Can't shift into low gear post-transmission swap

Hey all! New member here but have been lurking for years.

I'm in the midst of a 4x4 conversion on my 2013 Toyota tacoma (auto trans) and recently swapped in a 3k mile A750f (also auto) from a 2018 4runner. Pre-install walked everything down between the two transmissions and didn't notice any immediate differences - big oops.

Now that the trans is installed I've shaken it down and it runs and shifts as expected, WITH the exception that I can't put the shifter into low gear manually. My OBDII reader has a pending P0705 fault but after driving truck for 50 mile shakedown it hasn't tripped.

A few troubleshooting steps I've taken:

• Un bolted shift linkage from under truck and verified shifter not binding up in any locations
• Swapped Neutral safety switch sensor from known good one on transmission
• Tuned neutral safety switch sensor
• Taken apart shift linkage on interior and played around with adjustments to see if anything helped (ended back up at initial settings)

I'm at a loss here because the transmission itself shifts through all gears as expected without any issue when in PRND (including 4,3). My leading theory is that the hydraulic circuit to go into 2nd gear is air-locked, because it almost feels like an air spring when trying to push into gear.

Few notes on new trans:

• 3k miles, came from front end crashed 4runner
• Refilled, with Toyota ATF several days ago and it took 6 quarts. Had the truck level and in temp check mode to do so
• No bent connector pins anywhere on trans/transfer case
• No vibrations
• No high temps after highway driving

I found an A750f manual online and was reading through the configurations the transmission goes through when in different mechanical settings. After looking at the below table it looks like every brake and clutch configuration are used in other configs EXCEPT for B4. Am I going down a loop hole? Any help would be appreciated!

 

@gearcruncher might have an idea

 

When you say low gearing you mean 4L or the gear L in the shifter?

 

Gear 2 in the shifter! Haven't wired up the electronics for transfer case yet

 

I doubt its an internal issue. I call it a linkage issue. You didn’t use a J-case? Did you went non add?

 

Are you saying the shifter won't physically go into 1st or the transmission won't start off/shift into 1st?

 

My first guess is one tooth out on your PRNDL detent .
Put the transmission in park and take the key out . Throw the key on the passenger seat until you are done .
Next , unbolt the linkage under the truck so the shifter is removed from the lever on the transmission
Using your hands , shift the transmission into park position . You can click the detent by hand all the way down to low gear and then all the way back up to park . How many clicks did you count ?
Have a look at the second picture in this write up , it shows what the rooster cowl looks like inside the transmission.
https://www.tacomaworld.com/threads...th-pics-for-second-gen-4-liter-trucks.289913/
Go to the back of the truck and try to push the truck by hand .
You should hear the transmission click into park when you try to roll the truck .Now that you have verified the transmission holds in park and the shifter is in park , reconnect the linkage .
This should solve any external shifter issues .
Truck should be able to start in Park as well as neutral .

Strange that the 4 runner still had the 5 speed in 2018 . I thought they stopped producing the A750e in 2015 and started using the AC60 series transmission ?

 

Hey all - sorry for uber late reply to this thread and thank you for all the suggestions.

Since my last reply I have put ~7,000 miles on the transmission (including a cross-country move). I've wrapped up my 4wd swap (including ADD delete and setup an arduino transfer case controller - no J-shift!). Hoping to share more exciting news on that controller and setup after I finish tidying everything up to look OEM (dash lights, OEM transfer case switch). For now my 4wd "brain" is housed in a rock auto cardboard box - few fun photos attached of that. @gearcruncher I can confirm the transmission from 2018 4runner was an exact match - I'd wager the 4runner kept A750 alongside the 4.0L engine until upcoming refresh for that lineup.

A little more context on the issue:

• Truck shifter can physically shift from Park -> Reverse -> Neutral -> Drive -> S4 -> S3 but CAN NOT shift into S2 or S1 (picture below of shift diagram).
• When I say I can NOT shift, I mean that the shifter cannot physically go into those positions, even when (gently) applying force. It feels hydrolocked - I can get some deflection on shifter which seems to slightly bounce back. Don't want to plastically deform my shifter so haven't pushed it super hard and don't plan on it.
• All gears in accessible range (Park -> Reverse -> Neutral -> Drive -> S4 -> S3) behave perfectly. No rev spikes, hard shifts, no net new vibrations, etc. When in "Drive" the truck will go through all gears as expected without any hiccups. Never had any issues city or highway driving, and have confirmed the transmission will cycle through all 5 gears
• I have got 2HI, 4HI, 4LO mapped and working as expected - this problem is independent of any 4wd components (incl transfer case)
• In researching the solenoid mapping from A750 repair manual (attached), on pages 20/21 I see Brakes 2/4 as the ONLY components not used in my other accessible positions. Considering the transmission was nearly brand new when installed I'm having a tough time picturing the brakes as the issue.

At this point I have verified:

• Shift linkage undamaged (externally)
• Shift linkage detent is mapped and spaced correctly
• Neutral Safety Sensor switch in good condition
• Verified trans and harness connector pins undamaged and mated correctly
• Disassembled all interior/exterior shift linkage components/switches
• No codes/alarms thrown from ECU in past 9 mos, transmission did not throw itself into any limp mode

What I have not done:

• Removed trans pan to expose TCM
• Any additional troubleshooting with TCM exposed (solenoids, internal connectors, etc.)

Since this vehicle is my daily driver (and my driveway is now super difficult to work in) I'd like to plan out troubleshooting steps as best as possible before taking my truck offline and dropping the pan.

My current plan:

• After gathering more background info on troubleshooting steps, remove trans pan and TCM
• With TCM removed, try to physically move gear shift into S2 or S1. Verify shift that system without hydraulic fluid works as expected. If not, internal linkage likely to blame
• If shift linkage verified as non-issue, move to solenoid troubleshooting. All brakes and clutches (with exception of Brake 2) are used during normal operation to my understanding and have been verified healthy.
• With hydraulic passages empty, remove/test solenoids for function
• If faulty solenoid found as root cause -> replace
• If shift linkage issue found as root cause -> investigate further (maybe disassemble my spare 2wd trans)
• Hail Mary option - pull known working TCM from my 2wd configured trans and transplant to transmission currently installed on tacoma. This won't fix anything if linkage is to blame

Anyone have strong opinions on what it may be? Still seems super weird to me, have tried to be pretty methodical with troubleshooting, super excited to finally fix this issue.

• 

 

Have you disconnected the shift cable at the transmission and tried to manually shift the linkage on the transmission?
As well as trying the shifter when the cable is disconnected?

 

Yes - have isolated the issue to within the trans, can not shift into gear manually with linkage undone

 

Yeah, unfortunately it looks like you’ll be dropping the pan.

 

I am wondering if the 4 runner transmission uses a different strategy for grabbing the lower gears ?
You may have to swap out your original rooster cowl and install it into the 4 runner transmission when the pan is off .
I was just looking at interior pictures of a shifter from a 2018 4 runner .
Visibly , Its much different than what you find inside the interior of the tacoma .

That being said , when you get the pan off , compare all the parts for your manual valve configuration .

 

Hi. Any Update to this problem? I'm in the same situation, just installed a 2020 low miles 4runner transmission into a 2013 Tacoma. And I also can't shift to second and first. Did you have any other problems with this transmission swap? I didn't drive my truck yet, but the valve body solenoids are making some weird nosies even with the engine off, ignition on, there is a constant buzz out of the SL2 solenoid.

 

I took the pan off on both transmissions and indeed the two rooster cowl are different shaped. Thank you gearcruncher for the hint. That on taco transmission has a "B3" stamped on it and the other is "C10". I removed the valve body on the old transmission to get the rooster cowl out.
Does anyone know how to separate the rooster cowl off the shaft? It looks like there is a thin metal sleeve on the rooster cowl an underneath is a pin that goes thru the shaft but the metal sleeve is pressed into the hole where the pin goes so that it covers the pin hole. It looks like the metal sleeve would not be reusable after disassembly. Probably I could drill that indented part of the sleeve out, but shavings are a problem, and how to reuse the sleeve. I attached some pictures of the rooster cowl sleeve.