TH400 fluid drainback
 

So my th400 takes anywhere from 2 to 10 minutes when the engine is cold to kick into gear. Another forum said it could be the check valve in the pump letting trans fluid flow out. Anybody else come across this and if so how did you fix it? Does it need to be rebuilt? Do I need a new trans fluid pump? Do I need to scrap the whole truck and leave while im ahead? Thanks.

Re: TH400 fluid drainback
 

There is not a check valve in the front pump of a Turbo 400 transmission. Have you checked Fluid Level, Shifter Adjustmnet, Changed Fluid and Filter?

Re: TH400 fluid drainback
 

First thing I did after buying it was changed all oils and filters. That didn't fix the trans so I went to the forums and someone said to check the trans oil before starting and mark the level. Then start the truck and run it until it powers into gear. Then shut it down and wait for a couple minutes and check the oil again. It was significantly lower. If there's not a check valve then what keeps the oil from flowing right back out like its doing now?

Re: TH400 fluid drainback
 

I do not know of the appropriate way to check this BUT. I believe you have bad seals somewhere on your input shaft. Once trans is warm the shaft or seals have expanded enough to heat up. The trans needs to be overhauled to fix these.

Re: TH400 fluid drainback
 

There are no seals on the input shaft in a TH400. Fluid is draining out of the torque converter back into the transmission because of wear in the front pump bushing or pump gear wear most likely. I would suggest checking line pressure to see what the general condition of the transmission is. When you changed the fluid and filter, what did the oil look like and what did the bottom of the pan look like? Check your fluid level with vehicle level idling in park.

Re: TH400 fluid drainback
 

The filter had a little bit of metal in it 6 months ago when I bought it. I cut the old filter with some dikes. The bottom of the pan had some sludge but not much for a truck that had been sitting for 9years. So if I had it rebuilt would that fix my problem? Or do I need a new pump?

Re: TH400 fluid drainback
 

Subscribed. Having issues like this as well. Thanks

Re: TH400 fluid drainback
 

Does anyone know where I can find a schematic or diagram showing the fluid flow for a th400

Re: TH400 fluid drainback
 

Rebuilding the transmission and replacing the torque converter with a remanufactured unit will fix your problem. What has caused the problem would need to be diagnosed during the rebuild and repaired as needed. The front pump would need to be inspected to determine if it needs replaced. It may only need the pump bushing replaced. But you will not know untill the transmission is taken apart. I do not know where you can get a scematic of fluid flow in a TH400.