Transmission - unable to downshift

[ckhorne]

Back before I pulled the drivetrain out of my Patrol, one of the problems I was having was the inability to downshift without either a) letting the engine slow all the way back down to idle or b) rev-matching (nearly impossible without a tach). I tried double-clutching, letting the clutch out while the shifter was in neutral, and everything else I could think of, and I just couldn't get it to downshift.

The manual states that there's synchros for the 3-2 gears, so I've been assuming that it was something up with my synchros. I had a transmission guy take apart my transmission, and aside from reporting that my gears are all pitted from sitting in a water / oil bath from the PO, he wasn't sure what to report on.

This is the main synchro assembly (best I can tell):

IMG_0888.JPG

And the main gear in that assembly:

IMG_0889.JPG

I'm not sure if this is the cause, but the transmission guy is putting his money on it, so I wanted to get some feedback here. Is this gear supposed to be missing teeth like this?

IMG_0893.JPG

The baulk rings are in the background, and based on other images I've seen here, seem to be fine.

Does anyone have any ideas?

[Esteban]

The "Sleeve -Synchronizer" that you're showing in your picture looks perfectly fine for me. The synchro rings, although not so clear, look fine as well. This sleeve-synchronizer (the manual call it like that) has nothing to do when you downshift into first gear. It only works from 2nd to 3rd, and 3rd to 2nd.

I should have started this with ...no synchronizer for first gear...you must be driving a Patrol...

Incredible as it sounds, in 18 years of production, they never improved the transmission.

They don't have a synchro for first gear, so you'll always have to do the double clutch feature. Forget about the tach. After 10 years of practice, you'll be able to do it by just the sound of the engine.. Kidding aside, it's not difficult to master, and it's a real beauty to do it.

[ckhorne]

Thanks for the quick response.

I should have clarified - I wasn't expecting to be able to downshift into 1st. I just want to be able to downshift from 3rd to 2nd. Is that supposed to be possible in the Patrol?

[Esteban]

Thanks for the quick response.

I should have clarified - I wasn't expecting to be able to downshift into 1st. I just want to be able to downshift from 3rd to 2nd. Is that supposed to be possible in the Patrol?

Yes. But if you are at high speed, it might prove elusive, and probably better to also do a double clutch maneuver. Al low speeds, say your going 30 mph in 3rd, it should be easy to downshift to 2nd. However, not as fast as in other gearboxes.

For me, the transmission is the weakest link, specially the synchro rings. Now I downshift like an old timer to avoid any premature wear.

[ckhorne]

Yes. But if you are at high speed, it might prove elusive, and probably better to also do a double clutch maneuver. Al low speeds, say your going 30 mph in 3rd, it should be easy to downshift to 2nd. However, not as fast as in other gearboxes.

For me, the transmission is the weakest link, specially the synchro rings. Now I downshift like an old timer to avoid any premature wear.

Well, since my drivetrain is in pieces at the moment, I can't go out and test again... I'm sure I've tried at multiple speeds and multiple techniques, and I just can't get it to downshift. But... it sounds like I may just be expecting too much out of the Patrol's gearbox....

[moore_rb]

It might also be your clutch... The Patrol's clutch throwout is only a few millimeters, and often the centrifugal effect of the flywheel will keep the disk (and therefore the trans input shaft) spinning even after the clutch pedal has been depressed...

Like Esteban says- finesse is one of the basic skills necessary to keep a Patrol's gears from grinding. I treat every shift as a "One click, two click" maneuver- powershifting and short-throwing is not the name of the game.

when you put everything back together, make sure you pay extra attention to the height adjustment on the pressure plate fingers, so that the clutch will disengage as much as possible - this should help smooth things out as mush as possible...

[ckhorne]

when you put everything back together, make sure you pay extra attention to the height adjustment on the pressure plate fingers, so that the clutch will disengage as much as possible - this should help smooth things out as mush as possible...

Ahhh- thanks for the tips. I would have never looked at the clutch...

[faux40]

Aaaah... I've gotten to know the clutch pretty well too! Because I do it right because do it twice... or more

In my experience (I've installed a Patrol clutch twice -- once a failure, once a qualified success), I've found the clutch to be pretty dang finicky. When adjusting the overall height, you have to take into account the size of the step on the flywheel. Each time the pressure plate is surfaced shims are supposed to be added to the arms in the cover to compensate for the loss of material. Also, remember that all three of the arms are supposed to be the same height within 0.008" (0.0138" according to the newer book).

My qualified success? I had a shop rebuild and adjust mine but, although it works okay, I'm suspicious that they either didn't shim it enough or that my throwout bearing is thinner than the stock one because, despite there being several inches of clutch adjustment, it's all the way out and there is no extra adjustment left in the linkage.

By the way, I love the language used to describe the need for shims...

Screen Shot 2014-09-03 at 9.43.06 PM.png

Good luck!

John

[ckhorne]

In my experience (I've installed a Patrol clutch twice -- once a failure, once a qualified success), I've found the clutch to be pretty dang finicky. When adjusting the overall height, you have to take into account the size of the step on the flywheel. Each time the pressure plate is surfaced shims are supposed to be added to the arms in the cover to compensate for the loss of material. Also, remember that all three of the arms are supposed to be the same height within 0.008" (0.0138" according to the newer book).

Gah... that's annoying. But good info.

So... what are you supposed to use for shims? Or is that part of the rebuild process?

[faux40]

So... what are you supposed to use for shims? Or is that part of the rebuild process?

Two answers: No idea & Probably.

That little blurb simply states "washer of corresponding thickness". Officially, you'd only add the shim when the plate is faced but it seems to me that you'd also want to shim when the flywheel is faced as the step is reduced which (at least in my mind) changes the geometry in exactly the same way as thinning the pressure plate surface does. Also, since they don't seem to publish the original thickness of the PP friction disk, we're flying blind. I can say that I'm suspicious of mine since I don't have any clutch adjustment left despite my clutch disk being at the full, brand-new thickness.

The places that I can see consuming the adjuster (on mine) are:

• The flywheel step being smaller (from surfacing) than original
• The pressure plate disk being thinner (from surfacing) than original
• The replacement throwout bearing being thinner than the original one
• Wear on the throwout arm tips
• Wear on the pads on the throwout bearing holder thing

A quick back of the envelope calculation shows that we have a 22:1-ish ratio between clutch pedal movement and clutch movement (Pedal has 7" stoke less the 1-1/2" free play so we have 5-1/2" effective movement; the pressure plate probably moves less than 1/4" so let's use 1/4" --> 5.5"/0.25" = 22 -- if the PP only moves 1/8", that ratio would be 44:1!). I would image that at the clutch arm pivots where they contact the PP, the ratio is even more severe. So, I don' think that takes much loss of material to affect the system dramatically.

The yellow arrow shows where I think the shim should go so I imagine that the shim washer needs to be at least the size of the pad to provide full contact.

clutch_shim.jpg

Anyway, that's my guess...

John