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Clutch problem - 2003 Nissan Sentra SER

I have a 2003 Nissan Sentra SER with about 175,000 kilometers. Recently, I have been experiencing clutch problems.

The first time, after about a 45-minute drive on the freeway, the clutch pedal became ? mushy ? : it didn?t spring back and I had a hard time changing gears. I managed to get home, but I didn?t want to touch the car. The next day, when I dared to try to drive it to the dealer, the clutch was fine.

The dealer felt that the fluid might be contaminated, causing air pockets to form. Therefore, they changed the fluids (clutch and brake) and bled the systems.

However, this did not correct the problem. Because the same thing happened again. The second occurrence took place a week later after a 3-hour drive on the freeway. The clutch become ? mushy ? after I left the freeway and was trying to maneuver in city traffic. I had to use my toe to pull the clutch pedal back up.

Now the dealer wants to change the master cylinder.

A month ago I spent an hour in a traffic jam ? crawling bumper to bumper, and I thought I would wear out the clutch. However, there was never any problem of the clutch pedal becoming mushy. Why would it become ? light ? after a long drive?

Since it has been an intermittent problem (only having occurred twice at unexpected moments), it?s hard to establish a cause - effect relationship. Both times the problem occurred was after driving for a long stretch in hot summer weather (with the air conditioning on). But can I draw any conclusions?

? Overheating of the master or slave cylinder causing air bubbles to expand??? [However, the fluids were changed and BLED by the dealer.]

? Defective master cylinder?? (How to ascertain this?)

? Defective slave cylinder?? (How to ascertain this?)

? Some relationship to using the aircontioning for long periods of time???

[When crawling along in bumper to bumper traffic a month ago, I can?t remember if I had the air conditioning on.]

I have been doing a bit of browsing on the net and have found various comments about clutch problems and the slave cylinder.

Do you have any opinions on this subject? Try bleeding the system again? Replace the master cylinder? Is the problem more likely to be associated with the slave?

Thank you very much for any help!

I can tell you for sure that your problems are not associated with how long or hot you drives have been, or heat period. The problem also has nothing to do with using AC or not. The hydraulic system your clutch uses is very simple. You exert force on your clutch pedal, which exerts force on the fluid in the master cylinder, through the line down to your slave cylinder. An intermittent soft pedal can only be caused by a failing master or slave cylinder. If there were air in the system it would be consistently soft all the time. There are seals inside the master and slave that can leak intermittently causing your pedal to feel soft at times. There isn’t really any way to test the master and slave for minor internal leaking, so replace both and your problem will be solved. Besides, if one is starting to fail, the other may not be far behind.

The problem is with the clutch master cylinder.

When the underhood temperatures increase, it heats up the clutch master cylinder. This then causes the bore within the clutch master cylinder to expand. If the cup seal in the master cylinder is at all worn, this bore expansion within the master cylinder allows the hydraulic fluid to by-pass the cup seal. This then prevents the proper hydraulic pressure from being produced to operate the slave cylinder. This then causes the mushy clutch pedal, the slave cylinder doesn’t disengage the clutch when the clutch pedal is depressed, and it becomes impossible to shift the transmission without grinding the gears.

There’s a quick method to determine if the clutch master cylinder is being effected by heat causing this problem. Carry a bottle of water in the vehicle. The next time the clutch pedal becomes mushy, pull the vehicle over, open the hood and pour the water over the clutch master cylinder. If the hydraulic pressure returns to the clutch system after pouring the water over the master cylinder, replace the clutch master cylinder.


Thank you so much for your explanation and your advice!

Thank you so much for your explanation and your advice. I doubt if I’ll get to the water pouring stage, although I love the idea of testing out a theory. I think I’ll just get the master cylinder replaced as planned. However, I already feel attuned to this idea thanks to the feedback that you knowledgeable experts have been so kind to send. Breaking down in decent weather is not to be wished for. However, winter is coming to Montreal, and breaking down in brutal weather is no fun.

I’ll though one more idea. You could be loosing vacuum boost. A bad vacuum hose or a leaking vacuum connection may be aggravated by the heat. You may want to check that out if you don’t get it straightened out by the time you get to the end of Tester’s list.

Thank you! I’ll check into that too.