Clutch replace

[Bitsyncmaster]

Have not done much with this project lately. I did a quick clean up of the flywheel friction surface by sanding it on a surface block with 120 grit silicon carbide sand paper. Note a surface block is a granite block with a flatness of 0.0001" inch. That showed the machine head when the flywheel was machined was a little tilted since my sanding removed the machine marks on the inside circumference and not on the outside. Still nothing that would cause the failure.

If you have not seen on DAP's web site the claim that:

"Beware of the newer Valeo clutch kit: The pressure plate takes 1450.00 PSI pressure to engage and the original took 1123.00PSI to engage."

https://www.deloreanautoparts.com/de...nsmission.html

That makes me think that maybe I should not increase my step machined onto the flywheel from the current 0.016" to 0.030".

Right now I'm thinking I just may replace my master clutch cylinder since I have not found any evidence of what caused my problem with clutch mechanics. I do need a new boot on the slave since it's torn (about 10 years old). The fork looks in great shape. The engine and transmission main seals look not to be leaking any. I assume they were already changed when the clutch was reworked 20 years ago.

I wanted to set up a test of the pressure plate but after looking at load cells I can't justify spending $500 for a load cell unit which would fit between my 20 ton press and the pressure plate fingers.

[Bitsyncmaster]

So how does the master cylinder work? The slave would be pushed back by the pressure plate. So does the master work like a check valve and return to it's resting position and fill fully with fluid ready to provide the full stroke of the master?

Why would an adjustable pedal set not to return all the way back cause problems?

[DMC-81]

Have not done much with this project lately. I did a quick clean up of the flywheel friction surface by sanding it on a surface block with 120 grit silicon carbide sand paper. Note a surface block is a granite block with a flatness of 0.0001" inch. That showed the machine head when the flywheel was machined was a little tilted since my sanding removed the machine marks on the inside circumference and not on the outside. Still nothing that would cause the failure.

If you have not seen on DAP's web site the claim that:

"Beware of the newer Valeo clutch kit: The pressure plate takes 1450.00 PSI pressure to engage and the original took 1123.00PSI to engage."

https://www.deloreanautoparts.com/de...nsmission.html

That makes me think that maybe I should not increase my step machined onto the flywheel from the current 0.016" to 0.030".

Right now I'm thinking I just may replace my master clutch cylinder since I have not found any evidence of what caused my problem with clutch mechanics. I do need a new boot on the slave since it's torn (about 10 years old). The fork looks in great shape. The engine and transmission main seals look not to be leaking any. I assume they were already changed when the clutch was reworked 20 years ago.

I wanted to set up a test of the pressure plate but after looking at load cells I can't justify spending $500 for a load cell unit which would fit between my 20 ton press and the pressure plate fingers.

FYI, I have a new Valeo clutch kit with a new DMC master, slave, and SS braided line. I didn't notice an increased pedal effort after installation. I suppose more pressure on the pressure plate will help prevent clutch slipping.

I wonder if there were problems with the older Valeo versions not lasting long enough due to the lower pressure?

[Ron]

I think it would only go back to normal after I stopped the car for a few minuets. I'm pretty sure I also had the problem with 4th gear which I tested after the first and many problems in 5th gear. No partial slipping or noises at all, was always like the clutch let go.

That helps.

I agree with David about the transmission not coming and going like that. Since the trans is quiet, tight (and 4th is not the only gear it happens in), but, it would not pull immediately after stopping then pull again in a few minutes, I'd say it is a clutch/hydraulic problem. If you bled it during the time period that it usually required to wait (?) and it wouldn't pull right then, then I'd suspect the hydraulics a lot less. Otherwise, since none of it makes any odd noises etc., I still rooting for hydraulics (adjusted too tight #1).

Replacing (not rebuilding) the MC is what I would do too. Then ensure everything from it to the slave is ok. You might want to measure/mark where the fork arm sits when you manually hold it against the throwout bearing before installing the slave (for reference later).

.

[Bitsyncmaster]

I'm guessing John tested the pressure plates by putting a pressure gauge on his hydraulic press since he is stating PSI and not pounds. I still wondering what the difference with force would make increasing the step cut 10, 20 or 30 thousands. I've looked on the internet and see clamping force of 1300 to 2100 lbs on a few clutch systems.

The clamping pressure you would measure the force to seat the pressure plate onto the flywheel.

The force to release the clutch would be the force on the fingers to release. They would differ depending on the mechanical design of the fingers.

[Ron]

So how does the master cylinder work? The slave would be pushed back by the pressure plate. So does the master work like a check valve and return to it's resting position and fill fully with fluid ready to provide the full stroke of the master?

Why would an adjustable pedal set not to return all the way back cause problems?

I'm guessing it relates to what I said before (post 50). Unlike most brake MCs, a clutch MC has one port in and one port out. If the rod is too tight before attempting to bleed, it would probably never would -- The piston can't return past the intake/fill port to allow the bore to be refilled... If adjusted too tight after bleeding, after the first stroke, the piston piston can't return past the intake/fill port to allow fluid to return to the reservoir (extra due to: fingers compensating for clutch wear, heat expansion, line damage, ...?) Again, everything would have to be just right (wrong;-), but there is nothing else left I can think of anyway (nothing but heat changes as you are driving down the freeway and stay in one gear...).

[David T]

When you release the clutch pedal the master cylinder, when properly adjusted, allows any pressure in the system to bleed back to the reservoir. If it malfunctions or is not properly adjusted, and the master cylinder won't allow pressure to release, as the brake fluid gets hot and expands it can make the clutch slave disengage. Same problem if the brake fluid is contaminated with water and turns to steam and increasing the pressure. Same cure, rebuild/replace the clutch master and then flush and bleed the clutch hydraulics. Good practice, if you do something to one cylinder you should do the other. While the clutch is out it is easy enough to do the slave cylinder. I am guessing, since you have an adjustable link, the pedal is maladjusted and not allowing the pressure to release back to the reservoir. Either get rid of the adjustable link or try to get it properly adjusted. The adjustable link was an ill attempt to overcome the plastic hose syndrome. The fix for plastic hose syndrome is to replace it with the braided S/S hose.

[Ron]

https://www.deloreanautoparts.com/de...nsmission.html

That makes me think that maybe I should not increase my step machined onto the flywheel from the current 0.016" to 0.030".

That says to remove the step for the thicker disk... I don't know, but if .016" makes a significant difference there, ~doubling yours (.015 to .030) don't sound right?? (Unless it is for a HO racing setup, the clutch-plate set should be made for the factory grind in any case, imho.)

Just saw this:
"18 - Remove the flywheel attaching bolts and the flywheel. CAUTION: Very Heavy! Have a machine shop resurface the flywheel, be sure they are aware that a .020 in step is machined into the flywheel and must be maintained."

[DMC5180]

That’s says .020 step. I can’t imagine .004 less causing a significant issue.




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[David T]

That step and all of the other dimensions are critical because there is no mechanical adjustment that can allow for any variance. If the step is not right, if the friction disc is too thick, if anything is not just right, the clutch will not work correctly and you can't adjust it. The clutch hydraulics is the only thing meant to compensate for wear and even that is very small.