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    HOW does failed tv bushing kill trans?

    Hi!

    So I've started interning at a local shop, and soon will be taking classes, to become a mechanic

    I asked two guys about the infamous tv bushing issue.
    I actually didn't even know what it did. For the first time I got to see my car up on a lift, and that was educational. There's lots you don't notice, because it's so inconvenient crawling around on your back with just 15" of jackstand clearance!

    So I understand, now, that what it does is link the throttle to a set of linkages that force the transmission into the next lower gear when the throttle is wide open-- i.e., when you accelerate hard. "passing gear." Don't laugh! I didn't know about "passing gear" last week

    SO. If that linkage breaks, why, really, should there be any negative consequence? You lose your automatic passing gear, so if you're in overdrive, your engine will start lagging as it can't maintain the torque to accelerate to pass. The correction, at worst somewhat inconvenient, would be to force the car out of overdrive and into drive, and once you've gotten in front of the car you're passing, shift it back into overdrive. And keep it in drive when first coming up the entrance ramp.

    I don't see how this can destroy your transmission in 20 miles if it comes undone. I only see that you'll have a hard time getting onto the freeway unless you downshift manually.
    Yet it's happened to people, who ruined their transmissions.

    What I am missing in my understanding of how it works/ what it does?



    thanks!!
    -Bernard

    #2
    TV stands for Throttle Valve. It is not simply a "kick down" valve like people commonly refer the function of a C6 and C4 linkage. The TV controls internal line pressure. There is no such gear as "passing" gear. It simply does not exist. What happens is that a 3 speed transmission downshifts to 2nd gear and a 4 speed transmission downshifts to 3rd or 2nd gear depending on tailshaft speed which effects the governor which alters transmission pressures. The valves within a valve body move based on fluid pressure overcoming spring pressure.
    In addition to altering shift points, low pressure means that the clutches and bands will slip. Slippage generates heat and destroys the friction material within a transmission.
    Last edited by Mercracer; 09-17-2010, 05:30 PM.

    Comment


      #3
      What he said. With a true kickdown linkage, it can be disconnected without any seriously ill effects, other than screwing with the shift timing. A C4 will not burn up if you unhook the rod. Most other (maybe all?) 3 speeds work that way. The GM TH400 doesn't even have a kickdown rod, it uses an electric switch on the throttle to handle WOT downshifts. The AOD and the GM 700R4 don't work this way, and must have the cable (or rod) connected and adjusted somewhere close to correct or the trans will smoke.
      86 Lincoln Town Car (Galactica).
      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

      91 Lincoln Mark VII LSC grandpa spec white and cranberry

      1984 Lincoln Continental TurboDiesel - rolls coal

      Originally posted by phayzer5
      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

      Comment


        #4
        Ahh.. I partially get it.
        I did realize that the passing gear is not true gear in its own right, just the next lower down gear-- hence "passing gear" in quotations.

        So other cars, it is just a kickdown linkage-- but the particular problem with the grand marqs is that it is more than that?

        How a transmission works in detail, and why on our grand marqs it affects transmission pressure to the point where it comes apart, I'm not sure I'll understand until I get a chance to see a transmission taken apart, and really grasp how it's put together.

        Oh btw, there were a couple detailed threads about how to change the bushing? Do I just pop out the old one and put in the brass one, 30 minute job (by the time I get my tools out, and put away again), no critical thinking required? Or is there some fine tuning and adjustment to be done?

        Comment


          #5
          TV cable directly controls the fluid pressure in the trans dependent on throttle position. A kickdown cable only activates a valve to engage a lower gear, any other time it is only along for the ride. TV cable is always an active part of transmission control, which is why everyone is very forcefull about ensuring its properly connected and adjusted.

          Alex.

          Comment


            #6
            If you have ever been in an aod car with the tv unhooked you would get a better picture its like is has no idea what to do, it goes through the gears into OD almost instanstly and hunts all over the place. No tv on an AOD is a serious no no, It controls when the tranny shifts based on throttle position.


            '90 LX 5.0 mustang
            Big plans

            Comment


              #7
              Originally posted by BerniniCaCO3 View Post
              Oh btw, there were a couple detailed threads about how to change the bushing? Do I just pop out the old one and put in the brass one, 30 minute job (by the time I get my tools out, and put away again), no critical thinking required? Or is there some fine tuning and adjustment to be done?

              There is some adjustment, sir.

              from an AOD transmission specific DVD:




              not from the dvd, with everything in the car
              Last edited by 1990LTD; 09-17-2010, 09:10 PM.
              sigpic


              - 1990 Ford LTD Crown Victoria P72 - the street boat - 5.0 liter EFI - Ported HO intake/TB, 90 TC shroud/overflow, Aero airbox/zip tube, Cobra camshaft, 19lb injectors, dual exhaust w/ Magnaflows, Cat/Smog & AC delete, 3G alternator, MOOG chassis parts & KYB cop shocks, 215/70r/15s on 95-97 Merc rims

              - 2007 Ford Escape XLT - soccer mom lifted station wagon - 3.0 Duratec, auto, rear converter delete w/ Magnaflow dual exhaust

              - 2008 Mercury Grand Marquis Ultimate Edition - Daily driver - 4.6 2 valve Mod motor, 4R75E, 2.73s. Bone stock

              Comment


                #8
                Originally posted by Mercracer View Post
                In addition to altering shift points, low pressure means that the clutches and bands will slip. Slippage generates heat and destroys the friction material within a transmission.
                And yet, "professionals" installing an AOD will still adjust the TV cable so that it's waaaay too loose.
                2012 Mazda5 Touring | Finally working on the LTD again!

                Comment


                  #9
                  Originally posted by 1987cp View Post
                  And yet, "professionals" installing an AOD will still adjust the TV cable so that it's waaaay too loose.


                  One transmission guy told me it was supposed to be like that because these are early shifting granny cars, after he took mine for a drive (I had adjusted the TV cable PROPERLY the day before) he said mine shifts way too late and hard. I thanked him and haven't been back to that shop since.
                  sigpic


                  - 1990 Ford LTD Crown Victoria P72 - the street boat - 5.0 liter EFI - Ported HO intake/TB, 90 TC shroud/overflow, Aero airbox/zip tube, Cobra camshaft, 19lb injectors, dual exhaust w/ Magnaflows, Cat/Smog & AC delete, 3G alternator, MOOG chassis parts & KYB cop shocks, 215/70r/15s on 95-97 Merc rims

                  - 2007 Ford Escape XLT - soccer mom lifted station wagon - 3.0 Duratec, auto, rear converter delete w/ Magnaflow dual exhaust

                  - 2008 Mercury Grand Marquis Ultimate Edition - Daily driver - 4.6 2 valve Mod motor, 4R75E, 2.73s. Bone stock

                  Comment


                    #10
                    Another way to look at things is like this:

                    The AOD chooses what gear to be in by looking at two variables. The first is road speed, and the second is fluid pressure, which is controlled by the TV cable, which is in turn controlled by the throttle. Closed throttle=low pressure, open throttle=high pressure.

                    If you are cruising along at 55MPH, and you have the throttle just cracked open, the transmission sees high road speed and low TV pressure, and selects a high gear (4th) accordingly.

                    If you then mat it in order to pass someone (possibly Jonathan, who might be sitting in the left lane doing exactly the speed limit), the transmission sees high road speed and high TV pressure, and shifts to a lower gear (3rd or possibly 2nd, depending on exactly how fast you're going and how high the TV pressure is adjusted).

                    However, if you're doing 25, and just cruising along, the transmission sees low TV pressure, but it also sees low road speed, and selects a gear appropriate for the road speed (probably 3rd). If you then mat it because you see a squirrel and you want to kill it, the transmission sees low road speed but high TV pressure, and will select a lower gear accordingly (probably first).

                    Keep in mind that this is a fairly simplified explanation of how the AOD works, but it covers the basics.

                    The problem is, that even with the throttle closed, the cable is still being pulled on, which keeps some pressure in the transmission, and helps it select the appropriate gear. With the cable slack, there is nearly no pressure in the system, and it wants to engage 4th gear at 10 mph. Not only does this lug the engine, but it also puts incredible strain on the transmission, since the gears are being asked to do things they weren't designed to do. So the transmission dies.
                    Originally posted by gadget73
                    There is nothing more permanent than a temporary fix.
                    91 Mercury CP, Lopo 302, AOD, 3.08LSD. 3g upgrade, Moog wagon coils up front, cc819s in the back. KYB GR-2 police shocks. Energy suspension control arm bushings. Smog deleted.
                    93 F-150 XLT, 302, ZF 5-spd from 1-ton, 4wd.
                    Daily--07 Civic Coupe. Bone stock with 25k miles
                    Wife--14 Subaru Outback. 6-speed.
                    95 Subaru Legacy Wagon--red--STOLEN 1/6/13

                    Comment


                      #11
                      Originally posted by 91waggin View Post



                      If you then mat it in order to pass someone (possibly Jonathan, who might be sitting in the left lane doing exactly the speed limit)



                      Uh yeah, I don't do that. Obviously you didn't read the thread very well. And keep this stuff out of the tech section.
                      Pebbles-1968 Ford F250
                      Pile of Junk! An Electronics Project Site (To get wet by)<---Clicky! NEW STUFF!!!!

                      Comment


                        #12
                        Originally posted by Jonathan View Post
                        Uh yeah, I don't do that. Obviously you didn't read the thread very well. And keep this stuff out of the tech section.
                        I did read the thread carefully, and I know you don't do that. I was just teasing, and trying to make my description a little humorous. I sincerely apologize if I offended you.
                        Originally posted by gadget73
                        There is nothing more permanent than a temporary fix.
                        91 Mercury CP, Lopo 302, AOD, 3.08LSD. 3g upgrade, Moog wagon coils up front, cc819s in the back. KYB GR-2 police shocks. Energy suspension control arm bushings. Smog deleted.
                        93 F-150 XLT, 302, ZF 5-spd from 1-ton, 4wd.
                        Daily--07 Civic Coupe. Bone stock with 25k miles
                        Wife--14 Subaru Outback. 6-speed.
                        95 Subaru Legacy Wagon--red--STOLEN 1/6/13

                        Comment


                          #13
                          Officially, there is only one way to properly set the AOD. It involves using a block of a specified thickness and a pressure gauge. The block is a V shaped thing placed between the crimp on the end of the cable and the plastic "stem" on the cable that goes through the clevis block to pull it out a specific amount. You then adjust the cable until the pressure is at whatever reading Ford says it should be and thats it. On rod cars, the block is just a flat stock of material, or I believe the book says you can use a specific drill bit placed between the screw on the tv lever on the side of the cfi unit or carb and the throttle lever. There is no min, max, or mid adjustment point, and pressure is not set by adjusting things until it shifts at a specific rpm or speed.


                          actually, here is the whole offical procedure for your reading enjoyment
                          http://www.tciauto.com/products/inst...31000_inst.htm

                          In reality, that stock adjustment is kind of early and mushy feeling so a lot of people do not like it. I immediately added more pressure to the Mark VII so it didn't shift so early and annoying. The Towncar I just messed with until it felt decent, which I'm sure is higher than official spec. Luckily these aren't hurt by higher than specified tv pressure so its not a big deal.
                          Last edited by gadget73; 09-17-2010, 11:29 PM.
                          86 Lincoln Town Car (Galactica).
                          5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                          91 Lincoln Mark VII LSC grandpa spec white and cranberry

                          1984 Lincoln Continental TurboDiesel - rolls coal

                          Originally posted by phayzer5
                          I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                          Comment


                            #14
                            Originally posted by 91waggin View Post
                            I did read the thread carefully, and I know you don't do that. I was just teasing, and trying to make my description a little humorous. I sincerely apologize if I offended you.

                            I cried for nearly an hour.




                            I was going to say something related to this thread in a technical aspect, but I can't remember what it was now.

                            Oh, right. If you ever have the chance to install a Lokar TV cable, don't do it. Or if you do toss out the spacer that it comes with to set the TV pressure, because it's wrong. And it's wrong on the wrong side, which is the low side. When I did my cable I used that spacer, and it ended up setting my pressure way low, and the shifts were too soon and some slippage could be felt. I threw a gauge on the trans to confirm and the proff was right there. I tossed the spacer and set the thing by hand and just watched the gauge. Then I bumped it a little above stock since I like my shifts firm.

                            Also for some reason the rod equipped cars don't burn up when it comes to the pressure being low or the rod being disconnected. I remember my grandfather drove around for almost two weeks with it shifting way too soon, finally took it to a shop and the rubber grommet in the rod had dried up and turned to dust, and the rod fell off of the arm on the CFI.
                            Pebbles-1968 Ford F250
                            Pile of Junk! An Electronics Project Site (To get wet by)<---Clicky! NEW STUFF!!!!

                            Comment


                              #15
                              Originally posted by Mercracer View Post
                              There is no such gear as "passing" gear.
                              If there ever was one, the early Jeep GC's 5 spd auto would have to be it. There was a "5th ratio" in the trans, between 1st and 2nd gear. It was only used in kick-down/passing situations. Supposed to lessen the shift shock, noise, and revs of going to the regular 2nd gear. Under accel it would just shift through the regular 4 speeds as normal.

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