1of1442

I had a switch pitch rebuilt for my 70 and when I was doing initial fill I thought I had lost my mind! Tried to creep up the dipstick a little bit at a time so as not to over fill. Vehicle running, level would stay near “pint low” mark and not change even though I was adding, then suddenly it would be half way up the stick! I pulled fluid out with a syringe and started filling process again 4 times , same results. Using the search on this forum and the fact that fluid would not drain out of the plug installed in the pan, I realized vent tube was not venting. I was able to poke a piece of mig wire through the vent tube and now it drains. I swear that in my search, someone had suggested that the vent tube could be blocked by an improper gasket or alignment of gasket and it would/could also affect the 1-2 shift.
Can’t seem to find that post and now and I have had a weird loud rotating type noise just after 1-2 shift happen only twice. Also after sitting much more than a few days it pukes fluid out the dipstick. Otherwise trans has been good, shifts well under cruise conditions.

TripDeuces

I had a hard time finding my level also. I'm not going to say I figured it out but it may have to with the switch pitch operation. Cycling through several switch pitch high and low operations seemed to get things right inside the transmission. The fill level is basically even with the pan gasket. If you suspect it's over filled the modulator valve is just above the pan gasket area. You can always throw a catch pan under it and remove the modulator until it drains to that point. It's a mess but...

1of1442

Thanks . I’m pretty sure I have the fluid level figured out . Once I determined the vent was blocked and cleared it ( somewhat ) the fluid level seems to be right , if not a touch low maybe. It will still puke a little ATF out on startup occasionally. I have since determined the shudder type noise happens when trans shifts to second under heavy throttle. Usually, when I push it hard, I shift it manually and I have not experienced the noise when I shift manually.

Schurkey

Check the dipstick tube for a crack in the O-ring groove where it pushes into the trans case. Common. There's a kit available that allows the replacement of the O-ring with a new-design "Top Hat" seal; but you need to modify the dipstick tube to use it. The "Top Hat" seal is ten times as reliable as the O-ring. Might be that you could get the entire dipstick tube from a newer vehicle at the Treasure Yard, and a fresh seal to work in your trans.

The fluid level rises in the trans pan over the course of hours or days--the torque converter is draining back into the pan. I've seen modulators leak after being parked for awhile, for the same reason. Fluid level rises, modulator O-ring has a small leak that doesn't seep much in use, but seeps when bathed in fluid.

Noise/rattle/vibration after a heavy-throttle, automatic shift to second? Sounds like a slipping intermediate sprag. If you shifted manually, the front band would take some of the load, and the sprag might not slip. I had the same thing happen in first gear, heavy throttle. Rear roller clutch slipped. Dashboard shook like it was having an orgasm. Almost scary. Absolutely fine at light throttle, a disaster at heavy throttle. Again, in manual low there's a band that reinforces the sprag and then it was fine.




Good catch on the blocked vent. I'm not sure that would have occurred to me. I'm impressed!

1of1442

Thanks for responding Shurkey ! I was able to speak with a local builder and he thought the same about the sprag. I plan to run the 1/8 mile track in Wyoming this Saturday. He didn’t think I would have issues with it if I shift manually. What is you opinion? Stock 455 with a cam, switch pitch locked in high stall, 3:42 gear and drag radials.

TripDeuces

You'll easily lose 2/10ths in a 1/8th keeping it in high stall the whole run. A simple toggle switch will work. I used to use a momentary switch which is much better than the toggle. Only when engaging the switch was it in high stall. All other times it was in low stall.

Schurkey

I would fix the sprag before I beat on the transmission.

matt69olds

Without a doubt! The intermediate band in a 400 has a very small servo, and a narrow work surface. It was never intended to hold any power. It’s only purpose is to provide engine braking in 2nd gear.

1of1442

Thanks for all the great info. I certainly do not want to chance any damage to my trans or converter but............I have been Dying to get to the track for over a year and something seems to always keep me from it.
My main reason for wanting to run is to feel/see the 60’ times with my new higher stall and drag radials and getting pressures set in rear air bags. Test and tune if you will. .
I admit there is a lot I don’t comprehend about how transmissions function. If I am just doing first gear launch’s will the faulty sprag still come into play or is it only involved in second gear?
As stated above, I plan to leave switch in high stall position and my Tri-Shield converter is supposedly flashing to 3600 rpm. I believe this accounts for the less violent 1-2 shift........I think? Or is it the sprag slipping, and that is why 1-2 in low stall is much firmer than the 1-2 shift in high stall?

Schurkey

If you're not shifting to second with WFO power; and the converter is loose anyway...I suppose you'd be OK.

That sprag isn't used in first gear. Won't matter if it's weak. That band isn't applied in first gear. So first gear should be "Ok" since you aren't having other symptoms. There is a sprag/roller clutch for first, and a band for "manual" first, but not the ones that are used in second/manual second.

Get your foot out of the throttle before the 1-2 shift until you're sure the intermediate sprag is OK.

1of1442

I appreciate the info. That is what I was hoping for! THANK YOU !!!

matt69olds

What year is the 400 trans? The later year 400 used plastic 2-3 accumulator pistons, they frequently break. If your comfortable pulling the valve body it may be worth checking out. A broken piston can cause the exact symptoms your describing. Replace it with the earlier aluminum piston, leave out the spring.

1of1442

I took you advice and decided to get it fixed first. Thanks again for your input.

1of1442

It was one of the Kenne Bell Switch pitch transmissions so who knows? I got it as a core. I do remember the person that built it for me said it had the earlier style sprag/clutch and that was supposed to be the better design.

matt69olds

The use of the early sprag-style drum ended In 1971. Hydromatic brought it back in 1991 (or whatever year the 4L80 trans came out). The plastic thrust washers and accumulator piston are the first things that go in the trash. I would assume whoever built the trans would know better, but anything is possible. I definitely wouldn’t beat on it until it’s opened up for a autopsy.

Schurkey

Let us know how that worked out. Did it fix the problem?

1of1442

So I have missed the two of the four total meets at the 1/8 mile track near me. I am a little bummed since I started this project a year ago . I had run the car with the stock th400 and it did ok but I started worrying about the 165k miles on it and it’s abuse since the 16 year old bought the car in 82.

On a brighter note, my trans guy thinks he found the source of the noise I was hearing. He was concerned upon tear down, about the dark sediment in the bottom of the pan. The internal parts did not seem to be wearing and were clean , which pointed towards the converter. A drain plug had been installed ,I assume as part of the original kenne bell product. When the drain plug was removed he saw scoring on the bottom of it. What he could see of the stator looked ok but it wasn’t much. He the put an input shaft into the converter and spun it trying to listen for noise but did not hear or feel anything until he applied a side load and bingo, mystery solved (I hope). I called Tri - Sheild that built the converter and Jim acknowledged that as a problem and stated that is why he did not ever put them in.
The converter should be in his hands today so fingers crossed, all goes well and I can make the Aug 22nd meet.
My trans guy also noticed a little wear in the case where the retaining bolt goes through the valve body area. Ironically I found a core the same day and learned about the Heavy duty th400 case and will be using it going back together.