Kick Down or Not?

[Virg464]

Question for the trans pros: Do I need to have the kick-down connected and adjusted for a car that will only run 1/4-1/8 mile at a time (no street duty)? I saw a post a while back that said a 727 can be destroyed if it's run without the kick-down set up right, I don't remember what the OP was about on that one but it raised the question. I'm going to be running a B&M ratchet mega-shifter, if that makes a difference. I will be installing a after market throttle cable, and the kick down cable can be bought with it if needed. Thanks for any input.

 

[Lefty71]

I'm gonna say you need it, unless you run a valve body that specifically says NO kickdown. Internal line pressures will be wrong without it, imo. BUT, I'm not a pro lol, so I'll grab the popcorn bucket and wait and see what they say..

 

[Fran Blacker]

If trans is stock you need the linkage.

 

[Virg464]

If trans is stock you need the linkage.

The trans was prep'd (not by me) for racing (good parts) but it is still set up to function as it came from the factory. So, I'm thinking I'll get the kit with throttle and kick down cables.

 

[YY1]

I wouldn't even drive around the block without properly adjusted kickdown. It's that critical

Whoever built your trans should be able to tell you if it has had the valve body modified to not require kickdown.

 

[Nxcoupe]

I had a 48 Anglia with a blown 392 hemi stroked to a 472", and put a built 727 behind it but didn't hook up a kickdown because there was no way to run linkage on top if the blower to the carbs. It lasted avout 3 or 4 passes before 3rd gear left the building. It was there under light theottle but at wot, nuttin. Flare up on every shift too. Pulled it, had same guy put in a full manual valvebody and never looked back.

 

[MoparMur]

In all automatics there are a number of different fluid pressures that are separate systems within the trans. The oil pump (or 2 if used) will supply unregulated pressure to the pressure regulator. From there these systems use different pressures for different jobs. For example, it takes more pressure to hold certain geartrain items in reverse than forward gears, so that "Line" pressure will be increased in reverse gear to allow bands or clutches not to slip. "Throttle Pressure" is what the kickdown linkage is involved in. At light throttle input throttle pressure is lower, and this helps to create normal, softer shifts for passenger comfort. At higher throttle openings, increased engine torque demands the clutched and bands to be applied faster and with with greater pressure to lower slippage between shifts. The whole key to this is "throttle pressure" increases with more engine load. Governor pressure is another type of fluid pressure that dictates when the transmission will upshift or downshift, dependent on engine load (directly affected by throttle pressure). "Kickdown Linkage" actually is referring to this same mechanical connection from the carburetor to the throttle pressure valve inside the transmission. Although we commonly refer to this as "Kickdown Linkage" (and it does have a say in kickdown) it more correctly should be addressed as the connection that controls throttle pressure. If there is no linkage installed an internal spring on the valve body will force the internal linkage to return to a kind of "idle" position, making the trans think there is very little or no throttle being applied. So if the trans "thinks" the engine is under low or no load when in fact it's at full throttle, you can see how the clutches/bands would be under heavy load with insufficient throttle pressure to prevent slipping. That in a nutshell is why we need that linkage. If you have a full manual valve body modifications to the valve body eliminate the need for this linkage.

 

[MoparMur]

Forgot to add that the line pressure will be directly affected by the throttle pressure. Line pressure applies the bands and clutches.

 

[Dave6T4]

A buddy of mine has a car he races 1/4 mile. I built the transmission originally, but did not realize he was using it with the kickdown lever wired back. He said he went to back the car off his trailer one day, and it would not move. He removed the pan per my suggestion, and said there were pieces in it. I told him the 727 would have to come out. On disassembly, I found the reverse servo has destroyed itself. The piston was in pieces, the sheet metal retainer was distorted and shoved through the retainer ring, and hanging on the apply lever. The reverse circuit in a 727 sees a lot more fluid pressure than any other. With the kickdown lever tied back, the transmission operates as though full throttle is applied. Every time this car was shifted into reverse, the reverse band was being applied with the piston having up to 300 psi. behind it. I was surprised it lasted 2 or 3 seasons for the guy. He ended up putting a proper reverse pattern aftermarket valve body in it that requires no linkage. The guys that use these claim much cleaner shifts with them, compared to regular V.B.'s with a shift kit in them.

 

[MoparMur]

Right on Dave6T4. On a different note (way off topic) when I was in 4th Year Motor Mechanics one of our groups was assigned to overhaul an Ford FMX 3 speed trans. They were used for years up into the '70's as I recall. On those dinosaurs there was a certain way these turds had to be re-assembled. If I remember correctly, the valve body needed to be installed and torqued to spec. before the front pump was installed. Well the group didn't do that (put the pump in then the valve body) and when installed on the trans. dyno it didn't work. Instructor (now one of my best friends) walked us through diagnosing it to show us the mistake. First thing we checked was pump pressure. The highest gauge we had went to 1200 psi. and it buried it. Shows you what these things can do. Never ever could give enough praise to an American built 3 speed auto for the **** and abuse they could take.

 

[68 Sport Satellite]

In all automatics there are a number of different fluid pressures that are separate systems within the trans. The oil pump (or 2 if used) will supply unregulated pressure to the pressure regulator. From there these systems use different pressures for different jobs. For example, it takes more pressure to hold certain geartrain items in reverse than forward gears, so that "Line" pressure will be increased in reverse gear to allow bands or clutches not to slip. "Throttle Pressure" is what the kickdown linkage is involved in. At light throttle input throttle pressure is lower, and this helps to create normal, softer shifts for passenger comfort. At higher throttle openings, increased engine torque demands the clutched and bands to be applied faster and with with greater pressure to lower slippage between shifts. The whole key to this is "throttle pressure" increases with more engine load. Governor pressure is another type of fluid pressure that dictates when the transmission will upshift or downshift, dependent on engine load (directly affected by throttle pressure). "Kickdown Linkage" actually is referring to this same mechanical connection from the carburetor to the throttle pressure valve inside the transmission. Although we commonly refer to this as "Kickdown Linkage" (and it does have a say in kickdown) it more correctly should be addressed as the connection that controls throttle pressure. If there is no linkage installed an internal spring on the valve body will force the internal linkage to return to a kind of "idle" position, making the trans think there is very little or no throttle being applied. So if the trans "thinks" the engine is under low or no load when in fact it's at full throttle, you can see how the clutches/bands would be under heavy load with insufficient throttle pressure to prevent slipping. That in a nutshell is why we need that linkage. If you have a full manual valve body modifications to the valve body eliminate the need for this linkage.

you really gave some great info there and obviously understand what you're talking about. I'm a newbie on these things and have been wondering about the effects of dialing in the correct kickdown linkage position. I'm running the Bouchillon cable setup with a Cope Racing 727 and kickdown kit and for a year or more it was adjusted so it only kicked down at WOT (so maybe not enough towards the firewall). Now I've got it adjusted so it kicks down at part throttle and drives much better. However, the shift from 1-2 feels a few seconds too late for around town driving so I think I have some more adjustment to do. Is a late 1-2 shift also bad for the trans?

 

[451Mopar]

Run the throttle pressure linkage/cable, or change the stock valve body to a reverse manual valve body.
The Reverse Manual valve body does not need the linkage.

 

[YY1]

What "usually" happens if you have no or poorly adjusted linkage is the 2-3 shift will be "soft" a few times and then start slipping.

Pretty soon, you will lose 3rd gear completely.

After that first 2-3 slip it's 90% probability your 3rd gear system is destroyed.

 

[fesser]

Very useful information here. Wish I had seen it sooner. My 68 didn't like backing up and the trans "banged" when put into gear and then slipped (in either direction I recall). I only drove it from where it came off the trailer to the shop (80') because I assumed something was wrong with the trans. Yesterday we were tearing stuff off of the engine getting ready to pull engine/trans. We were pointing out all the "bubba" things that the p.o. had done. Among those noted was absolutely no kick down linkage. I knew it wasn't a good thing, but after reading the info above, I know it was worse than I thought. I give my thanks to the poster and to the people who posted good information.

 

[Texas charger 73]

just call Cope racing trans and get a manual valve body and never look back

 

[Virg464]

What "usually" happens if you have no or poorly adjusted linkage is the 2-3 shift will be "soft" a few times and then start slipping.

Pretty soon, you will lose 3rd gear completely.

After that first 2-3 slip it's 90% probability your 3rd gear system is destroyed.

Holy crap! am I glad I asked the question.

 

[Virg464]

Very useful information here. Wish I had seen it sooner. My 68 didn't like backing up and the trans "banged" when put into gear and then slipped (in either direction I recall). I only drove it from where it came off the trailer to the shop (80') because I assumed something was wrong with the trans. Yesterday we were tearing stuff off of the engine getting ready to pull engine/trans. We were pointing out all the "bubba" things that the p.o. had done. Among those noted was absolutely no kick down linkage. I knew it wasn't a good thing, but after reading the info above, I know it was worse than I thought. I give my thanks to the poster and to the people who posted good information.

I couldn't agree with you any more. I asked the question just because I remembered someone said something bad about not having the kick down hooked up/and or properly adjusted. Sooo! glad I asked, I would have done a test drive thinking it was no big deal and could be done later.

 

[Virg464]

just call Cope racing trans and get a manual valve body and never look back

I think once I have the car up and running, and everything else is dialed in a manual VB will be the next upgrade.

 

[Virg464]

Thanks to everyone for all the great info! Much appreciated

 

[Texas charger 73]

I think once I have the car up and running, and everything else is dialed in a manual VB will be the next upgrade.

I run a reverse manual on the street and love it.