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I am installing a 5.0 Mustang motor in my 85' 4Runner, (engine and drivetrain installed, NV4500 trans, dual t-case crawler box, with external parking brake at driveshaft). The discussion at hand is how far should the clutch rod move into the master clutch cylinder in relation to the slave cylinder movement to move the clutch rod via the clutch fork. Another way to look at this is once the throw-out bearing makes contact to the clutch pressure plate fingers, how far should the clutchfork move in to disengage the clutch properly?

Notes: F150 Bellhousing, Luke pressure plate, 11" Centerforce clutch disk, special Advance Adapters pilot bearing, Throw-out bearing?, Clutch slave assembly Raybestos SC37745, Clutch master cylinder assembly Raybestos CMA39560 kit including preformed fluid line (for late model Jeep), custom slave cylinder support, custom slave cylinder rod about 8.5" long, highly modified clutch fork (shortened about 1").

"This discussion might involve leverage and physics volume of pistons, fluid displacement and pedal lever force" as Moses suggested.

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transporter...If the flywheel and pressure plate faces are in good condition, not warped, and parallel in service, it takes little release bearing movement to free the disk.  As far as the clutch fork/arm movement needs, this would depend upon the fulcrum point of the release arm's pivot ball.  Simply put, what is the ratio of movement between the release arm's end and the release bearing's yoke point?

First rule-of-thumb is to prevent the clutch cover release fingers from bottoming against the clutch disk hub with the clutch pedal at full travel.  (You obviously want less release arm travel than this!)  The second concern is pushing the clutch cover's fingers far enough to separate the clutch disk from the pressure plate face and the flywheel face.

Do the math, beginning with the release arm's measurements from the pivot ball center to 1) the inner yoke (centerline of the release bearing) and 2) the outer hydraulic slave cylinder's rod centerline.  Determine the ratio.  This should provide an approximate idea of the needed release arm movement.  The rest has to do with keeping the clutch master cylinder's piston safely within the master cylinder's bore over the full range of clutch linkage travel.  

The clutch pedal height can also determine the total release arm travel.  The pedal's range of travel, coupled with the release arm ratio and also the piston sizes in the master cylinder and the slave cylinder, will determine the amount of movement at the slave cylinder's piston, the release arm and the clutch cover fingers.  Piston size differences should be considered as a ratio, too:  a fluid volume/ratio that plays a role in the amount of slave cylinder piston/pushrod movement for each linear movement of the clutch master cylinder piston.

You also need the release bearing to retract from the clutch disk's fingers when the clutch pedal is released.  Without some clearance between the release bearing face and cover fingers, the release bearing and clutch cover fingers will wear out prematurely.  Also, as the clutch disk wears, the fingers move outward from the cover.  This removes release bearing clearance, and if your clutch linkage does not allow for this normal wear, and if the release arm cannot retract far enough, the clutch adjustment will be off.  Pressure applies continuously at the clutch release fingers, and the clutch cannot engage completely, causing clutch slippage and rapid failure.

Modern hydraulic clutch linkage is "self-adjusting".  The release bearing retracts from the clutch cover fingers by itself (force of the spinning bearing).  As the clutch disk wears and the cover fingers move outward, the bearing needs to retract further.  It does so if the linkage system and piston range of travel allow room for this movement.

Moses 

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Moses thanks for the engineering detail overview the question is specifically will three eighths of an inch be enough to disengage the clutch this would be the movement in the clutch Fork

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If you add free play to protect the release bearing with the pedal released, 3/8" sounds very shallow.  It will likely take more than this with the typical fulcrum point and arm leverage.  

A simpler approach might be to see how a stock Toyota truck clutch linkage works from your era.  Test a vehicle's pedal travel and see what distance it takes for release.  Use that as a place to start, and go from there.  Consider the concerns I shared in the long reply on Thursday (above).

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Thanks for the info I just welded additional piece on the master cylinder clutch pedal about another three eighths of an inch longer rod and it now moves the slave cylinder rod another whopping eighth of an inch. New slave cylinder distance half inch movement. Thx pete

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Pete...Sounds like very little slave movement.  Either the master cylinder or slave cylinder is leaking/bypassing past its piston seal, or you need a clutch master cylinder with a larger piston bore/diameter to displace more fluid with the current amount of pedal travel.  That would move the slave piston and release rod further with the current amount of pedal movement.

Moses

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Hello Moses thanks for the reply. The hydralic outfit has been sitting in a box for 12 years and it's for a 1987 Ford F150 set up and worked in many conversions I bet you're right on that one of the seals bad if it's sad that long

Thxx

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Pete, you might try simply rebuilding the Ford F150 clutch master cylinder.  Before doing so, confirm its bore size and compare that to the demands for the slave cylinder.  If these two Raybestos parts (master and slave) are a match, and if the pedal leverage and rod travel are similar to a Ford F150 for piston movement, this should work.  The only other factor is the release arm.  If it is also a match for the Ford master and slave, you should have the right travel.

Moses

On 6/21/2016 at 8:29 PM, transporter said:

I am installing a 5.0 Mustang motor in my 85' 4Runner, (engine and drivetrain installed, NV4500 trans, dual t-case crawler box, with external parking brake at driveshaft). The discussion at hand is how far should the clutch rod move into the master clutch cylinder in relation to the slave cylinder movement to move the clutch rod via the clutch fork. Another way to look at this is once the throw-out bearing makes contact to the clutch pressure plate fingers, how far should the clutchfork move in to disengage the clutch properly?

Notes: F150 Bellhousing, Luke pressure plate, 11" Centerforce clutch disk, special Advance Adapters pilot bearing, Throw-out bearing?, Clutch slave assembly Raybestos SC37745, Clutch master cylinder assembly Raybestos CMA39560 kit including preformed fluid line (for late model Jeep), custom slave cylinder support, custom slave cylinder rod about 8.5" long, highly modified clutch fork (shortened about 1").

"This discussion might involve leverage and physics volume of pistons, fluid displacement and pedal lever force" as Moses suggested.

 

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