A340F transmission rough 1/2 shift

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Thread: A340F transmission rough 1/2 shift

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    Default A340F transmission rough 1/2 shift

    I have had this 1/2 shift problem for the last nine years. The 1/2 shift seems slow then finishes with a bang or bump. The trans shop referred to this as "slide bump". This occurs when starting out with the shift lever in D position. If I start out with the shift lever in 2 position, the 1/2 shift is quick and fine. I noticed this rough 1/2 shift when I got the truck @39,000 miles. At 62,000 I had enough and took it to a trans shop. They said a rebuild would fix this. After four months of trying different clutch materials, different valve bodies, additives, and lightening my wallet by $1,000 they said this was the best they could do. I needed the truck so I just took it rebuilt trans, rebuilt converter, but still the same old problem. I now have 82,000 miles and it is still the same.
    I have my own theory on this and wondered what others thought. The second gear has what is called a sprag which is a one direction clutch. When in Drive and it is time for the 1/2 shift the clutch grabs the sprag and finishes the shift by powering the second gear set through the sprag. When the shift lever is in the 2 position the sprag is locked up and not used so that you don't have free wheeling and have the second gear as an engine brake. My question is could this sprag be worn and slipping and then grab with a bang.
    Any thoughts on this would be appreciated.

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    Junior Member I20RIDER's Avatar
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    Default Re: A340F transmission rough 1/2 shift

    Up your line pressure

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    Default Re: A340F transmission rough 1/2 shift

    According to my FSM, harsh engagement in the 1/2 shift is caused by a problem with the accumulator control valve or the B2 accumulator. I'm no tranny expert but I believe those parts are both found in the valve body.

    There's a simple test for line pressure. With a warm tranny, engine at idle and truck stationary, shift from N to D. The time lag from the shift to the "bump" should be less than 1.2 seconds. For the shift from N to R, the time lag from the shift to the "bump" should be less than 1.5 seconds. If the time lag is longer than those specified, your line pressure is too low.

    The line pressure for your '01 truck is mechanically controlled by a throttle cable, cam, and throttle valve ('02 and later trucks have electronically controlled line pressure). For throttle cable adjustment, the FSM says that with throttle valve (throttle butterfly plate) fully opened the distance between the boot end face and inner cable stopper should be 0 – 1 mm (0 – 0.04 in.).

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    Default Re: A340F transmission rough 1/2 shift

    Quote Originally Posted by rjrjs View Post
    I have had this 1/2 shift problem for the last nine years...
    So, you'd say this wasn't an emergency then, yes?
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    Default Re: A340F transmission rough 1/2 shift

    I'm surprised it wasn't covered under warranty; especially with the "bang" into the next gear. Visiting an independent tranny shop would've confirmed it for ammo to take back to the dealership before you got to the 5year/60K mark.

    Mine always shifted maybe 500 RPMs too late from 1st to 2nd and it bothered me at first, but I got used to it after several years. No change even after 10 years; granted I always change the fluid with synthetic Mobil 1 every 30K.

    If I had a bang getting into 2nd, I'd be raising hell with Toyota, but that's water under the bridge now for you.
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    Default Re: A340F transmission rough 1/2 shift

    My tundra is an 01 Limited and has no shift cable and is electronically controlled.

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