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KFunk740

521 clutch master cylinder OK?

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I can't find any parts listing for 320 or 520 on RockAuto, but the 521 clutch master pics look exactly like the one in my 320 that appears to be leaking.  

 

I had previously thought it was the slave (and didn't have any luck with the 520/521 slave cylinder bolting right up without mods).  Now I do see wetness around the master clyinder shaft, so I was probably on the wrong track with that anyways.

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Clean up you master cylinder and take it apart.  Look at the bore if it is not badly pitted hone it lightly go to NAPA and take your parts with you.  See if they can match up the the parts with a rebuild kit.  It probably just needs new rubbers.

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It's only $20 to $30 for a new one, and a lot less hassle than finding time to get to town while NAPA is open and explaining what I want to them.  

 

The one that's on the truck looks brand new (maybe a 521 one), as the PO appears to have replaced many parts like that.  But, I think it's a crapshoot these days getting parts like these.  They're probably all chinese made, and a good percentage are bad from the start.  I had a front wheel cylinder leaky from the start right after I bought one.  

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The 521 clutch master worked just fine.  I did have to swap the control (push?) rod from the other master cylinder, as the 521 rod was too long.  I think whoever replaced it on the truck before did the same thing.    

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Sorry to revive such an old threat but both my brake master and clutch master are leaking on the cab side of the firewall so I need to replace both. 

 

I see from the post above I've got swap the push rods. Is there any trick to it? Do they just thread into the cylinder body?

 

Any other tips or advise?

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I don't know the older trucks but all the 521 masters I buy all need to be cut as the rod is too long. As one mounts the master the rod is getting pushe by the pedal.

 

So one needs to cut about 1/2 so there is not pressure on the rod.

 

I guess one can swap the rods but I seen a nice 510 get smashed as a rod was swapped out and later fell out and rear ended a car

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You need to swap the 320 rod into the 521 master as I recall, they are both held in by spring clips again as I recall.

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Before you do any "rod swapping", measure the length from the 2 bolt mounting flange to the centerline of the pushrod clevis hole. Make the new measurement the same when installing the rod in the new master.

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I can't really remember that well, but don't think there were any tricks and pretty easy to figure out.  Don't think there was any difference in the length at all on the master cylinder itself once you remove the part that gets swapped.  It's been on the truck 2 years, and no problems.  Just hauled home a load of mulch today.

No idea about the brake master cylinder, haven't touched that one yet.  

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OK, banzai got me paranoid so I ran out and looked.  Still had the 521 rod on my shelf too for comparison.  The 521 rod has a lot of room for adjustment, but at its shortest its like 1/2 to 1" longer than what was in my 320.  

I had just swapped the entire rod, so the length will be identical as before.  To do this, you need to take the rubber boot off the firewall side of the master cylinder.  Then there's a little triangular spring clip on the inside, and you can fish it out with an o-ring pick or a tiny screwdriver.  Replace rod with your 320 one, put spring clip back,  and all is back as it should be.  

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I just did the 'rod swap' on both brake and clutch master, granted only the clutch has been bleed and the truck hasn't moved since install, but it worked fine.

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Thanks everyone for chiming in, I'm feeling fairly confident in the project. 

 

Once I do the swap can I bleed the masters installed with a bleed kit by running a tube from the outflow port back into the reservoir by pumping the pedals? Will I have to bleed the lines too?

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You should "bench bleed" the master by the method you stated. I usually do this in a vice before I install it in the car as it can be quite messy. You don't want to get the brake fluid on your paint.

 

But yes, after you install the master, you will need to bleed the entire system. If it has old brake fluid in the lines, blow them out with air first (wrap a rag over the end of the line so the fluid doesn't go everywhere), or just run a quart (or so) of fluid through the master when bleeding. Bleed until the fluid runs clear to be sure you got all the old fluid out.

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In the course of the 'Mighty Mouse' 320 project, over the past couple years, I've gravitated to juicing up the hydraulic systems from the slave cylinder back toward the master. It's a one person job. As Matt added, If you're adding new equipment upstream ( master, Proportioning valve, etc.) the old lines should be flushed to avoid introducing old fluid/crud into the new machinery upstream. 

Steve

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Or make a spacer for the fire wall and shim the master outward. Aluminum is easy to work with.

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I'm pretty sure the lines are 3/16" tubing. Stock had 3/8" SAE inverted flare fittings on the 320.

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Thanks! I'm thinking through the project and if I'm considering upgrading to a dual brake master. If I have to bleed the whole system anyways it seems like doing a little extra brake line work might not be that big of a deal. 

 

 

 

I'm pretty sure the lines are 3/16" tubing. Stock had 3/8" SAE inverted flare fittings on the 320.

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Dual system is the way. My first car was a '64 Dodge. Single master. I wouldn't even get in one today. ANY leak in the system and the brakes go out. When I was a kid it was common to hear on the news 'the accident was caused by brake failure'. You almost never hear this now.

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Can anyone who's done a dual master upgrade on a 320 post a pic of how you T'ed off your brake lines? My stock set up goes to a 3-way T in the middle of the firewall where the master comes in one side and lines go out the other two, one line to passenger side and one line to the driver side. 

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All I did was remove the rear brake line from the "T" and plug that hole, I then made a new brake line to the rear because mine had rusted thru, but I initially cut the rear brake line and put a metric fitting on it and then double flared the end of the line, I then installed it on the new master brake cylinder, but as I said it was rusted and blew a hole in the line while bleeding the brakes so I made a new one.

 

I also had to make a new front circuit line from the master to the "T", as the master is metric, I have the tools to make my own brake lines.

 

I also used spacers to hold the brake master out a quarter of an inch, I also slotted the brake master mount holes to fit the 320 bolt pattern, you cannot just bolt a dual master into one of these trucks.

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If the 620 master is what you end up using, you'll have to deal with the operating rod length issue that Mike pointed out and the slotting of the mounting holes of the master that Wayno mentioned. Also the hole in the firewall is too small to accept the rear snout of the 620 master and will need to be opened up something like 1/16-3/32". I did away with the plumbers nightmare on the cowl and used a small brass T near the master to split the front circuit to left & right wheels and used all new line on the front system. Used the original rear line, as it was in good nick and just put a loop in it near the master to take up excess length (snipped off the flare to change from SAE to metric fitting and reflared the line). 

 

The 620 clutch master bolts in after slotting the holes in master an changing out the op-rod to use the original from the 320 master. Still in the plumbing process in this photo:

 

New%20Master%20Cylinders_zpslot6olu0.jpg

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Rubber%20Skirt%20Left%20Re-Pop%20Install

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I'm doing a rebuild on my clutch master and slave cylinders. Once I've replaced the pistons and rubbers can I bleed both from the slave bleeder back to the reservoir using a long piece of tubing? 

 

*edit: The slave rebuild was a fail. I couldn't get the piston loose which I'm guessing means the cylinder is pitted. I tried soaking all afternoon in PB Blaster and using forced air to blow it out. No dice. I just bit the bullet and ordered one for $100 off eBay. Apparently the 2 3/8" bolt spacing means I get to pay more than twice what the 2" spacing slaves cost. 

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In my opinion it is never a good idea to push brake fluid through a system and return it to the master.  I will bet it will come out dirty at first and then clean up.

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