400 turbo shift 2nd to 3rd gear

[chris989]

Hello All,

I have a 400 turbo, 5.7 TBI, 4wd. The truck is finally running very well but i still get stuck between gears.

If i am accelerating very lightly, the transmission will jump back and forth between 2nd and 3rd gear. If i let off the gas or accelerate it will pick a gear and continue on fine. It is only when light on the pedal.

I have replaced the module and vacuum line and can not detect any leaks anywhere. Could this be something inside the trans or a symptom of a bigger issue to come?

thank you,
Chris

[willett]

Interested to hear an answer. Mine does thy occasionally too. Mines had a rebuild within the last 10,000 Km's

[chris989]

Originally Posted by willett

Interested to hear an answer. Mine does thy occasionally too. Mines had a rebuild within the last 10,000 Km's

I can't confirm how many miles on mine, I am guessing a few, but it shift perfect and strong as long as i keep my foot in the gas. I installed an adjustable module and it made no difference. I am putting the vacuum gauge on and trying to drive. see it the vacuum jump around

[Greenlee]

My first thought was vacuum problem also. Do you have the factory metal line with short rubber hose on each end? I read somewhere that you shouldn't use rubber hose for the entire length from the transmission to the engine. Not sure if it makes a difference of not. I put a TH400 in my truck and was lucky enough to find a factory metal line.

[chris989]

Originally Posted by Greenlee

My first thought was vacuum problem also. Do you have the factory metal line with short rubber hose on each end? I read somewhere that you shouldn't use rubber hose for the entire length from the transmission to the engine. Not sure if it makes a difference of not. I put a TH400 in my truck and was lucky enough to find a factory metal line.

I have the metal line and both ends have fresh rubber.

[ont_guy_38]

Could possibly be the governor is worn out or stuck. The plastic gear is known for getting stripped and then not shifting correctly. I had a similar problem once, turned out i had changed my carb and the linkage wasn't correct so so the throttle was being pushed so far it was setting off the downshift switch on the pedal.

[clapage6]

hmmm do you get this same 2nd + 3rd gear hunting at any MPH? and it will do it consistently until you change throttle position?

[chris989]

Originally Posted by clapage6

hmmm do you get this same 2nd + 3rd gear hunting at any MPH? and it will do it consistently until you change throttle position?

I mostly notice it around 30-40 mph. I can do it higher but at that point my foot in normally in the gas.

When i give it some gas and drop the vacuum it will go to second. then I just give it enough gas to run the RPM higher, get to my speed and then let off.

[chris989]

Originally Posted by ont_guy_38

Could possibly be the governor is worn out or stuck. The plastic gear is known for getting stripped and then not shifting correctly. I had a similar problem once, turned out i had changed my carb and the linkage wasn't correct so so the throttle was being pushed so far it was setting off the downshift switch on the pedal.

This is a 400,, i think the OD trans had a cable linked to the carb.

[MylilBowTie]

I have a friend and that is what his th400 does also but never looked into it. I would say it wouldn't hurt to take a look at the governor. Make sure the shuttle can move freely and is clean. Also check the governorgear to make sure iit's not worn out. They typically wear out in the center making an hour glass shape.

[MylilBowTie]

[clapage6]

imo, unlikely it is the governor but could check it to be sure... all mine just wouldn't shift down to first at a stop when it was stuck.

The modulator tends to be the one that manages when to shift to a gear and how long to hold a gear, so if fluid is good and not burnt you may just keep playing with that adjustable modulator and also make sure it is indeed free and moves smoothly...

I'm pretty sure your th400 SHOULD have a kickdown switch.. it's not the th350 style with a cable. It's just a wire supplying 12v when the pedal is to the floor or usually 3/4+throttle anyway, could be something to look into or bypass for testing purposes... whether or not it is still wired is a good question, plenty of people leave them off and plan to manually down shift when needed.

[chris989]

I confess, I have only put a shift kit in a few turbo 350s back in the day and I have no idea where that thing goes. I will look into it, it is a big PIA to replace the gear?

Chris

[clapage6]

no problem at all to replace that gear if needed,

4 bolts to the cover on passenger side of trans, slide the governor out, remove old gear from the shuttle if it's still there haha..

slide the new one on and gently replace governor into trans done

[chris989]

Anyone have a part number or source from a local type place. All i see is for ordering online? I would like to pick it up at a parts store and try it this weekend.

Chris

[WyattEarp18]

Sounds like its losing pressure once it hits third. Might check the trans fluid pump.

[Greenlee]

Don't really have anything new to add. Just want to point out that on TBI trucks there is not a kickdown switch behind the gas peddle like there is on older th400 vehicles. Kick down on TBI trucks is controlled by a signal from the computer and a relay mounted on the firewall next to the fuel pump relay. I don't think the kick down switch is your problem because it only engages at lower speeds. On my truck it only kicks down at around 25 mph. The shifts at higher speeds are controlled by the vacuum modulator.

[GRADYS Performance]

Check your Line Pressure with a Guage.

[chris989]

update,

THe governor gear was in perfect shape, reinstalled the old one and my problem still persist.


Greenlee, I have a TBI turbo 400 set up. I d not think there is anything electronic controlling this transmission, But then again, I have not scoured the casing. I believe there is only the vacuum module.


Grady. I will find some fittings and tap into the cooling line. Is this something i can test sitting stil with engine RPM or do i need to be under a load any driving?

Thanks everyone.

[GRADYS Performance]

Line pressure is taken at the 1/8" pipe thread port that has a plug in it. It located on the side of the transmission in the middle of the case. It is the only pipe plug in the case. The cooler lines are not for Line Pressure readings. You check the pressure in each gear at idle and with the rpm raised.

[chris989]

Originally Posted by GRADYS Performance

Line pressure is taken at the 1/8" pipe thread port that has a plug in it. It located on the side of the transmission in the middle of the case. It is the only pipe plug in the case. The cooler lines are not for Line Pressure readings. You check the pressure in each gear at idle and with the rpm raised.

Thank you, I hope to dig into this tomorrow.

[imjeff]

Originally Posted by Greenlee

Don't really have anything new to add. Just want to point out that on TBI trucks there is not a kickdown switch behind the gas peddle like there is on older th400 vehicles. Kick down on TBI trucks is controlled by a signal from the computer and a relay mounted on the firewall next to the fuel pump relay. I don't think the kick down switch is your problem because it only engages at lower speeds. On my truck it only kicks down at around 25 mph. The shifts at higher speeds are controlled by the vacuum modulator.

The newer TBI 400s us a 12 volt signal from the computer that originates from the throttle position sensor. You can use the older throttle pedal switches or newer stuff like lokar's. The kick down switch is a WOT function, not a low speed function. Unless yours is sensing WOT somehow, it's not the kick down switch. Sounds like a fluid/vacuum issue. A shift kit will probably fix this, but if the vacuum/fluid issue is outside the valve body you'll still have the underlying issue. Heat and dirt are the only enemies of an automatic.

[rexrandom]

my '73 has a kickdown switch (electronic) on the passenger side carb linkage. wires into the 400. I'm having problems with the switch/linkage on the carb. B&M makes a $50 kit. That'll be my next move....

[imjeff]

Originally Posted by rexrandom

my '73 has a kickdown switch (electronic) on the passenger side carb linkage. wires into the 400. I'm having problems with the switch/linkage on the carb. B&M makes a $50 kit. That'll be my next move....

Lokar makes a cool kit, too, but it's about $70. It is awful perty though.

[rexrandom]

Originally Posted by imjeff

Lokar makes a cool kit, too, but it's about $70. It is awful perty though.

$70 is their cheap one!