Manual Transmission - Issues shifting into 1st & Reverse (Compilation thread)

[roaniecowpony]

A lot of us are starting to think that the primary reason so many are having issues is due to a lack of drag from the input shaft. With how loosely the clutch disc fits on to the input shaft it could potentially lean into the clutch assembly, and any slight drag on the disc allows it to continue spinning with the flywheel and pressure plate. The extra drag from the gear lube helps to slow the disc down, thus allowing the synchronizer blocking rings to work more effectively.

I guess I'm not buying that a little bit of gear oil has that much drag, especially that thin stuff they call gear oil these days. It's more like 30w motor oil IMO.

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[basemodel]

I guess I'm not buying that a little bit of gear oil has that much drag, especially that thin stuff they call gear oil these days. It's more like 30w motor oil IMO.

All good, I’m just reporting my real world experience with changing from ATF to gear oil. It was a night and day difference immediately.

Also, sure gear oil might be thinner than 50 years ago, but it’s still a ton thicker than just about any engine oil this side of 20w50. The 85w140 I broke open was like honey. ATF is incredibly thin as it’s mostly a hydraulic oil. My plane even uses it as brake fluid, as do many other aircraft.

 

[roaniecowpony]

All good, I’m just reporting my real world experience with changing from ATF to gear oil. It was a night and day difference immediately.

Possibly the friction coefficient effects on the synchro assy is higher with the gear oil.

 

[basemodel]

Possibly the friction coefficient effects on the synchro assy is higher with the gear oil.

That’s a possibility as well! Potentially a combination of all things. Either way, it’s allowing the input shaft to slow down enough for the synchronizer blocking rings to do their job. Whether that’s through friction at the rings, at the input shaft bearings, a combination of both, or otherwise doesn’t matter a whole lot to me as long as it improves drivability and is not detrimental to long term performance.

 

[Stan B]

For those of you with this problem: When I'm rolling up to a stop sign in like 3rd or 4th gear, and I decide to finish decel with the brake, I push in the clutch and notice the engine RPM drop like a switch was turned off. I assume that's a sign of very good clutch disengagement. Do you notice the same thing, or does your RPM stay the same after pushing in the clutch?

 

[basemodel]

For those of you with this problem: When I'm rolling up to a stop sign in like 3rd or 4th gear, and I decide to finish decel with the brake, I push in the clutch and notice the engine RPM drop like a switch was turned off. I assume that's a sign of very good clutch disengagement. Do you notice the same thing, or does your RPM stay the same after pushing in the clutch?

Mine would either rise or drop depending on speed. For whatever reason, it wanted to sit at 1800rpm or so with the clutch in while moving. As soon as I stopped, it went to idle. Watching it on a scan tool, the factory tune was commanding it to a higher rpm until stopped. Since I tuned my JL, it’s drops to idle whether moving or stopped, as you’d expect.

 

[roaniecowpony]

That’s a possibility as well! Potentially a combination of all things. Either way, it’s allowing the input shaft to slow down enough for the synchronizer blocking rings to do their job. Whether that’s through friction at the rings, at the input shaft bearings, a combination of both, or otherwise doesn’t matter a whole lot to me as long as it improves drivability and is not detrimental to long term performance.

I doubt there is any detrimental side effects. The high sulfur content would be the only concern for the brass parts. But, that was the case with the old gear oil too.

 

[basemodel]

I doubt there is any detrimental side effects. The high sulfur content would be the only concern for the brass parts. But, that was the case with the old gear oil too.

I’m curious if anyone has opened up an AL6 yet to se if there’s any brass parts. I would assume there’s at least the blocking rings, but there’s plenty of modern manuals that use other materials. I’m planning on using a yellow metal safe oil sooner than later, just curious what it looks like inside.

 

[roaniecowpony]

I’m curious if anyone has opened up an AL6 yet to se if there’s any brass parts. I would assume there’s at least the blocking rings, but there’s plenty of modern manuals that use other materials. I’m planning on using a yellow metal safe oil sooner than later, just curious what it looks like inside.

If i ever get my factory service manual open again, I'll look for pix.

 

[basemodel]

If i ever get my factory service manual open again, I'll look for pix.

Thanks! There’s no info directly from Mopar that I can find. Part explosions and descriptions are pretty vague.

 

[SadRobot]

If i ever get my factory service manual open again, I'll look for pix.

You are the most dedicated non JL manual owner I've ever seen.

 

[gek]

You are the most dedicated non JL manual owner I've ever seen.

I really should stop following this thread ... but I still have hope that one day there will be a real solution and I can get another manual Wrangler.

Help us @roaniecowpony, you're our only hope.

 

[SadRobot]

I really should stop following this thread ... but I still have hope that one day there will be a real solution and I can get another manual Wrangler.

Help us @roaniecowpony, you're our only hope.

Apparently this Jeep can't leave either of our lives. @roaniecowpony and I are tied to it forever.

 

[Toycrusher]

Unlikely that heat would be an issue. Manual gear boxes have been run with 90 grade gear oil for decades, with cast iron cases and much more power running through them. The 90 grade gear oil of the past was much thicker than the current synthetic 75w90 stuff common now. The aluminum transmission case sheds heat much better than aluminum.

But, more to the comment about not enough friction to disengage the clutch, that's just not how a modern full synchro transmission works. The friction comes from the synchronizer ring. It is sort of a clutch itself.

Take a kids game, a spinning top. You can spin it and it will keep spinning for a long time, little to no drag on it. Synchros are designed to match speeds of the shafts but they can only handle a certain amount of differential. This motor idles high, when you are sitting at idle with the clutch engaged, the disc is spinning at full engine rpm. When you press in the clutch pedal, you need the disc speed to drop to the point where the synchros can do their job.
What causes the clutch disc to slow down? If it's riding on exceptionally good bearings, it could spin a very long time before slowing down.
"Normal" manual transmissions don't have an issue with this. Push the clutch pedal in, the disc speed drops quickly enough that you can engage whatever gear you want, pretty much when you want.
This transmission definitely has an issue getting the clutch disc to slow down enough for the synchros to work.

 

[basemodel]

Apparently this Jeep can't leave either of our lives. @roaniecowpony and I are tied to it forever.

If more people test it, I think:
-single disc clutch of your choice
-billet slave cylinder (such as McLeod)
-swapping ATF for gear oil
…is the closest we’re getting to a solution.

I am curious to see how it’ll work for anyone else since it worked so well in my case. Gear oil made the biggest difference, but I don’t know if that’s because of its inherent properties or if it’s due to the combination of parts. I’ve said it a few times, but my problems are essentially gone. It shifts like a normal manual transmission with next to no hang ups.

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