kickdown rod dilemma - throttle not opening fully SOLVED !!!

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66fyssh

66fyssh

Don't Stop Believin'
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After my 5.9 Magnum swap I noticed the carburetor throttle is not opening all the way. The car runs great and shifts great the way I adjusted the linkage. When I shorten the rod, I don't get enough throttle pressure and the transmission slips.

I have the early style solid rod with the bracket on the back of the head. Before the swap I had a 66 transmission, now I have a 74. Maybe throttle pressure is different on the later model transmission??

I adjusted linkage per the FSM but it's still not enough pressure. When I lengthen the rods, the throttle won't open all the way.

Anyone run into this before? Any ideas?

Here's the style I have.
IMG_20200829_135132.jpg
 
Fluid is good. I just rebuilt it during the swap. It runs like a raped ape with the Kickdown rod adjusted but the throttle won't go all the way open.

My plan is to drop the pan and increase throttle pressure at the valve body. I just wanted to see if anyone had any other ideas before I do that.
 
66fyssh said:
Fluid is good. I just rebuilt it during the swap. It runs like a raped ape with the Kickdown rod adjusted but the throttle won't go all the way open.

My plan is to drop the pan and increase throttle pressure at the valve body. I just wanted to see if anyone had any other ideas before I do that.
Click to expand...

I think you're on the right track with that, but it bothers me that the transmission slips without good throttle pressure. It should not slip....that is unless something is wrong. Even with the throttle pressure linkage chunked in the ditch, if the transmission is in good shape, it WILL NOT slip. At least not right away. It will simply shift very early. If it slips, something's up.
 
Maybe I'm feeling the early up shifts as a slipping. I just went around our little neighborhood and it's in 3rd gear almost immediately.
 
66fyssh said:
As soon as I go back to a longer rod and take all the slack out of the throttle linkage, it shifts great.
Click to expand...

But still doesn't get full throttle? I think I would double check all the exterior linkage and then if I didn't find something, pull the pan. Do you know how to check for proper adjustment?
 
When I rebuilt the transmission I adjusted the valve body throttle pressure per instructions.
The linkage seems correct per the FSM diagram above.

When I first did the swap I just took all slack out of the linkage. Ran great until I noticed the throttle isn't opening all the way.

It's as if the dang throttle pressure "pin" in the valve body is too short.

I'll pull the pan tomorrow and double check the pressure adjustment. I definitely want to be able to get to full throttle :steering:

Or... maybe that's God's way of telling me I don't need full throttle!!
 
Do you have the Chrysler throttle linkage adapter on the carburetor?
 
Ok, try this. Adjust the up and down rod to near max length. Adjust top rod to get all the clearance out at wot. See what that does 4 u. Kim
 
The trans will not shift firmly without enough throttle. Find a way to adjust the throttle linkage so the trans linkage is not stopping it to fully open. When the carb linkage fully open the trans linkage should be as far back as it can go. You may have to adjust or relocate the carb PIVOT point to allow this.
 
1)I’m not sure why this is happening but maybe in one of the swaps a lever is off. You know the length got changed. Like the kick down lever on the trans is different and not allowing enough throw or is bottoming out full throw before the throttle is open. Fulcrum angles are key.
2) I had to go to a locar cable for my throtttle pressure on my 66’ when the factory linkage kept giving me issues - very same as your but no slip- just bad shifting points. I am running FI Tech fuel injection so throttle lever is designed more for another brand engine than Chrysler - throttle hole is off and angles were out a tiny bit but enough to cause my issues.
3) If trans is slipping.... I would be dropping the pan and looking for discoloration and bits in the bottom. You may need full pressure to engage clutches like something is off internally I’m sad to say.
Post some pics when you
Can and keep us posted.
Syleng1
 
66fyssh said:
View attachment 1715586583
Click to expand...

Your home made throttle cable stand is too high, not giving you the proper geometry. Needs to be shortened 1 1/2" or so and then the throttle cable clamp angled up to be in line with the throttle shaft mopar bracket.

This way it is pulling down hill a bit opening the throttle all the way. Wide open throttle and wide open kickdown, that is where you set it.

Edelbrock Mopar.jpg
 
The lever at the trans is different for 4bbl. And 904 is different then 727 4bbl. Your trans lever is the geometry problem. There are different angles and different lengths. This is why I kept boxes and boxes and several drawers of throttle pressure. this is later linkage 2bbl and 4bbl note the lever difference and also the rod diameter difference so you cannot use one to the other. And there are several more for police 4bbl's in other years with 904's with the right parts and knowledge you can even use throttle pressure on a blower or tunnel ram for a tow vehicle. Yours should be an easy fix. You need the right parts .

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Thanks for the suggestions!! I'm at work today. Should be getting off around 5.

I work at a medical center and my boss and a supervisor under me are both out sick, which is why I'm working on Sunday. Hoping they don't have the 'Rona :eek:

I'll look it over when I get home. I'm thinking it's a fulcrum issue. The throttle has a large sweep whereas the throttle pressure travel is a lot less.

I'll post up some pictures later. The thing works great but the throttle can only open a little more than halfway. If I adjust for full throttle travel, there's too much slack in the pressure linkage and it up shifts immediately.
 
Here's what I would do. First VERIFY 100% WHAT is stopping the throttle from getting full travel. Are you 100% right now that it is the kickdown lever at the transmission reaching its full travel first, or could it be "some of the other linkage" bottoming out somewhere else? And I mean 100% sure. Not 99.9%. Once you find THAT, you'll be on the way to a fix. I also agree 100% about getting the correct parts in there. Sometimes youc an get by with mixing parts up, but the throttle pressure linkage is not a good place to try it. Just too much at stake.
 
You could try a longer kd arm. Or move the kd connection on the carb to a lower hole. These both will change the radius so that the kd is under pressure at the same time it is now, but the leverage ratio would be different.
 
Well shitz, I'll have to check it out tomorrow.

I left work at 6, got home and the cell phone we ordered for our grandson (whom we are raising) arrived. I spent the last nearly 3 hours getting the dag blasted thing connected and set up. And I consider myself pretty darn good at that stuff.

We have him set up on Family Link so we have to approve him downloading new apps, and we set timers that limit amount of time used and shuts it down at bedtime.
 
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