th400 not shifting to 3rd gear?

[leroyd92]

I have a 1980suburban that has the original tranny in it.

I've checked the modulator,govenor,fluid level. Filter is new, fluid is new.

The darn thing just one day stopped shifting out of 2nd gear...

I haven't checked the linkage but the truck is a offroader with no doors, and I can hear the linkage click into all the gears (not just in the column).

The kick down solenoid was never hooked up. So I doubt that's the issue... I think my next move is pull the VB and check for whatever may be stuck...

Opinions????? Suggestions?????

Thank you for the time and input!


Move this to proper thread if I was foolish and posted incorrectly

 

[Chris142]

Got vacuum to the modulator?

 

[supton]

I wonder if the kickdown "broke". IIRC it works by forcing a downshift when vacuum drops. It's surprising that it worked w/o a vacuum to indicate that it can go to high gear; I'm wondering if it was broken such that it worked just fine without it--until something jarred it loose, and now it's decided to work properly now.

Will it go into 1st gear properly?

 

[turtlevette]

If you can't figure it out, as a last resort you could put in a bottle of Lucas Trans Fix. It had worked for a few of us to get transmissions shifting again.

 

[leroyd92]

Originally Posted By: supton
I wonder if the kickdown "broke". IIRC it works by forcing a downshift when vacuum drops. It's surprising that it worked w/o a vacuum to indicate that it can go to high gear; I'm wondering if it was broken such that it worked just fine without it--until something jarred it loose, and now it's decided to work properly now.

Will it go into 1st gear properly?



I have vacuum to the modulator, steel line to the thick walled elbow...

IM really wondering if that solenoid is messed up, I thought about jumping it to verify if it (clunk) of not.....

I have 2bottles of transx in it right now...

 

[clinebarger]

Originally Posted By: leroyd92
Originally Posted By: supton
I wonder if the kickdown "broke". IIRC it works by forcing a downshift when vacuum drops. It's surprising that it worked w/o a vacuum to indicate that it can go to high gear; I'm wondering if it was broken such that it worked just fine without it--until something jarred it loose, and now it's decided to work properly now.

Will it go into 1st gear properly?



I have vacuum to the modulator, steel line to the thick walled elbow...

IM really wondering if that solenoid is messed up, I thought about jumping it to verify if it (clunk) of not.....

I have 2bottles of transx in it right now...


The Detent Solenoid cannot stick open if power was never applied to it.
Possible causes.
Stuck 2-3 shift valve.
Direct Clutch Piston seals hardened/worn.
Center Support sealing rings worn &/or Worn Direct Drum.

If this TH400 has gone 34 years without a rebuild??? It's about time for one.

 

[leroyd92]

Originally Posted By: clinebarger
Originally Posted By: leroyd92
Originally Posted By: supton
I wonder if the kickdown "broke". IIRC it works by forcing a downshift when vacuum drops. It's surprising that it worked w/o a vacuum to indicate that it can go to high gear; I'm wondering if it was broken such that it worked just fine without it--until something jarred it loose, and now it's decided to work properly now.

Will it go into 1st gear properly?



I have vacuum to the modulator, steel line to the thick walled elbow...

IM really wondering if that solenoid is messed up, I thought about jumping it to verify if it (clunk) of not.....

I have 2bottles of transx in it right now...


The Detent Solenoid cannot stick open if power was never applied to it.
Possible causes.
Stuck 2-3 shift valve.
Direct Clutch Piston seals hardened/worn.
Center Support sealing rings worn &/or Worn Direct Drum.

If this TH400 has gone 34 years without a rebuild??? It's about time for one.


Reverse is instant and easily breaks 33"tires loose in D321.

IM thinking a vb removal and inspection is the next step... does anyone have a diagram showing the innards of the VB ? I've found a few but they were kinda funky

 

[Merkava_4]

I had the same thing happen to my Cadillac with the TH400.

Replaced the vacuum modulator and got 3rd gear back.

 

[Chris142]

I know that trans shops will stuff one into park at speed hoping to free up a stuck governor. I dunno if this pertains to you,

 

[Robenstein]

If its cruded up and you want to give an additive a shot I have seen the BG stuff fix a few transmissions. Not sure for how long they lasted but a few were TH400's and TH350's

 

[leroyd92]

Hmm, the modulator is new (2)years old...

The governor is free and spotlessly clean...

Tranny got a (Leroy) flush 3years ago when I got it and the fluid still came out rather clean, and now 2changes since then, so idk.

I have too many projects right now to rebuild... looks like I'll check the vb and the modulator.