Is clutch slipping

saturn
sl

#1

2000 Saturn SL Manual 5 speed



I recently parked on an incline and left the car in 4-th gear while I rested and drank some coffee. The parking brake was off. I noticed that the car rolled slowly backwards. It didn’t move at a constant speed. Instead, it would lurch backwards, and the hold for a while, and lurch backwards again.



I didn’t think the incline was very steep, and that it shouldn’t be doing this, so I took it to the dealer. The mechanics there said this behavior could be expected. But I have my doubts.



I decided to replicate the situation when I got back home, and this time, to measure how steep the incline was with a carpenter’s level.



On a 4.5% grade, the problem was worse than what I had originally experienced. On a 2% grade, the car stayed put. The weight of this vehicle, together with miscellaneous contents, including me, is 3500 lbs. Doing the math (I knew that BA in Physics would come in handy some day), that means that a force of only 160 lbs, applied to the rear of the car when it’s parked on a level surface is enough to get it to move forward in 4-th gear. This doesn’t sound right at all.



Look at it another way. If I drive up a 4.5% grade at constant speed in 4-th gear, my clutch would be slipping (assuming it’s the clutch and not the compression). It’s true that compared to the number of revolutions of the clutch needed to move the car forward, it wouldn’t be slipping by very much, but I’ll bet that it shouldn’t slip at all under these conditions.



Is my dealer lying to me … again?


#2

You can’t park a vehicle on a grade in any gear except first or reverse…period. The parking brake should be used as well. Your vehicle did what any other vehicle would do when parked in fourth gear. I’m surprised it did not take off and roll to the bottom of the incline. A 2000 Saturn engine does not have enough compression to hold it’s own weight. Your clutch must be in very good condition to keep the vehicle lurching instead of rolling. A strong 160 pound man could push a Saturn in fourth gear just about anywhere he wanted to.


#3

Why are you leaving the car in 4th gear when you park? What is wrong with applying the parking brake?

There is better holding power by the compression of the motor in 1st or reverse. The lurch you experienced was the motor rotating until the next cylinder hit the compression part of its stroke.

If you want to see if your clutch is slipping the clutch test is to put the car in 4th or 5th, apply some gas (about 2,000 rpm) and release the clutch. If the car stalls the clutch is fine.

If your “parking brake” works you should apply it when you park and leave the transmission in 1st or reverse to make sure your car stays put.


#4

All the above… Plus, when rolling to the rear in a forward gear the engine is turned counter clockwise. This can cause the timing belt to jump and/or damage the belt tensioner.


#5

If you don’t want it to roll, put in first or reverse. I had a 1971 VW bus that needed frequent valve adjustments (every time I changed the oil) and I left it in high gear (4th) and while I was under it with the valve cover off I would roll the van forward and back in gear to adjust the valves without getting out from under it.


#6

Here’s the good news:
-Your dealer won’t be a Saturn dealer for much longer :wink:
-Your car is perfectly OK, and there is absolutely nothing wrong with it.

Here’s the bad news:
-Your car-operator technique is somewhat deficient, but could be very easily improved/corrected.

All cars should ALWAYS be parked (whether on level ground or grade) with the Parking Brake firmly applied AND the transmission in Reverse or First gear-if equiped with a manual transmission, or in Park-if equiped with and Automatic.
On many cars the rear brakes self-adjust every time you pull on that parking brake lever, which keep your brakes functioning with the highest efficiency.


#7

This would be expected for a car with this many miles one it. The fact that the rollback was not steady indicates that the engine compression is still adequate. When you try to hold a car from rolling using the gear box, it is the static friction of the engine that does the holding. If you are relying on the compression alone, the engine will continue to turn as the air leaks past the rings. All engines leak some air past the rings through the ring gap. As the mileage builds up on an engine, the static friction of the rings against the cylinder walls drops and the engine will break free at a lower torque.

Hope this explanation helps you understand that to hold a car from moving you have to use the lowest gear i.e. first or reverse. To make sure that the engine does not break free apply the parking brake to increase the static friction of the entire vehicle.


#8

Well, your BA in Physics will not help you in this case. You would have better luck parking in your lowest gear, 1st, or reverse. And most folks on here will reccomend that you set the park brake. Did you learn in Physics that a vehicle is a lot easier to move in 4th than it is in 1st?