TH 400 won't go into gear after sitting.

[Killer]

After sitting overnight it won't go into gear at all. No noise or anything. Can take anywhere from 1-3 min to go into gear(engage). Reverse or drive it doesn't matter. Happens too after coming out of the store to go home. This is an every day thing not just once in a while. Longer it sits the longer it takes to move. Fluid level on the stick is really high when this happens. Been doing it since I bought it 6 months ago and has not gotten any worse. New filter and fluid, B&M RV shift kit still does it. Linkage, detent, etc. is fine shifts perfect. Engine speed slowly drops when it decides to kick in. Like pressure has finally developed.


Need real help here I have been a mechanic for 31 years but have no domestic trans experience. This is my first post so please be kind

 

[Jrgunn5150]

So you bought it and it was doing this, and you changed the filter and fluid, and it's still doing it?

 

[likesoldtrucks]

Sounds like a trip to the tranny shop..bummer
Been there done that

 

[firebane]

Yup time to start looking for a replacement or rebuild.. My TH350 is being the same.

 

[74propu]

I had a 400 that did the same thing found out the filter was lose in the valve body put a bigger o ring on the filter and it worked fine after that . get a new filter and go to a hydraulic shop and get a thicker o ring for it and see if that will fix it

 

[Jrgunn5150]

I had a 400 that did the same thing found out the filter was lose in the valve body put a bigger o ring on the filter and it worked fine after that . get a new filter and go to a hydraulic shop and get a thicker o ring for it and see if that will fix it

That's my first guess, my second is the seals are hardened.

 

[Killer]

I had a 400 that did the same thing found out the filter was lose in the valve body put a bigger o ring on the filter and it worked fine after that . get a new filter and go to a hydraulic shop and get a thicker o ring for it and see if that will fix it

I used 2 O rings when I changed the filter so that's not it. I also checked the O rigs a second time when thew shift kit was installed. Thanks

 

[Killer]

That's my first guess, my second is the seals are hardened.

That's a good suggestion, might be leaking down past the seals. Bought it cheap because of the tranny problem guess it's time for a rebuild.

 

[Jrgunn5150]

I used 2 O rings when I changed the filter so that's not it. I also checked the O rigs a second time when thew shift kit was installed. Thanks

So then the seals are likely hardened internally, once it warms up, they swell up, you get pressure, and zoom.

You can try Lucas Transmission additive, or some of the other rebuild's in a bottle. It may do nothing, or cure it, or somewhere in between lol. It's a crutch basically.

But unfortunately you do have a rebuild coming.

 

[Killer]

So then the seals are likely hardened internally, once it warms up, they swell up, you get pressure, and zoom.

You can try Lucas Transmission additive, or some of the other rebuild's in a bottle. It may do nothing, or cure it, or somewhere in between lol. It's a crutch basically.

But unfortunately you do have a rebuild coming.

Or live with it, shifts nice and crisp once it gets going.

 

[Jrgunn5150]

Or live with it, shifts nice and crisp once it gets going.

Yeah, extended warm up's should keep it going for who knows how long lol.

 

[Killer]

Not really a warm up thing. Only takes 1-3 min for the fluid to drop down to the correct level and then slow bump into gear. Does like my first car a 69 Charger when the converter drained back. been told TH 400's don't drain back or at least they have never seen it happen??

 

[87scotty]

Shes just making sure motors good to go before she moves lol

 

[Jrgunn5150]

Not really a warm up thing. Only takes 1-3 min for the fluid to drop down to the correct level and then slow bump into gear. Does like my first car a 69 Charger when the converter drained back. been told TH 400's don't drain back or at least they have never seen it happen??

Warm up, extended period of runtime before you move, whatever you want to call it lol.

If you're not losing any fluid, and it has TC drainback symptons, it's most likely the pressure regulator valve. Which is accessible through the pan, inside the pump.

One of two thing's can happen. Some builder's liked to mod this valve for full time converter feed, which sometime's led to converter drainback as a side effect.

Or, the seals on it are bad for one reason or another, and again, the drainback is a side effect.

Sonnax, as usual, has a solution, http://www.transmissionpartsusa.com/TH400_pressure_regulator_valve_kit_1971_on_p/400-03491003k.htm

 

[Killer]

Thanks for the info on the pressure regulator and link! I think you have defiantly hit on the most likely cause of my problem. When I installed the shift kilt the regulator spring was replaced but I didn't remove the valve itself. It stayed up in the bore so I figured leave it be. Guess I should have had a look and compared it to a stock one. Before I waste any money on a rebuild the valve is going to get replaced.