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switching master cylinder


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There's a big ol' thread on this here... "Disc Brakes On A Kingpin Truck"... I think that's what it's called... may as well keep questions in that thread. I'd give ya the link, but my connection is bad, and it should be right in this forum.


im aware of that.


i thought it was justified starting a new thread.

mayeb not.


merry christmas


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Sorry, didn't mean to sound like a bastard with that post...


I think there was some mention of master cylinders and all in the other thread... I suppose, if you could, just pull the master cylinder/brake booster at the same time you get the calipers. IIRC, you might have to check clearance for the master cylinder/booster and the air intake... I know the 521's have an issue with that, not sure about the 620's...

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A larger diameter booster will not fit well beside the 620 clutch master or the steering column even on that little pedestal. The 720s had a huge booster on a much longer pedestal but have lots of clearance for the air filter as it's on the other side of the motor.


Here is a booster with 7/8" m/c from an S11:




This is from an '80- '82? 720




And this is from an '83- ? with 15/16" m/c :



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Hey Mike, I have a couple tricky questions... do you have any idea by how much those boosters increase the force applied to them? And do you know if it's possible to plumb the booster to the clutch with any of the following: brake booster, directly connected to a clutch master cylinder; brake booster/master cylinder plumbed directly to the clutch slave; or brake booster mechanically connected (linkage, cable, etc?) to either the clutch master or slave cylinder, or the pressure plate (or whatever it is) directly?


I'm back to considering modifying the clutch pedal to a hand lever so that I can use a standard...

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Ask Bleach, he mentioned a booster for the clutch in one of the Z cars? or something?


As for the booster. The 720 booster can supply and operating line pressure of well over 1,900 PSI for a pedal pressure of 130Lbs. input. Way too much (I think). Probably a smaller 620 m/c with booster mounted on the floor or between the seats, or under? Bicycle hand brake cable and lever mounted on shifter? You would have to trial and error to get the correct amount of travel versus the effort on a hand lever.


An automatic is looking a lot easier!:D:D:D

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I went to a dealer to ask about the Z car clutch boosters, and no-one had any idea what I was on about... I'd likely have to go to a junkyard and either search myself, or look through service manuals... but, it'd likely be cheaper to get a brake booster... I could pick one up from just about anywhere.


I was considering a motorcycle/bicycle hand lever mounted on the shifter, with the cable running down the shifter stalk and under the transmission tunnel... after that, I could either run it up to the engine, or maybe even backwards under the bed... there's probably more room to mount the setup there. All that I'd need after that would be an electric vacuum pump to power it...


I found out that the clutch master cylinder piston(with the J13, not sure if it was the same for the L-Series) moves only an inch in total, from engaged to disengaged. I have about the same amount of throw on a hand lever... I just don't know how much force the master cylinder requires. If I knew that, I could sort out whether or not this would be doable...


Sorry for the thread hijack, btw...

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If you go to a dealer, NEVER talk to a salesman, they are morons as far as info goes. Actually they are just plain morons. The parts department guy is better, but again, he's there to run the counter. I try to talk to a mechanic, someone who's actually worked with what you are asking about. A mechanic who's now running the parts counter is best of all.


I love going to an auto parts store like Lordco and say Datsun and the guy says " that's some kind of old Nissan, right?"

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Yeah, I think I'll have to talk to the mechanics one of these days... maybe get some better info...


As for Lordco... I don't know who hires these people. I remember going in there to ask if they had a 12 volt vacuum pump, like diesel engines use to provide vacuum... The guy asked me why I wanted it. I told him I needed to power a brake booster, and didn't want to use the engine vacuum. He gave me a funny look and told me that the brake booster provides the vacuum to the engine, not the other way around...


Voleurz: As far as the boosters go, I'd personally try to get the best one you can find... It's probably better to have too much stopping power than too little... But, as far as I know the amount of boost generated depends a lot on the diameter of the booster, so you might just try going to Lordco or a Nissan dealership and asking to see both boosters, and comparing the physical sizes... If they're pretty close, then you might get away with the 280Z one...

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i dont "need" booster. im trying to make a master cylinder work with what i got.. not worried about maximum power as i think anything wil be better then stock drums


was only asking about booster see what fits etc it looks like 280z will almost if not will bolt up.

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Voleurz, For what it is worht at this point, I have a 15/16" master cylinder from a Z car installed on my 620. Bolted right on, both brake lines lined up perfectly and it is bolted to a stock booster. My truck has the D21 V-6 twin piston calipers up front and stock drums in the rear. This master cylinder works perfectly, would not change anything about it in my application. It was designed for the 4 disc car, but is excellent for my disc/drum.



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Thanks for the info! I have a 1970 PL-521 that I need to get running first, then I will start upgrades to it. Actually, I have two of the pickups, when I get one running, then maybe I can work on the second one, and be able to do mods on one, and not have to worry about not being able to drive it.

I want to get the one running, because of fuel prices, and my daily driver is a 1996 ford Aerostar. The Aerostar is a type of vehicle that is no longer being made. A fairly econimical mid sized rear wheel drive van.

Have a great new year!

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