R150F won't downshift into 2nd

[Flynasa]

Hi All,

I'm after some help with an R150F I have just rebuilt, It had an issue with popping out of 1st gear.  I have replaced the shift fork, 1st gear and the reverse collar.  That has solved the popping out of gear problem.

However it has presented a new problem where it will not downshift from 3rd gear into 2nd.  It feels like it is mechanically blocked.  If I quickly go from 3rd to 1st, it will then go into 2nd.  It does not chrunch or grind at all, it just feels like the linkages wont allow it to move into 2nd.  If I am stationary it will all work fine, it's only while I am moving that the issue presents itself.

I have no doubt I have put something together wrong, I just need some help to know where to look.  Thanks for reading.

[RUGER]

to    flynasa

does double clutching help.

did you replace the shifter pivot bushing(plastic thing at the end of the shifter). Ive found a few cracked over the years that effected shifting.

RUGER

[Flynasa]

Thanks Ruger,

I have not tried double clutching yet, I have pulled the top off the engine to replace the Knock sensor, so I will have a play with that once I get it on the road again this weekend.

Yes I have replaced the shifter bushes, that was one of the simple things I changed when trying to solve the popping out of 1st gear problem.

[Flynasa]

So Im still scratching my head on this.  After a bit more testing I can confirm that double clutching doesn't help at all.  The only way into second is by glancing it into 1st while the clutch is in then it will shift straight into second.

[RUGER]

my moneys on worn dog teeth and/or synchro.

RUGER

[Flynasa]

Thanks Ruger, just to help my understanding, if a synchro was bad, wouldn't that also affect my ability to shift forward through the gears?

Also, can you please explain what the dog teeth are/do?

[RUGER]

cut and paste from search "worn dog teeth and synchro r150f"

Worn dog teeth and synchronizers in a Toyota R150F transmission typically lead to grinding during shifts, difficulty engaging gears, or the transmission popping out of gear. The R150F, used frequently in Toyota Tacomas and 4Runners, often experiences issues with 1st, 2nd, and 5th gear synchronizers due to wear.
Symptoms of Worn Synchros and Dog Teeth (R150F)
Grinding: A grinding noise during shifting indicates that the synchro is failing to match gear speeds, or the "dog teeth" (engagement teeth) are too worn to lock properly.
Popping Out of Gear: If the dog teeth are excessively worn or rounded, they cannot maintain engagement, causing the transmission to slip out of gear, particularly 1st or 5th.
Hard Shifting: Difficulty getting the transmission into a specific gear.
Metallic Debris: Finding small metallic "dog teeth" fragments in the transmission oil.
Causes of Wear on R150F
High Mileage/Age: General wear and tear over time.
Heat & Dirty Lubricant: Inadequate lubrication or high heat breaks down the synchros.
Abusive Shifting: Forcing gears, particularly into 2nd gear, can bend shift forks and wear down teeth.
Repair and Diagnosis
Inspection: To diagnose, the transmission must be disassembled to check for worn, rounded, or chipped dog teeth on the gears and synchro sleeves.
Measurement: Use a feeler gauge to measure the clearance between the synchro ring and the gear; if it is below specification, the synchro must be replaced.
Replacement: When repairing, it is crucial to replace both the worn synchro ring and the corresponding gear with worn dog teeth.
Common Failure Points: 5th gear is a common failure point due to its location at the back of the transmission, sometimes suffering from lubrication issues.
For the R150F, it is often recommended to replace the gear and synchronizer assembly rather than trying to repair the dog teeth, as worn teeth indicate significant structural wear.

[RUGER]

video explaining synchro

https://www.youtube.com/shorts/Tzjl-tlZGG4

edit
video rebuilding r150f.
around 27:30 shows the dogs

https://www.youtube.com/watch?v=ISHkarHC0_w