TH350 kickdown adjustment question

[rich weyand]

I was not always getting the secondaries to kick in on the Edelbrock. Sometimes yes, sometimes no. Not good, especially when the 'sometimes no' finds you in the passing lane on a two-lane road. My Edelbrock has a lockout on the secondaries when the choke is engaged, and it was not always opening. The lockout is to keep you from killing the engine by dumping the secondaries on a cold engine and running off the lean end of the range where the fire goes out. OK, so I know not to do that. Duh. And not all Edelbrocks have this "feature". I removed the secondary lockout lever and replaced it with a like-thickness washer (otherwise the fast idle cam will slide over on its pivot and interfere with the throttle cam), and now I have secondaries in all modes, all the time.

My next tuning problem is that the TH350 at WOT will hold second gear way too long. When it finally shifts into third, the truck lurches forward as the engine gets back into its best power range, which is lower than normal due to the cam. Shifting in other situations, without the kickdown, is at the appropriate rpm for good response and all, so those don't need to change. I currently have the kickdown switch cable adjusted as per spec.

On to my question. Is the kickdown switch purely on/off? Or would it reduce the shift point rpms under kickdown if I adjust the cable out of spec, by pulling it a little further out than the throttle does when adjusting it? That is, if I move the kickdown point "down the pedal", will the shift point rpms come down, or will it make no difference at WOT?

Anybody know?

[bd]

The TH350 doesn't use a 'kickdown switch," it uses a detent cable. 

Gradually move the detent cable housing toward the carburetor one 'click' at a time until you're satisfied with the shift.  You can also "tune" normal shift points by recalibrating the governor and - to a lesser degree - the modulator.

The TH400 uses a 'kickdown switch' located above the accelerator pedal that is either On or Off, and that can be adjusted by changing the switch position.

[rich weyand]

Yeah, it's a cable to some valve or other.  That I knew.  The issue is whether moving it will cause the WOT shift points to change, or only change the spot on the throttle where the kickdown is invoked.  I really want the WOT "pedal to the metal" shift points to move down in rpms, and it sounds like that's what you're implying.

To do it, all I need to do is put a spacer between the end of the slot in the cable terminus and the pin on the throttle, then adjust as normal.  Just not sure it will help.

[bd]

I mistook what you were asking before.  To bring detent in sooner, lengthen the cable housing by pushing the housing "away" from the carburetor.  You will find this is somewhat limited in its effectiveness, because it will resist WOT and possibly reset to factory default the first time you hammer the pedal.  You may be better served by researching shift kits and reprogramming the valve body, pressure regulator, governor, etc.  Modifying the cable as you're suggesting will have a similar effect to adjusting the cable housing, it's just more work.

[rich weyand]

I would just put the spacer in to hold the cable out further when I'm adjusting it, then remove it.  Basically, stick a small screwdriver in there for the adjustment.  But I think that doesn't make any difference in the shift points once the kickdown is hit.  Looking into it, my understanding is that the kickdown overrides the governor, so modding the governor will change the shift points when the kickdown is inactive, but it won't change anything once kickdown is active.

Sounds like what would be best to try is adjust it far enough out that it nevers kicks down, and run on the governor and vacuum alone, or just disconnect it.

[rich weyand]

Looking into it, my understanding is that the kickdown overrides the governor, so modding the governor will change the shift points when the kickdown is inactive, but it won't change anything once kickdown is active.

OK, got that wrong.  The kickdown overrides the modulator, and it is the governor alone that determines the shift points when the kickdown is active.  Which is why it isn't accommodating the new camshaft the way it does when the kickdown is inactive.

Sounds like the best thing to do is just disconnect it and see how that works out for me.

[bd]

Disconnecting the detent cable will eliminate forced kickdown, but you already know that.  I've read reports that on some models, it will lower/soften the shift points, probably because disconnecting lowers line pressure on those models.  So, disconnecting the detent may decrease clutch apply pressure and subtly shorten service life in the long run on an otherwise stock transmission.  There are several camps on this topic.  You may have to experiment and continue researching for a suitable solution.  Let us know the outcome.

[rich weyand]

I think I am going to adjust it so the existing throttle travel will never hit the kickdown point.  Then it is still connected, and it just acts as if I never quite hit full throttle.

I don't worry about not being able to kick down, because there's a lever on the steering column I can use to do that manually.  ;-)
 

[rich weyand]

Update --

I found the correct part number governor for a 1978 K-10 350 as NOS on eBay.  Had that installed and shift points at WOT with the detent cable adjusted properly remain in the same place -- way late.  I took the replaced governor apart and weighed the stock weights at 12g.  I need to go heavier for earlier shifts.  The B&M governor calibration kit includes #1 and #2 weights at 16g and 14g.

Anybody got some #1 and #2 weights from a B&M calibration kit laying around?

[nlauffer]

I have a governor in my tool box that I replaced with a different one that had lighter springs and not sure on the weights.  I will weigh them when I get home.

[rich weyand]

Update after a month of screwing around.  Here's what I did.

I bought a stock governor NOS on eBay that matched the 1978 part number for C/K, Caprice, Camaro, etc. with 350.  When I put that in, there was no change, so the stock governor was in there.  I had been afraid that the governor had been changed out or modified some time in the last 35 years.  The stock governor has purple springs, and bare-steel weights of 12g that are .0625" thick.

I found another governor on eBay that matched the 1978 part number for diesel engines, high-ratio rear axles, and "G" trucks.  That governor has one white spring, one red spring (very stiff spring), and two gold-anodized weights of 16g that are .0800" thick.  That governor resulted in normal-driving shifts from first to third at 20mph, and WOT shifts at 30 and 45.  Way too low, and too close together.

I made a combo governor: the stock purple springs, one stock 12g weight and one 16g weight.  This results in WOT shifts at 35 and 60.  That may be a little soon, but I can hold the gear longer with the shift lever.  What I can't do with the shift lever is force an earlier shift.  Before, the engine topped out before it hit the shift, and once it finally shifted, it lurched forward.  Now, it is pretty smooth through the shift.  Shift points moved down a bit in normal driving, too, but not much, and they're fine.

So, I am happy with the shifting now.  I won't get stuck any more in the passing lane with my foot all the way in it and it winding out and not shifting until way late.  If you put a torquer cam in your 350 and have the same problem, that's the fix.  You could go with the factory 16g weight, or with an aftermarket 16 g weight, or maybe use the aftermarket 14g weight.

I have one extra GM 16g weight laying around now if someone needs to move their shift points down a bit.