Yet another transmission mystery. TH400

[skyline2250]

Its plenty possible that there is gunk in there fluid. What I would do, it pull the tranny pan and change the filter, gasket, and the fluid.

[Erock80]

I guess this has already been put out there, but I had a TH350 (similar enough right) that I put in place of a 700R4, of course there was some rigging to do to connect the different vacuum lines. At first I couldn't get it to upshift, it just stayed in 1st. After monkeying around with more vacuum lines, I got it to upshift, but it did something very similar to what you've described. After a little more tinkering, I got it right and those rear tires never knew what they had coming, haha

[hotrodpc]

So is this just a fresh insall on this job? Meaning, it has sat for years, you have just installed it, and its not working??? IF that is the case, one of my guess is going to be that the seals are hardened up from sitting, and will not hold a piston applied to compress the clutch packs. Likely your forward clutch or direct clucth packs and/or all of them? So it will compress the piston, but then the fluid starts leaking around the seal and can't hold it so it losses its grip and goes into what you think is N. Basically like the principle of a bad master cylinder. The fluid gets around the seal, you have brake pedal fade away. SO... give this a try, try a good additive for a seal conditioner. Sometimes you can get the seals the soften and swell and it will correct your problem. But try not to let it slip to much, you are damaging the clutches every time you do that. Also make sure you have enough fluid in the trans. With that deep pan, if not enough fluid, as you are using the fluid, and it circulating into the trans, the pan will get low on fluid and the filter can't pick it up, so be sure your fluid level is correct too. I seen a suggestion of torque converter issue too. That too could be suspect, but usually when a TC goes bad, they tend to make alot of noise, either chunking and clanging, or whining and screaching. As stated though, my 1st guess will be hardened seals. Don't be afraid to use 2 quarts of conditioner.

[Stitz Love]

I will post an update, hopefully by Wednesday of this week. Thanks for the various suggestions received so far.

[lukasmcdukas]

my ranger does something similar, but only between 2nd and 3rd gears... just a thought, have you changed the trans filter? i noticed a SLIGHT improvement when i changed mine but it still slips... just not as bad. worth a shot?

[lukasmcdukas]

oops i see skyline suggested that already, my bad!

[Stitz Love]

Current Status:
Well gang, it was Thursday that we were able to replace the brake hoses and take the truck out for a serious analysis. Here is the new data.
It is in fact “downshifting” NOT slipping into neutral, (Hereafter referred to as ‘freewheeling’) at whatever speed above 45-ish I try to maintain.
From a dead stop when floored, it shifts smoothly through all 3 gears, we cruised along at 65… take foot of gas, coasting in third… around 50, touch the gas pedal (intending to maintain speed of 50-ish) and it DROPS into 2nd! Engine rpm roaring, yet when forcibly step on the gas, she revs up a sec and shifts (smoothly) into 3rd again.

We tested vacuum at idle and under load. That was a challenge with the ‘just-too-short’ length of hose running up through the hood to the gauge resting on the windshield, handle and release barely reachable, but 20 to 25 inches was the satisfactory verdict.
Also, once at operating temp I sat in one spot, foot on brake, shifted manually through all gears and checked Trans fluid level (in Park as per instructions and in neutral just for the sake of it) and level is fine at the top of the hash-marks.

We did test drives from stops to third gear for a total of about 12 miles. Each time, once at a regular cruising speed (in 3rd.) was attempted, it downshifts into 2nd. By “regular cruising speed” I mean the speeds typically driven during normal daily driving… 35 mph, 40, 45…etc. up to 65. EACH time when the gas pedal is merely touched to maintain speed, we get downshift into 2nd. Each and every time put our foot into it, shifts right back into third. (within a reasonable moment of rpm rev up to engage 3rd.)

There is no kick-down, and I was told the 5.7 is a ’94… not a ’92 as had previously thought.

We both spent some time Friday searching the internet for like symptoms on a TH400 on various truck forums and articles. The three or four we found indicated the “Governor”, either worn, damaged or disintegrated… the later stayed in 1st. gear no matter what.
I ordered a Governor gear repair kit from NAPA auto parts ($4.75) Friday afternoon. It will be here sometime next week. I plan to remove the Governor this weekend, (Memorial Day weekend) I will take photos to post here.
If upon physical inspection there are other components of it damaged, I can order a whole new Governor on-line for about, $17.99 plus shipping.
The reason for my spread of days between truck operations is that the truck is currently kept about a 30 minute drive from where I live, and I am fortunate enough to also have a full time job, so weekends and after work if there is time, are the only opportunities I have to tend to it.
I will post a final resolution when one is achieved, in the meantime, thank you for your ideas, thoughts and suggestions… please keep ‘em coming as I appreciate your counsel. Particularly any experiences with TH400 Governor.

Also, allow to take a moment here extend my respect and a "Thank You" to those of you who have formerly or are currently serving our great Country.

[hotrodpc]

As I read your updated post, I am thinking of your governor the whole time. Is that what you are referring to as regulator? Sounds like governor to me. T400 does not have a detent pressure (often reffered to as throttle pressure), so it relies heavily on the governor and vac modulator to control shift points. If it were vac modulator, it would be shiffing late and probably harder, so my guess is going to be governor. T400 does have a kickdown switch designed to be activated at WOT for passing gear, and it will downshift from 3rd to 2nd, and from 2nd to 1st.

[Stitz Love]

Right, sorry about that, I have edited the post to put the proper part name. "Governor" ... not regulator.... jeesh, I gotta quit watchin those cowboy movies.

[hotrodpc]

Then I'd say you are on the right track by replacing the governor. It could be just a dirty governor and the valve it stuck. Since this is a 92 Truck it probably is not wired for the kickdown switch. You will likely have to wire something in your self if you want the passing gear feature.