1978 Mori Seiki MS-850 brake caliper and master cylinder equivalents?
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    Default 1978 Mori Seiki MS-850 brake caliper and master cylinder equivalents?

    HI Guys,

    So I've got a new-to-me '78 Mori MS-850.
    I'm doing the usual 'new toy' inspection, and the brake master cylinder seals have died.
    So I yanked the master cylinder, and now I'm trying to figure out what Japanese car it came out of, so I can either replace it, or get a rebuild kit. There are references on PM from someone who rebuilt a Wacheon clone, and that used the clutch master out of a '79-80 Mazda, but being a '78, this Mori didn't. (The units have different spex too, I checked.)

    So, anybody know what the older Mori's used for their master cylinders and brake calipers? (I figure having a rebuild kit for the calipers is probably wise.)
    The existing unit is a 3/4 Nabco, but that doesn't tell me much except it's Japanese. 2.25" between the bolt-down holes on the flange, FWIW.
    (So it's an Imperial spec unit.)

    Here are some pictures. Anybody recognize the parts? (and/or know what car they came out of?)
    The brake caliper says "Dunlop" if that helps. It's still got the original Japanese info tag, so I figure it's probably the stock unit, whatever that was.

    Speaking of which: the manual (vaguely) says don't yank the caliper if you don't want to fuss with realigning the unit. How painful is it, and what is required to realign it properly?

    Thanks,
    Brian
    img_3742.jpgimg_3740.jpgimg_3741.jpg

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    Pretty much everything brake and clutch wise in Japanese cars is imperial to this day - other than 10 x 1.25 (early) or 1.0 (late) tube nuts for the plumbing.

    Single circuit brake master and the caliper scream 60s datsun. If nobody comes up with an answer, I'd probably try that avenue at a brake and clutch specialist.

    Don't know what they called them over there with the odd numbering system used in the US, the old mid 60s Roadster (Fairlady) or the old fugly bluebirds of the same vintage would be likely candidates.

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    Greetings all,

    I'm updating this thread in the hopes it's of some use to the next poor bastard down this road.

    Mori themselves are out of luck. The oldest manual they have in house in the US is 1986. Mori HQ in Japan was asked and had no idea either.

    It turns out that it's probably the brake master cylinder out of a 65-67 Datsun roadster. The brake caliper and pads as well.
    DatsunParts.COM Inc.- Datsun Roadster Parts seems to have some in stock, and some of their parts callouts do list them as being compatible with 'moriseiki' lathes.

    I yanked the brake calipers for a rebuild as well. As much oil as there was in the bottom of the machine, I figure the odds are about 90% that the brake piston seals are dead too. May as well get them all at the same time.

    The funny part is watch out for the brake line fittings. The fitting to the master cylinder (on my machine) is metric, but the fitting for the brake caliper is SAE. That was fun to discover.

    Once I have definite info, I'll follow up.
    Good luck.
    -Brian

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    I'd be tempted to get a cheap, complete new 3/4" trailer master for ~ 30 bucks total, looking at that. 2.25 flange is industry standard.

    Was the caliper shimmed based on the warning?

    Suppose Dunlop was the giveaway on weird. Did have one of the first early 60s disc brake Alfas with similar Dunlop calipers....too long ago to recall any pertinent details though!

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    Update as I get ready to button the beast back up.
    The brake system is actually out of a 1965 Datsun Roadster. (Fairlady in Japan)
    The master cylinder and pistons are available as new manufacture aftermarket parts. But they're pricey.
    There are rebuild kits from Nissan at least for the pistons. Apparently the first 6 months of the 280ZX had the same pistons, so the rebuild kits are in Nissan's parts book as 280ZX parts. The kit I got was: Nissan seal kit # D1ABM-73425. The piston units themselves are Sumitomo Mk21, 2 1/8 B. (2.125 bore?)
    They may have been used in other things.
    The break pads are available as well, but I don't know the number. They don't have anything on them.
    I got my kit from DatsunParts.COM Inc.- Datsun Roadster Parts
    Expensive and grouchy, but he had the gear.

    The master cylinder is just a 3/4" bore piston. You'll have to salvage the front yoke off of your existing master, and replace the piston yoke on the new one. They're different lengths. You'll also probably need to mill up a pair of spacers to space the new piston a bit farther back into the body of the lathe. On my unit, there's a .362" difference between the resting 'zero' or 'out' position of the piston, versus the mounting flange, compared with the original part. (translation: the new one sits a bit farther forward at rest, relative to the mounting flange, than the old one did.)
    Since you're dealing with the brake bar, and have no adjustment for slop, you need to space the piston farther back to get the same 'home' position.

    Watch out for the tube flanges: on the original master unit, it had a 10MM bubble flange fitting for the hose. The new aftermarket part has a 3/8-24 reverse cone fitting. So your original brake line won't fit without reflanging.

    Watch out for the new brake pistons. The original ones had 10mm bubble flange ports on both sides. The new aftermarket ones have 10mm bubble flange on one side each, but 3/8" reverse cone on the other two. Use the reverse cones for the brake line coming from the master, and for the bleed screw. Save the two 10mm fittings for the transfer pipe between the two pistons. That one is 10MM bubble flange, and is a pain to redo if you don't have to.
    Also: know of the wonder of copper crush washers. I just *COULD NOT* get the (new) brake line to seal to the master cylinder properly. Reflanged it twice, etc. Just would not stop leaking.
    UNTIL! My local hose shop suggested I use a little 5 cent copper crush washer in-between the two sides of the joint.
    Problem solved in one. They make them in 45 degree cone, intended specifically for this sort of thing. Absolute lifesaver.

    I ended up pulling the caliper once I decided to rebuild (ended up replacing) the pistons. Putting it back isn't too hard, but I'm still having alignment issues.
    The current problem is that the pads won't retract as far as they drive in when pressed. So the pads rub after you hit the brakes the first time. Still working on solving that, but the brakes themselves work well, and no leaks.

    Now that I've seen how these brakes work when they're working right, all the Moris and Whatcheons I've used in the past had bad brakes. When you hit that pedal now, it *STOPS*. Right now. So it's a thing worth doing.

    Thoughts for the next poor bastard down this road:
    I replaced mine with original parts. That's getting difficult and expensive. Think hard about what the guy above this said about replacing the master with a 3/4" trailer piston. It'd probably work just as well. The brake pistons aren't sacred either. Find a good auto parts guy, take him the entire caliper setup, and see if he can find you a set of pistons that'll fit the caliper, then get pads to fit them. Probably easier than what I went through tracking down the parts for a 65 Datsun. Certainly cheaper. The brake line can be replaced with flex hose. For this, it'll work just as well, and a whole lot easier to deal with. (Especially if your new master has 3/8" ports, rather than bubble flares. You'll have to change the line anyway.)
    The original master cylinder has its port vertically, on the rear. The aftermarket has the port on the left side, as you look from the piston. That's a *much* easier place to be. Because you can see it, and it isn't obstructed by the fluid tank the way it is on the original design. Remember this when looking at trailer masters.

    To change the brake pads, there's a slot in the rear of the caliper mount. (Right side of the motor axle, as you look at it in the lathe.)
    There's a little gold clip in there, with a cross bolt holding it in. Remove that, then pull the clip straight out back through the hole in the caliper mount. The pads will pull straight out through the hole once that's gone. They have a groove in their piston-side faces that locks into a mushroom shaped tab that holds them in contact with the piston. Make sure that tab realigns when you put the new ones in. The put the gold clip back in, replace the bolt, and you're good to go. Try hand spinning it a few times with no belts on the pulley to make sure it's not dragging or binding.

    Hope this is of some help to you.
    Regards,
    Brian
    Attached Thumbnails Attached Thumbnails img_3758.jpg   img_3753.jpg   img_3752.jpg   img_3755.jpg   img_3757.jpg  


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    More pix.
    Mostly the brake caliper showing how the pads come out.

    -Brian
    Attached Thumbnails Attached Thumbnails img_3759.jpg   img_3761.jpg   img_3765.jpg   img_3766.jpg   img_3767.jpg  


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    Quote Originally Posted by Alberic View Post
    More pix.
    Mostly the brake caliper showing how the pads come out.
    Those look a lot like the calipers on the XK-150 Jaguar. Those probably aren't any cheaper

    Did you drill the rotor while you were in there ? High performance, man !

    About the pads hanging, if the rotor has a little bit of side-to-side runout that'll knock them back a touch when you let off the brake. If it's only a tiny bit you won't feel it when braking. We also used to cut the o-ring grooves in the pistons wider and deeper for race guys who didn't want any brake drag at all, but you probably don't care that much.

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    If you start screwing around swapping master cylinder push rods you MUST make sure the push rod is a bit loose between the stop disc and the piston and is not pushing on the piston at rest. if you ignore this the bleed port inside the master cylinder will be covered and the brake will drag. Sounds like you have this issue already. You sure don't want to rely rotor runout to push the pads back unless you enjoy a foot massage when you step on the brake. I did the brakes on a lathe and "improved" them to the point that it stopped so fast that the whole machine jumped when that 12" chuck stopped instantly. I let a bit of air in the caliper so you could hit the brake without this issue.

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    Did you call Greer Machinery? I would assume they would have the replacement parts, no idea if they would be competitevely priced.

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    Quote Originally Posted by moonlight machine View Post
    You sure don't want to rely rotor runout to push the pads back unless you enjoy a foot massage when you step on the brake.
    Nah, if it's only a couple thou you can't feel it at all, and it kicks the pads back enough to stop dragging. Now if the rotor is not equally thick all the way around, that'll give you pulsing. But not a little backy-forthy, the fluid is happy to deal with that.

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    Quote Originally Posted by moonlight machine View Post
    If you start screwing around swapping master cylinder push rods you MUST make sure the push rod is a bit loose between the stop disc and the piston and is not pushing on the piston at rest. if you ignore this the bleed port inside the master cylinder will be covered and the brake will drag. Sounds like you have this issue already. You sure don't want to rely rotor runout to push the pads back unless you enjoy a foot massage when you step on the brake. I did the brakes on a lathe and "improved" them to the point that it stopped so fast that the whole machine jumped when that 12" chuck stopped instantly. I let a bit of air in the caliper so you could hit the brake without this issue.
    HI Moonlight:
    I'm not sure I understand. The piston's got a spring loaded return. It was pressed up against the stock pushrod at rest, as issued. When I swapped the old one in, it presses against it at rest as well. Where's the bleed port?

    The way I figured these things handled retracting the pads was to rely on the negative pressure generated by the spring, as it pushes the piston out once the foot pressure comes off.
    So how does a bleed valve come into play? (serious question, I genuinely can't see how that works.)

    Thanks,
    Brian

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    Quote Originally Posted by Alberic View Post
    HI Moonlight:
    I'm not sure I understand. The piston's got a spring loaded return. It was pressed up against the stock pushrod at rest, as issued. When I swapped the old one in, it presses against it at rest as well. Where's the bleed port?

    The way I figured these things handled retracting the pads was to rely on the negative pressure generated by the spring, as it pushes the piston out once the foot pressure comes off.
    So how does a bleed valve come into play? (serious question, I genuinely can't see how that works.)

    Thanks,
    Brian
    I'm pretty sure the "bleed port" MM is talking about is the passage from the fluid reservoir into the master cylinder itself, which is open when the MC is in its static position (not activated). As soon as the piston in the MC is pressed, the piston movement covers the port and prevents backflow from the MC into the reservoir.

    So if you have the wrong pushrod (or pedal setup when in an actual car), you might be covering the port all the time, preventing the MC from getting fresh fluid drawn in. But if the rod is loose in the linkage that's unlikely the case here.

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    Quote Originally Posted by Milland View Post
    I'm pretty sure the "bleed port" MM is talking about is the passage from the fluid reservoir into the master cylinder itself, which is open when the MC is in its static position (not activated). As soon as the piston in the MC is pressed, the piston movement covers the port and prevents backflow from the MC into the reservoir.

    So if you have the wrong pushrod (or pedal setup when in an actual car), you might be covering the port all the time, preventing the MC from getting fresh fluid drawn in. But if the rod is loose in the linkage that's unlikely the case here.
    OK, thanks. That makes sense.

    It's getting plenty of fluid out of the tank. When I bled the brakes, it sucked down most of a whole reservoir's worth in about 6 pumps. So it's getting fluid.

    I think the next step is to mill of about .020" off the pads to see if the extra clearance helps. They're old pads with plenty of meat left, and I've got 2 more new sets, so nothing to lose. Also the pistons are new, so that may have affected the clearance. (?Maybe?)
    Can't hurt, anyway.

    Thanks,
    Brian

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    Did the freshly rebuilt caliper and pads slip over the brake disk without issue during assembly?

    If so, it's unlikely cutting the pads will do any good - as soon as you activate the brake again, the piston and pads will shift, and probably continue to ride the disk.

    There's either something wrong in the pad retraction process (like the wrong piston seals if that's supposed to do it, or wrong spring if that's the retractor), or perhaps there's residual pressure in the lines for some reason.

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    Sounds like the pushrod/clevis arrangement was swapped between masters, did you check the "mushroom" end matched, they look a touch different in the pics?

    Usually try to make the pushrods adjustable, as they're normally too short in vehicle use. In this case I'd probably be tempted to cut'n shut, rather than swap.

    AP Racing ones even used to be shimmed individually, so it wasn't a great idea to mix and match even in the same manufacturer.

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    Quote Originally Posted by Alberic View Post
    HI Moonlight:
    I'm not sure I understand. The piston's got a spring loaded return. It was pressed up against the stock pushrod at rest, as issued. When I swapped the old one in, it presses against it at rest as well. Where's the bleed port?

    The way I figured these things handled retracting the pads was to rely on the negative pressure generated by the spring, as it pushes the piston out once the foot pressure comes off.
    So how does a bleed valve come into play? (serious question, I genuinely can't see how that works.)

    Thanks,
    Brian
    You will have a .06 and a .015 or so port for the fluid. If you have a push rod with an incorrect ball on it it can be against the plate that keeps it from falling out and pushing the piston in slightly. This will cover the bleed port and pad dragging will result. Did you rebuild the caliper? did you use the correct seals? the seals more than anything cause the pistons to retract, incorrect seals or standard "O" rings will cause trouble. You will be amazed how fast a carbide end mill is destroyed by milling brake pads so good luck with that.

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    I have the Webb/Whacheon version of this lathe and I had to replace the brake master cylinder but did not need to replace the pads or caliper seals. I did replace the dust covers on the pistons. With that said, after experiencing the same issue that are are in that after bleeding the system, the pads dragged which caused the rotor to heat so much that it would smoke.

    It sounds counter intuitive but I resolved the issue by cracking the fitting at the caliper and actually inducing a small amount of air into the system. It resolved the issue and my lathe can stop the spinning chuck almost instantly and there is no drag or heating of the rotor whatsoever. It's been working perfectly for several years. It can't hurt to try it.

    Good luck.

    Joe

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    HI All,

    I'll try Joe's trick about adding a bit of air on Monday or Tuesday. Cheap and easy, can't hurt.
    If that fails, I'll yank the push rod and really get serious about comparing it with the one that came with the master cylinder.
    (I >>>hope<<< I didn't trash that one yet.... I was starting to clean up, thinking I was finally done...
    Worst comes to worst, I can re-machine the ball on the old one to match the new one, and see if that helps.
    (who knew they were *that* twitchy??) (Hey wow, a use for my old comparator! First actual job this year...)

    The pistons were brand new aftermarket units, installed as complete units, so the seals should be whatever they're supposed to be.
    (I bought the rebuild kit, and then discovered that the brake fluid had gotten wet, and pitted the hell out of the piston bores. Simpler to just replace.)
    The caliper itself is just a frame. Not much room for adjustment or mis-alignment, so I'm operating on the assumption that that's good.

    I'll let you all know how it turns out.
    Thanks for all the help.
    Regards,
    Brian

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    Well. That didn't work.

    I tried adding a bit of air. No dice. The dragging got a smidge worse.
    (I think. Hard to hear with the compressors and CNC's going.)

    So I pulled the pushrod, and used the comparator to figure the profile differences between the old (short) pushrod, and the one that came with the MS.
    It's hard to tell for sure, but it looks like the new (too long) one only sat about .006" farther back, when measured against its washer.
    The profile was a little different, but the overall change in depth appears to only be .006".

    So I took .030" off the front of the old (short) pushrod, and reprofiled it a bit, to make it closer to the profile of the issue pushrod.
    Put it all back together, bled the brakes, and.....
    Nada.
    Still dragging after one clamp.

    As long as I was down there, I fiddled with the pushrod a bit, once everything was installed, to see if there was any slack in the positioning between where the MS spring stops pushing, and where the pushrod ends up when the pedal returns to full 'up'. There seems to be, so as far as I can tell. It feels like I've got plenty of clearance so that the MS returns to full stroke before the pushrod stops moving back to rest position.

    Now that I think of it, milling the pads won't help. The system will see that as wear, and just pull a bit more fluid out of the reservoir to compensate for it. So no joy on that idea.

    So.... next idea was to unhitch the pushrod from the pedal, and yank it forward, to as far out as it'll come without ripping the end out of the MS, and see if *that* un-drags the pistons.
    Nope. The pedal is actually still pulling 'out' when the pushrod runs out of 'out' travel. So it's actually pulling the thing to full out. Still drags.

    Anybody got any other notions about what's going on?

    Thanks,
    Brian
    Last edited by Alberic; 10-05-2021 at 10:30 PM. Reason: update on pushrod test

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    Quote Originally Posted by Alberic View Post
    Anybody got any other notions about what's going on?
    Those things have big heavy dust seals and iirc the o-rings are actually square rings. That stuff takes a fair amount of energy to push. There's nothing pushing it back, so the pads stay pressed out against the disk.

    Modern calipers don't have those dumb dust seals, and I can't see any purpose for them inside a lathe anyhow. I'd remove them.

    With regular o-rings we'd widen the grooves a bit so they could roll - that meant they'd roll out under pressure and roll back pretty easily when the pressure was released. Can't do that with square rings tho

    You probably don't want to try cutting the grooves deeper so the rings aren't as tight, pita to do. Keep in mind as a last resort tho ?

    For a quicky, I would stick about a .005" shim under one or two of the ears so the disk wobbles a little. Easy to do and if it doesn't work you haven't lost anything, but when the pressure is released the tiny bit of wobble should kick your pads back. You might get a tiny bit of feedback at the lever but I don't think it'd be objectionable. The fluid itself should deal with that small amount of runout.

    You do have to make sure all the way through your control system that the piston can retract far enough so that the fluid is free to go back into the master cylinder reservoir. If it can't, your pressure doesn't get released and the brakes drag. Maybe some part of the linkage is blocking full retraction ?


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