99: Another shifting problem.

[Leigh]

Two weeks ago, started in neutral—Clutch-in-- Would not go into ANY gear-----
With the engine Off—Went into all gears with minimal effort.

A half hour later, I tried again, & it shifted normally—OK for a couple hundred miles “stop & Go” driving with no problems.

Today, moved easily through gears with engine OFF / clutch OUT no problem.
Started engine in neutral, but would not shift from neutral into any gear again.

I started it in 1st gear, clutch-in, & it shifted through the gears OK for awhile, but “soon” got “hung-up” again. I had to shut the engine OFF, & start it in 1st gear again to get home.

Truck's been “parked” for about & hour since previous incident--- I went out & tried “shifting” through the gears with engine OFF / clutch IN, & this time it was difficult to engage into any gear; so I started it in neutral / clutch-In as before, & this time I was able to shift effortlessly into any gear????

Whatever the problem is, it's intermittent!

Clutch reservoir is at correct level; & Transmission fluid replaced 1.000 miles ago.

Best regards,
Leigh

 

[tomw]

The most obvious diagnosis is a failing master or slave cylinder. If the fluid in the reservoir ever got low, you might have air bubbles entrained in the fluid line. You could try bleeding as a sort-of last resort before repairing/replacing things. An intermittent to me would (first thought) be a leaky cup in one or the other, allowing the fluid to slip past the seal & piston, and in effect do nothing.
Used to was you could get repair kits that had the rod seal, the cup(forget actual name) and maybe a spring or two, but I don't know it that is possible any more. Quickest replacement would be the master as it is more accessible. Do either one of the cylinders leak? Do you have to add fluid to the reservoir?
If either one leaks, I'd tackle that one first.
tom

 

[Leigh]

Thanks Tom,

The clutch fluid level in the reservoir has “never” dropped below the top fill line.

I don't think it's a problem with the clutch failing to disengage, as yesterday I was driving, I stopped, & put it in Neutral, and it “locked-up” (Wouldn't go into any gear); I turned the engine Off, shifted into 1st gear, clutch pedal down, & started the engine.
If the clutch had failed to disengage, the truck would have “attempted” to move forward when I engaged the Starter, but it didn't, nor was there any indication that the Clutch was “dragging”.

I had suspected a possible Synchronizer problem, but sometimes (Not always), it's difficult to put into gear with the engine Off-- Clutch In-or-Out, so the Synchronizer would not be “in play”.

I read in another post, that a leaking Clutch- Slave Cylinder could deplete the Transmission fluid level, so I'll check that today?

I'm not familiar with the anatomy of this transmission, but it feels like some sort of “Positioning Guides”, for lack of a better term, are wearing / failing, intermittently preventing it to shift into any gear???

Leigh

 

[tomw]

The synchronizing rings can block gear selection if the pointy ends are worn or the synchro ring is worn. There is supposed to be a small clearance between the ring and the cone, giving a smaller 'friction area', allowing the ring to rotate a smidge to align with the splines. The tips of the splines are also spozta be sort of pointed, or tapered from a sharpish edge to thicker on the cone teeth and the synchro teeth. If the ends of the splines have been 'ground' and are now rounded or blunted, it can be hard to get into gear as the blunts will run into each other and fail to allow the engagement of the collar.
The shift mechanism has gates and an interlock system. The gates guide the shift lever and the interlock prevents shifting into two gears at the same time. Most interlocks use spring loaded ball bearings that move one way or another to either allow movement or block movement depending on the gear selected. They will sit in a hole, and pop out into depressions or detents on the shift rods, or be forced out in one direction or the other, into a detent or hole, to prevent movement of a shift rod.
If the linkage was worn out, it might be locking when it was not proper, or if the linkage was loose on the top of the gearbox, it might be failing to move stuff into proper position, leading to jamming.
In short, if the clutch is disengaging, but you cannot move the lever to select a gear, it may be internal to the transmission as you seem to suspect with the "Positioning Guides" comment.
tom

 

[Leigh]

Thanks Tom,

Something puzzles me, that I hadn't mentioned:

I had problems in the past, where it took forceful jiggling for it to go into gear, but it never felt "locked -up" solid as in this case, & seemed to be resolved after replacing the fluid.

So when it "locked-up" as described, two weeks ago--- With the Clutch pedal depressed, the shifter moved freely from side to side, but wouldn't move a fraction of an inch forward or aft, & felt like it was "mechanically" "blocked" from going into any gear.

I tried pulling it into 2n'd by carefully exerting additional force, and the gears "scraped metal" indicating that either the clutch had not released; Yet when it "locked-up" in the same manner the next day,--I shut it off, then started it in in 1st. gear with Clutch pedal down & the clutch was released.

It doesn't make sense that the clutch would fail to disengage intermittently, which seems to point to a possible Synchronizer problem???

Leigh

 

[Leigh]

Thanks Tom,

This morning:
checked the Transmission fluid level, & it was level with the bottom of the filler "port", so no indication of either transmission, or Clutch cylinder fluid leakage.

Had a friend work the Clutch pedal a dozen or so times while observing the Clutch & it released every time; It shifted effortlessly in to every gear engine Off, with Clutch either in or out.

Started engine, Clutch pedal down, & it shifted effortlessly in to every gear.

So it appears that there's nothing wrong with the Slave Cylinder, or the Clutch not disengaging, so it's hard to figure why it would intermittently fail to go into any gear???

That leaves the Synchronizer, which I was told do not come into play when truck is not moving???

As to worn Shifter Rails/ bushings, Forum threads seem to indicate would only cause slop/play in the shifter, but not prevent it from going into gear???

Totally mind-boggling to me!!!

Leigh

 

[Leigh]

Hi Tom,

Are the Gates Guide & shift lever Interlock mechanism, that you refer to, accessible to repair from the top with the Shifter removed or is that a "tear-down" project?

Leigh

 

[tomw]

First last. You would have a pretty hard time doing anything to the shift linkage mechanism, or even inspecting it with the transmission in place. IMO.
Second, I have a 85 that was parked for several days, and it was RAINY outside. I went to take off to work, and no go. Could not put into gear. Truck was not very old.
I put it into gear, and started it up. I felt a slight 'lurch' as the engine started, but things worked fine after that. I have had it occur since, very irregularly. I have deduced that the clutch plate & disk will get rusted together, and not want to release, even though the hydraulic mechanism is working fine. Starting in gear is apparently easier than breaking the two apart with the shift lever after starting the engine.
If your problem is like that, put into gear, then start. But I don't quite get that impression.
tom

 

[Leigh]

Thanks Tom,

Since this problem is "so-far" intermittent, I've decided to just drive it & see how it goes.

Many thanks for your help, & useful information.

Best regards'
Leigh