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510 7/8 Bore Master Upgrade?


mattyhacks71

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So I have 200sx brakes on the front now, buddy at work suggested upgrading the master cause theyll need to be more fluid be pushed. Local parts store has a good price on a 7/8 bore master for a Z car. I was wondering if it'll bolt right on no modification? Are the flare nuts for those the same size as the og 510 master? The 7/8 seems significantly bigger. Pictured below is the same style, little front reservoir and a big rear one.

brake-master-78.gif

 

Thanks!  :thumbup:

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Look in the end of the master. The cup the push rod fit's should be the same distance in as the 510 cup. If so, nothing need be done. If slightly different adjust the push rod length... you must check the pedal play, about 1/16" and adjust anyway, so do that.

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I only had a 7/8" to replace the 3/4" on my 710 sedan. Yes there is a stock brake booster and yes it is noticeably stiffer. Pedal travel is less and like stepping on a rock. Brakes work just fine. It's an automatic so you need to be on the brakes all the time at a stop, unfortunately. I'm used to it.

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I'm running the 13/16" on my car for now.  I've got the 280zx fronts, and stock rear drums. There is less pedal travel and firmer pedal pressure.  I did something with the push rod... I will have to dig up my pics, but the lines just took a little massaging and they screwed right in. 

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Ok that's right,  the push rod for the 13/16" was different because that master was used in conjunction with a booster.  The stock 3/4" master has a smaller retaining washer that keeps the push rod from dropping out of the master.  The 13/16" and 15/16" does not.  I'm not sure if the 7/8" is the same or not (I would assume it is, if it was used with a booster, but that pic you posted looks like one from a non-power setup... maybe I'm wrong on that?...).  If the master you buy is from non-power setup, then what I'm about to say next will probably not be relevant.

 

What I did was, I found a washer that had a small inner opening, but the outer diameter was large enough to fit in the master bore.  I did have to grind a little off the washer diameter.  The problem with the 3/4" retaining washer is that the outside diameter is obviously 3/4", so it won't work with the larger master.  I also beveled the inside hole a little to match the bevel on the rod.  I thought about putting the 3/4" washer behind the 13/16" washer, but there just wasn't enough meat on the 3/4" washer that made me feel confident that it would not slip and bind in the opening of the 13/16" washer.  Looking at it now, I could have just welded the smaller washer to the back side of the 13/16" washer.... 

I did not have any issues with rod length after I adjusted it to the specs in the FSM, but that rod I used came with my New 3/4" master cylinder, that I got from O'Reilly.  Surely it was the same length, but I can't say for certain. It also came with a new "U" connector that attaches to the pedal.

 

I only found 3 pictures....

Here is a view of the 3/4", 13/16", and 15/16" in that order:

 

003-1.jpg

 

 

Here is the stock 3/4" rod, with stock 3/4" retaining washer on the left.  The 13/16" washer in the middle, with my new washer on the right:

 

009-1-1.jpg

 

 

Here it is assembled:

 

023.jpg

 

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Which 200SX brakes are you using? Early 200SX or S12 200SX?

 

You could also use a 13/16" master which will be tighter than the 3/4" but not require as much leg pressure as the 7/8".

 

s12 I think.. Struts are from an 1987

 

Ok that's right,  the push rod for the 13/16" was different because that master was used in conjunction with a booster.  The stock 3/4" master has a smaller retaining washer that keeps the push rod from dropping out of the master.  The 13/16" and 15/16" does not.  I'm not sure if the 7/8" is the same or not (I would assume it is, if it was used with a booster, but that pic you posted looks like one from a non-power setup... maybe I'm wrong on that?...).  If the master you buy is from non-power setup, then what I'm about to say next will probably not be relevant.

 

What I did was, I found a washer that had a small inner opening, but the outer diameter was large enough to fit in the master bore.  I did have to grind a little off the washer diameter.  The problem with the 3/4" retaining washer is that the outside diameter is obviously 3/4", so it won't work with the larger master.  I also beveled the inside hole a little to match the bevel on the rod.  I thought about putting the 3/4" washer behind the 13/16" washer, but there just wasn't enough meat on the 3/4" washer that made me feel confident that it would not slip and bind in the opening of the 13/16" washer.  Looking at it now, I could have just welded the smaller washer to the back side of the 13/16" washer.... 

I did not have any issues with rod length after I adjusted it to the specs in the FSM, but that rod I used came with my New 3/4" master cylinder, that I got from O'Reilly.  Surely it was the same length, but I can't say for certain. It also came with a new "U" connector that attaches to the pedal.

 

The one I'm getting is from a 240/60/80z. I figured they weren't power

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So me and my uncle attempted to get this thing to work... It didnt. I put the pushrod and stock washer behind the retainer ring that keeps the piston in the bore. Its got rears, they bled great but the front has nothing... Not even fluid comming out of the master with the lines disconnected!

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Assuming the master cylinder is good, and you've tried bleeding the master at the bleeder valve on the side, then that just leaves the push rod like ggzilla said.  What to look for:  When the pedal is at rest, is the rod loose?  There should be a little play in the linkage.  Or in other words, the pedal should have a 1/16 or an 1/8" ( I don't remember for sure) travel before it starts to engage the rod. If there is play, then check to see if the rod ball is loose in the master cylinder. The play/travel in the linkage should be between the  push rod ball and the piston in the master cylinder.  If there is no play there, then try removing the retaining washer and see if it will pump up with out it.  My thought is, maybe there isn't enough room between the piston and that washer you added for the size of the rod ball.  Thus, it's not allowing the piston it's full travel. 

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So me and my uncle attempted to get this thing to work... It didnt. I put the pushrod and stock washer behind the retainer ring that keeps the piston in the bore. Its got rears, they bled great but the front has nothing... Not even fluid comming out of the master with the lines disconnected!

Sounds like the problem i had.You can adjust the pushrod all you want,if its not long enough it wont push far enough to get to the " front brakes" part of the master cylinder.I also could get nothing from the front brakes before i added some length to the pushrod.That master cylinder is probably fine.What pushrod are you using ?

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I just dealt with your same pushrod issue...posted this earlier on "General Discussion - How long does a Datsun live?"...

 

"Who needs a lathe when you have a drill press and an angle grinder. It was a little bit of trial and error to get the bolt centered perfectly in a drill chuck since I was clamping on the threads, but once I got it, it had minimal wobble and ground up great....

 

http://i557.photobuc...gleGrinder.jpeg

 

 

Result - new master cylinder pushrod for Z master conversion....

 

http://i557.photobuc...CylPushrod.jpeg

 

Rust protection. Ooops! I guess I shook the can too many times.....

 

http://i557.photobuc...ledtoohard.jpeg"

 

I also added a dust boot just like the stock setup made from one of these EDPM rubber boots from McMaster Carr (trim to length with scissors and cut center hole for rod pass-through with an Exacto knife). It's a perfect fit on a 260z master...

 

http://www.mcmaster.com/#6448k38/=qp8pi9

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  • 2 months later...

Ok I need Some HELP....

 

I swapped my stock 3/4 master cylinder a couple of moths ago to a 7/8 unit. It ran fine for a awhile, but the rear brakes are locking up now after driving the 510 for about 10 mins. I thought the problem as with the rear brakes heating up and expanding. The brake adjusters are at the lowest level. So I replaced the drum shoes, wheel cylinders and the replaced the drums with a new 240z drum. I still have the same problem. The car would have to sit for about 20-30 mins before the rear brakes would loosen up again.

 

I pulled the drums off when there was still some friction and found that the wheel cylinders were not retracted back into the unit. This must me the cause of the problem? Some how there was a build up of brake pressure causing the brakes to be slightly applied? It must be coming from the 7/8 master cylinder? There is a little play between the brake pedal and so that is not the issue?

 

I've been dealing with this issue for two months now and just need some advice? I've search this site, but couldn't find the answer. Please let me know what you guys think.

 

THANKS!!!

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Make sure the brake pedal has some small free play. Lightly push down on pedal with your thumb. It should have several mm (or 1/16") of looseness before there is resistance. If you look up under the pedal you should see this looseness before the brake push rod begins to move. This play assures that the brake push rod is in it fully back rest position and allows any brake fluid under pressure to return to the brake reservoir. If the master push rod can't return properly brake fluid pressure can be trapped in the lines.

 

Now usually this applies only to the front discs. Never heard of the rears doing this with drums. If the push rod play is fine perhaps the master is defective.

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