Transmission assistance needed

[brownjeans]

Okay, I have a 96 Lexus LX450 with some odd transmission behavior. When I approach a stop sign the transmission "clutch" engages. Then when I remove my foot from the brake and press the gas to proceed, the engine revs because the "clutch" is still engaged. A moment or so later the "clutch" releases and the car moves. This same sticky "clutch" sensation happens in reverse as well. All shifts while driving are normal with no issues.
I adjusted the transmission cables and no change. Then I suspected it was the lockup solenoid so I bought a set of the solenoids for the A440 series transmission (got the entire set for $200) but once I took the pan off, it seems that's not the transmission I have - so unless the solenoids I have work for the transmission I have I'll be returning those.
It looks like I have an A340 series transmission with a Type 1 valve body? Maybe?

So here are my questions:

1. What transmission do I have (so I get the right solenoids)?
2. What does the behavoir suggest? Maybe lock-up? Definitely not lock-up?

Here are some photos to help with answering some of these questions:

 

[family80]

You would a have a A343 trans if my info is correct. Your issue sounds like a torque converter problem. Since you have it drained out I would refill and put in a tube a lubeguard you can get it at any parts store if the slipping lessens or goes away you know it’s a TC problem.

 

[ajax1]

Do you have the issues in low range?

 

[brownjeans]

You would a have a A343 trans if my info is correct. Your issue sounds like a torque converter problem. Since you have it drained out I would refill and put in a tube a lubeguard you can get it at any parts store if the slipping lessens or goes away you know it’s a TC problem.

What makes you think it's the torque converter rather than the lockup solenoid?
Is this the product you are talking about? Type F ATF Protectant - Lubegard - https://lubegard.com/products/2634/

 

[brownjeans]

Do you have the issues in low range?

Not sure... I think I tested this before and it was still the same. Can't re-test without putting the filter, and pan back on and re-fill with oil.

Why do you ask? My tranfer case doesn't have a viscous coupler (removed it and converted my rig to part-time 4wd with locking hubs), would that make a difference with your question?

 

[family80]

I believe it’s an TC because of previous TC issues dealt with. If your symptom is slipping on acceleration but normal shifting once moving the trans is working properly, but the connection between engine and trans is the issue if it’s only on acceleration. This is what I would try

 

[brownjeans]

I believe it’s an TC because of previous TC issues dealt with. If your symptom is slipping on acceleration but normal shifting once moving the trans is working properly, but the connection between engine and trans is the issue if it’s only on acceleration. This is what I would try
View attachment 4031233

So it's not like a slip, or shudder. It's more like it's in neutral and the engine revs - then it instantly connects like a hammer and if the revs are still up it squeels the tires and gives you whiplash. If it was a manual it would be just like holding in the clutch and then releasing the pedal with zero feather and doing a burnout. With it behaving this way, I have to be careful with the brake and gas becuase it can't be good to have the trans slamming the truck forward every time I stop for a short time.

I should also note that it rarely happens at a stop light - because I'm stopped for longer and it gives time to whatever the problem is so that it re-engages the transmission after the stop and before I need to go.

From what I've read the lockup solenoid locks the torque converter to the transmission similar to a clutch - that's why I wondered if the problem was the lockup solenoid. Solenoids are only about $50.00 and easy to replace since I have the pan dropped already. So I figured it wouldn't be a huge deal to replace it as a test to see if it cures the problem. But I'm not sure which solenoid of the three I'm looking at is the lockup, or which part to buy online

 

[family80]

Thread 'A343F Transmission Solenoid Part Numbers'

Jan 26, 2025

I have a 1997 LC and would like to confirm the correct part numbers for the A343F transmission shift solenoids. I understand there are 3 shift solenoids, and two of them are the same solenoid, so 2 part numbers are needed for the 3. Nearly all of the transmission solenoid discussions on here are about the A442F transmission. Perhaps the A343Fs haven's quite reached the age where these solenoids need replacing, thus the lack of discussion.

If I plug my truck info into the Toyota parts website, it does not list any available transmission shift solenoids.

If I plug my truck info into...

• Tyland Cruiser
• Replies: 5
• Forum: 80-Series Tech

• 

Maybe this will help in your search for the solenoids.

 

[Malleus]

Okay, I have a 96 Lexus LX450 with some odd transmission behavior. When I approach a stop sign the transmission "clutch" engages. Then when I remove my foot from the brake and press the gas to proceed, the engine revs because the "clutch" is still engaged. A moment or so later the "clutch" releases and the car moves. This same sticky "clutch" sensation happens in reverse as well. All shifts while driving are normal with no issues.
I adjusted the transmission cables and no change. Then I suspected it was the lockup solenoid so I bought a set of the solenoids for the A440 series transmission (got the entire set for $200) but once I took the pan off, it seems that's not the transmission I have - so unless the solenoids I have work for the transmission I have I'll be returning those.
It looks like I have an A340 series transmission with a Type 1 valve body? Maybe?

So here are my questions:

1. What transmission do I have (so I get the right solenoids)?
2. What does the behavoir suggest? Maybe lock-up? Definitely not lock-up?

Here are some photos to help with answering some of these questions:
View attachment 4031073

View attachment 4031076View attachment 4031078

View attachment 4031074

You have an A343F transmission.
» The solenoid you bought will not work in your transmission.
» Your problem is not a torque converter problem; it only engages above 53–mph and disengages around 45–mph. The details are in the service manual; I suggest you download a copy from the Resources forum.

If your fluid level is correct, and if your fluid is clean, and if your electrical connections are good [you really need to check all of these items FIRST]:
» Your problem is most likely a sticking shift spool valve.

My recommendation would be to flush your transmission fluid, completely, using the transmission cooler soft lines near the radiator. You'll need 12 quarts for a complete flush. Do not attempt to replace the fluid by simply draining the pan; it won't work. This method is based on totally false economy; you will only be mixing dirty fluid with clean fluid.

Check your fluid level (and condition – is it bright red, dark brown, does it smell burnt or faintly sweet?) and the electrical connection to the solenoid pigtail (sub–harness) (it's the wire on the side of the transmission, near the rear) and report back after you've done those two things. You can use CRC QD plastic safe electrical contact cleaner to clean the connection INSIDE the connector housing (it won't hurt to clean the outside, it'll make disengaging the halves easier).

 

[Malleus]

The fluid I use is Mobil 126505 multi vehicle ATF. Summit Racing has the best price I've seen. Buy two (6 count) cases).

 

[Malleus]

BTW, pouring anything that is not ATF in your transmission will make the transmission rebuilder very happy.

 

[Malleus]

If you are desperate to buy parts, the correct 1-2 shift solenoid part numbers are 85420-21090; you need two. Don't bother buying the lock–up solenoid (352050-50030), because that's not your problem.

...and if you're buying solenoids for $50, you're buying Chinese crap.

 

[brownjeans]

You have an A343F transmission.
» The solenoid you bought will not work in your transmission.
» Your problem is not a torque converter problem; it only engages above 53–mph and disengages around 45–mph. The details are in the service manual; I suggest you download a copy from the Resources forum.
View attachment 4031319

If your fluid level is correct, and if your fluid is clean, and if your electrical connections are good [you really need to check all of these items FIRST]:
» Your problem is most likely a sticking shift spool valve.

My recommendation would be to flush your transmission fluid, completely, using the transmission cooler soft lines near the radiator. You'll need 12 quarts for a complete flush. Do not attempt to replace the fluid by simply draining the pan; it won't work. This method is based on totally false economy; you will only be mixing dirty fluid with clean fluid.

Check your fluid level (and condition – is it bright red, dark brown, does it smell burnt or faintly sweet?) and the electrical connection to the solenoid pigtail (sub–harness) (it's the wire on the side of the transmission, near the rear) and report back after you've done those two things. You can use CRC QD plastic safe electrical contact cleaner to clean the connection INSIDE the connector housing (it won't hurt to clean the outside, it'll make disengaging the halves easier).
View attachment 4031313

Thanks for this response.
Bummer about the lockup not being the problem. Seemed like a simple, easy fix. But good to know it's not the torque converter. The fluid doesn't smell burnt, isn't brown or bright red. It looks a lot like new Type F fluid actually. I can do a flush though to make sure. It's got 250K miles so a flush is probably a good idea. I might as well change the filter while I have the pan off.
I'll check the connectors too.
No idea what a shift spool valve is... Hope the connector cleaning and flush take care of it.

 

[Malleus]

The spool is what the solenoid moves; it is the valve which causes the gear selection. If you are brave, or if you have the transmission unit repair manual (which is in the Resources forum), you can clean the valve spools and their galleys with kerosene (the procedure is in the manual). Just make sure you back flush the galleys and wash the spools in new ATF before you reassemble them. You can use any A343F unit repair manual for cleaning instructions.

» If you choose to clean the valve body, BE VERY CAREFUL when you separate the upper and lower halves (the procedure is in the manual). If the check balls fall out, you will play hell trying to figure out which variant you have to get them back in the correct positions. You should also replace the gasket(s) if you do this.

The fluid should smell faintly sweet, or not at all if it's old, and should be bright pink. The darker it is, the dirtier it is.

Your ATF fluid, and brake fluid, should be changed yearly; more often if you tow. Both are extremely hygroscopic and water doesn't respond to compression very well. Or, I should I say, it compresses very well, which is exactly the opposite of what you want in a pressurized hydraulic system.

 

[brownjeans]

The spool is what the solenoid moves; it is the valve which causes the gear selection. If you are brave, or if you have the transmission unit repair manual (which is in the Resources forum), you can clean the valve spools and their galleys with kerosene (the procedure is in the manual). Just make sure you back flush the galleys and wash the spools in new ATF before you reassemble them. You can use any A343F unit repair manual for cleaning instructions.

» If you choose to clean the valve body, BE VERY CAREFUL when you separate the upper and lower halves (the procedure is in the manual). If the check balls fall out, you will play hell trying to figure out which variant you have to get them back in the correct positions. You should also replace the gasket(s) if you do this.

The fluid should smell faintly sweet, or not at all if it's old, and should be bright pink. The darker it is, the dirtier it is.

Your ATF fluid, and brake fluid, should be changed yearly; more often if you tow. Both are extremely hygroscopic and water doesn't respond to compression very well. Or, I should I say, it compresses very well, which is exactly the opposite of what you want in a pressurized hydraulic system.

Messing with the valve body terrifies me. The reason I bought the solenoid and was hoping it was the problem is because I'm not experienced with trouble shooting complex systems such as vacuum, automatic transmissions, electrical. I get propper scared that I could make something worse. At the same time, I am afraid that if I take it somewhere they will want to rebuild the transmission and charge me thousands when it might not be necessary. So I effort where I can...

I'll take a look at the A434F repair manual and see if it give me bad dreams tonight.

 

[Malleus]

...and just to be clear, you'll be using the transmission pump to flush the fluid – the process duplicates the normal fluid flow in the operating transmission. Instead of routing fluid through the front cooler and back into the case, you'll be dumping the cooler contents and replacing that volume of fluid through the fill tube. There is no risk of harm, as long as there is fluid in the system. It does help to drain the case overnight, if you can; this speeds up the fluid replacement process by about 10 minutes and removes some of whatever is sitting in the bottom of the pan.

Since you already have the pan off, wash everything you can in kerosene and then again in new, clean ATF. You can use the pan as a cleaning tank, just be sure to replace the drain plug gasket first.

Even using this method, which is the best option you have without tearing the unit apart, you will not be able to replace 100% of the fluid. Whatever is in the torque converter (about a quart or so) and most of what is hiding in the valve body (unless you split the halves) will still be there when you're done.

 

[Malleus]

Messing with the valve body terrifies me. The reason I bought the solenoid and was hoping it was the problem is because I'm not experienced with trouble shooting complex systems such as vacuum, automatic transmissions, electrical. I get propper scared that I could make something worse. At the same time, I am afraid that if I take is somewhere they will want to rebuild the transmission and charge me thousands when it might not be necessary. So I effort where I can...

I'll take a look at the A434F repair manual and see if it give me bad dreams tonight.

It looks worse than it is. Make sure you get the correct manual, there are two. One is an excerpt from the primary service manual; it only describes what you can do with the transmission installed, and how to remove and install the transmission. That's not the one you want. You want the UNIT REPAIR manual. That manual has a section in it concerning the valve body.

There may not be a copy in the Lexus area. The one in the Land Cruiser area will be good for both the 80 and LX450, for your purposes.