I noticed this the other day - maybe it's some kind of inertial thing. I started my car in the garage - normally the clutch is in, and I immediately put the car in reverse to back out. That morning, I depressed the clutch and started the car. I let the clutch out while it was in neutral, and the car rolled forward about an inch or two. I repeated this a few times. After the car warmed up a bit, it wouldn't do it any more. Is this normal, or do I have something misadjusted in the clutch? I had it replaced at 42K (now has 49K miles). I'm almost out of warranty, so I need to make my final list of issues for warranty work next week.

 

When a M/T car is in neutral and the e-brake isn't on.....they can roll where-ever they want!!
There is nothing wrong with your car, it just must have been sitting on a little slope and decided to roll forward.

 

No, this isn't a case of the vehicle being on a slope. I'm well aware that an M/T in neutral can roll. What I said was it rolls forward in my garage (level surface) when the clutch is let out while in neutral. Clutch in = no roll, clutch out = roll forward. The act of letting the clutch out while in neutral caused it to roll.

 

could be a bad pressure plate. did engine rpms fall at all??

 

when changing my brake pads the other day i turned the car on with the rear wheels off and on jack stands, the rotors turned forward without being in gear

 

When the clutch is out, it spins the transmission input shaft which churns up the oil in the transmission. When cold, the oil must be thick enough the start the output shaft spinning which moves your car forward. Once it gets hot, the oil's too thin to spin the output shaft. No amount of clutch adjustment can affect this because, when you're in neutral, the input and output shafts are not connected (but the input shaft is spinning from the engine and the output shaft is freewheeling). When you press the clutch pedal, the input shaft is now disconnected from the engine and it becomes freewheeling just like the output shaft so no motion should occur. In other words, it sounds normal. (This also explains why some transmissions don't shift well when cold).

 

Seems to me that if it doesn't do that with the clutch disengaged (pedal to the floor) it isn't a problem with the clutch/pressure plate. It only does it with the tranny in neutral and the clutch engaged, right? So the engine is, in that case, connected to the tranny and turning the tranny main shaft. In which case, the main shaft gear(s) is spinning in the cold, heavy oil and transferring some of that motion to one or more of the other gears through the motion of the heavy oil. Once the oil warms up and thins out, there is no such transfer of motion.

 

Get a level and make sure it's level. It will keep you "level"-headed? :-P

I'm sorry in advance for that stupid joke...

 

I think the same.

F

 

Both my 7 & 8 do this sometimes.

 

Thanks to all for the very informative explanations. I figured it was something like that, but I was hoping one or more of you geniuses would provide the technospeak It's great to have such knowledgeable folks on the forum.

 

maybe there's a dip in your garage floor

 

Any temp below freezing is enough to get the car rolling pretty well if the ebrake is off or lightly applied.
The effect lasts less than a minute even well below freezing and once you get used to it it can even have advantages: I can pull my car out of the garage in neutral when it's cold so there is no chance to stall it and risk a flood.
My question is whether synthetics such as RP will reduce this effect or fix the cold shifting issues.

 

What others have said about thick oil causing some torque to be transfered even thoug the transmission is in neutral is correct. If anyone is interested in some more technical details, google "constant mesh transmission". All modern mainstream manual transmissions are done this way. In this type of transmission, all of the input gears are always meshing with all of the output gears. When you select a gear, what you're effectively doing is coupling one set of gears to their respective shafts. All of the other gears just spin on the shaft at varying speeds, which is fine because they aren't coupled to the shaft. When you're in neutral, all of the gears are de-coupled. However, since there is transmission oil between the gears and the shafts, there is viscous friction that does transfer some load between the gears and the shafts. When the oil is thin (ie, the oil is warm), this friction is very small. However, when the oil is cold and thick, it can easily tranfer enough torque from the input shaft to the output shaft to move the car on a level surface. The reason it goes forward is that we have multiple forward gears that are all pushing in the same direction.

Here's a quick reference. I'm sure there are better ones out there.

http://www.edmunds.com/ownership/tec...9/article.html

 

Mine does this, too. It is just the oil.

 

This thread is GREAT!!!

 

Very good info. I was just wondering about this.

 

I agree, its the oil. Mine does the same but much less with a synthetic gear lube. Go Amsoil MTG 75W-90 and forget it.

Great,
Jeff B.

 

I second the Amsoil gear lube, but like xabjw4 said, it still does it when it is cold just not as much.


So is it better to let the car warm up with the clutch disengaged or engaged?

 

I don't know but I figure with the clutch engaged the tranny oil gets to warm up too. That way when you drive off the syncros might work and you won't crunch 2nd gear.

 

I would rather leave the clutch engaged to save wear on the throw-out bearing. Same reason I'll slip it into neutral and release the clutch at long lights.