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Need guidance on Master cylinder and slave cylinder

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FordThunder
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Joined: Tue Sep 18, 2018 3:13 pm

Need guidance on Master cylinder and slave cylinder

Post #1 by FordThunder » Mon May 06, 2019 5:53 pm

Hey guys,

96’ f-150 2wd, M5OD transmission. I am not getting full return on my clutch pedal and can not shift into gear. I have pulled the transmission. I have installed a new internal slave cylinder, clutch/flywheel, rear main seal, release bearing and new master cylinder (two new masters now) and end result is the same. I bench bled both master cylinders off the truck. I have gravity bled the entire system. I have pressure bled the entire system ( pedal pumps) I have pulled vacuum on the entire system. I have zero leaks on the line, MC, or out of transmission. I have bled over a gallon of fluid through the system without air bubbles. With the MC disconnected from the slave, I have pressure but pressure doesn’t begin until 30% down and pedal returns, but only returns 3/4. I’m stuck. I’m guessing I have to drop the transmission again and buy another new slave and master cylinder... (brand is performance clutch) Any suggestions please, I’m at wits end and this is my work truck and my only lover.

Backwoodswalker375
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Joined: Wed Apr 04, 2018 4:17 am

Re: Need guidance on Master cylinder and slave cylinder

Post #2 by Backwoodswalker375 » Tue May 07, 2019 6:57 am

Check where master cylinder mounts to firewall. I have seen cracks in this area allowing movement when pushing pedal down. Have someone push down on pedal while watching for movement under hood. I have seen hydraulic clutches that were a bugger to bleed too. Good luck on your project. Steve

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GPGoverMPG
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Location: South central texas

Re: Need guidance on Master cylinder and slave cylinder

Post #3 by GPGoverMPG » Tue May 07, 2019 7:29 am

Those systems can be a real pain. I've had motorcycle front brakes wear me out. The bleeders are at the bottom and the air rises in the system. You may need to bleed at the master by loosing the line while the pedal is pressed. I have also had problems with the vehicle being jacked up in the front changing the angle of the slave cylinder and keeping air. Make sure the vehicle is level or nose down a bit. Last thing is line swell. Hold the line between the two and have someone pump the pedal and feel the line for expansion. The system seems so simple it's really frustrating. In conclusion I hate vertical systems with the bleeders at the bottom. Good luck
71 F350 4x4 Super Duty 7.3 IDI
72 F250 4x4 4speed 300 I6
72 F100 2x 428 Tri Power
2014 SHO

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MechRick
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Location: Las Vegas, NV

Re: Need guidance on Master cylinder and slave cylinder

Post #4 by MechRick » Tue May 07, 2019 11:41 am

Air gets trapped in the master and slave from the angle of the drive line and master cyl mounting.

Raise the back end of the truck until the valve cover is level, and rebleed.

Remove the master from the firewall and depress the master plunger with a Phillips screwdriver, keeping the line fitting higher than the rear of the master.

Those are the only two methods that seem to work for me.

One of these days I'm going to invent a device that forces fluid into the slave bleed screw.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

Max_Effort
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Re: Need guidance on Master cylinder and slave cylinder

Post #5 by Max_Effort » Tue May 07, 2019 4:21 pm

I've used a big plastic syringe to push the fluid backwards.
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In the ZF with external slave, stroking the slave cylinder helps get a good pedal.

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I think there are two master cylinders one around 3/4" bore and one around 7/8" bore. It make a difference if you swapped a smaller for large bore into the truck (more travel in the pedal)

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Pushrod length is important, you might need to check the length after swapping parts.

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I've seen the cracked firewall too. There is a repair kit.

Harte3
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Re: Need guidance on Master cylinder and slave cylinder

Post #6 by Harte3 » Thu May 09, 2019 12:08 am

MechRick: "One of these days I'm going to invent a device that forces fluid into the slave bleed screw."

Years ago I worked for a farmer that built such a device. He was quite the genius at building all sorts of stuff. He made a tank out of a piece of well casing that he could put brake fluid in, screw the lid down, pressurize the tank and with a pick-up and hose in the tank and the other end over a bleeder, open a valve on the tank and force fluid into the system. Reverse bleeding, it worked like a charm. I put a 289 Ford into an old Cornbinder Scout that had a burnt out 4 banger in it. I fixed the clutch to run hydraulic, used that tool to bleed the system.
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

FordThunder
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Re: Need guidance on Master cylinder and slave cylinder

Post #7 by FordThunder » Mon May 13, 2019 10:50 pm

Hey guys,

I appreciate all the replies and I am happy to announce the truck finally drove today. Turns out my issue was the distance traveled by the master cylinder rod wasn’t enough. Remedy, I pulled the clutch pedal assembly. Replaced the bushings and rotated the lever (had to pull it off, rotate a one “spline”). After putting it all back together. I was driving. Thunder is back on the road and I don’t have to drop the transmission for a second time!

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