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Disc brake m/c conversion question


burrito213

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i bought the mike klotz brake disc conversion kit and i have been pulling my hair to get the right stuff. i figured i am not the only one so i wondered what the correct one was. these are my questions:

 

so is this what i buy?

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-or-

 

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1979 NISSAN 280ZX 2.8L 2753cc L6 MFI (H) [L28E] SOHC : Brake/Wheel Hub : Master Cylinder WikiPriceCoreTotalA-1 CARDONE Part # 111837 MoreInfo2.png Reman. - Return and Rebuild Service Only - By ordering this service you are agreeing to send your original part to the manufacturer to be rebuilt. Rebuild time is approximately 3-5 business days. You will be contacted with directions once the order is placed. For more information please contact Customer Service.

us.gifca.gif $29.99$5.00$34.99Add to Cart AddToCart2.pngCENTRIC Part # 13042604 MoreInfo2.png Centric Premium

us.gifca.gif $154.89$0.00$154.89Add to Cart AddToCart2.pngWAGNER Part # MC96906 MoreInfo2.png {#F96906}

us.gifca.gif w/Vac. Boost; 15/16" Bore * Non-stock item--shipping delayed up to 3 business days$201.79$0.00$201.79Add to Cart AddToCart2.png$39.79$5.00$44.79Add to Cart AddToCart2.png

 

 

is this how i do it?

 

Brake_System_Diagram.gif

 

pic02_brakefacts.gif

 

what else do i get?

is it called a proportioning valve, residual valve, metering valve?

 

this is finally starting to make sense. i just dont want to get the wrong stuff. its the M/C that i am really not convinced with because each item looks different and the part numbers are unclear.

 

any help and i promise i will put this question to rest.

 

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You're not the only one. I've been debating what to get for my 521. I figure I might as well do a conversion since I have to run new lines and put in a MC (since there isn't anything current in it). But I haven't put too much time into figuring it out, but if thread clears it up, it'll make it that much easier. And, at least, I didn't have to ask! whew.gif

 

So, it's a matter of finding a MC that was originally intended for a front disc/rear drum set-up. I browsed some of those other threads. Not a lot of talk about MC's most people say 280zx, but is that kosher with disc/drum? Or is that adjustable proportioning valve that goes on the rear line able to compensate? I saw someone talking about a 620 with that disc/drum set-up. I wonder if that's true.

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Your NL will likely have a single master cylinder feeding both front and back brakes so when switching to a dual master the front and back brakes must be separated for maximum benefit. You may have already realized this.

 

Since the front brakes do 80-90% of the braking because of engine weight and extra weight shift to the front when braking, the rear wheels will tend to lock up well before the fronts. There are two ways to lessen this. The wheel cylinders can be made smaller so there is less braking effort at the rear or a pressure proportioning valve can be added in line to the rear so that there is a front bias in pressure with less to the rear.

 

The 280zx master is designed for use with rear disc brakes where the pads are just in contact with the rotor. Drum shoes are pulled well away from the drums by return springs and have further to travel before there is any braking effort. To reduce this, a residual pressure valve is usually mounted in the outlets of the master. A drum brake will have a 10? pound valve and spring to keep 10 pounds of residual pressure in the rear system. A disc brake master will have much less, 2-5 pounds residual pressure, just enough to keep the rotors clean. Obviously a rear disc brake master will not have the proper residual pressure valve for use with rear drum brakes. Something to think about.

 

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In this picture the top most reservoir is the rear brake half of the master. The fitting on the body below it is the outlet line. The residual valve is up inside the master above the fitting.

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so i know mklotz and many others have bought this kit as well as beebani's and they have most likely had to revamp the whole m/c system but no one has a specific answer or part as to use to help accomplish this

 

 

i am sure it isnt difficult but i have no clue what to get now, if i need a hydraulic assist, what pressure regulators to put or buy, or even if i am suppose to get a 79' 280zx m/c.

 

i dont mind being schooled as to what to get.

 

the issue is safety. i plan on taking my 5 year old daughter out for cruising around in the truck and this has major significance for personal reasons but if i can not safetly drive this truck then i wont.

 

if this sounds like a plea then it is. :crying: lol :lol:

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I understand your position and I was speaking in generalities.

 

 

thank you for the help Datzenmike.

 

once i have that path, i am going to take it. ;)

 

 

i am sure this will help others who are in doubt too.

 

its funny how there is no thread on the m/c conversion with the disk brake conversion. seems they go hand in hand.

 

any takers? :D

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I bought the kit that Mike K. sells burrito, and with the kit he says to use the 79 280zx m/c. I bought his NL from him, and he mounted a proportioning valve just under the drivers seat. I don't know if he used a residual pressure valve, i guess i'll have to ask, but I know he told me about the proportioning valve only. I suppose if the rear drum brakes are kept adjusted a residual valve may not be required, but I put them on my 1947 chevrolet pickup, 2 lbs. on each front wheel(two outlets for the front disc brakes), and 10 lb. for the back drums, keep in mind that you mount the residual valves as close to the master brake cly. as possible. wayno

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wayno, i h8 to ask but do you have pics of your set up?.... i would like to see the m/c for reference and where the proportioning valve is located...

 

 

but then there is a conflict because Datzen mike says that the 79 280zx m/c is a set up for discs in the rear. would i just switch the plumbing to fit the current need being disks in the front?

 

 

thanks for the info Wayno.

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I'll try to get a few Oics. tomarrow, I sent an email to mike just now asking if the 79 280zx m/c is on my NL, and if he used any residual pressure valves. Here are a few Oics from Mikes NL 320 thread, this is what is on the truck now I beleave, this oic. was taken in june of 2008, so that m/c has been on there a long time. I have not driven it much yet, but I do beleave that it could use a power brake booster, i'm spoiled, i have power brakes on my austin mini, and it don't hardly weigh nothing. The porportioning valve is just under the front edge of the driverside seat between your legs, at least the adjustment knob is, i'll bet the rest of it is connected to that knob on the bottom of the truck. :lol: wayno

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I like this diagram the best, it's simple and gets the idea across. It's how my 47 chev is set up.:rolleyes:

pic02_brakefacts.gif

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wayno, i h8 to ask but do you have pics of your set up?.... i would like to see the m/c for reference and where the proportioning valve is located...

 

 

but then there is a conflict because Datzen mike says that the 79 280zx m/c is a set up for discs in the rear. would i just switch the plumbing to fit the current need being disks in the front?

 

 

thanks for the info Wayno.

 

I think "The King Rat" meant that the 79 280zx had/has disc brakes all the way around, and I don't beleave you want to switch the front to the back and the back to the front on a master brake cylinder, there is a chance that the porportioning valve could compensate for the rear drums, but this statement is just a guess, but half the shit I do to my datsuns is just that, a semi-educated guess, I put disc brakes on my 521 several years ago, i had never heard of ratsun, i made everything out of parts from other vehicles. I will admit that it didn't work very well at first, but I figured it out. :wacko: wayno

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I am running the 79 280zx master cylinder(15/16") on my 76 620 that is converted to front disc only, the rear brakes are still drum and this master cylinder has been on the truck for about 4-5 years. The 620's have a power booster though. My pedal is a little too stiff, indicating that i need more power assist(bigger booster). Or a smaller master cylinder bore.

 

On a truck that does not have power assist and still has rear drum brakes, i would be looking at the 78/79 620 master cylinder that is 13/16" bore and set up for the rear drum OR the 75-77? 280z(not zx) master cylinder that is 7/8" bore and also setup for rear drum.

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Just went through mikes posts on the 411 brake conversion and came across this in the parts list.

 

-Nissan 280z(x) Brake Master cylinder (280z(x) 77-81)

-Bolt to fabricate longer M/C pushrod

-New steel lines from M/C to block and to front wheels?

 

I'm guessing it's the same for the 521 conversion.

 

Still I'm leaning with going with the 1979 620 master cylinder just because it was originally made to work with the disk/drum combo.

Still will need to fabricate a push rod though.

 

EDIT: thanks Yello620 that makes sense to me off to order the 620 master cylinder.

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so it would be safer to run a 1979 620 M/C with the conversion kit? this is vertical bolt pattern set up?

 

this can be accomplished without a power booster but i would need a proportioning valve for sure.

 

proportioning valves i am looking at are:

wilwood

baer

ssbc

summit

 

any good ones?....i was looking at ssbc but pricey

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so it would be safer to run a 1979 620 M/C with the conversion kit? this is vertical bolt pattern set up?

 

this can be accomplished without a power booster but i would need a proportioning valve for sure.

 

proportioning valves i am looking at are:

wilwood

baer

ssbc

summit

 

any good ones?....i was looking at ssbc but pricey

If your strapped for money, go to the wrecking yard and get the porportioning valve off the type of vehicle m/c your going to use, a vehicle with front disc and rear drum brakes, of coarse. But sometimes this don't work because of some complicated brake system, I like the ones with one line in and one line out, but there not all that way.

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hey ya'll..so i went to rock on auto (rock auto) and bought a m/c for the 79 620

 

this one was on closeout and like Charlie69 said, :huh: well, he said they have a lot of cool closeouts :lol:

 

this one was 1/2 the price so i got it...if it doesnt work out, you will know, and if you need one please check the datsun stuff for sale :P

 

here is the info if you want to track

 

Part NumberPart TypePrice EACore EAQuantityTotal1979 NISSAN 620 PICKUP 2.0L 1952cc L4 2BBL (H) [L20B] SOHCBECK/ARNLEY 0726570 Master Cylinder

<a href="/lang/en/answers.html#closeout" target="blank" onClick="return aPopup(this, 'FAQ')">Wholesaler Closeout -- 30 Day Warranty$ 47.79$ 0.001$ 47.79

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I have thought about this for a day now, I need to understand more about bore size as it applys to how hard you have to push on the pedal for a desired result, but I think I understand about the 79 280zx now, you all understand that a 4 wheel disc brake m/c has a residual pressure valve for a disc brake inside both outlets, somewhere around 2lbs. of pressure, it works great for the front disc brake calipers, that will not work properly with rear drum brakes. So how can that be fixed? It's easy to fix, just put a 10lb. residual pressure valve on the rear master brake cyl. outlet before you pipe the rear brake line to the rear brakes. If any of you can shoot this fix down, please do. wayno

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whoo hoooo... thanks charlie69

 

now is it official - if anyone gets the mklotz or beebani's disk brake conversion, they should buy a 79' 620 m/c?...or is the 280zx an option. or even going back to what wayno said, trial and error.

 

 

charlie69, do i need to buy residual valves or any of the sort?... i know i need a proportioning valve which will come soon (still doing research)

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Hi guys....wayno asked me about it, but I forgot to look for this thread until gcmustang said something to me about it today. I don't get much time to scan the new threads that are started.....when you guys come up with specific questions like this, send me a link to the thread and I'll make a point to check it out. I'm late for bed, but I'll lay down the basics. :) I've only scanned the rest of the thread, so I'll probably repeat what others have said.

 

The '79 280zx is what I've been running, but as Wayno said, it takes a bit of leg....but I've got short, fairly stout legs.....so someone with long legs and more knee bend will notice the extra effort even more. I've been wanting to try the one yello620 mentioned. The difference being that the '79 280zx m/c is a disc/drum(the '80 was disc/disc) unit with the residual valves built in. It has a 15/16" bore. The '79 620 m/c is a disc/drum unit with residual valves built in, but it's a 13/16" bore.

 

The smaller the bore, the easier it is to push....but it will travel a bit more. With the rear brakes adjusted correctly(since most of the pedal travel is because of the drums), the pedal travel isn't really an issue, so the smaller bore should work just fine. The 7/8" bore is right between the two and probably not enough of a difference to notice.

 

The proportioning valve is to limit the pressure to the rears to help avoid lock up. Seriously, I could have eliminated the rear brakes on the NL and stopped just fine :)

 

The residual valves are commonly seen in the hotrods because the m/c is below the floor board and they keep the fluid from backfilling the m/c too much. When they are used in systems with the m/c on the firewall, it's typically to help keep the pads/shoes close to the disc/drum so there's less pedal travel. You just don't want them dragging while driving. You know the pressure you get when you try to push the piston back into the caliper when you're servicing your brakes? That's the residual valve in the m/c fighting the fluid from going back in. It goes back in, but it doesn't just flow back in with no effort.

 

Anyway.....I'm about to pass out....this posting will have me subscribed now, so let me know if you have any more questions. You guys are always welcome to pm with questions. A lot of times, when they're questions that will benefit the group, it's better to pm me with a link to a thread.....then the info can get shared with all :) Night. :)

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Mike K. is saying that the 1979 280zx is a disc/drum car, and 1980 280zx was disc/disc, then that 1979 280zx master cylinder should work fine. So my previous post about putting a 10lb residual pressure valve on the rear brake line of a 1979 280zx m/c should be ignored, maybe the post should be erased.

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Ok, did a little more research on this and found a few interesting things. Searching on www.raybestos.com and www.rockauto.com

 

First thing is that 15/16" master cylinder that we have been talking about fits 77 280z - 81 280zx. Now the 77/78 280z is rear drum and the 79-81 280zx is rear disc. Same part number master cylinder. So it looks like it should work fine for either application for us.

 

So we should have a few options here:

78/79 620 13/16" bore disc/drum --Raybestos part #MC39279, Dorman part #M96889

 

70-76 z car 7/8" bore disc/drum -- Dorman part #M96583

 

77/78 280z disc/drum and 79-81 280zx disc/disc 15/16". --Raybestos Part #MC39277

 

This info is a little different than what Mklotz posted. I listed where i got my info from, feel free to look it up and verify anything or add to it.

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LOL! Last time I posted the m/c info, slodat came on and corrected me.....I was pretty sure I had it right this time!! Oh well :) I stand corrected. You'd think after all these years of doing this, I'd have this crap memorized better! Anyway.....go with yello's info.

 

Wayno....I don't see why your info would be wrong....the 10lb residual valve would be to hold the shoes closer to the drums. I'm sure the 10 lb rating is higher than the m/c's. If it were less, there wouldn't be any point. I don't know that it's necessary either way, but I don't think it would hurt unless it caused the shoes to drag. And hey...if they're going to pull your info, they'd better pull my wrong info while they're at it!!! LOL :)

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A 10 lb. pressure valve in the line going to drum brakes will NOT cause the shoes to drag, unless you have a brake shoe hardware(return springs) problem. When the shoe hardware is working properly on a drum system, it takes approximately 50 lbs. on line pressure before the shoes begin to move under the spring hardware resistance.

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