Subtle Clunk when Shifing into 1st Gear
 

Hey all,

I'm a proud new owner of a 2007 Galaxy Gray GT. Will post pics later and give a proper introduction.

But for now have to ask this question...

When shifting into first from neutral at a stop, I hear and feel just a slight clunk. That is, when starting from a stop, clutch in, shift into first from neutral, and as I'm doing this motion feel the clunk, let out clutch and give gas, everything's fine.

With a little experimentation, I think it's the clutch not fully disengaging even though the clutch pedal is fully depressed. Once I get the clunk, I can shift through all gears easily (with clutch pedal depressed), including first. However, if I let the clutch back out while in neutral, and then repeat clutch in and shift into first, I get the clunk once more, which sure feels like it's the clutch plate finally fully disengaging.

Anyone else get this? Is it a sign of a problem? No other trans issues at all--just this.

TIA

Check the clutch pedal bracket and see if all the welds and metal is intact. The bracket is known for snapping. If you do a search for the bracket, you will know what I mean.

is this when the windows are open? If your hearing it outside the car its pretty normal to hear gears click into place. If its really really loud with the windows closed then I would be worried.

Thanks... looks like it is not the clutch pedal bracket, and it definitely is not just the gears clicking into place.

It is specifically that the clutch is not fully disengaging even with the pedal depressed, as evidenced by the small jolt I feel when trying to select first gear from neutral. It is as if the clutch has trouble disengaging from the layshaft in neutral even with the pedal fully down. Anyone else encounter this?

nah its normal. my S2 does that too. very faint donk sound.
what it is the syncro trying to stop the input shaft and the force gets sent to the drive shaft and rear diff. the sound is made by the slack in those components.

Woah, nice, that sounds like a great explanation! Thanks jason. That's exactly right, a very faint donk and a feeling like the force was transmitted/relieved somewhere.

if this is normal... relief!

transmissions do make noises :)

it's not just a noise though... you can feel it through the car.

This noise/clunk when I shift into first from a stop is just continuing to bug me. Are you sure this is normal? Are others experiencing this? Have driven many manuals and have just never seen this before. Thanks.

More tham 47k miles on your car, perhaps?

Hmmph, well, it's a 2007 that I bought with 42k miles on it. Clunk was present at the time. Now have 45k on it.

Suggesting this happens with age? Is it normal or abnormal?

Mine does this too, jason explained it nicely so I don't have a whole lot to add.

mine does it too. 2006 41K miles.

Have you tried changing the transmission fluid?

Will put in Motorcraft Full Synthetic 75w90 soon as I get a chance... but I'm skeptical this is the real issue. Will update thread.

There's no issue, it's just the syncro stopping the input shaft.


Try this... with the car running in neutral and your foot off the clutch, depress the clutch and quickly shift to first. Car tries to move a little and you hear a small clunk right... it's the syncro doing its job which is to make the input shaft match the speed of the output shaft. This transmits a very small amount of energy to the output shaft and consequentially the rear wheels when the input shaft is suddenly stopped from moving.

Now with the car running in neutral, depress the clutch and count to 10. In the time it takes you to slowly count to 10, the input shaft will come to a stop on its own. Now shift the car into first. No movement right? It's because while the clutch pedal was depressed the input shaft stopped and wasn't suddenly stopped from spinning by the syncro, it was already stopped when you shifted into gear.

Why is the input shaft spinning?

I thought the input shaft was in motion when the car is in neutral and your foot is off the clutch?

It is.

In the context of this particular conversation, though, the OP has already pushed the clutch pedal all the way to the floor. What is supposed to happen at that point?

After I installed my short shifter I'm able to hear the input shaft of the transmission spinning, and when I press the clutch pedal to the floor it takes about 1-2 full seconds for the input shaft to come to a complete stop. So if you were to press the clutch pedal to the floor and immediately put it into first, the input shaft would still be moving when 1st gear is being engaged. I saw that the OP mentioned that the clutch pedal was being pushed to the floor but I didn't see anything about how fast he's shifting to first after pushing the clutch pedal.

The other thing that makes me believe this is what's happening is that he mentioned that if he depresses the clutch and moves through some gears and back to first, the clunk is no longer there. This would have allowed time for the input shaft to come to a complete stop.

Mine does this too, and its almost definitely the input shaft.

Let me try and help with a diagram, This is your drivetrain:

Engine}------|Clutch|--------|Synchros and Gears|------------{Diff and wheels
..............^Flywheel......^Input Shaft..............................^Drive Shaft

So if your engine is spinning, clutch engaged, trans neutral, Your input shaft is spinning with your engine at idle. Then when you clutch out, the Input shaft isnt connected to anything, but still spinning. Then when you put it in gear, the input shaft has to stop, because your hooking it up the diff and wheels which arent moving (youre at a stop). The gears smacking into place and taking up all the slack in the driveline is the clunk.

This is also why some people choose to double clutch (engage the clutch in neutral) on shifts with large RPM changes. You can spin the input shaft up to the right speed to match to take work off the synchros and extend their life.
(Without double clutching, the engine might be rev matched, but the iput shaft would still be spinning at the speed the engine used to be running)

I hope this helps. :dunno:

Precisely. The short shifter really allows us to hear what is going on inside the transmission, doesn't it? :)

Would the real answer to his question/concern not involve swapping trans fluid (as others have suggested) but to simply wait a second or two for the input shaft to slow down before making that initial engagement into first gear?

As for my own opinion; I would not call this characteristic "normal", but something that we all should accomodate so as to limit future transmission issues.

Yeah changing trans fluid won't do anything about it. Mine did it with the stuff Mazda uses and with Red Line MT-90. I don't think it's particularly harmful to the transmission since it's just the synchros doing what they were designed to do, but waiting a couple seconds for the input shaft to stop spinning may help lengthen the life of the 1st gear synchro so that doesn't hurt either.

I agree, but I also caution people (as I have for a few years, now) on the relative weakness of the RX-8 clutch pedal assembly. The factory release bearing is also not the most robust available and weakness in each of these components can exacerbate the issue we are describing. As it gets worse, similar shifting difficulties can arise in the higher gears too.

I've noticed the clunk going into first on mine too. I'm not going to worry about it unless it gets worse. Shifting is fine. I'm using redline oil.