Can cooler weather cause a grabby clutch? Its been raining occasionally(causing a slight drop in temp. as well) in Kolkata these days. I noticed something minor but peculiar over the past few days . On days it has rained or the weather is cooler my clutch feels grabby. By 'grabby' I mean that when I start pulling away from a stop in 1st gear the clutch seems to 'bite' a bit earlier than usual, causing shuddering(just like if you let the clutch go way earlier without giving much accelerator input). If the day is warm or the clutch pedal has been pumped a few times it works perfectly like it should.
I have an Innova (72000 kms, regularly serviced at A.S.S. ,driven with care and no clutch riding) The car is mechanically very sound.
Now I thought about it and I came up with something. Lets get technical :
The Innova has a hydraulic clutch. Hydraulic fluid is essentially a special kind of oil. Now we know that with a drop in temperature, viscosity of a fluid increases(naturally,density increases as well) & vice-versa.
Physics says : Mass = Volume X Density.
Assuming there are no leaks, the hydraulic system should have a constant mass of fluid in it.
With an increase in density, volume decreases(Mass being constant like in this case).
Now when I press the clutch pedal I'm transferring the hydraulic fluid from the clutch master cylinder to the clutch slave cylinder under pressure. So, let's suppose that the clutch pedal is held in a fixed position. One of the following cases should happen : Case 1 : If the fluid is warm(lower density, higher volume) - Then pressure inside the slave cylinder should me more because of a greater volume of fluid entering the slave cylinder. Anyone who knows the clutch mechanism will know that more pressure in the slave cylinder means more clutch disengagement. Thus in this case, the pressure plate should disengage the clutch centre plate a bit more.
OR Case 2 : If the fluid is cold(higher density, lower volume) - Then the opposite of Case 1 i.e. Lower pressure inside the slave cylinder hence a little less disengagement.
In my situation Case 2 is applicable because due to the rains I've got lower atmospheric temperatures thus a colder clutch fluid. So when I pull away from a stop in first gear, because of a cold fluid my disengagement is lesser. Thus the clutch has a earlier 'bite' point due to more engagement - Hence the shuddering. Note : I said earlier that the clutch works perfectly when it's warm outside or the clutch pedal has been pumped a few times. If its warm outside, Case 1 is applicable, and if I've used the clutch pedal a few times the fluid would warm up(because of Compression of the fluid, Friction of the pistons on master and slave cylinders against the cylinder walls) and have similar consequences of Case 1. This might explain why the clutch works normally after sometime.
Am I right people? |