

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    didn't the 904 start off as a TF6 for the slant, 3 clutch packs and then beefed up later on to handle 318 and 360s?
     
  12. kkritsilas

    kkritsilas Well-Known Member

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    TF6 is the marketing name (Torqueflite 6); they were always A904s by part number.Some 3 clutch pack A904s were used in the milder 273 V8s in lighter cars. I think they started to increase the clutch packs when the 318s and 360s started to be used in the pickups and vans.

    A999s are on both of my 318-4BBL cars (Mirada CMX and Cordoba), so not 360s only. There is am A998 in my base Mirada 318-2BBL. I don't know if it has to do with the slightly higher power of the 318-4BBL cars, or if they stopped making/using the A999 in 1982 (base Mirada is a 1982).
     
  13. Bruceynz

    Bruceynz Well-Known Member

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  14. BudW

    BudW Moderator Staff Member

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  15. Bruceynz

    Bruceynz Well-Known Member

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    Good news so that might be the go! I have the correct speedo gear for my tire size and diff ratio, I have a new neutral start switch as my reverse lights seem to have stopped working and I have a spring to increases the lock up speed on the auto, so I might do all that at once, drop the auto out and change the TQ at the same time. Small problem that TQ converter on ebay does not ship over seas, hmmmm
     
  16. 80mirada

    80mirada Well-Known Member

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    Summitracing has them
     
  17. BudW

    BudW Moderator Staff Member

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    Might look into a torque converter specialist.
    I don’t like an advertised stall speed - because engine size and a number of other factors can/will change stall speed.

    Example that same converter behind a /6 could be a 1200 RPM stall speed.

    I would recommend calling a specialist and telling them what you have and what you want to do - and they will get you what you need.
    Yes it costs a bit more - but there are no questions unanswered and you generally get a better quality part.

    The next question is, has your 360 been balanced internally?
    If not, does it have an externally (360) balanced flex plate?
    If not - then you will need to either get a “360" balanced flexplate or make sure the replacement converter has the appropriate weight(s) on it.
    A balanced flex plate is the best answer.
     
  18. Bruceynz

    Bruceynz Well-Known Member

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    Have a B&M 10239 balance flex plate for the 360 and running 318 converter
     
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  19. Justwondering

    Justwondering Well-Known Member

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    I don't want to hijack this thread, but I'm having trouble sorting this out.
    I've been reading things on the web trying to understand, but I just don't get it.

    Whats this stalling, torque converter, balance plates? Isn't stalling a bad thing? I kinda get the torque converter but if its round how can it be unbalanced? Is it something inside it that gets knocked loose?

    Why is one that locks up better/worse than one that doesn't lock up? Why the drain plug ? Does it spew fluid somewhere if it locks up to reduce pressure somewhere?

    I am woefully ignorant on this issue. What I'm finding online assumes I know more about engines than I do.
     
  20. kkritsilas

    kkritsilas Well-Known Member

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    Stall speed is the rpm at which the maximum torque multiplication happens. It has to do with the internal design of the fins and the angle at which they are at. It should be matched up with the torque peak of the engine. That being said, it varies a lot with the input torque, as BudW pointed out. It is one of the main specifications. The higher the stall speed, generally, the smaller the diameter of the torque converter.

    Lockup torque converters are more efficient than non-lockup converters when they are locked up. All non-lockup converters have some losses because they are relying on the fluid alone to move the car. A lockup converter uses a mechanical device (sprag clutch is the name, I think) to mechanically join the input and output shafts, eliminating the losses of the non-lockup converter. This is only during steady state highway cruising, and has the added benefit of slightly lowering the transmission fluid temperature, and engine rpm as well. The efficiency increase is not huge, but it is noticeable. It would be anywhere in the 5-15% range in terms of gas mileage. A lot of peformance oriented people don't like the lockup converters, as they believe that the lockup mechanism is prone to failure. For street cars, it is a benefit in many ways.

    The torque converter is not unbalanced, the 360 engine sort of is. The 360 is designed to be in balance with the torque converter and flex plate/flywheel attached (i.e. externally balanced). Weights are added to the flexplate or the converter to bring the entire assembly into balance. The 318 is internally balanced, which means without the flex plate/flywheel or the converter attached, the engine is in balance. So all 360 torque converters/flexplates will have extra weights added to bring the entire assembly into balance. The 318 converters may have weights, but only the balance the converter, not the entire engine assembly as well. The 318 converter will have fewer and smaller weights. The weights to balance the 360 can also be added to the flywheel alone, permitting the use of a 318 converter. B&M for one makes a flexplate that balances a 360 properly. I believe that the factory used weights on the converter for 360s.

    Torque converters, even if they are round, can have imbalances, just like wheels can. Wheels are round, yet they need to be balanced properly. Torque converters are the same, except that the standard 360 torque converter also has weights added to bring the engine into balance as well. You can think of the 318 converter as being balanced on a balancing machine. The 360 converter is like a wheel being balanced on the car, where it balances not only the wheel, but the disk brake rotor as well; in the 360 case it balances out the engine as well.

    All that being said, you can, with the proper machine work, internally balance a 360. It involves adding denser weights onto the crankshaft, and is usually done during an engine teardown/rebuild.

    If you use a standard 360 torque converter/flexplate on a 318, you will get severe vibration, as the added weights on the 360 torque converter/flexplate will throw the 318's balance off. If you use a 318 torque converter on an externally balanced 360, you will also have severe vibration, as the added weights to balance the engine are missing.

    The drain plug on the converter is a convenience when changing transmission fluid. The converter is full of transmission fluid, and when changing transmission fluid, to get the fluid out of the converter takes a flushing operation without a drain plug on the converter. With the drain plug on the converter, you just open up the drain plug and it runs out.
     
    Last edited: Aug 10, 2016
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