4r70w Problem

[zanddattack]

97 F150 4.6 with 85,000 miles transmission unmodified Hello, I posted a problem with this transmission a few months ago which then had an occasional (every 250-350 miles or so) slip when shifting between third and overdrive. I have since changed the fluid/filter and replaced the nuetral safety switch, and throttle position sensor, but this did not fix the problem. This slipping issue lately happens often and my wife told me she barely made it home tonight so I test drove the truck around the block and from what I can tell I now have completely lost third gear. While stopped on a straight and level road and watching the tachometer I accelerated smoothly, the tranny shifted to second and I brought it as high as 4000 RPM and it would'nt go into third and when I released the accelerator the engine did not slow the truck and the RPM went to about 1200 . When the speed of the truck slowed to about 30 MPH second gear then re-enagaged.When this issue first appeared a few months ago no code was produced and I have never seen a check light. Does anyone know how I might go about troubleshooting this? I thank all that respond Steve

Register today or sign-in to remove these ads!

[Drdexron]

It's probably time for an overhaul. Does the trans fluid look or smell burned?

[zanddattack]

The fluid is not burnt and when I changed it and the filter about 1000 miles ago the bottom of the pan was fairly clean, and the magnet had a thin layer of tiny ferrous material around it, conditions which I believe can be considered normal.
Thanks
Steve

[subford]

The Direct Clutch is not being applied.

A no 2-3 shift condition may be caused by an open in SS2 or its wiring, provided first and second gears were achieved. SS1 could NOT be at fault if both first and second gears were achieved.

A sticking 2-3 shift valve could cause a no 2-3 upshift. If the valve is OK the problem may be in the mechanical domain (direct clutch worn, damaged or leaking). Check the direct clutch pressure tap for correct pressure (45-75 psi).

[Drdexron]

In third gear the forward and direct clutches are applied. The forward clutch is probably ok because it is applied in first and second gear also, and those gears are ok.
Most likely you have a problem with the direct clutch, or a component that controls it, such as the 2-3 accumulator or sticking shift valve. You need to have the computer scanned for codes first, just to rule out anything electrical.

[zanddattack]

Thanks for the replies,
I intend to check for codes but lets say it is the direct clutch/2-3 accumulator or shift valve, are any of these components accessible by dropping the pan or is a major disassembly on the horizon?
Steve

[Drdexron]

The 2-3 accumulator can be accessed by first removing the pan, then dropping the valve body, which is pretty easy, although messy. You will need a container that holds at least 10-12 qts of fluid. Underneath the valve body is the 2-3 accumulator retainer, piston and spring.