1998 4runner MT shifting difficulty
 

I've got a recent problem with very difficult shifting when stopped with my 5VZFE/R150F 4runner.

When stopped, it does not want to shift into ANY gear. No grinding, no noise, just very high resistance to push into any gear.

I did some basic checks on the clutch, master cylinder fluid looks normal, no sign of leaks. When in gear, the clutch pedal has to be released several inches from the floor before any kind of engagement happens (any noticable sound or reaction of the engine, or movement of the car), so it doesn't seem like the clutch is not disengaging properly.

Clutching multiple times while in neutral does not seem to have any effect.

Sometimes I can get it into 3rd gear, and then after that it will go normally into all the other gears (as long as the clutch is still disengaged). I can go through all the gears/neutral as many times as I want, still fine. Once I let the clutch out in neutral, and then put it back in, the problem is back (can't shift into any gear). Shutting off the engine shows similar behavior. If I shut it off while in the state where I can't shift, the problem remains when the engine is off. Similarly, if I can get it into 3rd gear, then it will go into all other gears. Of course, when the engine is off, now it makes no difference if I press the clutch or not. One it can shift into all gears, it stays that way.

So I would conclude from that that the problem is not with the clutch, as the behavior is basically the same whether the engine is on or off.

I took apart the shifter from the top, the shifter seat look totally fine, and the bushing looks fine as well. No obvious signs of anything there.

So does is there anything left but a transmission problem? Is this a syncro problem? I read somewhere that if it won't go into a couple gears, that's a syncro problem, but if it won't go into all gears, that unlikely. Is that true?

Any other things to check/test?

Is it a fixable problem?

Sitting at a stop, with the engine running and clutch pressed down, what happens when you try to shift into reverse?

Reverse doesn't have a syncro, so if anything it dragging (clitch, pilot bearing) then you'll head some grinding.

So, with engine idling, and clutch in, there is definitely no grinding or any noise like that going into reverse. So I don't think anything is dragging.

Reverse is still kind of stiff to get into, but not as bad as the other gears. 3rd gear is also easier to get into than the other gears (but still way stiffer than normal).
Once I get it to into reverse (or 3rd gear), with clutch still in, I can then cycle through all the gears. Once I let the clutch out in neutral, then put it back in, everything is stiff again (can't get into 1st, 2nd, 4th, 5th), and the process repeats.
This is probably why I don't really have an issue while moving, because when shifting while moving, I put the clutch in while in one gear, and shift from one gear to another without letting the clutch out. This problem seems to happen only when I let the clutch out in neutral, then put the clutch back in, and then try to shift.

I just wasn't clear if you'd included reverse in the 'all the gears' thing. Sounds like it isn't any drag from the clutch, so it's really a trans issue.

As mine has aged, I've gotten a similar issue, but only with 1st gear. If you leave the clutch out for a long while, it will feel like 1st gear is 'locked out' - the synchros won't let you into that gear until you either get it into another gear (2nd works well in my case) and then back up into 1st, or if you briefly let the clutch out to get things moving again and then (after a slight pause as it syncros the gears) into 1st.

I think it's wear on the synchro rings (AKLA blocker rings) that causes this - instead of some pointed or rounded edges where the shift collar engages, it slowly develops a worn flat edge where it can rest as opposed to being guided into alignment.

Not much short of a rebuild will fix that, but you could try changing the trans oil to something slicker like Redline MT90.

I see what you are saying. It just seems a little weird that the problem happens simultaneously with all the gears. As 5th gear is has it's own synchro and shift collar, I would think that would be independent of the other gears.

Does it make sense that once into one gear, it would go freely into all the other gears over and over again? I would think since there are different synchros for each gear, they wouldn't all have the same problem at the same time...but maybe I misunderstand how this all works together exactly.
It's alsmost as if it gets "stuck" in neutral.

Yeah, it sure sounds like some residual movement from the clutch, but a lack of grinding in reverse rules that out.

1st and 2nd share a shift collar, then 3rd and 4th, and 5th and R have their own. But they do all have their own synchro/blocker rings, and those should all have different wear patterns and levels. And even on the gears with shared collars, there's nothing to really align both gears at once, so they shouldn't be any more prone to locking up in those pairs either. On mine, when it seems sort of stuck out of first, it goes easily into 2nd, which moves things slightly and will 'free up' 1st again.

Dunno, really, other than reverse not grinding it would still seem like there's some residual movement going on that the synchros are still fighting against. But since reverse isn't grinding, I'm a bit stumped.

I'd still try an oil change, just to see if the new oil makes things work better. Synchros are very sensitive to oil slipperiness/tackiness and viscosity, and being slipperier isn't necessarily better.

i keep playing with it, looking for more clues.

What I notice now is that that after putting the clutch in (while in neutral), it is very stiff and doesn't want to go into any gear (including reverse). But if I just push the shifter gently go towards a gear, then back to center, and repeat multiple times, it will usually go into gear without much pressure after about the 4th time (approximately). This seems to be true for every gear, including reverse. I find it hard to blame the syncros if reverse has the same problem? Again, once it goes into any gear once, then I can easily go into all gears one after another as many times as I want.

As I mentioned before, once I let the clutch out in neutral, and then put it back in, the problem starts over again. Interestingly, if I only let the clutch out very briefly (enough to hear the transmission react and feel the small effect on the engine), then the problem is not so bad. Shifting is a tiny bit stiffer, but I can put it right into gear. It's only when I let the clutch out fully that the problem is at its worst.

It's almost like the input shaft rotating in neutral causes something to go slightly out of alignment, but it takes some number of revolutions to do it, and then it can be slowly coaxed back into working normally by repeately putting a little pressure on any of the shift rods?

Maybe the oil is too slippery/low viscosity, and the synchro rings are having a hard time slowing the gears down? Not really a dragging clutch, but just the momentum of the clutch disc spinning at whatever speed the engine was turning, very little drag from the bearings and seals, and the synchro rings, which mash some oil between two cone shapes to create the drag, are just spinning instead of 'smearing' and dragging the motion down?

Normally reverse on a manual trans doesn't have a synchro, more to prevent people doing some stupid human tricks than anything else, I think. But I've never tried that on my 4Runner's trans, just (accidentally) on other makes. And that made me wonder if there's a synchro on reverse in the R150/1F, and googled: https://mytuff4x4.com.au/shop/terrai...-transmission/

If there is a synchro on reverse, I think it could still go back to a slightly dragging clutch? I know some manuals do have synchros on reverse, but I might be jumping to a conclusion on that based on the part description. Based on the parts diagram: https://parts.toyota.com/a/Toyota__T...4460-3305.html
the 'reverse synchro' isn't one of the 5 'normal' synchros, it's a different looking one (33388, near the right on the bottom row).

I believe this is my transmission, and I do see that exact part in the parts diagram (I also have the service manual which shows the same thing).


However, as the video shows, what puts it into reverse is the idler gear being slid into contact with the gears of the output and input shaft at the same time. It seems to me if the input shaft was rotating, this would cause all sorts of nasty noises, in the same way as if the output shaft was rotating (as when shifting into reverse while moving).

However, maybe you are onto something with your comment about the syncro rings having a hard time slowing the gears down. I experimented some more, and it seems that iti I wait long enough after putting the clutch in, it goes into gear easily. Maybe 4-5 seconds. Would that be normal, with no clutch drag?
So, I don't know how long the input shaft will continue to rotate (in neutral) once the clutch is disengaged (due to angular momentum vs friction losses). Perhaps it is taking 4-5 seconds to stop rotating? Then when it stops, then it shifts easily? (I supposed that would be made worse by a very slight clutch drag, although you would think if it was dragging at all, it would never fully stop rotating). In that case, what you say could be true, that the synchros are having trouble stopping the shaft rotation (as their job when the car is not moving is essentially to stop the input shaft).

Something like this would seem to explain the symptoms, except that I get the same "stuck" shifting problem with the engine off. If the problem was simply that the input shaft rotation had to fully stop, then the problem should never happen with the engine off. So that could again possibly be explained by a very slight clutch drag, such that the synchros struggle to move the input shaft slightly to align the ring teeth?

Is there any way to confirm any of this? Like could I remove the fill plug from the side of the transmission case and see if the gears are rotating at all when the clutch is out?

You're probably better off doing that by ear. It's noisy with the engine running, but you should be able to hear when the gears in the trans stop turning with the clutch out. There are a lot of gear teeth moving against each other in neutral, so some bearing and whirring noises, put the clutch out, and it should quiet down after a second or two.