Torque converter questions

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by SummitXMK, Oct 9, 2001.

  1. SummitXMK

    SummitXMK 1/2 ton status

    Jun 6, 2001
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    I am totally confused about torque converters. Could someone explain to me about stall number and what the different ones would be needed for. Also about lockup or non lockup versions. I have a 78 Blazer do I even have a lockup. What if I upgrade to a Raptor. (when I win the lottery) Then what torque converter would I want. I think I am about in need of a new th350 so I thought I would check this out. Maybe I should also get a new torque converter. Anybody bought summits rebuilt tranny. 600 bones doesn't sound to bad. Of course I'll burn the on eI have up in the middle of snowmbile season and end up with a used one out a junk yard for 200 but hey maybe it will make it 6 more months!! hah!

    78 K5 Cheyenne 400 th350 203 With lots of miles
  2. Leadfoot

    Leadfoot 1/2 ton status Premium Member

    Nov 28, 2000
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    Western Massachusetts
    I'm no expert, but here's a shot. A converter takes torque output from a motor and multiplies it to transfer it to the input of the tranny. Up until a certain RPM the converter will slip, when the RPM is reached (Stall) the converter will engage and transfer power. The stall is dependant upon the size and internals of the converter, but it is also dependant upon the output of the motor. A converter that stalls at 3000 RPM's behind a 305 may engage at 2300 RPM's behind a 502. The reason for different stall speeds is A.) Due to different motor outputs, B.) due to differing launch needs. A motor that is built for drag racing and doesn't hit the power band until higher up in the RPM range would want a higher stall (so the motor starts off in a higher RPM range where the power is and since it produces more torque, the actual stall speed may be lower) plus the motor will redline at a higher RPM, but a street driven vehicle that redlines at 5700 would want a lower stall converter for more useable RPM's. Also the higher the stall the longer the converter "slips" and the more heat is generated (remember heat is an automatic tranny's enemy). Drag racers can use really high stall because they make a pass and shut down, they are not under steady long duration use. You want to determine your usage and motor characteristics before selecting a converter. Too low a stall and you will have to hold two feet on the brake to keep the tranny from pulling you at a stop light, and too high and you will leave rubber at every takeoff, but it will be hard on parts and generate alot of heat. The best thing to do is talk to a tranny rebuilder, tell him/her what kind of tranny you have, what tire/gear combo, and motor specs and they will give you a range to look for.
    I don't know when GM started with the lockup converters, but essentially there is a clutch inside the converter to lock the converter to have a 1:1 relation with crank rotation. In a normal converter there is alway a little slip and the converter internals spin slower than the motor. Lockup converter pro's: Keeps tranny cooler and helps lower rpm's save fuel....con's: There is clutch in there that can (and usually does) wear out, you must plumb a vacuum switch and brake over-ride switch in (which controls lock and unlock), and when it doesn't engage at the proper RPM (usually due to poor tire/gear combos) the clutch can wear out and lead to severe converter shudder. I prefer to run a manual control on the converter lock. Some also say the lockup version of the TH350C is weaker than the regular TH350 (but I don't know for sure).
    Hope this helps. If any thing in here is wrong please correct me.

    See my rig at <a target="_blank" href=></a>

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