At low speeds (under 40), there's no greater thrill than when the kickdown system works correctly on this V12 car. It downshifts into 1st and hauls the mail.

However, it's very hard to get it to do this consistently. It will ALWAYS downshift into 2nd gear, but only once in awhile does it do the aggressive performance kickdown, as it should, into 1st. Yes; I know that above a certain speed the 1st gear option won't force, but any ideas what is going on? I believe the kickdown microswitch that rides on the TPS cam assembly is not the problem.

Is it something in the TH400 transmission? Any ideas?

I really want to get this car running to its potential, in preparation for a full cosmetic restoration.

Thanks,

Lou

Submitted by fastxb2003@aol.com on Tue, 12/29/2009 - 18:02

Impatient to get the new switch, removed it and took it to my electronics lab (I own a company that services specialty biomedical instruments used in the fertility fields) for a thorough investigation.

I read anywhere from 34 to 2.6 ohms in repetitive switch closings.

Subjected the offending switch to a rigorous cleaning with mulitple chemicals designed for this purpose. No guarantee, but worth a shot.

The contact resistance cleaned up to 0.02 ohms, consistently. Reinstalled switch; kickdown now works, consistently.

Question: Is the kickdown solenoid at the transmission on the left side, with one wire going to it (I presume its other contact is the transmission body for ground)?

Thanks,

Lou

Submitted by dougdwyer1@com… on Mon, 12/28/2009 - 23:37

Yes, the vacuum modulator (or bad vac hose) can cause various problems, including lack of *part throttle* kickdown.

The full throttle kickdown is strictly electric

I'd try a new switch. Sometimes those tiny switches just don't work relial=bly after 15-20-25 years. About $3.00 at a electronics supply store or on-line. Search "Burgess Snap Action Switch"

DD

Submitted by fastxb2003@aol.com on Mon, 12/28/2009 - 23:04

Well today I discovered that indeed the cable-ferrule mechanism was seized, because the tri-flow must've seeped in and freed it up overnight. The whole cable casing moves "backwards" at WOT, closing the microswitch.

Just for good measure I screwed that pedal stop further into the floor, Doug thanks for that and all the other help too.

I went on to measure the resistance of the switch when closed, it's 0.05 ohms so all good there.

Despite all these fixes, consistent kickdown is still elusive. It's still intermittant. Today at 60mph on the highway it kicked down and tore up the road like a raped ape, did this a couple of times in succession but then it quit kicking down again. I'm beginning to think it's that solenoid you mentioned.

The local British car wrench says the Turbo400 has a "vacuum accumulator" associated with the kickdown system....whatever that is. He thinks it may be a leaking or cracked vacuum hose. Any sense to that?

Thanks again,

Lou

Submitted by dougdwyer1@com… on Mon, 12/28/2009 - 08:32

With the pedal to the floot the throttle turntable should hit the stop, yes.

My memory is a little foggy but I *think* each throttle blade has a full-ope stop as well.

Personally I'd go to square one and adjust the whole mechanism. I'd start at the throttle bodies by disconnecting the linakage, cleaning the bores and adjusting the throttle blades to the proper .002" gap. You'll see the adjustment screws for this...sorta like an idle speed adjustment on a carburetor.

Reconnect the linkage and, as to do, make sure the throttles do not move but the the linkage rods have virtually no free play.

There are some bellcrank linhages at the rear of each intake manifold. If the plastic bushings are crumbled you'll have to replace them as well. If not, none of the adjustments work.

Anyhow, just keep working rearward with your adjustments to remove any slack in the rods but being careful not to introduce any actual movement at the throttle blades. It's all very intuitive once you get started.

If all the slack is taken out of the linkages you should get true WOT with the pedal floored, and the little operating ferrule should pass thru the opening in the throttle cable casing and operate the kickdown switch. If not, go inside the car and adjust the pedal stop (looks like a button of the floor) downward to allow more pedal travel. It just screws in and out.

If still no luck I begin to wonder if the cale was stretched.

There are other methods of adjusting the throttle linakge system but I've described what works for me. Others will chime in.

Cheers
DD

Submitted by fastxb2003@aol.com on Mon, 12/28/2009 - 01:35

THANKS Doug,

I think I had it wrong--the switch just to the right of the TPS must be the enrichment switch, not the kickdown switch. Duh, that's why idle speed increases when I manually activate this switch.

The other switch, to the left of the TPS turntable, has a little "roller" on the tip of its lever. However, with the car off and an assistant flooring the gas pedal, nothing happens mechanically here. The cable goes tight but the TPS stops just short of hitting its limit screw on the top of the turntable, and the switch with the roller just sits there with no switch lever action. I sprayed the whole affair with Tri-Flow in an effort to free it up if it's frozen, but now I'm wondering if it's working at all, seized, or just out of adjustment.

Anyhow, with full pedal to the metal (engine off), no switch action at the left switch and no knob moving on the cable to activate the switch.

I tried to figure this out earlier today and just shrugged. The roller is sitting in a "valley" of a little ferrule sort of thing. 180 degrees around the cable barrel from the roller is a small phillips screw (which I could not loosen) and what appears to be a spring inside an oval window. My thought was, that the ferrule or whatever you call it SHOULD move to push the switch on when the throttle cable is tight, but this isn't happening.

I'll try your three points as above and really appreciate the help.

Question about 2) above: How do I define full travel of the throttle cable? Should the top of the TPS with the arms, hit the stop screw on the turntable?

If I can send pictures or anything to aid in a diagnostic, please let me know.

Best regards,

Lou

Submitted by dougdwyer1@com… on Sun, 12/27/2009 - 21:39

Edited on 2009-12-28 2:04:39

The system is designed so that a full throttle kickdown occurs, actually, beyond full throttle. The switch on the throttle cable (to the left of the throttle turntable) is acuated by a little knob on the cable after the throttles are fully open.

A few things to look for:

1) Adjustment of the switch via the tiny mounting screws and condition if the switch itself.
2) Make sure the stop under the throttle pedal is adjusted far enough downward to actually allow full travel of the throttle cable
3) The throttle pedal has a couple nylon bushings at the pivot point. If one is missing or worn the pedal will sorta flop over a bit and will result in lost motion and not enough "pull" the operate the kickdown switch
4) Poor contacts at the kickdown solenoid "pass through connector" at the transmission itself

For a more agressive kickdown use the enrichment switch on the right side of the throttle turntable) to operate the kickdown circuit. The enrichment switch closes at about 3/4 throttle rather than full throttle. Its a simple modification....just a bit of wiring and a relay will do the trick. I can send info if you're interested.

Cheers
DD