tranny issue

I have a 64 425 with an sp400 tranny in my modified. Dynamite setup, but the tranny likes to puke up atf out of the filler tube now and then. Any ideas on that? it was a low mileage drive train and runs great. did have a slight issue lining up the torque converter on the build, could I have damaged it? No apparent leaks below, just a barf out of the filler tube at random times, then it burns on the header

If you had some issues with the installation, you might went to ensure the "switch-pitch" function is still operating, for good measure.

If the trans is not over-full, the engine/trans temps are "normal", there should not be any "volcanic eruptions" of ATF.

In setting the fluid level . . . aim more toward the "ADD" line than the "FULL" line on the dipstick, with the engine and trans at full operating temperature (as in after driving at least 10 miles on the freeway). The dimple below the "ADD" line is where the fluid should be at 32 degrees F, as to "ADD". Trying to set the "HOT" fluid level in the middle of the grid between "ADD" and "FULL" will allow for fluid expansion as the fluid might heat more in certain driving conditions.

ALSO ensure that the external trans cooler is not internally-restricted so it can work as it needs to work, plus that it has sufficient air flow across it to do its job.

Just some thoughts,

NTX5467

If the eruption happens on first start after sitting for usually days, then the torque converter may be draining back into the pan. When started the pump rapidly fills the torque converter forcing air out causing the overfull pan contents to erupt.

Yes, it tends to do it on startup, and it can toss out a good cup of ATF! This is definitely not good, but the tranny appears to operate quite well. Definitely draining back ATF and then doing a surge. I have not hooked up the switch pitch, which I understand to be the electric connection. Perhaps that is the problem, or part of it. The tranny cooler is a straight shot and attached to the radiator, but both of those would be logical problem areas. Anything that could cause the ATF to drain back and overfill the pan, then a little back pressure and the filler tube turns into an ATF gun. Definitely an irritation as I want a clean engine compartment but the worst part is what drips onto the exhaust making nasty fumes. Perhaps I need an overflow tank on the filler tube.

Tranny levels are always difficult. The engine should be running so the torque converter is full, so cold the level does go up as the TC drains. If the oil goes up the filler tube, it's going to be an ATF cannon. That's obviously happening, I suspect the switch pitch might have an effect on that. It's a mess!

I know you don't have a dynaflow ( and I don't know how your unit seals the torque converter ) but the dynaflow input shaft has grooves that hold steel sealing rings. This is what keeps fluid in the torque converter from leaking into the pan (and out of every orifice) Even new rings do not make a perfect seal since there is a small gap. This is not an issue if used regularly, but extended sitting will drain the torque converter. If you fix all the external leaks then the overfull pan contents will regurgitate out the dip stick tube when first started. In most cases adding a couple of bottles of STP will slow the leak or fix it.

Willie

54 Fins, If your trans is not overfilled, I think you are right about the switch pitch. I am not experienced in internal transmission operation but I read the section of the 1969 manual concerning the ST 400 trans. In 69 there was not any switch pitch. But the crucial passage I read says that at start up the vanes of the stator need to be in the right direction OR the flow of oil would impede the torque converters pumping action.

I can't speak for the switch pitch operation. I don't have one of those manuals. But it seems to me that the switch pitch would be in play on start up, and if yours is disconnected I imagine it is holding the stator in the wrong position for a start up causing excessive oil flow restriction or turbulence.

Make sure the trans vent tube is open.

Appreciate the comments. Just don't want to pull the tranny, so that is the last resort. I almost wish the tranny had an obvious shift problem, it is easier when its just plain shot. But it shifts like new. The drive train came out of a very primo electra, little old lady that didn't drive much and kept it up well. The first and most obvious issue is overfilling and I will bet it was overfilled at first, so the first few burps were not a surprise. The first question, could an overfill have damaged something internal?

The next issue was it was difficult to set the torque converter, so no doubt that possible damage could have happened there. We had to get an even space around the bell housing before the TC would key into the tranny so it is possible some stress happened. The first burp we figured came out of the TC, but it's definitely out of the filler tube.

the burps are random, but a week of sitting definitely make it worse. Suffice to say that the TC is draining to the pan after sitting a few days and the burp is worse. There are a lot of TH400 people with some good ideas, but once you mention the switch pitch even the Buick people are not really sure how that TC works. Now I just had one more idea, I always use mobil 1 synthetic ATF in automatics but not in my old cars. (the stuff is majic, it will revive a bad tranny) However, older cars have older seals and synthetics are not a good choice. I wanted to use Dextron, but the mobil 1 was ready to go. That could be a contributing factor.

I'm going back to Dextron and the STP idea sounds good to. If that fixes it, it just confirms don't use synthetic oil in old cars. If it doesn't do it, then autopsy is probably the only choice. I have another good SP400 but I just don't want to tie up a few weeks messing with a tranny. The common thread I get from the old timers that know trannies is the filler tube has to be clear- any restriction will overpressure the tranny. It seems clear, but given the tube curves there could be a restriction that still lets the dip stick through.

Since it is random, I might suggest looking at the vacuum modulator valve. While it does not sound like the valve is bad, it does sound like this problem is not strictly mechanical or it would occur every time. The modulator valve is supposed to provide smooth shifts. Maybe the line to that is restricted or piped to the wrong port on the engine? It should be coming off the manifold on a wedge engine. I'm not sure there is a manifold port on the nailheads. In which case maybe it is hooked up to the wrong port on the carb?

Obviously, this is just a guess.

The vac modulator does go to the manifold but that is another suspect point. With the internet, amazing how much info you can call up. I know the tranny was overfilled, so step 1 is just drain it and get the level correct. The switch pitch was used on BOP cars from 64 to 69. It was a really cool idea but probably more cost than what it was worth. SImple too, just a ring that pushes the vanes to a steeper angle. The high stall keeps the car from creeping, then it drops to low stall, kicking back to high stall for passing just before the kickdown. If not activated, just stays in low stall like a normal TC. This is why that era of cars were quick off the line, it increases your torque 30% but at the cost of a lot of efficiency. sounds like the 400 was one tough tranny too for racing. Narrowing it down to filler tube, dipstick and oil level.

Solved-tube had a booger in it. Being curved, you couldn't see it but the dipstick punched right through

Did a lot of research and now I'm getting the switch pitch hooked up right

Thanks for the update!

I suspect the "default mode" for the sp is the "low stall" position, which would be the normal driving stator angle. In the other mode, at idle ant WOT, it would be in the "high stall" position to decrease "vehicle creep" in gear at idle and also have a little more torque multiplication at WOT. Hence, the "idle switch" and the other switch (as the THM400 has an electric kickdown switch also).

The should be an "anti-drainback" valve to keep the torque converter full when the engine is stopped. IF the converter might have drained-back, starting the engine with the selector lever in "N" (and foot firmly depressing the brake pedal!!) can result in quicker re-filling than in "P". Otherwise, when you put it in "D", it'll take a second or two to fully engage/refill and move the car.

If the Mobil1 synthetic atf is "ester-based" (as the motor oils seem to be), that would explain the additional cleaning action the synthetic Mobil1 atf might have. GM also has an "Automatic Transmission Conditioner" which is a detergent-based additive to do the same things. Back when we had Dexron II, I added a pint to my '77 Camaro and it seemed to make it shift a little quicker and firmer, similar to a Camaro a friend had who had put Type F fluid in it (for the firmer shifts), but not completely the same. Dexron III happened after the Dexron IIA (for the first electronic-valve body uses by GM), with Dexron III taking over after that.

Enjoy!

NTX5467