A434 not shifting properly (1 Viewer)

[Pajaman]

A343f not shifting properly
I have an A343f on a KZJ95 that isn’t engine shifting as it should. It behaves absolutely normally going down and engine braking between gears 4, 3, and 2. It goes up through all the gears perfectly fine. The problem is first gear. If I put it in L (1st gear) at a stand still and accelerate, it shifts out of first and into 2nd around 2k rpm (it should stay in 1st). When it’s in 2nd and moving, and I shift to L, nothing happens until I’ve applied the brakes and slowed to around 5 mph and then it goes to first with a noticeable clunk (according to every manual, it should shift in to 1st at 33mph). When on a hill and at a stop, I can put it in 1st and it will start engine braking while driving up until about 2k where it shifts up to 2nd. It kind of feels like putting the clutch in and accelerating down a hill if this was a manual. This happens in both high range and low range and is rather disconcerting when off-roading as the truck feels like it drops off a cliff and starts moving quick. There was one time where it didn’t shift to 2nd and it stayed around 15 mph through a descent and felt amazing and as I imagine it should perform. This truck has always had this issue and I want to fix it.
I copy this post bit I have the same problem

 

[petegangies]

have you had the fluid flushed and replaced properly by a transmission place?

 

[Pajaman]

have you had the fluid flushed and replaced properly by a transmission place?

Yes,fluid Is new...

 

[petegangies]

Yes,fluid Is new...

have you done the manual shifting test to rule out the solenoids?

 

[Pajaman]

have you done the manual shifting test to rule out the solenoids?

No....i try found it....

 

[Pajaman]

have you done the manual shifting test to rule out the solenoids?

hi everyone, i did a manual gearshift test....after disconnecting the solenoid connector the transmission shifts exactly the same as before. In L it shifts from 1st to 2nd gear, when you let off the gas it shifts to 1st gear for a moment and then immediately shifts back to 2nd gear

 

[Malleus]

To start, do not try a "hit or miss" solution method. You need to systematically inspect each subsystem to rule out that system's potential for being the root cause of the problem. This may sound tedious and time consuming, but it really isn't, compared to guessing and being wrong, and it will allow ou to find and resolve the problem.

There are two likely root causes (IMO):
1» your Park/Neutral postion switch circuit is faulty (this is the easier of the two to troubleshoot).
2» you're getting bypass flow. Your boost piston may be in need of a new O-ring. It's under the valve body.

Download the A343F Automatic Transmission Repair Manual (not unit repair) dated 18JAN2020.
1» problem solving matrix begins on page AT-62. I would disregard "shift points too high/low" because your problem is only with one gear position. Instead, I'd look at the next line "Up-shifts to 2nd..." (page AT-82). The next possible root casue, if this is the problem, per the martix, is the ECM (page AT-59).
2» instructions for removing the valve body (pages AT-14 through AT-15).

 

[Malleus]

If you need to replace the piston O-ring(s), you can use the A343F unit repair manual (dated 28JAN2022), or just look, it'll be obvious once you remove the valve body. In fact, it may fall out on its own.

The Toyota part number is 90301-24010. If you use a generic O-ring, make sure it's nitrile, not Buna-N or natural rubber.

You want the C0 piston, (page AT-2). You might as well replace all the O-rings, while you have it open, if you get this far. You'll also need a tube of RTV (00295-01281, which replaces 08826-00090, specified in the manuals) Three Bond 1281, or equivalent. Permatex Automatic Transmission RTV Gasket Maker or something similar will work. Just make sure that whatever you use is rated against ATF, or it'll leak.

 

[Pajaman]

Pro začátek se nepokoušejte o řešení metodou „nahodilého výsledku nebo špatného výsledku“. Musíte systematicky prozkoumat každý subsystém, abyste vyloučili, že by daný systém mohl být hlavní příčinou problému. Může to znít zdlouhavě a časově náročně, ale ve srovnání s hádáním a chybami to tak ve skutečnosti není a umožní vám to problém najít a vyřešit.

Existují dvě pravděpodobné příčiny (podle mého názoru):
1» Obvod spínače parkovací/neutrální polohy je vadný (toto je snazší z těchto dvou řešení).
2» máte obtokový průtok. Váš přepouštěcí píst možná potřebuje nový O-kroužek. Je pod tělesem ventilu.

Stáhněte si manuál k opravě automatické převodovky A343F (ne opravu jednotky) ze dne 18. ledna 2020.
Matice řešení problémů 1» začíná na straně AT-62. Nebral bych v úvahu „body řazení příliš vysoké/nízké“, protože váš problém je pouze s jednou převodovou polohou. Místo toho bych se podíval na další řádek „Řazení nahoru na 2. stupeň...“ (strana AT-82). Další možnou příčinou problému, pokud se jedná o toto, je podle matice ECM (strana AT-59).
2» pokyny k demontáži tělesa ventilu (strany AT-14 až AT-15).

ThanksI'll try it and let you know...in my country it's very difficult to find someone who services these gearboxes

 

[Malleus]

Don't lose heart...if this guy can do it, anyone can.
A343F transmission teardown
A343F transmission assembly

 

[Pajaman]

Don't lose heart...if this guy can do it, anyone can.
A343F transmission teardown
A343F transmission assembly

well..i'm not sure...