Clutch needs adjustment?

[humfrz]

Well, is the OEM clutch self adjusting or not? -


humfrz

[Ultramaroon]

Originally Posted by RallySTI

I am curious on what info you have that shows that the clutch actuation system self adjusts.

The only reference other than the one you found earlier, is on the offline BRZ manual. The last page of the attachment describes manually retracting the fork to confirm the proper function of the 'self adjustment' mechanism to which I am referring.


I could have sworn there was something more obvious but... :/

[churchx]

From pic in this googled story, seems that unless with clutch pedal piston in master cylinder in fully released pedal is still past hole from reservoir, at same pedal travel it will always move slave cylinder's piston by same amount, taking in "extra" fluid from reservoir, if needed.
Adding here Ultramaroon's clutch pedal adjustment manual, i guess it's about that "auto-adjustment" is related to clutch wear, that fork on normally adjusted pedal will push by same travel both worn and new clutches, instead of different free play depending on clutch wear.
I see two problems here. 1) it doesn't account aftermarket clutches that may need different slave cylinder's piston travel range, 2) misadjusted clutch pedal travel with popular mod to reduce dead travel/move bite point lower in "pedal travel", that may result in too short travel left, resulting in slight clutch drag/synchro & gear grind.
imho (1) should be fixed by aftermarket clutch makers so as to work well with same travel as OE hydraulic pedal mechanism, or they should include in set different slave cylinder or piston or linkage or fork that would change piston/fork travel to one that is needed for their clutches. Or so that their needed travel range falls within what can be adjusted with adjusting pedal travel, with according instructions in manual.

[Ultramaroon]

If someone has modded their car so much that the stock clutch no longer hooks up, then the stock transmission's days are numbered.

As with any other mod, it's up to the owner to make good choices.

No offense intended against anyone but if folks aren't able to determine for themselves whether or not a clutch is dragging, they oughtn't be in there tinkering in the first place.

[humfrz]

Originally Posted by Ultramaroon

If someone has modded their car so much that the stock clutch no longer hooks up, then the stock transmission's days are numbered.

As with any other mod, it's up to the owner to make good choices.

No offense intended against anyone but if folks aren't able to determine for themselves whether or not a clutch is dragging, they oughtn't be in there tinkering in the first place.

Yep, that goes for a lot of things -


humfrz

[RallySTI]

Originally Posted by humfrz

Well, is the OEM clutch self adjusting or not? -


humfrz

No, the OEM clutch is not a self adjusting clutch nor is any aftermarket clutch for these cars.

Below is some info from LUK who manufactures almost all of self adjusting clutches (SAC) on the market. You can see how the pressure plate they have shown in that link looks nothing like what is used in the BRZ/86.

https://www.repxpert.us/en/work/prod...product_ds3046


The one used in our cars is a DST type, as EXEDY calls that type of pressure plate assembly. It is just a plain 'ol conventional push type clutch. With this type of clutch as the disc wears the diaphragm spring will move away from the engine increasing the stack height of the clutch. As this happens the clutch will disengage sooner in the pedal stroke. If the clutch were to wear out before the release bearing you would actually notice this happening. However since the clutch wear generally happens slowly over time you don't really notice how much the engagement point changes. I changed my clutch at 80k (because of the bearing) and when I measured the clutch disc thickness it still have about 55% remaining.

The clutch disc wear for our cars from new to discard thickness is only 1.5 mm.

The lever ratio for the EXEDY OE pressure plate is 2.744:1 meaning for 1 mm of disc wear the diaphragm spring height (or stack height) will increase 2.744 mm.

So over the 1.5 mm allowed wear the stack height will increase 4.116 mm.

For what it is worth and to the validity of the info I have provided in this thread I work for EXEDY USA as a technical coordinator. If you call our tech line you are likely to talk to me.

[humfrz]

Originally Posted by RallySTI

No, the OEM clutch is not a self adjusting clutch nor is any aftermarket clutch for these cars.

Thanks for the detailed explanation -

So, with the OEM clutch, under normal wear, is it ever necessary to adjust the clutch?

TIA


humfrz

[Ultramaroon]

Originally Posted by RallySTI

So over the 1.5 mm allowed wear the stack height will increase 4.116 mm.

Let's add the lever ratio of the fork into the mix for shits & giggles.



A 4 mm increase in stack height translates to about 6 mm compression of the piston in the slave cylinder over the life of the clutch. Where does that adjustment happen?

We're not talking about self-adjusting pressure plates. I didn't even know that was a thing.

[RallySTI]

Originally Posted by humfrz

Thanks for the detailed explanation -

So, with the OEM clutch, under normal wear, is it ever necessary to adjust the clutch?

TIA


humfrz

Usually not.

An adjustment may be needed if a slave or master cylinder is replaced or for driver preference.

When the clutch is replaced the clutch pedal free play should be checked and adjusted as necessary.

Looking at the other clutch options for these cars any ACT, Southbend ( modified EXEDY OE pressure plate), McLeod, Spec...etc. will need to have the clutch pedal adjusted for proper function. This is due to the change in the lever ratio due to the design change between manufactures.

[EndlessAzure]

Originally Posted by RallySTI

Usually not.

An adjustment may be needed if a slave or master cylinder is replaced or for driver preference.

When the clutch is replaced the clutch pedal free play should be checked and adjusted as necessary.

Looking at the other clutch options for these cars any ACT, Southbend ( modified EXEDY OE pressure plate), McLeod, Spec...etc. will need to have the clutch pedal adjusted for proper function. This is due to the change in the lever ratio due to the design change between manufactures.

Which way and by how much does the adjustment typically need to be made for aftermarket kits?

[RallySTI]

Originally Posted by Ultramaroon

Let's add the lever ratio of the fork into the mix for shits & giggles.

Where does that adjustment happen?

There is no adjustment that happens. This compression is why the clutch disengages sooner in the pedal stroke as the disc wears thinner.

The fork lever ratio is 1.6:1 (120 mm/ 75 mm) according to my measurement of the sample (30531-AA220) that I have. Your calculations are about the same at 1.62:1 so our math jives. YAAAAA math class

So the OE clutch diaphragm spring needs to see 7.5 mm of movement to achieve the 1.0 mm of plate lift to allow disengagement of the clutch disc.

So lets say the disc is worn to a point that the stack height has increased 4.0 mm from the "new" installed stack height.

So with the factory set pedal adjustment and the same volume of fluid is moved to the slave the extension of the slave cylinder will be the same. The clutch with the 4.0 mm increased stack height will achieve the needed 7.5 mm of movement sooner in the clutch pedal stroke.

Does this make sense ?

If we use the 1.6:1 lever ratio for the fork and the 7.5 mm DSP stroke needed (max stroke on the drawing says 9.0 mm) we want to see around 12-15 mm of extension from the slave cylinder with the OE EXEDY clutch for proper plate lift. Which I showed this in the video I linked earlier in this thread.

There are multiple variants that can affect the needed travel and clutch function such as disc wear, fork deflection, fluid viscosity, clutch and flywheel stack height, release bearing, debris in the pressure plate assembly from disc wear, conditions of internal seals in both cylinders...etc.

[RallySTI]

Originally Posted by EndlessAzure

Which way and by how much does the adjustment typically need to be made for aftermarket kits?

There is not set amount. I would contact the manufacture of the clutch to get their recommendation.

Make small adjustments, like half to full turn and check.

If the engagement point is to close to the floor, this is generally the case when you have disc drag or when the vehicle lurches when the clutch pedal is moved up away from the floor slightly.

To correct this you will want to rotate the master cylinder rod counter clockwise this will move more fluid to the slave cylinder and move the engagement point up in the pedal stroke.

Rotation of the master cylinder rod counter clockwise out of the pedal assembly clevis will move the engagement point up in the pedal stroke and reduce the amount of free play in the pedal. This increases the amount of fluid moved from the master to slave cylinder. More clutch actuation.

Rotation of the master cylinder rod clockwise into the pedal assembly clevis will move the engagement point down in the pedal stroke and increase the amount of free play in the pedal. This decreases the amount of fluid moved from the master to slave cylinder. Less clutch actuation

My advice for pedal adjustment is to set it where the engagement point is comfortable for the driver with out over stroking the clutch or pre-loading the release bearing against the clutch.

You do want to retain some free play in the top clutch pedal like the amount given in the factory service manual. The free play ensures that the release bearing is not loaded up against the diaphragm spring which can prematurely wear out the bearing and/or put the clutch in a semi disengaged state.

To ensure the clutch is not in an over stroke condition you will want the pedal stroke to stop approximately 1/4-1/2 inch past the point where the clutch is disengaged.

[MrDinkleman]

Originally Posted by Ultramaroon

A 4 mm increase in stack height translates to about 6 mm compression of the piston in the slave cylinder over the life of the clutch. Where does that adjustment happen?

We're not talking about self-adjusting pressure plates. I didn't even know that was a thing.

Thanks for the picture. It's worth a thousand words...

The "self adjustment" for clutch wear is handled by the little spring pushing the piston in the slave cylinder. Which is how, AFAIK, all hydraulicly actuated clutches are set up. Without the spring, the pushrod would just fall out. Mechanically actuated clutches (e.g., cables or linkages in old American cars or cables on motorcycles) need periodic adjustment.

The adjustment you find at the pedal is just for pedal freeplay.

Edit: just remembered, as clutch wears, the amount of stroke necessary to disengage the clutch increases. You can increase the slave cylinder stroke a tiny bit by adjusting the clutch pedal.

The problem with this whole discussion is people thinking the clutch and/or pressure plate is "adjusted". They are not, at least in any (affordable) production street cars. I dont know how exotics and DCT cars are set up...

[Ultramaroon]

Originally Posted by RallySTI

You do want to retain some free play in the top clutch pedal like the amount given in the factory service manual. The free play ensures that the release bearing is not loaded up against the diaphragm spring which can prematurely wear out the bearing and/or put the clutch in a semi disengaged state.

To ensure the clutch is not in an over stroke condition you will want the pedal stroke to stop approximately 1/4-1/2 inch past the point where the clutch is disengaged.

There is no free play at the top of the clutch pedal movement except for that which is required by the equalizing port.

Once again, for the original reason that I chimed into this thread, the clutch operating mechanism is self adjusting.

When the master piston is fully extended, it opens a port between the reservoir and the working area. This allows the working fluid to drain back into the reservoir as the clutch wears. The TOB is in constant contact with the pressure plate fingers. This is why the initial setup of the clutch pedal is critical. The master piston must be allowed to fully retract.

This is also why, in the Subaru version of the service manual, there is a step at the end specifically to verify this function. See the document I attached earlier in this thread.