Some TH400 questions
 

I recently learned I may not be treating my trans well by not using the kickdown switch (on the gas pedal). Months ago my kickdown seemed to quit working and I just started using the shifter to downshift when I needed to. So I decided to take a closer look and try and get it functional. It used to downshift once or twice and then stop working after I reset it. Just went for a test drive and it seems to be working now. I wanted to clear up the whole “tube” or spacer thing people put on the switch to try and get it to come in sooner. Many, many posts online state that is the way to get it to come in sooner. From what I understand this is totally incorrect. Am I right on this ?
This brings me to my bigger concern. The car seems to shift way too early. It won’t hold first through an intersection and second seems to shift into third way to early as well. It’s a little hard to know exactly when the shifts happen because they are so incredibly soft. This is also true when the kickdown works. It only downshifts from 3 to 2 for a second or two before returning to third. And when doing so the shift is also very soft. The shifts are barely perceptible when driving normally. So, first I want to clear up the whole adjustable modulator thing. So many posts claim this adjustment will make a difference with the shifts points. From what I understand this is also not true. It only adjusts the shift points by like 2-4 mph and won’t make a very noticeable difference. Is this true as I understand it ?
So if my kickdown is working and my modulator isn’t the answer what should I be looking at for possible solutions to increase the time the car holds the gears before shifting ? The transmission is custom built and made to sit behind a high HP engine. I did recently switch from a 3.08 rear to a 3.55 rear without making any other changes to the car. (other than working on the efi tune). Maybe it was built for soft smooth shifts ? Is that possible ? It’s been in the car for over 5 years and has always behaved like this. A friend suggested the cable linkage could be off, but it seems to check out to my limited knowledge of the subject. Hopefully I haven’t been abusing the trans for some time now by not having it set up correctly. The receipt I have for the trans rebuild is cryptic but it does say that it has a “shift kit” without specifying any details. Any insight would be greatly appreciated. I suppose it’s even possible it’s working correctly and I just don’t understand what’s going on. :noidea:

If you have a higher than stock convertor this will make the shifts come in sooner than expected. I believe the modulator does affect the shift point some if it has an adjustable modulator. The shift points and the kick down are operated independently of each other. On the side of the trans is a round removable cover and inside is the governor that controls the shift points. it's controlled by weights and springs. Kits are available with replacement springs and weights so it will allow you to change shift points. The process is complicated and takes time patience and a lot of trial and error.

Your GOVERNOR has the final say on shifts. Those adjustable modulators are like above said only good for a few mph. If you changed to a higher rear end the rpm's are going up higher and quicker. A governor works off rpm's.

Thanks guys. The converter is a TCI Breakaway 2,400-2,600 Stall Torque Converter 240901. I’ll look into what my governor is doing. I guess I can dial the modulator in a little just to see what I get as well. The transmission is due for a fluid change so I guess it’s time to pull some things apart before this spring.

Hm. I guess the governor MIGHT be hanging if there's crap in there, a fluid change might correct that.

Did it ever shift right?

Not sure, but shift cable adjustment may also have a say in the shifts, like if it's not fully engaged in the detent?

Maybe someone can chime in on that theory?

Is it the 1-2 or 2-3 shift doing it, or both shift points?



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Both shift points. Feels like it’s in 3rd all the time. If I floor it from a stop it will smoke the tires for a nice long romp but I never feel the gears shift or hear the revs change. I’m usually so focused on steering that I never look at the tach. It has so much power in 3rd that the only time I notice it is when I go up a steep hill. It will shift out of first before I even get going up the hill and I never feel second to third shift. The shifts are barely perceptible. I am assuming that if I hit the gas hard enough to launch fast without spinning the tires I would feel the car shift from 1 to 2 and then from 2 to 3. This is not the case. What I can feel is the car shifting from 1 to 2 sometimes after traveling about 10 feet on low acceleration.

Early Upshifts are typical for high vacuum, and you'll appreciate that.

Vacuum mod valve in case is prone to stick: pull modulator to access the valve; pull valve and 320 grit the valve in a drill press. until it slides in the case without binding. Turn vac mod screw ccw about 2-turns if you never adjusted it.

Govenor outer weights are to be left alone.
Govenor inner weights should be the short metal tabs (in chevys) compared to stock pontiac TH400s, and the springs should BOTH be flimsy. Pontiacs will have 1 medium tension and 1 flimsy tension.

A govenor with high inkstamp number: 21, 23, 25, 27, 29, will be all set as stock compared to PMD govenors like 11, 13.

That’s great info ! Just to be clear. You do mean turn the modulator adjustment screw CCW not CW ?

Yea, i might be mistaken on ccw. I'm 1000 miles away from my notes right now.

Adj modulator clockwise raises shift points and shift firmness a little bit. That increases tension on the spring which requires more engine vacuum to move the valve. This raises line pressure which affects shift timing and feel.

Governor weights and springs adjust shift points and shift spacing. If you've gone from 3.08 to 3.55, the governor now thinks you're going a LOT faster than you really are, when it shifts. The gov is geared to the output shaft inside the trans.

Shift "harshness" is a function of torque converter coupling, line pressure, valve body calibration, spacer plate orifice sizing, number of checkballs, type of frictions and any waved apply spacers in clutch packs. Stock TH400 shift early and soft for cadillac shifts in big sedans. There are a lot of ways to increase shift feel and authority. I've found that a loose converter makes even an aggressively calibrated tranny feel soft. My TH400 makes 210 PSI line presssure (stock is 160) but it shifts softly at part throttle because my converter is so loose. At WOT, it's wham-bam, too hard and late for my liking. I suspect my tranny has a shade-tree shift kit, with pump line pressure jacked to the moon, checkballs removed, accumulators blocked and spacer plate drilled out. I need to open it up and see what's in there, but I'm afraid of what I might find.

You really need to know what shift kit was installed and line pressure in all ranges to know how much you can impact the shift firmness without changing the converter.

I want to install a TransGo II shift kit I've got, but I'm afraid I'll break something if the tranny has been modified for dual feeding of the direct clutch or the converter feed has been restricted.

From what I understand, you can pull a seal ring from the stator and and a seal from the direct clutch and block a passage in the valve body. This will dual feed the direct. The TG kit also dual feeds but it uses a special spacer plate and does not require pulling the tranny down to remove the seals. 160 PSI line pressure is good to 700+ HP. Above 180 you risk pushing the converter and taking out the engine's thrust bearing. To prevent that with high line pressure, you restrict the pump feed to the torque converter to reduce charge pressure. No idea if either of those modds were done to my unit. Can somebody comment on that? I'd really like to install this shift kit and drop the line pressure into the 180s.

That’s great info chiphead. It’s been quite awhile since I bought it so I’m doubting I’ll find out what’s in it at this point. I guess I’ll do what I can with the governor and the modulator for now. It has less than 5K miles on it so will be some time before it really comes apart. I may have to live with what I have.

Your high stall convertor will certainly soften your shifts and make the trans shift earlier. Before you do anything I would install the proper speedo gears for your rear end ratio and tire size. That plus an adjustment to your vacuum modulator might just be enough to make you happy. The ole Pontiac V-8 has enough torque to handle the early shifts for everyday driving it may be fine. You always have the shifter to control your shifts when you want to get with it. But if you want everything to shift like you want without grabbing the shifter handle then you know what to do.

Tim the one thing I have done since changing the rear is swap out the speedo gear. It appears the gauge is very close to being correct (as measured by driving past those radar signs that post speed). This post has made me wonder how close my combo is to ideal. It was not put together all at once so there may be some elements that need attention. I’ll start a new post that lists all the components.

Make sure your vacuum line to the modulator is hooked up to full vacuum and try adjusting it some as recommended above. After that run it as is, unless you want to get into the governor.

My 72 Lemans 400 (310HP, 400 ft. lbs.) with rebuilt tranny, shifts like yours. I wanted it like my Camaro (350 with about 330 hp). I put a shift kit in when I had it rebuilt with stock torque convertor. It shifted solid and quick in all three gears (turbo 350). My Pontiac I believe has a new stock style convertor (I told the rebuilder what I wanted to cruise with solid shifts), so I really don't know what I got. He said there was already someone in the tranny before with a shift kit, so left it. It's not like my Camaro as I wanted, but it works well manually shifting for my liking. I feel your desire for higher shift points and knowing when it shifts.

I adjusted the modulator clockwise 3 turns and felt no difference…I’m using a hard line to the terminator efi. I may try to replace it with something else and see what I get. Maybe it’s the soft bit connecting it to the port collapsing. I have the stock molded line at the modulator end.

Governor check out ok? No hanging up or weak, broken, missing spring(s)?

I changed the fluid and filter also with no difference. I have not inspected the governor….would not know what I’m looking at. Never seen the inside of one so not sure I’d be able to diagnose.

The governor is under a 4 bolt cover on the passenger side. Unbolt the cover and it slides right out. Put a clean drain pan or a large paint cup underneath to catch the pint or more of fluid that'll come out. The gov has two sets of flyweights and a set of small springs. It's very simple to work on and there are weight/spring kits to change the shift points and timing between shifts.

As far as the kick down switch goes, they are adjustable. You can move the ratchet mechanism and reset it by depressing the gas pedal all the way, without floor mat in the way.

They typically get out if adjustment for a number of reasons but sticking a vacuum hose on it to make it contact sooner is the wrong approach

I’m going to get into that governor and see what’s going on as soon as it warms up around here.

Just to get an idea of how the governor is made when you can check it out….
https://m.youtube.com/watch?v=-0Ry1Z92CGk

That looks like something I could handle.

There are at least two designs of kickdown switch at the gas pedal. The early design is fairly rare, the later design was common as dirt.

Putting hose on the arm of the switch as a substitute for proper adjustment is crazy.

IF (big IF) the "ratchet" assembly--the plastic washboard and the copper/brass contact were to wear-out, I suppose the adjustment wouldn't hold. I've never actually seen a worn-out washboard or contact.

Is there a procedure in the service manual for adjusting the kick down switch?

I never realized they were adjustable.

It is surprising how many experts out there on the internet suggest doing just that to get the downshift to come in earlier.

Correct me if I am wrong here….when it’s described as “adjustable”. Am I to understand that after pushing the switch forward I can then depress the gas pedal partway to “set” the switch to activate when the pedal is only about halfway depressed rather than when it’s on the floor at WOT ? My switch will not hold a setting where the pedal is only partly depressed. It defaults to activating only when the gas pedal is pushed to the floor.

I see they sell these kickdown switches on Amazon….

https://www.amazon.com/gp/product/B0...AC83YGI6&psc=1

I don't know if the service manual shows how, I just figured the op wasn't aware so I mentioned it. There are all kinds of wrong on the internet and figured that's where he found the hose trick. That just comes from people that don't know how to adjust it properly.

A lot of them get out of adjustment, usually from people grabbing it by hand to pull it, and all that does is move the ratchet to the end of adjustment, then the gas pedal doesn't activate it.

I think once you look at it, it's pretty easy to figure out how to move the ratchet back to the top of the movement. I just use a small screw driver. Then reinstall the switch and use the gas pedal to set the depth. If your careful you can pull it by hand slowly with the key on and you'll hear the solenoid in the trans click. Then you'll know it's working. Just dont pull it so far to move the ratchet or you'll be taking it back out to adjust again.

No, you press the gas pedal to the floor to set adjustment.

My switch will push forward to the initial setting without having to depress the small plastic tab to get it there. Think it may be time for a new one.

"If I floor it from a stop it will smoke the tires for a nice long romp but I never feel the gears shift or hear the revs change"

Sounds like a "mushy" converter to me. If the trans was slipping or not making short/quick shifts you'd have "smoked" it by now.

Common problem I see with aftermarket torque converters. They typically "flash" high and get the tires smoking easily, but never couple well, at least within the RPM range Pontiac engines make their best power in...FWIW.

As far as shift "feel", firmness, etc, the modulator will only help move that range slightly, and unlikely you'll feel firmer shifts if you have a "mushy" converter that isn't coupled well in the "normal" driving range either. I suspect the converter is 80 percent of the issues here.

As far as forced downshifts the TH400 uses a solenoid, so it's basically an "on-off" switch. You can adjust or modify things to require more pedal movement, but that's about it. I would add here that I have never used that feature on any of my cars. I want FULL control of ALL upshifts, especially at full throttle. Dropping down into 2nd or even worse 1st gear would be extremely dangerous as my engines make enough power the tires would go up in smoke, even at higher vehicle speeds. NOT something I want to happen when I'm not expecting it, so I set the TH400's up to retain automatic upshifts, but modify the 1-2 shift valve for full manual control with the shifter.......

Thanks Cliff that’s kind of what I need to hear. I was mostly concerned something isn’t working correctly and possibly doing damage. Not working as well as it could isn’t the same thing. I have been driving it and manually shifting when needed and not feeling unhappy with the performance just wondered what “should be”. I definitely don’t want it downshifting on its own in poor conditions like wet or sandy pavement. All that said… I still love to work on improvements so looking to swap into a better convertor can go on the list….if I don’t end up with an overdrive transmission that is. :):):)

So the governor is ok then?

You are most welcome.

I'd add that the last two engines I had in my Ventura would ROAST street type radials upwards of 50mph if I pulled the shifter back into 2nd gear. NOT something I'd want to happen when I was least expecting it!

So any type of "automatic" kick down was NOT on the table for any reason........

I will pull it to check operation asap but will probably not adjust weights and springs.

Sure, but checking it to ensure it’s operating freely will be one quick way to eliminate a potential for your problematic shift. Easy things first…

Could not agree more on that.

I have found that w/o a functional kick-down the TH400 will upshift earlier than when it´s functional.

If you choose to disable kick-down and earlier upshifts are not desired, the governor needs to be modified.

For a street driven car this is a waste of time, IMHO.

I'm still leaning towards the kickdown switch.

If the one you have doesn't look like the link you posted, its the wrong one. And, the lever needs to be on the correct side of the throttle rod. (just saying it out loud).

Make sure it has power with the key on too. It should, but it's possible it doesn't.

If it's not a new one or if it doesn't look like the one in your link, buy a new one.

The trans is fresh, from a known-good builder. The converter is new, TCI break-away.

Although the converter is off the shelf, it's not considered a 'sloppy' one, and they work pretty well.


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The kickdown switch in my car looks like the one in the Amazon link. If you look close at the pics it does not have the same little plastic tab for resetting like the one Shurkey posted a picture of….close but not the same. The kickdown switch in the car is currently functional. My complaint about the function of the kickdown is that it only activates when the peddle is all the way depressed and the trans only downshifts for a brief moment when it does downshift. It’s not really “functional” in the way that I almost never completely depress the gas pedal when in an rpm range that makes sense for it to kick in. If I am looking to really get a good shift from 3 to 2 it’s much more effective to use the shifter and hold it in 2 for a second or two longer. I’ve NEVER felt it downshift from 2 to 1 when pushing the pedal to the floor at much lower speeds. I am probably completely wrong about how it’s supposed to work but I feel like it should kickdown a bit before the pedal is all the way to the floor. Once the pedal is all the way to the floor I am already moving fast enough that a downshift isn’t really part of the driving experience. Maybe I am trying to compare it to a modern transmission with more gears that will downshift without being at full throttle. During normal driving the car never really sees full throttle so the kickdown never really comes into play. If I’m trying to get down the road as fast as possible then the downshift isn’t needed as I floor it from a stop. I don’t need it to downshift when passing at highway speeds. I keep hearing it needs to be working right for the trans to be healthy but as it is setup it really is a non-player when driving the car unless I intentionally try to get it to downshift at like 30-40mph and like I said even then it only does so for a brief moment….yes the tires will spin for 10ft or so when I do that. Not to mention I go up a few steep hills and it sure would be nice to have the trans shift into 2 when doing so without having to push the gas to the floor. It just shifts all the way to 3 almost from a stop and stays there for the hill climb. I’m probably not understanding how to drive a 3 speed with this much power :noidea:

Edit: the kickdown sold at Ames appears to be identical to the one sold at Amazon.

It just sounds like it's out of adjustment.


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Maybe so but from what I understand there is only one way to adjust it. I have repeated that adjustment several times with no change. I did buy a replacement from Amazon and will swap it out when it arrives.

It has to be in the initial position, then just somewhat slowly press pedal to floor and let up slowly.

But it certainly has to be in the proper position before you start, with the tab bent for initial position/adjustment.

You can't just push it to the floor by hand over and over expecting it to change. Or even with you're foot, you pretty much get one shot at it. If you question the adjustment, you have to reset the switch before you try again.

Not sure that was clearly stated before.

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Yes, of course, that’s the way it’s done. In fact it’s so simple that it would be hard to do it wrong in my opinion. My replacement switch is actually due to arrive today. I’ll be able to compare the new one to what’s in the car soon. I’ll post a pic of what I get from Amazon.

Ok so this is what I got. Purchased from the link I posted. Looks like junk to me. I feel no ratcheting or hear any clicking in the movement. There is no tab to push so that it will set to the initial position. It won’t even travel the full length of the slot. Won’t even click into place when it hits the end of the travel. It just springs back and forth with a slight metal rubbing sound.

That looks like it should.
Install the switch and then push pedal to floor.
Done.

There is no 'ratcheting'. The switch comes in the 'unadjusted' position.
If you try to ratchet it or see how far it will move you will defeat the adjustment mechanism.

:confused:

Really it only travels from the halfway position shown in the one photo to the point where I have pushed it in the one with my hand and then snaps back to center. No other action at all. It appears it would just be an on/off switch. There is no initial setting.

The one in the car now will travel the full length of the slot.

The new one on the right will not travel to the position of the older one on the left.

In fact I can also see now what is wrong with the old one. The small plastic tab on the white slider won’t keep the switch from going all the way forward anymore. It is constantly slipping back into the initial setting mode.

I was able to “modify” the old one to work as intended. Only took 5 minutes now that I see what was wrong with it. I indented the end of the metal housing where the red circle is with a punch and hammer to catch the little tab when it snaps back. Then I had to use a utility knife to carve out the plastic on the slider where the blue line is to keep it from rubbing on the indented metal. It now is able to be pushed into the initial setting mode and won’t snap back into that position after the gas is released. And YES after it is pushed into the initial setting you can hear the soft ratcheting/clicking noise as it takes the final setting.

If someone can tell me how this new brown one can be pushed into the initial setting mode I’ll try it in the car to see if it also works but I’m betting the old OE stuff will be better even if modified.

1. To reset the new switch you need to pinch the slider and pull it out as far as it comes. (Blue arrows).
2. Then push the slider in until it gets close to the mark, NOT further. (Red arrows).
3. Mount the switch in the pedal bracket, and i will self adjust at the first WOT.

Jobs done!

Thanks for the help but no amount of pinching will allow the slider to move into the position shown in your pic with the blue arrows, and on this unit there is no triangular mark on the metal housing as in your pic with the red arrows.