Trans linkage 2 bbl vs. 4 bbl

[Paul G]

I think I am finding that there must be a difference between 2 bbl kickdown linkage and 4 bbl linkage. Is that true? Anyone have pics of the different linkages?

It was originally a 318 so probably 2 bbl. Now a 360 with a Holley 4 bbl.

I had to use a bolt in the slot  to get the linkage back far enough to get a firmshift with a longer time between shifts. The trans shifts much harder now. Normal cruising, second comes in around 18 mph, 3rd around 36 to 40. Shifts are even further apart with more throttle. I guess having the linkage further back raises the pressure in the trans as well as delaying the shift points. I have read on here that not having the kickdown (throttle valve pressure) adjusted correctly can burn the trans. Can having too much pressure also be harmful?  Hard shifts with the higher shift points made it a whole lot more fun to drive!   

[John_Kunkel]

The throttle lever on a 2-barrel carb sits roughly in the center of the carb, a 4-barrel lever sits further forward on the front barrels so the top rod on the TP linkage needs to be longer. Depending on the type of top rod there are extensions available or one can simply fabricate a longer rod. Putting a screw in the slot defeats the purpose of the slot, it's better to extend the rod.

Throwing aftermarket carbs and minifolds into the mix often makes it difficult to get the TP linkage to work correctly, that's why many go the the cable setup but I prefer the linkage.

If you prefer the higher/firmer shift points there is no harm done, lower/softer shift points are more likely to shorten transmission life than high/firm.

[MTPOCKET]

I had conversion from a 2 to 4 barrel and used a rod extension. Here is a link on
jeggs that is selling 1/4 and 5/16 under throttle extensions.

http://www.jegs.com/p/Edelbrock/Edelbrock-Carburetor-Linkage-Adapters-Studs-Cable-Extensions/753856/10002/-1

[Paul G]

This is my linkage.


Where do I screw on the rod extension?

[John_Kunkel]

The extension only works with round threaded rods, for the later flat bar top link you'll have to cut the link and weld in an extension that is the same length as the difference between the 2 and 4-barrel lever positions. Or you can find the correct longer 4-barrel link.

[375instroke]

When I went from 2bbl. to Thermoquad, I think I bent the throttle cable outward, but can't remember.  I know that I cut the rods in the linkage, and welded a bolt in there to make them longer, then hit them with a belt sander.  Couldn't tell a bit.

This is small block 2bbl. linkage:



This is a small block 4bbl. throttle bracket.  It looks like the 4bbl. mounts one bolt hole further back than a 2bbl.

[Paul G]

This is small block 2bbl. linkage:



This is a small block 4bbl. throttle bracket.  It looks like the 4bbl. mounts one bolt hole further back than a 2bbl.

Mine is not like either of these. It must have changed between 2nd gen and 3rd. I spent most of the afternoon today messing with the linkage. I had to elongate the slot in the lever that rides the throttle, and put an extension on it. Tweaked the down rod a little and it is much better. I can get the throttle to fully close with the kickdown all the way back now. Just need to adjust the rod at the trans for a little more pressure. Got to wait for the exhaust to cool. Cant get my hands in there at the adjustment with the exhaust hot . My 73 had the kickdown adjustment up at the carb. Much better design than the 72. Next weekend I plan to take it back apart and repaint the brackets. I'll get pics of how it turned out.