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Old 05-21-2020, 10:26 PM   #1
maxitoman007
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Default Adjusting hydraulic clutch grab point

How would one adjust the grab point on a hydraulic Volvo 740 clutch? Does this involve shimming the pivot ball?
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Old 05-22-2020, 06:48 AM   #2
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that could be an effective method, yes

EDIT: 142 guy is right, it would preload the throwout bearing if shimmed excessively.

Last edited by bmos; 05-23-2020 at 06:53 AM..
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Old 05-22-2020, 07:57 AM   #3
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If you want the clutch to grab earlier in the release stroke, you could put a shim (aka wooden block, etc) behind the clutch pedal.
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Old 05-22-2020, 06:11 PM   #4
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Been there, not done that! No provision in the design for adjusting the release / engagement point on the 740 hydraulic clutch system.

I don't think the shim idea will work as all it does is push the slave piston back into the slave cylinder. The amount of slave piston travel (and pedal travel) required to move the release fork remains unchanged (unless you shim it so much that you start to preload the release fork).

The best solution would be a master cylinder with a slightly larger bore. This would increase the ratio of slave piston to master piston movement giving you earlier release; but, would give you a slightly stiffer pedal.
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Old 05-24-2020, 08:30 PM   #5
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Quote:
Originally Posted by 142 guy View Post
Been there, not done that! No provision in the design for adjusting the release / engagement point on the 740 hydraulic clutch system.

I don't think the shim idea will work as all it does is push the slave piston back into the slave cylinder. The amount of slave piston travel (and pedal travel) required to move the release fork remains unchanged (unless you shim it so much that you start to preload the release fork).

The best solution would be a master cylinder with a slightly larger bore. This would increase the ratio of slave piston to master piston movement giving you earlier release; but, would give you a slightly stiffer pedal.
This is what I have discovered. After trying several shimming combinations with the same pedal feel each time. It then clicked that as long as the slave is using its full travel, the grab point will be the same.
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Old 05-25-2020, 02:00 AM   #6
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Just curious... which way did you want the "grab point" to move?

Grabbing too close to the floor is often a worn master leaking internally, or air in the system.

Grabbing too close to your nose could be a clutch so worn there's only a few days left before it starts slipping.

The only adjustment spec I can find is 1mm clearance between the pushrod and the piston in the master. IE: a tiny bit of free play at the pedal is normal.
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Old 05-25-2020, 03:33 AM   #7
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Anyhow... it'll never spool. As mentioned, the travel is a fixed entity in a hydraulic system. Shimming or otherwise altering the throw will only result in the master and/or slave traveling into previously unexplored bore. This will in turn result in rapid failure of either the master, slave or both.

Replace the master and slave cylinders. Be happy.

Edit: If you haven't yet, bleed some fresh fluid through and make sure all the air is out. You just might get away with it. Do *not* fully depress the clutch to bleed, see above.
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Old 05-25-2020, 02:25 PM   #8
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Quote:
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Do *not* fully depress the clutch to bleed, see above.
Ummm... isn't it the nature of the clutch to be fully depressed to the floor when shifting? Maybe you're thinking of *brake* masters, that (in a good system) only use 1/2 or less of their travel?
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Old 05-26-2020, 06:28 AM   #9
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Yeah... got me there.
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