The elusive master cylinger upgrade ???

I swapped in a Dodge Dakota MC, bolted right up. I'm running big bore gm rear calipers that have a 2.75" piston in the rear tho so can't offer up a comparison but I know it fits.

Jeep Driver said:

1" bore is sufficient. I takes no more fluid/travel to actuate two pistons than it does one.

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I still can't get over this..... :roflmao: :roflmao: :roflmao:

Hey Jethro(I think Jethrene), We no yu gradeatod the syxth grad, but in seventh grade we learned that......
If it takes "X" cc's to move piston "Y" so far....
Than it will take "2X's" to move 2Y's the same distance......

Mathematics is amazing!

RCP Phx said:

I still can't get over this..... :roflmao: :roflmao: :roflmao:

Hey Jethro(I think Jethrene), We no yu gradeatod the syxth grad, but in seventh grade we learned that......
If it takes "X" cc's to move piston "Y" so far....
Than it will take "2X's" to move 2Y's the same distance......

Mathematics is amazing!

Click to expand...

You need enough bore and stroke to remove the air gap between the pads and rotor.
Same amount of fluid whether caliper has one piston or six pistons.

You simply do not understand how it works.

1" or 1 1/8" bore........one won't make that much difference over another.


I will have 16 pistons, could have 20 pistons...........

So, by your logic I'll need a 12" stroke and a 4" bore...........no, you fail.


You are not nearly as smart as you think you are, none of you here are.
In fact, much of what most of you people have to say is, well, simply stupid.

RCP Phx said:

I still can't get over this..... :roflmao: :roflmao: :roflmao:

Hey Jethro(I think Jethrene), We no yu gradeatod the syxth grad, but in seventh grade we learned that......
If it takes "X" cc's to move piston "Y" so far....
Than it will take "2X's" to move 2Y's the same distance......

Mathematics is amazing!

Click to expand...

Below is Wilwood's most popular master, it will run a 24 piston brake system with no problem. 1 1/8" bore.

I think they know better than you. Hell, I know better than you.

https://www.wilwood.com/MasterCylin...luminum Tandem M/C Kit with Bracket and Valve

RCP Phx said:

I still can't get over this..... :roflmao: :roflmao: :roflmao:

Hey Jethro(I think Jethrene), We no yu gradeatod the syxth grad, but in seventh grade we learned that......
If it takes "X" cc's to move piston "Y" so far....
Than it will take "2X's" to move 2Y's the same distance......

Mathematics is amazing!

Click to expand...

Holy **** lol. Is this post serious???

You need to look at the total surface area and travel of the pistons involved, not the number of pistons. The number of pistons does not matter at all. You will find that the pistons on a dual piston caliper are MUCH smaller than the piston on a single piston caliper, but combined volume will be about the same.

A little tech.........
https://www.joesracing.com/rt-4172-master-cylinder-math.html

RCP Phx said:

A little tech.........
https://www.joesracing.com/rt-4172-master-cylinder-math.html

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Yeah, I get tech, lots of tech.


Your poor pedal travel is related to something else, not bore and stroke of the master.

Since you are stuck on 'stock' parts........dont' really know what the point of your question is anyway?




On a personal note: you called me out on wires, got it, I admit I was wrong. It'll get rewired, it's only the leads to my relays anyway and not a big deal.
But don't get personal with me, I'm not an idiot.

So after a couple days of testing, I am really impressed with (my) set-up. I like a firm pedal w/ no travel and lots of feedback and besides a slightly increased pedal pressure, there's almost no travel. I don't know whether I'll proceed with the axle shimming if this holds out!

Jeep Driver said:

I'm not an idiot.

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you're a douchebag though, which is close enough.

RCP Phx said:

Update... last night I did install a 1-1/8" bore MC from a 2000 Durango. It barely fits under the hood (clearance to the cap 3/16") and you have to grind/clearance the prop valve bracket because of the larger MC body. I will bleed the brakes today and report back on the change.

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How has this worked out for you?

What axles do you have? I’m doing a 1 ton swap and need better brake pedal feel. Using the stock one is crazy soft.

Still loving the entire install. I'm running a D30/C8.25 with WJ/KJ disc's.

Who dug this little piece of history up from the dark corners of the web..

On kinda related note my pedal travel with wj brakes is good but i have only slightly better braking than stock xj. Wtf.

Need to clean out proportioning valve and go from there

Sent from my SM-G781U using Tapatalk

Evan03 said:

Who dug this little piece of history up from the dark corners of the web..

On kinda related note my pedal travel with wj brakes is good but i have only slightly better braking than stock xj. Wtf.

Need to clean out proportioning valve and go from there

Sent from my SM-G781U using Tapatalk

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I did because I wanted more information on the Dodge Ram 2500 master cylinder swap. If it is as bolt in as people say it would be an awesome upgrade. If it needs hoot cuts and new brake lines it might not be worth it.

In my case I did not modify anything and used the factory brake lines and proportioning valve. The pedal travel is super low and the brake effort is minimal and with my dis-ability I would complain if it got harder.

I think you have to make a push rod cut to the correct length.
Chuck a bolt in a drill and taper tge end so it fits the master cyclinder then cut it to length its like 6-8"
Thats as much as i know ive looked into it alittle. No idea on lines fitting with out modifications or not.

Also no idea if a master cylinder upgrade is needed. In my case the system has 100 years of sludge and brake mud in tge proportiining valve and line's

I have minimal rear braking even after rear disc swap. But i swapped for old parts.

Ill take xj proportional valve off clean and go from there. I should easily be locking up rear brakes but they suck.

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just went through all this when my booster blew out. stock MC is big enough for most applications.

denverd1 said:

just went through all this when my booster blew out. stock MC is big enough for most applications.

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Rear disk do not give better brakes over a set of drum brakes in good working order. It does give improved pedal feel and no constant adjustment. My XJ have the same master cylinder from 25 years ago. It is on the second set of brake booster, JK Rubicon brakes in the rear and WK twin piston calipers in the front.

The master cylinder on my XJ have only been removed (without loosening the lines) to replace the booster.

My 94 XJ has a Exploder 8.8 rear, 95-96 booster upgrade (which I wholeheartedly recommend as easier than WJ), ZJ valve internals and the same pads all around. The rear locks up ever so slightly before the front, which is exactly how I like it.

Installing a larger diameter master cylinder alone NEVER increases braking performance. Sure, it improves peddle feel, but pressure at the pads is reduced. Too small a MC makes the brakes "touchy". Nothing, nothing, nothing, face plant into steering wheel... All because the smaller diameter piston generates a higher pressure from the input force from the vacuum booster and your leg. Think grease gun vs bicycle tire pump...

That's not to say that there aren't times when a larger MC is warranted, particularly when you install calipers with more piston surface area. The area ratio is restored, pedal feel is improved and they're no longer "touchy", but do understand that you reduced pressure at the pads in doing so. As you continue to increase MC piston area, you eventually end up with the same low pad pressure you get with a single-diaphragm booster and stock brakes. The ONLY way to improve braking performance once a larger MC is warranted for "feel" reasons is to install a larger diameter dual-diaphragm (do they make triple diaphragm?) or convert to hydro-boost. It's all about ratios. Keep all ratios roughly the same and all is well. Check out the booster on that 3/4 ton truck. It's 11" diameter (190 sq in) vs 8" (100 sq in) for the WJ, almost double...

Braking performance isn't solely about pressure. Haven't done it myself but I hear you can do a WJ swap, install a slightly larger MC to get a better pedal feel and still have improved braking over stock do to increased pad sweep area, but do understand that actual performance at the tires is reduced compared to the smaller MC. WJs, XJs, all the same 1" diameter MC but one has small calipers and drums, the other big calipers and discs in the rear.

Back to the 95-96 booster swap. Completely bolt in other than the brake lines to the prop valve and a 1/4" spacer at the firewall. Done. Not nearly as many of them in JY so it's not as popular, but the diameter is same so the same performance. Other than regular maintenance items, before making any changes to your braking system, if you do not have a 95 or newer XJ, or have done the 95-96 XJ or WJ booster swap, you MUST do it. You're almost doubling pressure at the pads by doing so...

So I tried the Durango master swap. It didn’t fit the WJ booster. It was from the correct year and the stops on the booster were too far apart for the master to slip on. Any idea what I’m doing wrong?

This is on an 89. I did the WJ booster upgrade a while ago because it was supposed to be easier than the 96 XJ booster because of the pedal attachment. I swapped in 1 tons and the brakes are BAAAAAAAD.

I can't answer this as I am using my stock 2000 booster.