Automatic Transmission Issues

[Frederick W.]

Q. What is the most complex component on modern cars?
A. The automatic transmission
Q. Should a novice attempt to work on a TH400
A. Sure why not, what could go wrong?

Ok here's the deal, my 68 TH400 wouldn't kickdown, otherwise working great. Messed around with the switch on the gas pedal, no luck.
Hooked up a remote switch to the leads on the gas pedal switch and lifted the car.
When I throw the switch I get 12 volts to the kickdown terminal on the tranny, but no "click".
So I ordered a new Kickdown solenoid online and tonight pulled the tranny pan. Pulled out the old solenoid. It looks different. More on that below. I tested it out of the tranny and it now "clicks" and actuates. Maybe an intermittent problem.

Question 1.
If the kickdown solenoid is working, what else could be the problem?

Question 2.
Look at these two kickdown solenoids. The new one is on the right. It looks less robust. The old one has a round disc with a tiny hole that a tapered needle/pin centers in. There is also a shim that you can see next to it. The new one has a litte circular "screen" instead of the pin/disk.
I think I'll go ahead and put in the new solenoid.
Should I put the shim in with the new solenoid or leave it out?
Is the new solenoid correct despite it's different design?
(ok that was 2 questions)


Question 3.
The pick up filter has a tube with two O rings. I just kinda pulled it down to remove it. One O ring is still in the bore, the other is on the tube. Should I just shove it back in?



Question 4.
While looking over the tranny, I found this connection "nipple" on the right side, top of the case with nothing attached to it. What is this? What should be attached?




Any help appreciated!
Fred

[Joe L.]

Re: Automatic Transmission Issues

Q. What is the most complex component on modern cars?
A. The automatic transmission
Q. Should a novice attempt to work on a TH400
A. Sure why not, what could go wrong?

Ok here's the deal, my 68 TH400 wouldn't kickdown, otherwise working great. Messed around with the switch on the gas pedal, no luck.
Hooked up a remote switch to the leads on the gas pedal switch and lifted the car.
When I throw the switch I get 12 volts to the kickdown terminal on the tranny, but no "click".
So I ordered a new Kickdown solenoid online and tonight pulled the tranny pan. Pulled out the old solenoid. It looks different. More on that below. I tested it out of the tranny and it now "clicks" and actuates. Maybe an intermittent problem.

Question 1.
If the kickdown solenoid is working, what else could be the problem?

Question 2.
Look at these two kickdown solenoids. The new one is on the right. It looks less robust. The old one has a round disc with a tiny hole that a tapered needle/pin centers in. There is also a shim that you can see next to it. The new one has a litte circular "screen" instead of the pin/disk.
I think I'll go ahead and put in the new solenoid.
Should I put the shim in with the new solenoid or leave it out?
Is the new solenoid correct despite it's different design?
(ok that was 2 questions)


Question 3.
The pick up filter has a tube with two O rings. I just kinda pulled it down to remove it. One O ring is still in the bore, the other is on the tube. Should I just shove it back in?



Question 4.
While looking over the tranny, I found this connection "nipple" on the right side, top of the case with nothing attached to it. What is this? What should be attached?




Any help appreciated!
Fred

Fred------


I can't help with most of your questions since automatic transmissions are not at all an area of expertise for me. However, I can comment on one question: why would you even consider re-installing the pick-up filter that you removed? This should be replaced with a new filter assembly.

By the way, the filter you need is a GM #12360651, aka Delco #TF231.

[Frederick W.]

Re: Automatic Transmission Issues

Fred------


I can't help with most of your questions since automatic transmissions are not at all an area of expertise for me. However, I can comment on one question: why would you even consider re-installing the pick-up filter that you removed? This should be replaced with a new filter assembly.

By the way, the filter you need is a GM #12360651, aka Delco #TF231.

Thanks Joe,
I guess I should go get one, but this transmission was reconditioned by the previous owner only a few years ago and driven minimally since. I suspect the filter is barely used. I'll try to pick one up tomorrow.
thanks for the part number
Fred

[Joe L.]

Re: Automatic Transmission Issues

Thanks Joe,
I guess I should go get one, but this transmission was reconditioned by the previous owner only a few years ago and driven minimally since. I suspect the filter is barely used. I'll try to pick one up tomorrow.
thanks for the part number
Fred

Fred------


This might be a Delco-only item. It lists for only about 10 bucks.

[Terry M.]

Re: Automatic Transmission Issues

I can't tell you much about questions 1 & 2 -- however I do recommend 1) your 1968 Chassis Service Manual (CSM)-- get it from the NCRS store on the button at the top of the page. And while you are at it get the 1968 Chassis Overhaul Manual (COM) as well -- you might need it later. 2) TH 400 Transmissions published by HP books. I can't recall the author and I am too lazy to go to the library this time of night (someone is sleeping in there anyway). Check with the NCRS store they might have this book too. 3) Read the CSM & TH 400 books as your homework assignment. You get a break in the CSM because you only need the automatic transmission (TH 400) part, and at that only the part about the "passing gear operation." It has been a long time since I looked, but I think there is a troubleshooting tree for a non-functioning passing gear. I would have recommended these books before you took the pan down, but better late than never.

The TH400 book should give you answers to your #1 and #2 questions.

3) DO NOT take the O-ring out of the bore, DO remove the O-ring from the filter tube. This only needs one O-ring. It is easy to damage the bore if you don't have the proper tool to remove that O-ring -- that is why I recommend leaving it. Just put the filter (old or new, I am not that fussy) back in. Lubricate the end of the filter pipe with ATF (Automatic Transmission Fluid) before attempting to install it onto the O-ring in the bore. If you can get your pinkie into the bore to feel that O-ring, try to feel if it is hard and brittle or soft and flexible. I know that sounds a little kinky, but let me know if it feels hard and brittle. I’ll get into more detail about how to get it out if you need to, but most of the time it doesn’t need changing.

4) That pipe in your picture is a vent for the transmission. Nothing attaches to it. If it has transmission fluid coming out of it something is wrong. It is just an air vent.

It has been years since I worked on a TH 400. We might have some detail books at school, but I would bet they were pitched long ago.

[Frederick W.]

Re: Automatic Transmission Issues

I can't tell you much about questions 1 & 2 -- however I do recommend 1) your 1968 Chassis Service Manual (CSM)-- get it from the NCRS store on the button at the top of the page. And while you are at it get the 1968 Chassis Overhaul Manual (COM) as well -- you might need it later. 2) TH 400 Transmissions

Thanks Terry,
I do have the CSM and COM, but neither gives much information on the kickdown function, troubleshooting, etc. None of these questions are really addressed in the manuals.
I understand the vent pipe is correct as is, so that's good.
One guy told me that he has seen many occasions where the kickdown function stopped working after installation of a shift improver kit. Not sure why. I have a suspicion that one was installed by the p.o., so maybe this is it.

Fred

[Terry M.]

Re: Automatic Transmission Issues

Shift kits often contain, among other parts, a plate that goes between the parts of the valve body. This plate replaces the original plate, and can contain fluid flow restrictions that disable the kick-down function. The really bad thing at this point is retrieving that original plate might be difficult at best. Getting another might be even more challenging.

The Turbo-Hydromantic Division of GM (boy that was the old days) used to publish a most excellent TH 400 manual. It has a dark green cover. I know we used to have several at school, and they may now be "surplus," if I am not too late. Unfortunately school is closed for the holiday weekend. Maybe someone has one lying around in their library. I will have to try to find one to see if it has the troubleshooting tree I am thinking of. I know I saw one and thought it was in the CSM.

[Terry M.]

Re: Automatic Transmission Issues

The extra o-ring in the pump I'm not sure about. Normally, when there are two (or more) o-rings on the filter stem or in the pump bore, somebody left an extra in there during a previous service. I think Terry is referring to the late model seal with the steel shell like they use from about mid 80's-up. (They are almost impossible to remove unless the pump is on the bench). I don't recall this seal being used in or with a TH400. But I don't remember. I haven't touched a 400 for over 20 years. If you can reach up there with your pinky, and slide the o-ring out, it shouldn't be there. And nothing wrong with two o-rings. But put them on the filter, and let them 'roll' up into the pump.

Dave, Good call. I was thinking of the shell type filter seal, and that is probably a TH 350 feature. It has been close to 20 years since I played with a TH 400. And when I was doing that I had both transmissions in various vehicles, so it is one of those -- they all look alike from this perspective -- kinds of things. Sorry for the confusion.

The B&M shift kits seem more popular in the Midwest, but I have no direct experience with them. I remember seeing one of my classmates install a shift kit with a different plate, and more or less little balls, but to remember if it was in a TH 350 or TH 400 is beyond me now.

Perhaps Frederick should clean the little hole, check the solenoid and put it all back together and see if it works. Never overlook the obvious.

[Terry M.]

Re: Automatic Transmission Issues

400 Trans trivia time:

What are the purposes of the features in the red and blue squares:

One of those, and I think it is the red square, is for the Kent Moore bench holding bracket -- there is a similar recess on the other side of the trans for the other part of the holding fixture. It a large C-shaped rig that fits into a bracket bolted to the bench. If it wasn't the holiday weekend I could get a picture from the shop in school. No TH 400 on the bench there though.

You got me on the other one Dave, but there is a port around there someplace to measure line pressure, but that doesn't look like what I would expect the port to look like. It would be easier to see out of the car.

[Steven B.]

Re: Automatic Transmission Issues

Neither of are remembering correctly then. I went back and looked at the pics. Sure looks like a metal shell to me. That's why I took my post down. I'm not going to add to the confusion.



Yep. That sounds like a B&M kit. They often change the separator plate. Trans Go has you drill out (larger) or plug or restrict holes in the origional plate (smaller). More of a cost thing probably. But very difficult to revert to stock, because the origional part has been modified. But I still use Trans Go kits in my current stuff like 4L60e. I like the results. They "cure" what they say they will fix.



I went back and read that too. He said it didn't click until he removed it. I remember that failure mode too. Intermittent. Replace it. Just be careful about a good seal to the valve body. If it won't up-shift, it's leaking.

Yes, the B&M's used plate and balls to "reprogram". I put one in my TH 400 in '77 as soon as the warranty was expired and it is still in there today, even after a rebuild. Very "efficient"! Autocrossed/track days the heck out of it and over the years only lost a modulator downshifting on IRP road course.

Steve

[Edward J.]

Re: Automatic Transmission Issues

Q. What is the most complex component on modern cars?
A. The automatic transmission
Q. Should a novice attempt to work on a TH400
A. Sure why not, what could go wrong?

Ok here's the deal, my 68 TH400 wouldn't kickdown, otherwise working great. Messed around with the switch on the gas pedal, no luck.
Hooked up a remote switch to the leads on the gas pedal switch and lifted the car.
When I throw the switch I get 12 volts to the kickdown terminal on the tranny, but no "click".
So I ordered a new Kickdown solenoid online and tonight pulled the tranny pan. Pulled out the old solenoid. It looks different. More on that below. I tested it out of the tranny and it now "clicks" and actuates. Maybe an intermittent problem.

Question 1.
If the kickdown solenoid is working, what else could be the problem?

Question 2.
Look at these two kickdown solenoids. The new one is on the right. It looks less robust. The old one has a round disc with a tiny hole that a tapered needle/pin centers in. There is also a shim that you can see next to it. The new one has a litte circular "screen" instead of the pin/disk.
I think I'll go ahead and put in the new solenoid.
Should I put the shim in with the new solenoid or leave it out?
Is the new solenoid correct despite it's different design?
(ok that was 2 questions)


Question 3.
The pick up filter has a tube with two O rings. I just kinda pulled it down to remove it. One O ring is still in the bore, the other is on the tube. Should I just shove it back in?



Question 4.
While looking over the tranny, I found this connection "nipple" on the right side, top of the case with nothing attached to it. What is this? What should be attached?




Any help appreciated!
Fred

Fred ,The kick down soloniod test is missing one componet, the switch on the accel pedal supplys power, the ground for the switch is pressure activated by the that the little round switch on the valve body, so if you want to do a test of the solonoid ground the blue? or black wire wire on the round switch at valve body and power up the Orange wire on the side of case. I have rarely seen the solonoid fail on the kick downs in my years.

The kick down operation on the turbo 400 trans. tends not to operation much after about 40-45 mph. since it is pressure driven by the round switch in valve body.

There is only one o-ring on the filter, But I may differ from Terrys response, only because if you happen to push the o-ring into the pressure port or even a small fragment this will cause problems, so I would say install onto plastic tube and smear a liitle fluid onto o-ring to ease the install.

The tube on top of trans. is a vent overflow, sometimes a overfilled transmisson will vent the fluid to this point.or even a stuck pressure valve in pump will cause fluid to vent.

[Terry M.]

Re: Automatic Transmission Issues

Ding, ding, ding. Terry gets the TDB bucks.




The blue one is the anchor for the 2nd braking band. There's two more anchors side by side further back for the lo/reverse band. The pressure port is 1/8 FPT on the other side of the case.

Thanks for playing.

I thought the line pressure port was on the passenger side. I must be mixing up the TH 350 and TH 400 again.

[Frederick W.]

Re: Automatic Transmission Issues

OK Gentelemen thanks for all the replys and advice.

I got 'er fixed today, and she drives like a dream. Entirely different, and better, driving dynamics when you get a 3-2, 2-1, or 3-1 downshift at the appropriate times.

To provide some feedback: it was the kickdown solenoid. It demonstrated an "intermittent" failure mode as mentioned by Dave Perry. This was very tricky because it wasn't making the "click" noise when I sent it 12 volts. Then when I pulled it out and benched tested it it worked, so I questioned myself ("maybe I didn't hear it...").

In the end I put in the new kickdown solenoid (aka detent solenoid) that I bought from AR Transmissions in Fresno via ebay for $20. I called them and they said not to put the metal gasket on with the new solenoid. The new solenoid seals via an integral rubber gasket ring that you can see on my pics.

The o-ring in the bore had no metal ring, it just pulled right out on my pinky. I put both o-rings on the filter tube about 1/4 inch apart, lubed with AT fluid and pushed it in. No problems. I figured an extra o-ring was just a little insurance for a good seal.

I put in a new trans filter, but had to use one from Advance Auto Parts (ProKing brand) stamped "made in China". That hurts. My local AC Delco parts place didn't stock the one I needed. Looked the same other than the China stamp. I debated just putting my old filter back on (it is stamped "made in the USA"). I kept the old one.

I used a Fel Pro Gasket for the pan also from Advance Auto, much better than the one that came in the filter kit. I re-soldered the terminal to the orange wire and attached it to the terminal on the trans. Torqued the pan bolts to 12 ft lbs as per the CSM. While the pan was off I bead blasted it and the bolts in my blast cabinet.

Then I added 7.5 pints of Dexron ATF, and took it out to test. I still had the test switch wired in so I was sure it was getting 12 volts when I threw the switch, and wallah...kicked right down, yippee!

Took it back and had to fix the kickdown switch attached to the accelerator pedal assembly. While attempting to diagnose I was adjusting this and broke the old brittle plastic POS switch. I ended up fabricating a repair using some steel from an electrical plate. I'll spare you the details. Working under the driver footwell was quite interesting. I haven't twisted my 47 year old body into such contortions for many moons. Maybe never. I fear my wrist is permanently damaged from twisting it beyond what nature allows. Getting that stupid wire and plastic doohickey on the pedal lever was the most irritating part of the whole job.

Then, I found that even with maximal adjustment, I was not getting WOT on the carb with the pedal to the floor. I have heard others had to bend the pedal lever to get WOT. I ended up doing a temp bubba fix that worked great. If anyone is interested send me a message and I'll describe. Not sure what the permanent fix will be. I'm in no hurry to disassemble the accel pedal assembly again to modify, bend or otherwise fix. I would commit hari kari first. Maybe another day.

Good news, the fabbed kickdown switch was being actuated by the lever as it is supposed to. It wasn't quite right, so I put a piece of fuel line hose over the plastic rod on the kickdown switch to increase it's caliber. This was a tip from the Corvette Forum. ( A little bubba, but if anyone crawls under there to see it it, they may never be able to get back up to tell about it). This was then perfect as far as causing a downshift at the proper point.

So that's about it. Sorry about the long post, but I know from my experience that hearing the end results are very helpful to future readers.

Took all day, but well worth it. Now a nice cold one is waiting.

Thanks again, guys.

Fred

[Terry M.]

Re: Automatic Transmission Issues

Thanks for the update. I am pleased your solved your problem. Congratulations.