The following statements are my opinions but they are based on 26 years of wrenching on mitsubishis and 21 of those years on DSMs. This applies to 4g63 cars only. I am not commenting on a 420a clutch although some things do apply.
This is not meant to be just DSM specific but could be applied to many cars. That being said a few basic things need to be pointed out.
1. There are not AWD or FWD clutches. A turbo DSM uses the same clutch whether it's FWD or AWD. They do NOT use the same flywheel.
2. An NT flywheel is flat and is not the same as a turbo flywheel nor is the clutch the same. Turbos use a stepped flywheel and a 225mm clutch disk vs the NT 215mm disk.
3. Extended slaves do not work. They are a bandaid. Now before you go and bash me read this. If you install one and it makes a difference the following is why or why not. A clutch hydraulic system must be allowed to self adjust as a clutch wears. When the system is static there is no pressure on anything and the fluid is free to move. As a clutch wears the fingers on the pressure plate will change positions because the thickness of the disk is changing so the position of the fork changes. If a hydraulic system could not self adjust then as the clutch wears the system would become preloaded (similar to riding the clutch). DSMs do not work this way. You'll notice you should be able to push the slave back into it's bore easily unless one of the following exists.
a. The master has been adjusted so far you have effectively pressed the clutch pedal which closes off the valve in the master and you have a nonadjusting system at that point.
b. You have installed an extended slave rod and have bottomed the piston out in its bore so you have effectively limited its travel backward and preloaded the system. It's like you are pressing the clutch slightly before you ever press the pedal. Yes, this could aid in clutch disengagement but at the expense of the same types of wear you could expect from constantly having your foot on the clutch. Throwout bearing, crank thrust bearings, clutch pressure plate, fork, pivot, slave, and master all experience increased wear.
4. Shims under the pivot ball are a bandaid. I am not a fan but I can understand why people use them. It's is easily understood that the travel of the slave does not transmit in a straight line to the clutch. There is an arc involved and some trigonometry would help. If some angels/distances are changed one could see why people think it's necessary to add shims. The differences are most certainly real (flywheel step height machining for example) but the changes are very very small, thousandths of an inch. Could this be enough? Who's to say. Unless you have objective measurements of clutch disengagement travel, slave travel and throwout bearing travel I don't see how anyone could objectively comment. I do not use shims. I make damn sure the components I use elsewhere are up to spec and fresh. If you machined .020 off the flywheel and add a .020 shim to the pivot ball, that is your business. haphazardly adding various thickness shims is a bad idea, again, in my opinion.
5. Besides wearing a clutch can slip if it doesn't have enough pressure holding the disk and flywheel/pressure plate together. If you're a turbo car and the step height is too deep you just potentially reduced the clamping force of the clutch. If it's too shallow the same could happen in addition to possibly not disengaging. If you preloaded the clutch because the master is over-adjusted or you use an extended slave rod you could potentially be "riding the clutch" causing it to slip.
Now with those out of the way let's discuss how a clutch works and why we seem to have so much trouble. Any clutch design similar to a DSM (and many are) you have a pressure plate diaphragm spring system with internal pivots that provide pressure against the disk. Now here is where it gets interesting. We need stronger clutches to hold more power but clutch manufacturers do not just simply make the springs stiffer. It isn't practical as the system gets too stiff. We are talking about a system of springs and fulcrums etc. So what manufacturers do in addition to upping spring pressure is they change the pivot point to gain more leverage. What is the disadvantage to this? It requires more travel to completely disengage. Add this to a relatively narrow window of adjustment, worn components etc and you can see why so many DSMs have problems with clutch disengagement. This is unfortunately something we live with within the small surface area we have to work with. Eventually somebody came along with a twin disk clutch and changed all the rules. Lots more friction area within the same 225mm space.
Did you also know that there are different diameter slave bores available? Parts stores often list 90-99 ALL the same. Slaves are out there with either 3/4" or 13/16" bores depending on year, model and options. Mix and match NT and turbo etc and it's starts to get interesting. For the record on OEM there was a color code that may still exist. Red pistons are 3/4 and green ones are 13/16.
It is well known that our pedals are prone to wear but few know what wears or what it affects? On a 1g there are several bushings both on the pedal assembly itself and where the clevis pins goes through the clutch pedal lever. The largest wear point is usually where the clutch lever bolts to the pedal assembly. You can see this at the opposite end of where the master cylinder clevis attaches to the clutch lever. Usually, you can simply grab the two and twist them relative to one another. If this is the case a repair must be made. 2gs do not have this issues because their pedal design is completely different.
I wrote this because I am tired of people posting about how their clutch is doing this or that and there are no objectively statements being made and a lot of assumptions....for instance.
A new flywheel is the correct step height.
For what clutch? Even the same manufacturer. Are you sure? Did you measure? Did you measure with a caliper or a proper depth mic?
On a similar note, "my machinist made sure it was the correct step height". how do you know? Did you measure? If the answer is no you do not know, you assume. A good machinist should not mind if you ask for a depth mic to check the work.
My master and slave are new so they must be good? See the points above about different bore sizes. Not all parts allow the same amount of travel either. If a master gets pushed a little further before it closes the valve what happens? Less travel at the slave. I trust OEM and no other unless I had objective data to support they are the same.
I check the pedal and it looks good. What does that mean? Checked it how? Looked at it?
I'm all about helping people but some objective comments need to be present in order to do so.
Please, discuss, rant, comment etc. These comments are my own and are meant to provide information. Nothing more.
This is not meant to be just DSM specific but could be applied to many cars. That being said a few basic things need to be pointed out.
1. There are not AWD or FWD clutches. A turbo DSM uses the same clutch whether it's FWD or AWD. They do NOT use the same flywheel.
2. An NT flywheel is flat and is not the same as a turbo flywheel nor is the clutch the same. Turbos use a stepped flywheel and a 225mm clutch disk vs the NT 215mm disk.
3. Extended slaves do not work. They are a bandaid. Now before you go and bash me read this. If you install one and it makes a difference the following is why or why not. A clutch hydraulic system must be allowed to self adjust as a clutch wears. When the system is static there is no pressure on anything and the fluid is free to move. As a clutch wears the fingers on the pressure plate will change positions because the thickness of the disk is changing so the position of the fork changes. If a hydraulic system could not self adjust then as the clutch wears the system would become preloaded (similar to riding the clutch). DSMs do not work this way. You'll notice you should be able to push the slave back into it's bore easily unless one of the following exists.
a. The master has been adjusted so far you have effectively pressed the clutch pedal which closes off the valve in the master and you have a nonadjusting system at that point.
b. You have installed an extended slave rod and have bottomed the piston out in its bore so you have effectively limited its travel backward and preloaded the system. It's like you are pressing the clutch slightly before you ever press the pedal. Yes, this could aid in clutch disengagement but at the expense of the same types of wear you could expect from constantly having your foot on the clutch. Throwout bearing, crank thrust bearings, clutch pressure plate, fork, pivot, slave, and master all experience increased wear.
4. Shims under the pivot ball are a bandaid. I am not a fan but I can understand why people use them. It's is easily understood that the travel of the slave does not transmit in a straight line to the clutch. There is an arc involved and some trigonometry would help. If some angels/distances are changed one could see why people think it's necessary to add shims. The differences are most certainly real (flywheel step height machining for example) but the changes are very very small, thousandths of an inch. Could this be enough? Who's to say. Unless you have objective measurements of clutch disengagement travel, slave travel and throwout bearing travel I don't see how anyone could objectively comment. I do not use shims. I make damn sure the components I use elsewhere are up to spec and fresh. If you machined .020 off the flywheel and add a .020 shim to the pivot ball, that is your business. haphazardly adding various thickness shims is a bad idea, again, in my opinion.
5. Besides wearing a clutch can slip if it doesn't have enough pressure holding the disk and flywheel/pressure plate together. If you're a turbo car and the step height is too deep you just potentially reduced the clamping force of the clutch. If it's too shallow the same could happen in addition to possibly not disengaging. If you preloaded the clutch because the master is over-adjusted or you use an extended slave rod you could potentially be "riding the clutch" causing it to slip.
Now with those out of the way let's discuss how a clutch works and why we seem to have so much trouble. Any clutch design similar to a DSM (and many are) you have a pressure plate diaphragm spring system with internal pivots that provide pressure against the disk. Now here is where it gets interesting. We need stronger clutches to hold more power but clutch manufacturers do not just simply make the springs stiffer. It isn't practical as the system gets too stiff. We are talking about a system of springs and fulcrums etc. So what manufacturers do in addition to upping spring pressure is they change the pivot point to gain more leverage. What is the disadvantage to this? It requires more travel to completely disengage. Add this to a relatively narrow window of adjustment, worn components etc and you can see why so many DSMs have problems with clutch disengagement. This is unfortunately something we live with within the small surface area we have to work with. Eventually somebody came along with a twin disk clutch and changed all the rules. Lots more friction area within the same 225mm space.
Did you also know that there are different diameter slave bores available? Parts stores often list 90-99 ALL the same. Slaves are out there with either 3/4" or 13/16" bores depending on year, model and options. Mix and match NT and turbo etc and it's starts to get interesting. For the record on OEM there was a color code that may still exist. Red pistons are 3/4 and green ones are 13/16.
It is well known that our pedals are prone to wear but few know what wears or what it affects? On a 1g there are several bushings both on the pedal assembly itself and where the clevis pins goes through the clutch pedal lever. The largest wear point is usually where the clutch lever bolts to the pedal assembly. You can see this at the opposite end of where the master cylinder clevis attaches to the clutch lever. Usually, you can simply grab the two and twist them relative to one another. If this is the case a repair must be made. 2gs do not have this issues because their pedal design is completely different.
I wrote this because I am tired of people posting about how their clutch is doing this or that and there are no objectively statements being made and a lot of assumptions....for instance.
A new flywheel is the correct step height.
For what clutch? Even the same manufacturer. Are you sure? Did you measure? Did you measure with a caliper or a proper depth mic?
On a similar note, "my machinist made sure it was the correct step height". how do you know? Did you measure? If the answer is no you do not know, you assume. A good machinist should not mind if you ask for a depth mic to check the work.
My master and slave are new so they must be good? See the points above about different bore sizes. Not all parts allow the same amount of travel either. If a master gets pushed a little further before it closes the valve what happens? Less travel at the slave. I trust OEM and no other unless I had objective data to support they are the same.
I check the pedal and it looks good. What does that mean? Checked it how? Looked at it?
I'm all about helping people but some objective comments need to be present in order to do so.
Please, discuss, rant, comment etc. These comments are my own and are meant to provide information. Nothing more.
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