SBC 1972 Clutch slave with 1977 4 speed ISSUE?

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Swapping over from 3 speed to 4 speed. AA kit. Clutch is bled and disengages, but if I push to the floor the trans locks up again. Wrong slave? Adjust the pedal? I need to look at the slave rod and see if it's adjust too far out.

I guess the main question would be is there a critical difference between the 1972 slave and a 1977 slave that would cause this? I haven't fired up the motor yet, testing by turning the rear output shaft by hand. Thanks!
 
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What clutch are you using?

I’ve had no problems with my LUK 11” low diaphragm clutch over the last 25+ years. However, @Downey no longer recommends a Chevy clutch and sells one custom for this application. The Centerforce clutch he sells is designed to disengage with less travel.

The Landcruiser clutch master and slave doesn’t have enough travel to disengage most Chevy clutches. I followed the instructions that came with my Downey conversion kit in ‘96. I lucked out when the jobber supplied me with a LUK clutch. The combination of a 1974 clutch master, 1974 clutch slave, custom made braided SS line, and LUK clutch has worked perfectly for 25+ years. I have never had issues with the clutch dragging & not disengaging, and have always had more than enough free play for the throw out bearing not to ride on the clutch fingers.

It is my belief that all the variables need to be the same for it to work. Over the years numerous mudders have made it work, however, even more have had nothing but headaches trying to make a stock Chevy clutch work.

Jim and I have butted heads over this many times… he has argued that what I have shouldn’t work reliably and will in the end cause grief. My argument has been that Downey wrote the instructions I followed to get the setup I have and it has worked great for me. The instructions said to use a standard 11” low-diaphragm type clutch and after contacting almost every shop in town an older parts guy interpreted that and hooked me up with a 11” LUK clutch. Had I done the conversion now, I’d have used the currently recommended clutch.

That said, if I ever need to replace my 25+ year old clutch with 50k+ miles on it, I’ll likely replace it with a matching LUK clutch.
 
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I have the center force kit that AA recommends for the FJ40 SBC to 4 speed swap. So it should be the proper disc and plate?
 
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Which fork and bearing did you use? Mine recommended the 2F fork and bearing. Which does AA recommend?
 
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How much free play do you have at the clutch pedal. OEM Toyota spec is 1” at the pedal.

Is it fine so long as you don’t push it all the way to the floor?
 

Downey

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Never intended to butt heads, and will admit the LUK should work perfectly for a zillion years IF you maintain a very fresh (working as new) clutch master cylinder and slave cylinder, with good bleed- - -no wear/weakness/damage in the system. Problem with the LUK's is you only have a .020" window for getting the clutch completely disengaged with you stock hydraulics- - -glad that .020" has worked for you bikersmurf.
 
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I have a 2F fork and all that AA recommends. That’s the wierd thing… if I depress the clutch it disengages fine, and then as it gets to the floor it locks up the trans again. I am assuming it is pushing to far? I have to check the play in the pedal and the slave rod as soon as I get outside.
 
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Never intended to butt heads, and will admit the LUK should work perfectly for a zillion years IF you maintain a very fresh (working as new) clutch master cylinder and slave cylinder, with good bleed- - -no wear/weakness/damage in the system. Problem with the LUK's is you only have a .020" window for getting the clutch completely disengaged with you stock hydraulics- - -glad that .020" has worked for you bikersmurf.

@Downey any thoughts on what is happening? You’re more knowledgeable than I in this regard.
 
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Could the clutch disc be in backwards? Not likely but it does lead to weird problems.
 

pb4ugo

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I agree it sounds like it's going too far. An initial check with return spring hooked up, crack the slave bleeder bleeder and see if fluid is forced out and the rod retracts into the slave. . If that happens then the clutch is probably to tight snd the throw out bearing is riding on the pp. I'd start at the basics and follow the fsm. Check and adjust the pedal height. Then freeplay at the pedal. I recently went thru this. I Watched when the slave starts to move when i started to press the pedal by hand and adjusted the freeplay at the pedal. Then finally, install the return spring and adjust the slave rod. There needs to be freeway at the rod and clutch fork. This insures the t/o is not riding on the pp. The slave piston needs to be fully retracted in the cylndr at rest.
 
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I will triple check that but I’m 99.9% positive it’s okay. Hoping the throw out bearing didn’t somehow get in backwards. But I’m grasping at straws there.
 
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My concern was the clutch disc could be in backwards… it happens.

Also wondering if the bearing or fork are somehow connecting in unwanted ways at full depression.
 
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I asked my brother who was a mechanic, his thought was that the slave may be pushing to far and causing the fingers of the diaphragm to hit the clutch disc.
 
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I will get under there and get a pic of the set up and post here shortly. Maybe I missed something.
 

pb4ugo

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What bell housing are you using,? If AA. You should be able to look at the clutch t/o and pp. Again crack the bleeder and see if there's pressure from the pp.
 
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I will get under there and get a pic of the set up and post here shortly. Maybe I missed something.
It happens. Unfortunately when we start modifying the original design things can go wrong. If you replace your slave with one with a larger diameter you’ll have less travel and a somewhat lighter pedal.

Just to be certain, I believe it was already asked, do you have a strong return spring at the slave pulling the end of the fork towards the slave? If not you’ll have nothing but headaches.

You’ll have to excuse us if we ask something that seems obvious to you. We mean no offence, we are flying blind and just trying to help. :cheers:
 
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ALL advice is appreciated!! And almost always helpful! I do have a brand new return spring. Will check play in the slave rod first thing and then start posting pics if necessary :)
 
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Adjusted the pedal height. That did it. I remember doing that when I put this new one in a couple years ago. Figured it was good, I was wrong. Lol I do have one more question. The slave rod is REALLY short. Does this pose a problem? From a engineering standpoint, I imagine that the slave doesn’t care how much room there is between itself and the fork? But I am throwing a pic up to see what you all think.

AD01CB08-B166-490F-8C8A-56E6D6214171.jpeg


BE8F6B2F-23A1-4492-95E7-ECD7F14C01AE.jpeg
 

A10Driver

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Adjusted the pedal height. That did it. I remember doing that when I put this new one in a couple years ago. Figured it was good, I was wrong. Lol I do have one more question. The slave rod is REALLY short. Does this pose a problem? From a engineering standpoint, I imagine that the slave doesn’t care how much room there is between itself and the fork? But I am throwing a pic up to see what you all think.

View attachment 3020623

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Nothing wrong with short as long as it still has a little play before engaging the clutch. Gives you room to adjust outwards as clutch disk wears down
 

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