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OT: Hotrodders-Modulink Auto Trans Modulator?

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  • OT: Hotrodders-Modulink Auto Trans Modulator?

    I know there's a few hotrodders here and I'm hoping one of them can help. Some years back I recall seeing a cable operated vacuum modulator replacement for cars with really hot cams and automatic transmissions. It tied into the throttle linkage to sense engine load rather than using manifold vacuum. I believe it was called Modulink. I can't seem to find these online. Who makes(made) them? Still made? Anybody have experience with them?

    The application in mind is not hotrod related. A friend has a GM P30 truck with TH-400(475?) trans & 6.2 diesel engine. The vacuum pump is mounted crooked, and he said fixing it will not be easy. He wants to do away with the mechanical pump(easy) and install an electric vacuum pump. Brakes are hydraulic boosted, modulator is only vacuum user. I suggested that one of these mechanical linkages may be a better, more reliable solution. Any comments?


  • #2
    I'm not sure I've ever heard of such a thing. Electronic, maybe- few modern autos have a vacuum-actuated modulator, instead using a servo controlled by the engine management computer (that does, however, typically have a manifold absolute pressure sensor, so the ECM does reference "vacuum" to a certain degree.)

    The problem is, the trans was designed to reference manifold vacuum, which is an excellent indicator of engine load, and often has little corellation to throttle position.

    I would imagine that if such a thing was ever available, it likely failed as a marketable product because it didn't or couldn't do what it was intended to do. (Like those old "water injection" systems- anyone recall those?)

    Doc's Machine. (Probably not what you expect.)


    • #3
      Yeah, I can't imagine such a system working correctly to replace the modulator. It does not account accurately for varying load due to incline and such, though it may work almost as well as the diesel systems did, which was never quite right anyway. But at least the typical diesel vac pumps were tied directly to engine rpm, not just throttle position.

      Perhaps you are confusing it with the TV cable of later model 700R4s and the like?
      Master Floor Sweeper


      • #4
        B&M years ago did make such an item for use on engines fitted with a blower.
        A search of their site shows up nothing.

        However This may be just what you need. Looks like you may need to supply your own cable etc.


        • #5
          Huh - a mechanical modulator...

          Thats pretty cool, i've only seen a very limited selection of real radical hotrods but the ones i've seen with A/T's used a manual valvebody and ratchet shifter. I always thought it was just for the extra control it gave them, maybe it was also partly to compensate for the fact they had just about no vacuum.


          • #6
            WOW, Blast from the past. The B&M modulink! Holy smokes I had forgotten about that thing.
            Well IMO, it is so easy to either build your own manual valve body or just purchase one that such a gizmo is a waste of time and I don't think it's available anymore.
            Th400's are great transmissions. Possibly one of the all time best trannys Gm ever made. Super simple to rebuild and modify and very robust with a few easy mods.
            Personally I like the forward manual valve bodys as they retain 2nd gear band function and braking for street use. And it is fun to shift and nice to have full control.I mean it's not like it's a clutched manual. Flick the shifter with one finger at any time, under full power or coasting. Just use common sense and unless you need to drive with a cell phone and coffee cup a full manual auto is great fun on the street.
            Oh, and I hate ratchet shifters. Junk IMO. A gated shifter is the only way to go IMO. But it's just a personal preference.


            • #7

              Google "performance automatic transmissions"
              I used to work for the owner, Tom Cyr, he pioneered most of the trans brakes for Ford C4 transmissions for drag racing applications. He is beyond any doubt the smartest automatic trans guy I ever met. His shop was the last automotive shop I ever worked for before hanging up my wrenches in 1995. His inate knowledge of all things transmission far surpasses anyone I have ever known in 18 collective years in the bizness. He sold off the standard repair biz to just concentrate on racing transmissions. If any one knows about these modulaters it would be him. He may even have a better idea.
              Robert in Santa Cruz.
              grumpy old fart