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  1. #21
    Nothing but a Thing
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    Quote Originally Posted by Majik View Post
    The only issue there is that that kit just upgrades pads and makes your rotors slotted and drilled. That really does little for increasing brake torque. There is no upgrade in rotor size, thickness, or material in that kit. Master cylinder is still unchanged, and rotor size (the most important aspect) is still stock.
    Agreed! In order to have more stopping power you need to have more then just slotted rotors and bigger pads.
    Betty - 2013 Black JKU Rubicon Unlimited
    Wilma - 2013 Dozer JKU Sport Unlimited (Wife's)

  2. #22
    Nothing but a Thing
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    It will be interesting to see what you find out. I have the TF Big Brake Kit and I can tell you that it makes all the difference in the world. I would love to be able to upgrade the rear brakes too.
    Brian McKenna
    Puyallup, WA
    2012 White JKRU w/Bells & Whistles

    Yeah... I wheel. Nuff said.

  3. #23
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    Checked on master cylinder off of older Dodge Ram 2500/3500 pickups with diesel. Brought measuring calipers (not brake calipers) Mounting ears to bolt to booster are (surprisingly) narrower than on JK. Mounting bolts approx 3.375" apart, while on JK, they are more than 4". This is adapatable however. MC bore is awesome at 1.25" !! Height of reservoir is not an issue. Brake line ports same thread size as JK. Bad part: ports on wrong side.

    Have several more to check. Lots more to come...

  4. #24
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    Found a great resource that has helped me more quickly narrow down some parts to compare bolt patterns, rotor specs, master cylinder specs, etc. It is through Centric's website. They are an OEM brake component manufacturer that produces and supplies a large portion of the OE brake parts. Through their catalog and reference tools, I was able to obtain measurements and specs on a large number of parts.

    I think I may have found the master cylinder that Teraflex is selling as part of their 'Big Brake Kit'.

    Here is the stock JEEP JK 2007-current master cylinder:

    2012 jeep jk MC.jpg


    ... and here is the master cylinder for a 2010-2011 Dodge Nitro!

    2010 dodge nitro mc specs.jpg


    So what's the difference? Well, first, what is the same: brake line port thread sizes match; overall dimensions of master cylinder and reservoir. There is a subtle 0.06" difference in the plunger lengths, but there is a threaded adjuster in most vacuum boosters to allow some tweaking. 0.06" is not anything to worry about. Many of those adjusters can accommodate almost an inch of play!

    What's the upgrade?? The bore size is 1/16" larger.

    So now for some math:

    The stroke volume of a master cylinder is determined by: pi*bore radius*bore radius*depth of compression of plunger

    Stock JK MC: 3.14159 * 0.5" * 0.5" = 0.7854 sq in (cross sectional area of cylinder bore)

    2010 Dodge Nitro MC: 3.14159 * 0.53125" * 0.53125" = 0.8866 sq in

    So what does this mean? If you depress the plunger of the stock JK master cylinder 1", you move 0.7854 cubic inches of brake fluid. If you depress the plunger of the Nitro master cylinder 1", you move 0.8866 cubic inches of brake fluid.

    If you calculate the increase in volume as a percentage, that comes out to a 13% increase in stroke volume! Why is this significant? Because, ironically, Teraflex advertises a "14% increase" in fluid flow with their upgraded master cylinder!! Strikingly similar numbers, huh??

    And here's the fun part: The MOPAR brand replacement master cylinder can be yours for the amazing low price of: $56.49
    Compared with the average price for the Teraflex unit of $190.
    I haven't verified yet whether or not this replacement includes the reservoir or not, however, most of these late model ones I've researched do. And it appears, anyways, that the reservoir for this 2011 Nitro is the same as that on our JKs, so you could reuse yours, worst-case scenario.

    I'll keep it coming as interest persists... much more to figure out here I like the potential $130+ savings already, though!! Honestly, though, I would really like to find a master with a bit bigger bore. 1.125-1.25" would be ideal, I think. But at least this is a start!!

    Even if you don't decide to do any rotor or caliper upgrades, this could be an easy $60 upgrade on its own to add some good, solid feel to your brake pedal!

  5. #25
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    i love threads like this! so much great info! subscribed!
    thanks for your hard and tedious work on this subject

  6. #26
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    Oh, and as one other interesting note:

    Here is the master cylinder used in the military version of the JK, the J8, produced through 2010 and exported to (unfortunately) numerous foreign governments. There have been alot of rumors about the "upgraded brakes and axles" on the J8.

    jeep j8 MC specs.jpg

    I believe that this is accurate info. The brake line ports are the same pitch/size and location as those on our JKs, and after researching literally hundreds of master cylinders, this is not a common combination of line port sizes and the fact that the lines are located on the passenger side of the master cylinder.

    Note that the important thing, the bore diameter, is 28mm. This translates to 1.102" Assuming this 28mm isn't a rounded off figure, this is a bit bigger than the 2011 Dodge Nitro master cylinder bore. In fact, nearly the 1 1/8" I was trying to reach.

    28mm bore = 1.102", so using this figure to compare flows as we did in the above post:

    3.14159 * 0.551 * 0.551 = 0.9538 sq in (cross sectional area of bore)

    ...compared with 0.7854 sq in from stock....

    ... yields a flow increase of (0.9538-0.7854)/0.7854 = 21.4%!!

    And the price, in stock currently, on this master cylinder: $80.02

    Not a bad option either!! Here's the link: Click here

    Check the second part listed on the page. Part Number: MC391385. Note the 13.07" rotor size listed for that part. Coincidentally the exact same rotor size listed on the upgraded Jeep J8 axles.

    I feel fairly confident at this point that we've identified the master cylinder being used by Teraflex, and a potentially even better one, used on the Jeep J8. Both of these would nearly be bolt-on upgrades. The J8 version likely would need a half-inch trimmed off the plunger. Well worth that minor modification, IMO.

    Hope this is all still keeping interest...

  7. #27
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    And on another interesting note: despite the same part number for all standard, domestic (non J8) master cylinders for Jeep JKs 2007-current, there appears to be a part number change for the power brake boosters that changes between 2010 and 2011. It's obviously not due to the change in motors to the 3.6L because that didn't happen until 2012. And here's the more interesting thing: There are 2 part numbers listed - one for with "light duty" and one with "heavy duty" brakes. I suspect the heavy duty version is an overseas model. The master cylinder is the same so the bolt patterns for the MC mount must be identical. Just wonder if, again, the booster for the "heavy duty" brakes is somehow linked to the 13" rotors I've been exploring...

    Here's a link to the two part listings:

    Click here to see 2 different brake boosters

  8. #28
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    Took a bunch of detailed measurements of the caliper clearances, bolt spacing, etc to try and find adaptable alternatives. Will post results later tonight.

  9. #29
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    I will start this post by saying one thing: if you are not looking for technical info, or really don't care how I am coming to these conclusions, you may want to stop reading now. If you like to know the how's and why's and also that I really am doing some in depth investigation, read on!

    So I'm trying to draw (ha ha) a diagram showing the measurements that I took. I measured things such as the circle radius from hub center to the caliper mount holes on the knuckle, the distance from hub center to the outermost edge of the caliper (to find wheel clearance issues), the clearance between the inside/back of the caliper housing and the axle when at full lock, and the distance between the caliper mounting bolts, and the clearance at multiple points between the back of the rotor and the inside of the rim. For this prelim trial I just used a stock 17" Rubicon rim. You guys will LOVE the results of those measurements

    1. The nice thing is that the stock rim is kinda a worst case scenario. Due to the huge backspacing of the stock rim, basically the entire caliper has to fit inside the rim. If you are running a 4-5" backspace rim like most of us with aftermarket rims on a JK have, the rear edge of the rim actually moves outward (unless you are using some huge-ass 12" wide rim) and thus the inside-most portion of the caliper is actually exposed OUTSIDE of the back of the rim. This eliminates having to even worry about caliper clearance of the back edge of the caliper.

    2. Even the factory rims allow use of a, get this, 14" rotor with the right caliper. I had mentioned this in a prior post. For example: a 2007 Dodge 2500 diesel pickup uses a massive 13.9" x 1.4" thick rotor, with a HUGE caliper...all inside a 17" rim. Our JK rims are 16.75" I.D. at the rearmost edge. At the point of tightest clearance with the outer edge of our stock calipers, the I.D. of the wheel is roughly 16.125" (radius = 8 1/16th). The Radius of the stock setup from hub center to outermost edge of the caliper is 6 19/32". What does this mean?? This means that there is about 1.5" of clearance, using a factory rim, with terrible backspacing that covers the entire caliper. So what happens if we theoretically could swap a nice, fat, 13.9" rotor, say, similar to off a late model diesel pickup, in place? Well, with the same old stock JK caliper in place, we would have a new maximum radius of rotor plus caliper of:

    6 19/32" + 1" (because 2" larger rotor = 1" bigger radius) = 7 19/32"

    And guess what? This STILL FITS INSIDE A STOCK 17" RIM! The cool part is that, when comparing several calipers, the stock JK caliper is actually kinda chunky in the back side (closest to the rim). There is a square-ish knob right in the center over the piston that adds probably an unnecessary 3/8" of height. The factory, huge, dual piston caliper off of a diesel Dodge Ram actually would give MORE clearance on the back side than our stock JK caliper.


    So I restate again, and lets go up to a true 14" rotor for simplifying the numbers:

    6 19/32" factory max radius of brake hardware + 1.05" rotor radius increase (to a true 14" rotor) = 7.644"

    The inner diam of a factory 17" rim at the point closest to the caliper is 16 1/8" = 16.125

    16.125 / 2 = rim inner radius = 8.0625"

    8.0625 - 7.644 = 0.4185" clearance <-- This is plenty of clearance, and using a 14" rotor and stock (dimensionally) calipers!!!

    So this means one thing: I'm gonna go as big as we can with this search. WHY?? Because the best increase in braking doesn't come from squeezing the rotor harder...it comes from braking torque. The farther away from the hub center that the caliper can squeeze (i.e. bigger rotor), then the more gross brake torque that can be applied. Same pads. Same caliper. Going to a 2" bigger diameter rotor, using the same caliper, will yield a 17% increase in braking power. Same force on the pedal. Same master cylinder. So the bigger, the better!

    Combine this with a higher-flow, larger-bore master cylinder like I discussed above and now we are talking REAL braking. Oh yeah... and I didn't even mention a big fat 2-piston caliper yet!

    ----------------------------

    So. On to rotors:

    I am fairly certain now that some version of late-model Dodge ram 1500 rotors and calipers are gonna some way be adapatable to our application. This would be about a 13" rotor. The hard part with rotor hunting is all of the other dimensions: bolt pattern and rotor height are the hard things. Our Jeep JKs use a very, very shallow hat height (the center part of the rotor that looks like a soup bowl, with the hub bore in the center). This shallow hat height severely limits our choices. I found one that is promising: Mid-2000s Dodge Vipers. Yep. I said Vipers. Specifically, the rear rotors. The rotor is 13.98" diameter. Yes!! They are a fat 1.25" thick. Awesome! The height is less than 3mm difference than the stock JK. (This is well within the range of motion of a floating caliper) Score!!. They are cheap!!!!!! ($56 each, new, with free shipping to your door!) They are in stock at numerous online sources!!! The only catch: The bolt pattern. 6 on 4.5" Damn. So I'm going to try to source the manufacturer and see if I can get undrilled blanks for this rotor. If possible, then we can drill them to either stock 5 on 5" or, like in my case, 5 on 5.5" for those running manual locking front hubs.

    Let's keep our fingers crossed on this.

    I will continue to research the J8 / Teraflex ~ 13" rotor setup with (likely) Dodge Ram 1500 equivalent calipers, but if I can adapt something better, just as easily... hell! Let's do it!!

  10. #30
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    P.S. I will periodically post a summary post discussing the key findings and parts that are in the running thus far, to consolidate all of these possibilities that I mention in lengthy posts like above.

    Have a great week, guys!

 

 

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