TH400 acting oddly

[DoubleDingo]

Okay @da_raabi, I'll give you the torque converter idea. I just looked up symptoms of a torque converter going bad and it could be a possibility. But I'm going to go about it in the order I mentioned, that way I know the vacuum leaks are gone, timing is correct, spark is good, fuel is flowing like it should, etc.

 

[DoubleDingo]

Fixed! It was two vacuum leaks. One at the canister, one on the air cleaner. Just drove it around for an hour and it never once stumbled, just purred and is firing on all 8 finally. No audible hissing while idling anymore. Got the air mixture screws set too. Did it while the engine was cold, so tomorrow I need to do it again at operating temperature. The trans could use another drain and fill, but the truck runs like a top now, power on demand. The distributor weights were operational, but I did spray a little wd40 on them. Replaced the spark plug wires, and some vacuum hose. Everything else checked out and I don't need the 85 carb I posted questions about in the carburetor section earlier today. So it'll become a backup again.

Thanks everyone for the comments and suggestions.

 

[DoubleDingo]

The exhaust has never smelled as good as it does after this fix, it always smelled like soot. Now it smells like an carburetor/engine that is tuned like it should be. That, and the engine has never ran so smooth and strong. Liking the truck even more right about now.

 

[da_raabi]

Wow, very interesting. Glad you got it fixed. Vacuum leaks can cause funky symptoms I guess. I'd love to know how they caused the creeping etc. issues you experienced.

Well done! Goes to show with troubleshooting you start with the cheapest and easiest!

 

[DoubleDingo]

Wow, very interesting. Glad you got it fixed. Vacuum leaks can cause funky symptoms I guess. I'd love to know how they caused the creeping etc. issues you experienced.

Well done! Goes to show with troubleshooting you start with the cheapest and easiest!

I didn't expect it to fix the problems, but I'm glad it did. I was expecting there to be way more to deal with. I pondered your question about how it can cause the creeping. My only theory is that with the vacuum leaks causing the engine to run like it dropped four cylinders, that perhaps the line pressures inside the trans fluctuated enough to cause them to surge and the weird things happening inside. On Friday while leaving work was at a light with the engine purring and the trans in gear, then the engine stumbled, the truck jumped forward a little while I had the brake applied. Then I tried neutral and it creeped forward. Now the engine is smooth and doesn't have any misses, so the vacuum is holding steady and the line pressures are too. It still doesn't explain why, with the trans in neutral, when the tailshaft should be disconnected by it being neutral, that it did creep forward, but the fluctuating line pressures and low vacuum is all I can think of. A coworker just stopped by, a fellow gear head, so I asked him if he had any ideas as to why, and he is at a loss too.

 

[DoubleDingo]

I guess I got lucky Saturday night when test driving the truck. Didn't go anywhere yesterday, but today, in neutral, it'll creep. If I put it reverse and then back to neutral, it doesn't. I followed the adjustment procedure, but I'll try it again. I think a drain & fill of the ATF may be in order too, even though it has minimal miles on it after doing it a few years ago. I figure it's sat for a while not being driven, so stuff may be hung up and since I plan on driving it more as a daily now that it's running good, some fresh fluids won't hurt anything, hopefully. If everything goes as planned, this truck will finally get to go camping. I've tried with it before and it broke down. Wanting that to change.

 

[DoubleDingo]

This morning I decided to get some Motor Purr Tune Up for the transmission. It will either clean it up and unstick things inside, or kill it. Ran it some at lunch and can feel a difference in how it operates. Will drive it some more after work to get the product working throughout the trans. This weekend I will drain and fill it with a new filter and drive it for a while and drain and fill again.

A break down on what it's doing. This morning backing out of the driveway it backed up fine but did shudder a little, and when I put it into Drive it did it's creeping thing. I didn't mess with the shifter and when I gassed it, it took off without issue and shifted just fine. First time it has done the creeping thing going from reverse to drive.

During the morning break I drove to the store that carries the product and poured it in in front of the store since things were warmed up. Ran it hard at various places during lunch to engage the passing gear and do WOT take offs. All of that was solid. Going into neutral at a light, it didn't creep anymore, but it took a couple seconds to catch when put back into gear and trying to move forward. Once it caught it moved forward without slipping and shifted well. Reverse seemed to not shudder like it has, but I was only able to back up in a couple locations. Tonight I will flog it on the back roads, and find some spots to back up a few times to get the product working through all of the gears.

Anything I need to be on the lookout for, or listening for when I am out test driving it and doing the drain and fill?

 

[da_raabi]

This morning I decided to get some Motor Purr Tune Up for the transmission. It will either clean it up and unstick things inside, or kill it. Ran it some at lunch and can feel a difference in how it operates. Will drive it some more after work to get the product working throughout the trans. This weekend I will drain and fill it with a new filter and drive it for a while and drain and fill again.

A break down on what it's doing. This morning backing out of the driveway it backed up fine but did shudder a little, and when I put it into Drive it did it's creeping thing. I didn't mess with the shifter and when I gassed it, it took off without issue and shifted just fine. First time it has done the creeping thing going from reverse to drive.

During the morning break I drove to the store that carries the product and poured it in in front of the store since things were warmed up. Ran it hard at various places during lunch to engage the passing gear and do WOT take offs. All of that was solid. Going into neutral at a light, it didn't creep anymore, but it took a couple seconds to catch when put back into gear and trying to move forward. Once it caught it moved forward without slipping and shifted well. Reverse seemed to not shudder like it has, but I was only able to back up in a couple locations. Tonight I will flog it on the back roads, and find some spots to back up a few times to get the product working through all of the gears.

Anything I need to be on the lookout for, or listening for when I am out test driving it and doing the drain and fill?

Sorry if I missed it, but how many miles are on that trans? I'd be concerned about the constant flushing if it has a lot of miles on it. You may be flushing what little friction material is left right out of it. I tried that on a Dodge a few years ago. It was just fine, but (being new to vehicles) I thought I would do a drain/fill and filter. It never shifted right again. In fact it started giving me all kinds of new problems.

So let me get this straight:

1. The engine issues appear to be fixed?
2. The only problem left is the creeping and failure to quickly engage?

Here is my thinking:

1. You have/had multiple unrelated problems. It would appear you have eliminated the engine-side issues.
2. The TH400 is almost completely controlled by hydraulics. The only mechanical engagement inside is the parking pawl.
3. Weak pressures inside the trans could potentially lead to erratic behavior that would go away under higher pressures provided by more RPM.

Deduction: You may simply have a worn out transmission. The best way to check this is to hook up a pressure gauge to the test port and see what pressures you are getting in the various gears. Its a PITA process, but it may be informative. If you are interested in this I believe the TH400 rebuild manual has the process instructions and what to look for based on the readings. The PDF is readily available online.

I would also highly recommend that you stop the use of "miracle cure" additives. Besides fuel cleaners and/or intake sprays (Seafoam) I have serious concerns with what these additives do to the insides of engines and transmissions. That same Dodge I mentioned required a whole new engine because of the regular use of Slick 50 (previous owner). I have NEVER seen so much gunk in an engine.

SO: My next step would be to take a close look at the transmission. If you are sure your linkages are all good outside the trans, the next step is to look inside. Starting with the pressure tests would be my recommendation.

 

[DoubleDingo]

The mileage on the truck is 76,***, and it's a numbers matching vehicle except for the vortec heads I put on it and the associated parts to run the quadrajet on it. It has sat most of its life, that's why I suspect it's just stuff sticking inside the trans. Last night I found a dirt road and did a bunch of reverse to drive to reverse to drive. After about 20 minutes out there I thought I should probably leave the area before someone called the authorities because of some dude in an old truck doing weird stuff...lol... I also did some full throttle take-offs, and engaging the passing gear at about 45 mph, then slow down and repeat. The truck is not afraid to get up and go that's for sure! It does take a couple seconds to engage when shifted to neutral at a light, and the creeping thing will happen going from reverse or neutral. I discovered that last night, so that was part of my driving checks. I'd put it neutral, let it roll back down the hill, then put it in drive and hit the gas to get it moving forward, and the trans would hesitate, then the truck would take off up the hill. I did that about ten times. Once I got home, with it good and hot I readjusted the carb since I didn't get around to it on Sunday.

This morning the transmission shifted way better than it ever has. I may have got lucky, or it may act up later. The ATF level was a little high when I checked it last night, but it was at operating level before I added the Tune-Up, and that is supposed to evaporate after 48 hours, so they say. It wasn't foaming or coming out the tube. I normally don't use the additives like I have been lately, but I will run the fuel additives every other oil change to keep the carb/fuel injector squirters squirting like they should. My reasoning on the fuel additive in the square is to clean out the tanks and lines. I recall when this all went south, and it started on the driver's side tank, so I switched over to the other tank. Then it started running crappy on that tank. Having other things going on, other projects taking my time, I only drove the truck when I absolutely had to, which left bad gas in it, and things to gum up again or even more than they already were. This year I am going through each vehicle in the fleet to fix what is ailing them so they are back to just preventative maintenance again. Running the motor purr in the tanks has cleaned thing up, it is noticeable in the throttle response and the way the engine runs.

The engine issues are fixed. It runs great. As of the short drive this morning, the transmission is back on track too. I have a transmission book somewhere. I leafed through it a few years ago and it had all kinds of diagnosis procedures and adjustments and things for the TH400. I tried finding it this morning but it's MIA. I bet it's with my Pop's train book that I can't find...lol...

If this thing acts up again, I will go through and check the pressures, etc. The fluid was a nice red and didn't smell burnt so I am leaning towards just leaving it in service. It only has about 5k miles on it and the filter. Perhaps at 90k I'll change it out, or if we plan to take it to Texas or something like that.

Thanks for the input, I really appreciate it.

 

[DoubleDingo]

Been dailying this thing now, and have discovered the issues. Sometimes it works like it should, other times it messes up. Been experimenting the last couple days.

Sometimes when I backup it does the shudder thing, and when it does that it will creep when put into drive. But hit the gas and it takes off like it should and usually shifts just fine through each gear. This morning it didn't shudder when backing out of the driveway, but when I put it in drive, it didn't shift through all the gears, it kinda did this one long shift from first into third. Next stop, take off and it shifted all the way through each gear. Granted, moving the lever into 1, taking off and shifting into 2 the trans does the coveted hard TH400 shift into 2nd. Going into 3rd it shifts solidly. Sometimes when putting into drive the gears engage strongly, other times not. When it doesn't it seems to only go into 2nd. That's that hang-up I've been experiencing, with the rpms up then it launches once it grabs. Or like it did last night, a couple times, slips like crazy because it never truly goes back into 1st.

So this is what I've been experimenting with yesterday during lunch, last night going home and this morning coming to work. At a stop, put it in neutral, then put it in drive, if it doesn't engage strongly I move the lever into 2nd and the trans goes into a different gear. It's noticeable because the truck jumps a little with the brake on. Take off and it is clearly in 1st because it launches like it should. Once I shift it into 3rd, if I leave it there at the other stops it runs just fine and shifts through all the gears. Reverse does the normal bang into gear so it is engaging like it should. Tomorrow I will be adjusting the linkage again and lubing the pivot points. I have a couple dump runs to make and some trips to the home center, so it will get a workout this weekend.

 

[da_raabi]

You really need to do the pressure checks. The symptoms you are mentioning are kinda all over the place. Is it a linkage problem? Is it a pressure problem? Is it just a worn-out transmission? We need some hard data to move forward.

 

[DoubleDingo]

I am not arguing the fact that we need some hard data. The baffling thing is that this stuff is all intermittent, and it shifts great most of the time. There is no slipping whatsoever, just up and go leaving everyone way behind. You scared me away from doing the drain and fill when you said it may get rid of the friction material, but I think it could benefit from some fresher fluid and a newer filter. With the transmission having 76k on it, and at least one drain and fill done to it, which I did about 6 years ago, I think it couldn't hurt to get some fresh fluid and new filter in there. I never did get around to readjusting the linkage last weekend, had many other things going on that kept me away from working on the truck, just driving it and the truck is running great.

 

[DoubleDingo]

Pop contacted me today, so I told him what the TH400 is doing. He said it's sticking inside because of varnish build-up. He said if it was pressure related there would be a lot of other issues. He said the creeping and other issues I described are caused by varnish build up making things hang-up inside the tranny. He also said to make sure the selector is dead-on, which I am sure it is because I followed the procedures that @chengny provided, although I will verify. So the rest of the week I'll be doing what he told me to do, along with the drain-fill and filter change, and making sure the selector is accurate. Will report back next week. He also agreed that because of this truck sitting most of its 76k mile life thus far hasn't helped at all. I told him if this doesn't fix it I will come up and we can check the pressures and such, but he was adamant that it was merely varnish build-up.

 

[DoubleDingo]

Keep in mind, all of this stuff I've reported in this thread recently started happening. Prior to this the transmission operated just fine. With years of little to no use, things gunked up inside it and this is where we're at.



Yesterday after work, per Pops recommendation to get a product that removes varnish from a transmission, I went to pep boys and got some sea foam hydra trans tune. Poured it in, and went for a drive to the same backroads I did last week. Pop said to use all of the gears including passing gear, so I shifted into each gear numerous times. He also said to shift it into reverse just enough to get it going, then into drive, into reverse, into drive. He said things are stuck and need to be unstuck and this will loosen them up. Probably did 100 of those reverse to drive. After that reverse grabbed like it should, no more shudder. Can now feather the throttle and get it to back up, not have to give a little extra gas and have it shudder to a stop, gas it, shudder to a stop, gas it, shudder to a stop. Can leave my foot off the throttle and it will idle in reverse now unless it's uphill, but even then it tries to go, whereas once all of this started happening it wouldn't. There's still a little bit left to unstick, but the trans is shifting more like a normal healthy TH400 again. Once I got home last night, there was still enough sunlight left to readjust the shifter linkage. I had a baseball inside the cab and some bungie cords, so I found the neutral slot on the column, semi-wedged the baseball between the shifter handle and the lock cylinder, and hooked the bungie cord on the shifter handle and ran it over to hook it on the door to keep the shifter holding tight towards Park. Then I crawled underneath and loosened everything up, turned the linkage on the trans to neutral, and tightened everything up, and lubed the rotating points. Started the truck and ran through the gears, each one hitting where it should, neutral is where it's supposed to be. This morning coming to work, at each light I put it into neutral and no more creeping in neutral. Putting it into drive, that's where things are still semi-stuck, but shifting into 2nd then 1st engages the lower gears, then can put it back in drive and it'll take off in 1st like it's supposed to and shifts through the gears like normal. I've almost drove the 30 miles recommended on the product label, and will exceed that today. Can't do the drain and fill and filter change today, but will leave the truck home tomorrow so it'll be cool when I get home after work, and then I can get some fresh fluid and a new filter in there.

 

[DoubleDingo]

Drained and filled and changed the filter today. These are my findings. Besides those flakes, nothing else. Catastrophic? Okay?

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