[71Formula]

I've got a problem with my th400 transmission, that I don't understand. Lets see if anyone here does. The car is already in the shop with the guy that originally rebuilt it. He's backing up his work, so I'm fine with it. As of yesterday he said he was stumped, but was still investigating... so here it is.

At ~35 mph or less I can let off the gas and manually drop it into 1st and the car freewheels when it shifts down instead of getting back compression. Also, when I'm cruising in 3rd gear and let off the gas it idles like its out of gear (same as manual down shift simptom), but then when I get back on the throttle it shifts down into 2nd and then quickly shifts back to 3rd. This causes a lot of unnecessary shifting and of course no engine braking so steep grades could be bad.

My guess is a bad torque converter causing the one way clutch to free spin both directions. One reason I suspect this is because I don't think the stall on the converter has ever been right and I think the bottom end power should be stronger too.

Any ideas? Like I said the car is already in the shop and I hope to get it back tomorrow or the next day (hopefully fixed). But I'd like to get some opinions, after all my tranny guys is stumped so far...

[lc2 tech]

I know some race trans are made to freewheel like that. where did the trans/parts come from. did you change the valvebody?

[pinballDan]

I would guess it is either a vale body problem or I have also seen a bad case cause that kinda problem .I would lean more toward the case .

Dan

[Half-Inch Stud]

I figure SEVERAL problems:

1: shifter alignment to select 1 gear may not be happening, so you gets 2nd gear, yet the thin band is nnot grabbing the DIR Drum for engine braking.

2: Low fluid level, AND/OR new filter is one of those crappy ones that cloggs on nothing.

3: Vacuum Modulator or Govenor way-out of adjustment.

Soooo, Hows does REVERSE hold?

[David Jones]

Not me.

[TTS]

Is there engine braking if you start in 1 then coast?

If so, I'd hang a pressure gauge on this thing.

How high of a stall?

If your converter sprag is out the transmission will overheat and the car will have no power.

[Schurkey]

Originally Posted by 71Formula

At ~35 mph or less I can let off the gas and manually drop it into 1st and the car freewheels when it shifts down instead of getting back compression.

Band problem?

Originally Posted by 71Formula

Also, when I'm cruising in 3rd gear and let off the gas it idles like its out of gear (same as manual down shift simptom), but then when I get back on the throttle it shifts down into 2nd and then quickly shifts back to 3rd. This causes a lot of unnecessary shifting and of course no engine braking so steep grades could be bad.

A friend had a ~'69 Cutlass with a 350/TH 400. Did the same thing until he put the modulator on MANIFOLD vacuum instead of ported.

Originally Posted by 71Formula

My guess is a bad torque converter causing the one way clutch to free spin both directions. One reason I suspect this is because I don't think the stall on the converter has ever been right and I think the bottom end power should be stronger too.

A freewheeling converter one-way clutch will cause piss-poor acceleration--but not a lack of engine braking.

[RAIV55]

If it does it both in manual Low and second with no engine braking, both bands aren't applying.

I'd assume if your tranny guy is in the business he didn't assemble anything wrong so the next thing I'd try is a different valve body.

Like was stated a torque converter won't cause the no engine braking. A rolled sprag could cause poor acceration.

[71Formula]

Thanks for the replies. I didn't hear from the mechanic today. I hope to have some news tomorrow. I don't know how to quote everyone on the same reply so I'll just try to answer in order.

I don't know where the parts and valve body came from or exactly what was used as far as they go. This tranny guy is supposed to be one of the best in town and supplies a lot of them for the local drag racers. So I trust his judgement on parts.

Shifter lever has been adjusted. I don't think it's the shifter alignment. It doesn't feel like it comes out of gear, it just freewheels when I idle at speed.
Fluid level was checked and good.
I tried adjusting the vacuum modulator and I actually couldn't tell a difference from one setting to another. Maybe a bad vac modulator?
Reverse holds good.

The Converter is a TCI with ~2200 stall

I'm not sure if I start out in manual first and then coast if it has engine brake or not... but I think it doesn't have. But not positive.

The modulator is on manifold vacuum now.

I should also mention, this has been a problem from the very beginning. But didn't do this before I sent the tranny in to be built. In fact, it worked good before I had it rebuilt, just leaked and wanted to have it gone thru and a shift kit and stall converter installed. Just my luck...

From the sounds of it a valve body and case are the biggest suspects.

[71Formula]

Oh yea... it was supposed to be build with a 'stage 2' shift kit. And I think he uses Transgo parts.

[toomanybirds]

I can tell you what causes this problem. I have experienced it.

The kickdown or "detent" solenoid is stuck or the switch is malfunctioning applying 12volts to the transmission full time.

To rule out the switch or a short in the wiring, simply unplug the wire from the trans and drive it. If the symptom is still there, replace the detent solenoid. (simple to do, only need to remove the pan)

If this doesn't fix it, it is a valve body problem. Or improper assembly, such as the valve body gaskets reversed, or no gasket on the detent solenoid.

Also, if you shift to low or second gear, you will have engine braking, in drive you will not.

This problem is not caused by the torque convertor, shifter adjustment, low fluid level, sprag (low or intermediate), vacuum modulator, governor, or low line pressure.

It is caused by the over-run bands not applying, but they are not the problem.

You can trust me on this one, it is the detent solenoid.

[71Formula]

Originally Posted by toomanybirds

I can tell you what causes this problem. I have experienced it.

The kickdown or "detent" solenoid is stuck or the switch is malfunctioning applying 12volts to the transmission full time.

To rule out the switch or a short in the wiring, simply unplug the wire from the trans and drive it. If the symptom is still there, replace the detent solenoid. (simple to do, only need to remove the pan)

If this doesn't fix it, it is a valve body problem. Or improper assembly, such as the valve body gaskets reversed, or no gasket on the detent solenoid.

Also, if you shift to low or second gear, you will have engine braking, in drive you will not.

This problem is not caused by the torque convertor, shifter adjustment, low fluid level, sprag (low or intermediate), vacuum modulator, governor, or low line pressure.

It is caused by the over-run bands not applying, but they are not the problem.

You can trust me on this one, it is the detent solenoid.

I don't use the kickdown switch so I can't have 12V to it all the time... so from your description it would be a bad detent solenoid or something related to it causing it to malfunction...right?

[briann]

I ran with the detent solenoid not even plugged in for years and I had engine braking in 1st, 2nd and drive so thats not the problem.I suspect your band lug snapped right at the round welded indent where it holds it in place if you constantly throw it down a gear to engine brake. Its been 10 years since I tore down/rebuilt a couple T400's and I cant remember which band I always saw broken side lugs on that had no engine braking for that drum. No braking in drive I forget if thats also band apply or not on rear drum as well. I just run a full manual T400 now so I dont have to worry about when my shifts occur automatically depending on vacuum or a weighted governor to control them.

Did this just start happening or was it right from the start? Might be something like a missing checkball in VB plate.

I hope the mechanic runs a pressure test on all gears before he tears it apart just to see whats going on but ifs its already out of the car I doubt he has the capability to do that..

[TTS]

Originally Posted by toomanybirds

I can tell you what causes this problem. I have experienced it.

The kickdown or "detent" solenoid is stuck or the switch is malfunctioning applying 12volts to the transmission full time.

To rule out the switch or a short in the wiring, simply unplug the wire from the trans and drive it. If the symptom is still there, replace the detent solenoid. (simple to do, only need to remove the pan)

If this doesn't fix it, it is a valve body problem. Or improper assembly, such as the valve body gaskets reversed, or no gasket on the detent solenoid.

Also, if you shift to low or second gear, you will have engine braking, in drive you will not.

This problem is not caused by the torque convertor, shifter adjustment, low fluid level, sprag (low or intermediate), vacuum modulator, governor, or low line pressure.

It is caused by the over-run bands not applying, but they are not the problem.

You can trust me on this one, it is the detent solenoid.

A small leak @ the KD solenoid is very possible, constant on or 12v supply wouldn't give him those symptoms. It's extremely rare for a shop to disassemble any of the detent circuit unless they mistakenly installed a sk spring there . I wonder if they put the early metal solenoid gasket under a late solenoid? Seen that done many times.

If there is no engine braking in 1, the transmission isn't downshifting to low. You would have to try very hard to not have low braking- on accident!

[TTS]

Originally Posted by briann

I ran with the detent solenoid not even plugged in for years and I had engine braking in 1st, 2nd and drive so thats not the problem.

If your solenoid started leaking it would still have a problem, if being used or not. Engine braking in drive?

Originally Posted by briann

I suspect your band lug snapped right at the round welded indent where it holds it in place if you constantly throw it down a gear to engine brake.

That wouldn't have anything to do with low, only second.

Originally Posted by briann

Its been 10 years since I tore down/rebuilt a couple T400's and I cant remember which band I always saw broken side lugs on that had no engine braking for that drum. No braking in drive I forget if thats also band apply or not on rear drum as well. I just run a full manual T400 now so I dont have to worry about when my shifts occur automatically depending on vacuum or a weighted governor to control them.

There are 2 bands; second brake and low/reverse. If the rear band breaks there is no low braking OR reverse. If the front one breaks...we've been over that one.

Originally Posted by briann

Did this just start happening or was it right from the start? Might be something like a missing checkball in VB plate.

I hope the mechanic runs a pressure test on all gears before he tears it apart just to see whats going on but ifs its already out of the car I doubt he has the capability to do that..

A pressure test is an everyday deal at most transmission shops.

[71Formula]

So here is the explanation I got from the mechanic.
After not finding anything wrong with the tranny he put it back together and took it for a more thorough road test. He says there is no compression (engine brake) in first, but 2nd does have compression when manually shifted down. He explained 2nd gear is acting normal, but first gear is not. He's pretty sure the rear servo piston applied pin (or rod) is too short which does not apply enough pressure on the rear band. He says this is caused from how the new rear band fits - some of them have a slightly different shape.

He performed pressure tests on the transmission and everything is good. He said the transmission is 'functioning' perfectly other then the problem mentioned above with the rear band/servo.

Does this sound resonable?

[toomanybirds]

Originally Posted by 71Formula

So here is the explanation I got from the mechanic.
After not finding anything wrong with the tranny he put it back together and took it for a more thorough road test. He says there is no compression (engine brake) in first, but 2nd does have compression when manually shifted down. He explained 2nd gear is acting normal, but first gear is not. He's pretty sure the rear servo piston applied pin (or rod) is too short which does not apply enough pressure on the rear band. He says this is caused from how the new rear band fits - some of them have a slightly different shape.

He performed pressure tests on the transmission and everything is good. He said the transmission is 'functioning' perfectly other then the problem mentioned above with the rear band/servo.

Does this sound resonable?

No, if the rear servo piston is not applying the low/reverse band, you will not have reverse.

---------------------------

TTS, clearly you are knowledgeable about these transmissions, but next time you have the opportunity to try it, apply 12 volts to the detent solenoid and drive the car. You will have these exact symptoms, in drive the car will not have engine braking in low or second gear. In selected low or second, it will have engine braking as the over-run bands are applied.

[stevep]

It almost sounds as if he skipped a step in the instuctions.
If the detent solinoid has 12 volts going to it, the trans should not upshift.

[briann]

So im curious if this transmission shop is actually a transmission shop or its just some guy that does rebuilding on the side of another business.

[TTS]

Originally Posted by toomanybirds

apply 12 volts to the detent solenoid and drive the car. You will have these exact symptoms, in drive the car will not have engine braking in low or second gear. In selected low or second, it will have engine braking as the over-run bands are applied.

There is NEVER ENGINE BRAKING IN "D" REGARDLESS OF GEAR OR DETENT VALVE/ SOLENOID POSITION. To obtain any braking in 1 or 2 they must be manually selected.