I just installed a rebuilt transmission in my 2000 f150 it will shift through all the gears and reveres works good. But unless I idle it up it won't go into gear it will not go into gear until I idle it up then it jumps into gear hard but then it will run until you let off of it

 

Double check the fluid level? Did the transmission come with a new converter?

 

This may be related to the P0720 code in your other thread.........

 

Here is how the system works.
Engine running turns the front transmission pump via the converter so pressure is instantly available.
When you go into gear, the computer opens the EPC solenoid (electric pressure control) to supply pressure to the first gear Servo so it can apply pressure to the disc clutches with the A solenoid opened..
You would normally see the Tach drop a small amount when this happens indicating the trans has readied to move the vehicle.
There after, depending on the shifter selector position, the PCM signals the trans solenoids to operate based on engine rpm, TPS position and Vss signals in combination for logic decision making.
The DTRS on the transmission tells the computer what position the shifter is in so the computer know how to handle the function.
.
It sounds by your description either the EPC is not opening or the front pump does not generate enough pressure until the rpm goes up, to operate the servo/clutch combination.
The sudden bang is the sudden application of fluid pressure to the clutch disc assembly.
Normally the Servo is spring loaded to soften this action and the valve in the valve body has a spring to also soften the application of fluid to the Servo.
There may be an issue somewhere along this operational path sequence.
If you had your trans rebuilt or installed by a shop, they need to find the fault for you.
I know it sounds like a lot of info but you need it to come to some conclusion on what to do based on how the system works..
Good luck.
.

 

the guy that rebuilt the transmission to me the same thing the it's the pressure regulator. I talked to him today the only problem it that he in florida and I'm in texas that what I get from buying of the internet. do I have to take the transmission back out or can I fix it in the truck

 

it came with a converter I don't no if it was a new one

 

Try to look for a fault code first involving the transmission.
This helps insure your going after the right source of the fault.
The reason for this is the computer looks at the operating current 'signature' of each solenoid for being open, shorted and sticking.
To service these solenoids, the pan has to be drained and dropped exposing the valve body.
On the valve body is all the solenoids.
Look up the ID and locations of them so you get to the right one.
Good luck.

 

thanks a lot , man. I am going to put in the shop this week