by Doug Dutra
(Click on any photos for a full size view)
The SL6 cars came with 2 very different throttle linkage systems. The 60-67 1 bbls used a mechanical "rod type" linkage and the 68 and later used a cable linkage. Both types used mechanical "kick-down" linkage on cars equipped with an automatic transmission (controls transmission throttle pressure). Note that cable linkage was offered on the earlier 64-66 V8 A-Body cars and also on SL6 cars equipped with air conditioning so keep your eye out for those setups. They are nice to have for an early car conversion and hard to find these days. Here is a look at the two main types of factory linkage systems. (We will keep referring back to this drawing so you may want to keep it "linked" to your "back button".)
There is special factory linkage for the "Super Six" 2 barrel setup, so if you are planning to do a 2 bbl conversion, try hard to get all the special linkage parts that it came with. There is no way to make any of the 1 bbl linkage work with the Super Six setup. Also note that the Super Six linkage is great as a "starting point" for an aftermarket 4 bbl setup, with the carb mounted in a "front to back" orientation. Bottom line, Super Six linkage is worth picking up if you see it for cheap.
The real reason for this article is to show owners how to set up the Hyper-Pak manifold with linkage. Note that the factory only had a "rod type" linkage at the time and that the Hyper-Pak was a "dealer installed" option. It is unclear if they ever had an automatic trans. kick-down linkage setup worked out. I made it a point to engineer in the cable type and kickdown linkages when I designed and reproduced the Hyper-Pak casting back in 1994. I have added additional casting bosses to the reproduction unit to help with mounting the special brackets needed to support cable type linkage and kickdown. As far as I know, Clifford has kept these extra bosses in place as they continue to produce castings off the patterns I built. (These extra bosses may need drilling and taping.)
Here is a look at some of the original linkage used on the Hyper-Pak and for some of the development prototype units. One key thing to note is the use of "bellcranks" or "turnbuckles" (more on that in a moment). Note that the factory Hyper-Pak has the carb mounted "sideways". An aftermarket manifold has an enlarged carb mounting flange to allow carb mounting and linkage placement to support "sideways" or "front-to-back" carb mounting orientation. If you have an original Hyper-Pak unit, you will be limited to the sideways mounting and the carb linkage shown.
The linkage shown here is for a cable activated "sideways" carb mounting system. One problem to overcome is finding a longer throttle cable. A good source for a longer cable is a front wheel drive "sideways" engine Mopar. There are many others to choose from at the yards. The one I have is about 3 feet long (longer is good). I had to make up a number of special linkage pieces and brackets so be forewarned, welding is required.
The first step is to get the throttle linkage in place. You must decide on your carb orientation and get it mounted. Make up a bracket as shown, using a factory "screw-down" cable holder, welded onto a piece of band iron. Next make a return spring bracket. There are a couple of bosses available for mounting this easy to build piece. If you are running a manual transmission, you are now done! That's right, let's go for a drive! If you have an automatic needing throttle pressure, we still have lots of work to do.
OK, work from the middle out. We need to make a cross-shaft and two support brackets. I actually used the main piece of the factory 1 bbl shaft (14-11-1) linkage for this. It has a lever (14-11-28) already installed on one end. Make two end support brackets from angle aluminum stock. I had to move the second lever forward on the shaft. You can have it clamp with a bolt or weld it into place. (Don't weld it solid until you get everything made up and correctly positioned.)
You can use many of the early "rod type" linkage pieces. Rod 14-11-9 was moved to the rear lever and dropped down to a "pivot pin" welded to the lower bellhousing support bracket. This pin supports bellcrank (14-14-1) or you can mount the entire bellcrank / plate assy (14-14-4) low on the firewall to act as the pivot point. The last piece of linkage is rod 14-11-9 (the lower two piece one with the same number?!?) I had to lengthen these rods and did it in a way that kept their length adjusters intact. Make all your linkage pieces with means of adjustment. You will need adjustment to fine tune the system.
At one end we have the tranny throttle pressure lever. Note that there are different lever lengths available to help tune your overall linkage "travel". At the carb, there is an adjustable rod with a short slot. Here again, this allows for some adjustment and throttle movement without boosting the trans. pressure for those late, neck snapping shifts.
Look at the photos for the pieces. I have some additional pics I need to find (Super Six shots) so I hope to do more on this article later.