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Manual transmission gets stuck

The car is a 2000 Honda CRV (4 cylinder), with a manual transmission. Basic problem is that the transmission gear gets stuck, and one cannot make a speed change. Pumping the clutch does not help. Clutch and transmission have been repaired but the mechanic says he doesn’t know why it would get stuck.

Symptoms have been the following:

? On a situation of highway driving, the car works fine shifting and the clutch works as expected.

? On a heavy city stop-and-go traffic, or a bumper-to-bumper traffic, the transmission will stop shifting gear. Only way to shift gear is to turn off the vehicle, let the car sit idle and cool off for about 5 minutes, then it will shift again.

? On occasion, I have to let the car cool off for more than a few hours to be able to shift normally.

? In all these problems, temperature gauge always remains normal (about 1/2), so the car is not overheated.

The problem might be caused from a worn out clutch master cylinder.

The master cylinder is located under the hood. As the underhood temperatures increase it also heats up the master cylinder. This then causes the bore within the master cylinder to expand. If the cup seals in the master cylinder are at all worn, it allows the hydraulic fluid to bypass the seals. When this happens, no hydraulic pressure is applied to operate the slave cylinder and clutch doesn’t function. So it will act as if you’re trying to shift gears without using the clutch and the gears grind. If you let everything cool off the bore within the master cylinder contracts, and clutch works again.

If you want to confirm that this is the problem, the next time it becomes difficult to shift, pull over. open the hood and pour a bottle water over the master cylinder to cool it down. if the clutch works again, that’s the problem.


Excellent analysis. Two questions, though: why would the master cylinder work in a highway setting, even if I drive for hours? Shouldn’t it also heat the seals of the master cylinder?

Also, how do I know which one is the master cylinder?

Mil gracias, as we say in Spanish!

When driving down the highway, enough air is being rammed thru the radiator to remove the underhood heat. As soon as you slow down or stop, that ram air effect is lost. But the radiator fan comes on. And that little fan doesn’t move nowhere the amount of air as driving down the highway. So underhood temperatures increase.

The clutch master cylinder is located on the fire wall, next to the brake master cylinder.


Mr Tester

So… we changed the master and slave cylinder. We still have the same problem, with a litle different set of symptoms:

  1. When driving for about 1/2 hour on heavy traffic, just fine shifting.

  2. Then I try to shift gears, it is stuck in neutral and cannot shift. I turn off the car and then shift into 1st so that I can park on the side for a few minutes. One time, I just went to the side of the street and kept the car running, then after a few minutes I could shift even with the car on. Strange.

  3. I opened the hood and noticed that the radiator fan (two small ones) only turn on when it’s real hot. My temperature gauge is allways at 1/2, and I don’t think the car is overheating, but I’m curious to know if the thermostat might have something to do with this situation.

Thanks for your help.

The thermostat cannot affect the clutch operation.

While I normally would have suggested that the slave cylinder was being affected by the heat and allowing the fluid to push past the seals, you’ve changed that already. The only other thing I can think of that might be heat affected is the hydraulic line itself. Perhaps the liner in the braided flex portion(s) has come detached inside and is closing the line when heated. Root cause for this could be a missing exhaust heat shield or exhaust leak, or the line could just have failed.

Ah! the catalytic converter heat shield was rattling months ago, and I took it to the mechanic and he took it off. He said that it wasn’t needed. Maybe the heat damaged the line?

Is the converter anywhere near the line?

I don’t know for sure (not a mechanic) but is very close to the transmission/clutch.

I think you’ve found the problem. Yours is a good example of why we always recommend to people that they not just throw away their heat shields when the rust & rattle.

I’d try changing the cat converter for one with a heat shield and see if that helps. If there is a braided line in the area, you might want to change that too.