Transmission, A750 issues

BMThiker

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So a couple weeks ago I started noticing that my transmission couldn't decide on the right gear to stay in... typically when feathering the throttle in the 1500-2000 RPM range. I figured overdrive was having an issue so I started just putting the transmission in 4th gear when surface street driving and then kicking it into D when I got up to 60 or so on the highway. It's been a while since I changed the ATF, maybe 80-100K.

I decided my first plan of attack would be to do a soft swap of fluids: drain and drop the pan, clean the screen and then refill. It's helping but after discussing with some friends at ACC it looks like it may be a stuck solenoid. We scanned it with Techstream and there are no codes in the ECT, so we're flying blind a bit.

Cleaned up the pan and screen before putting it back together and it looked remarkably pristine upon initial examination. The residue was a carbon black but very very fine and just a small amount of film stuck to the magnets. An even finer "patina" on the metal screen filter assembly but it wiped right off.

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BMThiker

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I'm going back into it soon to replace some solenoids, once I've got my research down. I will probably go ahead and replace the metal screen filter assembly and o-ring and a new pan gasket. For now I scrapped the old gasket and used red FIPG.

ACC techs were telling me they have seen where old solenoid valves get wallowed out and the fix is to replace with a new larger valve after carefully machining out a larger bore diameter. They say there are plenty of rebuild kits available for this transmission. I'll report back when I have some solid tech to share.
 
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Hey @BMThiker, I certainly appreciate this thread....
Our tranny has occasionally done this gear hunting almost since day one.
Our issue was always when shifting from 1->2 and very occasionally from 2->3.
And, as you mentioned, only during light throttle feathering, if I step on it a bit there's zero issues with shifting.

What I did find is if I filled an extra 100-200ml past when the "toyota" method said it was full then the gear hunting would cease to exist.
I went simply on the hunch that it felt like something was starving for fluid during a shift so I thought I'd try it.
I'm sure you're now laughing at my post given how unscientific it sounds......and I apologize if it sounds like a backyard fix.
We generally drain and replace our fluid every 30-40,000km (we do a fair bit of towing with this truck).

Anyhow, we went years with this "overfill" method with no hunting what so ever (perhaps just a coincidence, who knows?).
Given the amount of miles on our truck I'd say it's safe to say we didn't do it any adverse harm with this method as the tranny has never been touched other than drain and fills.

However, it recently started doing it again but this time was a little more violent (I dont know what other word to use) than usual. Plus it's now basically always the 1->2 AND 2->3 shifts.

I'm going to drain and fill again and see the results but given how long we've went without issues I suspect our luck has run out and it's going to require something further. Your thread timing may just end up being perfect to help with whatever is going on with ours if it turns out to be something more.

Thanks!
 
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BMThiker

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I've actually heard from my friends at ACC that they recommend filling until the overflow valves shows, then close that plug and add another 4-8 oz (118mL-236mL). So, I'm with you on this!

In the past, (I think I've posted about this before) I've had the infamous transmission shudder around 20mph and 40 mph. A simple fluid drain and fill with fresh ATF did the trick to fix that.

I'm thinking this is actual high mileage wear and tear on the A750. A new A750 from Toyota dealer is around $2600 last I checked, so replacing a few solenoids for a few hundred seems a reasonable way to go about this.

I've also seen high priced valve body replacements in which they have taken core A750 valve bodies and essentially done the same thing I talked about in the above post - drill out and replace the solenoid/valves with larger ones. I'm hoping to find a cheaper DIY option.
 

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Here's a good video on the WAT valve body and lock-up module from Cruiser Brothers.
 
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Hey!
Wow, some great information, very much appreciated.
I hope to do a drain and fill today, we'll see how that affects things and then go from there.
I'd like to buy a bit of time and get to spring before we go digging in deeper.
Thanks again for this thread and for sharing your knowledge.
 

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I talked with a guy at ImportPerformanceTrans.com today to ask about there valvebody service. John seemed fairly knowledgeable of the A750E and other Toyota transmissions. And he basically talked me out of replacing the valve body at this point. His argument was that based on the symptoms I'm having, that it sounded more like a signal issue than a solenoid issue. So we talked about the sources of such and thought that the throttle position sensor might be the lowest hanging fruit. So that's where I'm going to start.

I talked with my buddy at ACC and he agreed that there may just be a dead zone in the TPS that allows the signal to get jumpy in the middle somewhere and when I apply throttle, the RPMs increase and hydraulic pressures in the valve body increase making the shifting do what its supposed to do.

From there IPT suggested the pressure control valve. Then next would be the valve body in its entirety. He didn't argue that with my mileage (225K) that the valve body isn't worn, but that it's just not the fix all for the slipping/skipping I'm experiencing. Hoping to make some progress this weekend if the TPS comes in tomorrow.
 

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I was all prepared to replace the TPS a couple weeks back until I found out it's integrated into the throttle body and costs $$$$.

I still have some minor slippage issues after my first fluid swap, but not nearly as bad as before. I was talking with Dugan at ACC a couple weekends ago and he has a regular transmission shop they like. They went through this on a 5th gen 4Runner recently and replaced the valve body, fluids and filter. It still had the same problems. His recommendation was to do another fluid swap and add some GM limited slip differential fluid to the trans fluid.

I haven't had a chance to get my FJC back on the lift and remove the skid to do this, but I will say that my symptoms have diminished since the first fluid swap/filter cleaning. I may get back to it this weekend if the weather is as crummy as it has been. If the weather is nice, I'm headed to the mountains for a little R&R.
 
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Hey @BMThiker thanks for the update...interesting idea about the TPS........
I have yet to drain and fill our fluid, the symptoms on ours haven't changed any.
Power steering pump just started whining now so that's now first on the hit list.
Take care
 

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Draining and swapping the fluid also fixed the well known shudder that was reported early in the FJC production. This was a fairly low rpm shudder at around 20 mph and 40 mph. A little throttle would roll out of it, but a fluid swap made it go away.
 
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Yeah, I need to drain and fill the tranny before I do anything.....the weather is supposed to warm a bit this weekend up here so perhaps I'll finally get to it. With the amount of km on the truck I tend to start wondering about everything being suspect.....
The PS Pump whine I mentioned turned out to be the Idler pulley right next to the pump so I got off easy.
 
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Drained and filled the pan oil, made a difference, some shudder still exists but this certainly improved it.
I'll do another drain and fill again soon.......
The tranny already has an oil cooler installed, thanks!
Acquired a throttle body from a scrapped truck that I will keep on hand as a spare based on BMT's findings above.
Cheers everyone!
 
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Drained and filled the pan oil, made a difference, some shudder still exists but this certainly improved it.
I'll do another drain and fill again soon.......
The tranny already has an oil cooler installed, thanks!
Acquired a throttle body from a scrapped truck that I will keep on hand as a spare based on BMT's findings above.
Cheers everyone!
Now thats surprising as heat is the one thats responsible for ruining the clutch pack in the torque converter. One of the reasons I got a transmission cooler very early after my purchase.
 
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Well she does have over 600,000 km on her, we don't expect perfection at this point lol.
The shudder is pretty minimal and to be honest has been a slight on and off again thing almost since day one.
It did reduce though with this last drain / fill and since a pan drain only changes out a small portion I'm hoping another drain / fill or two will improve it that much more.
Yep she gets grease ever 2nd or 3rd oil change.
 
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