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supersix diy kickdown linkage
https://www.slantsix.org/forum/viewtopic.php?t=68724		 Page 1 of 1
Author:  lgu32 [ Tue Aug 11, 2026 12:10 am ]
Post subject:  supersix diy kickdown linkage
Image

Here it is!

Long time ago when I got bought a supersix setup including cast iron 2 bbl manifold and Carter BBD from a donor car I dint pick up the kickdown linkage. As it was Aspen it probably wont fit to my early A-body either.

So I had manifold installed and carburetor tuned, engine was at drive condition but I havent a kick down system. I had to build one!

I went to closest hardware store. I picked up a 8/10mm aluminum tube, couple of expanding wall plugs with M6 threads and couple of brass rings with 10 mm hole. Those are used at waterline copper tube joints. I also bought M6 threaded rod and 2 ball ends. Then I collected the system presented in the picture.

The left end in the part is for carburetor. Right end with bent rod is to A904 link. At first I screwed the bottom end to the 904 link. Next I measured the max movement from idle end of the 904 link to the "kickdown" position. Then I drilled to carburetor a hole (with some calculations and tests) which made similar but slightly less move from idle to WOT. You can see I have 10cm treaded area for adjustment. I used it so that when carbutetor is at WOT the 904 link touches to end.

I was ready from beginning.

Does it last long?

Yes it does. I built this system at 1999 and it is still in use. Now I have fuel injection but the throttle body shaft is at the same point as was the Carter was before.

This was and is my solution for kickdown of SUPER SIX.
Author:  Badvert65 [ Tue Aug 11, 2026 7:01 am ]
Post subject:  Re: supersix diy kickdown linkage
Any pictures of this on the engine?
Author:  lgu32 [ Tue Aug 11, 2026 11:16 pm ]
Post subject:  Re: supersix diy kickdown linkage
Here it is with the turbo+efi setup. The rod was exactly the same with Carter BBD. I just chose/made hole to carburetor link which makes a little shorter movement to rod as the 904 lever does. Then I adjust the rod so that 100% WOT at the throttle pull the 904 lever to the end.

Image
Author:  SlantSixDan [ Wed Aug 12, 2026 12:34 pm ]
Post subject:  Re: supersix diy kickdown linkage
That is nicely-done work, but it is not safe. See here for explanation.

(Also…how are you ventilating your crankcase? From this pic of your engine bay, it looks as if you aren't.)
Author:  lgu32 [ Wed Aug 12, 2026 9:32 pm ]
Post subject:  Re: supersix diy kickdown linkage
I dont agree. I have double or triple return springs there to get throttle closed and it has been doing well from 1999.

However the original factory throttle return system was just a single spring which I have got broken more than once. The factory system has built so all mass was fighting against that single spring.

Crankase is wentilated to a catch can which has set underpressurized with an electric vacuum pump driven by Maxxecu engine controller by measuring the crankcase pressure continuously From an connection at the oil pan. The fumes from the electric pump outlet are routed to the tube in between the K&N element and turbo inlet. For higher power the turbo makes the most of the underpressure to the crank. The rest of time the pump does the job. Crankcase pressure is compared to the athmosphere pressure and stays below it all the time.

Image

Pictures are not optimized for the presentation on going as my hobby is not to be an influencer in the media but keep the old Dodge running and keep it fast enough for todays traffic.
Author:  SlantSixDan [ Thu Aug 13, 2026 10:55 am ]
Post subject:  Re: supersix diy kickdown linkage
Quote:
I dont agree.
Maybe not, but it's still unsafe.
Quote:
I have double or triple return springs there to get throttle closed
Not responsive to the danger.
Quote:
and it has been doing well from 1999.
And your car didn't crash from the day it was built until the day you(?) installed that dual master brake cylinder, did it? But you did that anyway, right?
Quote:
However the original factory throttle return system was
…unsafe. Yup.
Quote:
Crankase is wentilated to a catch can which has set underpressurized with an electric vacuum pump
Sweet!
Author:  lgu32 [ Thu Aug 13, 2026 9:59 pm ]
Post subject:  Re: supersix diy kickdown linkage
Could you justify your position instead of just repeating the same phrases again? Do not send links to pages where is ongoing continuous discussion of opinions of nothing with a group of randomly selected people. You can do that with someone else but for me you have do better. If you can. Have you engineered something yourself? Or just copied things you could understand?

And do you think I have overengineered my car by building the brakes better than they were from factory when I have built it up to 3 times kilowatts of a slantsix? I did this because the original drum brakes - yes this have had discs and 10” rear drums for decades as well the dual master cylinder and proportional valve.

Yes I did it because I am driving in a traffic where 99,99% of cars are younger and better and safier and will still stop with less meters than my Dart. But I have tried to do the best. Some of guys have converted brakes with modern ones taken off modern cars but I have kept these because I have couple sets of small bolt circle wheels.

Sure I have thoughts when I see power adder in an old car with a single brake main cylinder and small drums blinking behind of expensive tires and wheels. But I am happy I have an Atlantic ocean between such builds and me.
Author:  mcnoople [ Fri Aug 14, 2026 10:14 am ]
Post subject:  Re: supersix diy kickdown linkage
Not to answer for dan...but the problem I see is the fact that the kickdown linkage had the POTENTIAL to prevent throttle from returning to rest. It has the chance to cause drag/binding/blockage of the throttle plate closing.

This is the reason that the factory units are slotted. Applying throttle would pull the linkage along with it, but the throttle could return to close even if the kickdown linkage didn't return as it should.

Dan is pretty digital when it comes to safety: it either is or isn't safe, and if a design has the potential to cause danger/damage/death then it is an unsafe design.

Personally I don't have a perspective on that linkage and am just pointing out what I see.
Author:  SlantSixDan [ Fri Aug 14, 2026 3:30 pm ]
Post subject:  Re: supersix diy kickdown linkage
Quote:
Could you justify your position
Go read the specific post I linked, to understand the danger and how the factory addressed it starting in '68 or so.

Or don't! Totally up to you. ¯\_(ツ)_/¯

Quote:
Have you engineered something yourself? Or just copied things you could understand?
Yes, I've engineered stuff, but so what? Here's a more relevant question: Have you spent your (ongoing) career professionally involved with vehicle and traffic safety engineering and technical standards?

Quote:
And do you think I have overengineered my car by building the brakes better than they were from factory
No, I think you've made a wise upgrade there. Why, do you imagine, would I (or anyone else) think that was a case of "overengineering"? C'mon.

(If you want, you could decide to choose not to be all offended. I said it was nice work you did, because it is. You could focus on that if you don't care about the safety hazard of the design.)
Author:  lgu32 [ Sun Aug 16, 2026 11:17 pm ]
Post subject:  Re: supersix diy kickdown linkage
Quote:
Not to answer for dan...but the problem I see is the fact that the kickdown linkage had the POTENTIAL to prevent throttle from returning to rest. It has the chance to cause drag/binding/blockage of the throttle plate closing.

This is the reason that the factory units are slotted. Applying throttle would pull the linkage along with it, but the throttle could return to close even if the kickdown linkage didn't return as it should.

Dan is pretty digital when it comes to safety: it either is or isn't safe, and if a design has the potential to cause danger/damage/death then it is an unsafe design.

Personally I don't have a perspective on that linkage and am just pointing out what I see.
Sure it can jam if something goes in between moving parts or if the transmission lever stuck because of valvebody damage. However the linkage does touch to anything but is ”on the air” from throttle body to the transmission - with no moving sub assemblies on it. So it has moves freely, has no worn parts and in practice has been working well for 27 years. ”Use a Lokar cable” wont be any better but have more separate risks to get jammed depending how it has been built.

As well old fashioned early a-body has a ignition key with no connection to steering so I could cut the engine running with no risk to get steering locked. I used that possibility once about 45 years ago when a Slant-Six-Dart with MANUAL transmission (no links from throttle) lost its factory throttle return spring suddenly leaving the throttle to about 90% of WOT immediately.

I am still sure this works well than chinese made cable kits installed with different ways depending how it has built.

I have used my time for medical equipment design. Been doing risk analyses as well. Against old cars which will here inspected perodically and no stupid diy constructions will pass those tests all medical equipments will be certified by inspection laboratories and not allowed to modify aferwards. That is the difference. Doing $#!+ design for automotive equipment will cause upgrade for next model year. But for professionally designed things dont have such brain farts at day one!
Author:  SlantSixDan [ Mon Aug 17, 2026 11:48 am ]
Post subject:  Re: supersix diy kickdown linkage
Finland's close to Norway, as it seems. :mrgreen:
Author:  lgu32 [ Mon Aug 17, 2026 7:09 pm ]
Post subject:  Re: supersix diy kickdown linkage
Yes. In contact to Norway, Sweden and Russia too. I have not had my Dart in Norway but we did a short trip with it to Sweden at june.
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