Joel's multipurpose XJ build (rocks/boulevard)

[frijolee]

ZJ Rear Brakes (continued...)


Next I spent some time trying to figure out how I wanted to run the brake lines. I thought I could do better than several setups I've seen (hard line loop-de-loops and/or a tight bend in the flex line) and I wanted this to be a bit more
OEM looking. Here's the factory stuff...

I debated tying that bracket directly into the u-bolts on exposed threads but then my hard lines wouldn't be long enough and I didn't want to redo those fully unless I had to.

I ended up with a compromise position that let the flex line have a gentle bend and still engaged the hard line in a good spot. The trick was cutting off part of the ZJ's flex line support and welding and bent angle in place instead. I quenched the weld with a quickness to avoid melting the flex line. That angle is then tapped and bolted to the leaf retainer plate.

To get a nice bend in the hardline I bend it straight first (couple pliers working slowly), then shifted a bit out toward the end and bent up using a 1/4" tubing bending over the top of the spring wrap.

Works on both sides equally well:

Ebrake cable is the ZJ cable on driver side and a NAPA p/n 95064 on the other. This works perfectly. I did add an adel clamp (aka P clamp, not shown) at the top of the diff to help support the long cable.

My e-brake cable splitter was looked pretty bad.

So naturally cleaned that up using XJ splitter bit with the other ZJ parts. ZJ has a different splitter so I couldn't use that but all other pieces are zinc plated and were in much better shape.

Lastly swapped out the prop valve internals. XJ on top ZJ on the bottom.

Make sure your reservoir is empty or you'll have a mess on your hands. Reminder of the prop valve appears common (quick shots comparing ports, again XJ up top)

...so I found it easier to swap internals only rather than all the lines and mounting.

I'll have to post driving impressions when it's up and running, but it can't be worse than the XJ's drums (especially considering one of mine was covered in diff oil from the leaky axle seal).

-Joel

 

[VAhasnoWAVES]

care to educate me? what exactly is the purpose of swapping out the proportioning valve? increased flow and/or pressure to the rear with the addition of rear calipers?

i ask because i was asked during my axle swap if i was swapping the valve. it was my understanding that people do so to increase pressure to the rear brakes. the previous owner of my axles reported that the rear would lock up way before the front with his proportioning valve modifications, though i dont recall exactly what he did. it stops great (aside from a plugged up bleeder... i cant bleed one front caliper completely, so there is a slight pull) so i never dorked with it. its largely a trail rig, and i know i could resolve the brake issue, but i dont notice it offroad. the overdrive pulley, high flow power steering pump, super deep gearing (high RPMs at normal speeds), and hydro assist make it far scarier to drive than the brake issue to be honest. its a little twitchy... lol. but turns amazing off road.

you just seem like the kind of person who doesnt do things for no good reason, and, "everyone else does it," isnt a good reason to me.

for the record im on GM calipers on all 4 corners, dodge 25/3500 master, (stock) dual diaphragm booster and proportioning valve.

 

[frijolee]

VAhas...

Thanks for the kind words. I can try but take this with a grain of salt as it's basically the result of a bunch of reading and a touch of practice. I'm operating on some basic rules of thumb and the assumption that the factory generally did stuff right to give me a baseline. Then, if I can keep the system ratios similar to stock, I should be good. This gets harder if you're starting from scratch but I'll try to help.

From the most basic... Any brakes that are powerful enough to lock up the tires are powerful enough. If you're dealing with a race car (or any other repeated heavy braking environment) thermal mass comes into play. For 4x4 stuff we mostly care about power, not brake fade so I'll set that aside. Assuming your brakes are powerful enough to lock up at least some of the tires and the fronts lock up first, you'll slide in a straight line (plow). If the rears lock up first and you're turning at all, you'll spin. That's why we always want the front to lock up before the rear.

That said, performance braking is all about getting the REARS to carry as much of their share of the braking as they can. That one statement in a nutshell seems to be the #1 secret of braking. At the same time, it isn't super intuitive since the rears might only be 20% of the braking potential under heavy brakes given weight transfer. However, if the fronts are at the threshold of skidding either way, it's all about getting the rears to do the 20% they can (without sliding first) rather than the 10% they might try to do if your system isn't set up right.

Make sense?

Getting the brakes to share load well between front and rear is first about sizing the parts and second a function of the proportioning valve. First a couple notes on braking power. Braking power is a function of the total ratio of force into the pedal vs. force exerted at the contact patches. That means we have to consider the following factors affecting system gain (power):

-Leverage of the pedal vs. master cylinder rod.
-Power from brake boosters
-Hydraulic ratios of master cylinder (dual piston in a single bore) vs. slave (aka caliper) cylinders
-Coeffecients of friction of the pads
-Radius at which force into rotors is applied.

All of the above gives us the potential twisting force (moment) into the wheel assembly. However since this is a torque, you divide by tire radius to get the horizontal reaction force you can put into the contact patch. Even without the extra mass this is why bigger tires put strain your brakes and it feels like the power has gone down.

We're only really going to play with a few of the factors above. Most folks aren't changing the pivots on their pedals to get more system gain (but you could). Boosters will affect the overall system power but don’t do much for a front to rear balance (great thing to go after if you have weak brakes though). They’re a bit of a black box if you ask me since there’s some internal valving that matters, but generally diameter and number of diagphrams are a good indicator of power.

If I were designing a system nearly from scratch in a 4x4 I’d keep the OEM pedal geometry, pick a booster with matching master cylinder from a vehicle a couple classes larger (which it sounds like you did), then pick from the options available for rotors and calipers trying to keep the front and rear diameter/piston sizes in the ballpark of a known vehicle, and finally fine tune bias with pads and prop valve. The reason I’m spending all this time on the build up is to point out that if you have the wrong calipers/rotors in too dramatic a ratio (say way oversized rear caliper pistons), the prop valve can’t compensate and you’re SOL.

To see if you're in the ballpark, I tend to start with an existing OEM design and compare from there. In this case what we care about are overall power and the balance of force between front and rear. As such, it becomes a game of balancing ratios. If you throw a big brake kit on car that gives you 20% more leverage due to increased diameters--all things being equal--you'd want to either increase the force in the rear by a like amount (can be a combination of rotor diameter, piston area, or pad coeffient of friction) or else decrease the piston area on the fronts by 20% to compensate. However the later would mean you didn’t increase braking power so that added diameter only helps with thermal mass (brake fade). We’re putting on big tires so we want to up power at the end that needs it.

You might consider putting together a little spreadsheet on a known 4x4 with 4 wheel disc brakes and start comparing ratios. Grand Cherokee might be a decent place to start. At some point I’ll end up doing this for my FJ40 since it’s using front brakes on the rear axle. You do this for front and rear and compare. I seem to recall fronts generally run a bit bigger so let’s a say it works out to total of a 3:2 ratio.

So that brings up back to the prop valve. Under light braking the tires theoretically COULD share about 50% of the braking force if give or take 50% of the vehicles weight is on each end (round numbers again). This is a good thing on a street car because you can slow the vehicle with less effort and get more even braking wear. However, the harder you brake the more weight shifts and any tire can only exert the cofficient of friction of the contact patch times force normal (weight of the vehicle on that tire) before it slides.

Without a prop valve, using the 3:2 ratio I suggested above, the front tires would always see 60% of the effort and the rears would always see 40% of the effort (not quite 50/50 optimal, but we’re rarely braking that lightly anyways, there’s always some load transfer). However if we’re braking hard, particularly with our higher CGs, it’s easy to get a great deal more than 60% of the weight of the car onto the front tires, and the rears would skid first. No bueno.

Proportioning valves are pressure limiting devices. That’s why they’re only ever installed on the rear brakes (never want to risk limiting pressure to the fronts). Each one has a setting after which they start limiting the fluid pressure reaching the rear brakes. It’s a curve (and the point of major change in influence is called the knee point). The few OEM prop valves I’ve tracked down info on maxed out their influence cutting the pressure down by ~1/2. Now suddenly our theoretical setup with ratios that started in the 60/40 range can operate in the 80/20 range when you’re on the brakes hard. Cool.

So back to the XJ/ZJ prop valve question that started all this. Why would you change a prop value? You’re seeking to change the amount of pressure limiting the valve does to better align to the system gain ratios of all the other parts used.

Compare the two internal prop valve springs in the picture I posted above. The wound wire is pretty similar diameter, similar free coil spacing, dramatically different length. Because they’re compressed into a similar void the longer spring is going to be exerting a lot more pressure on the fluid passage before the fluid is reaches high enough pressure to compress the spring, move that piston within the valve and allow whatever influence on the fluid pressure it does. Now I didn’t do the math on this, but by inspection we can tell they’re dramatically different in how much pressure limiting they’re going to be doing… which affects the ratio of front to rear braking, which affects how much work the rears can be doing, which affects how quickly I can stop.

If we did try the math on the ratios of wheel cylinders and leverage for drum brakes vs. disk brakes and piston area, we could figure out if it’s up or down, but in this case I don’t really care. My guess would be the lighter ZJ spring makes pressure limiting come into play sooner which means the ZJ brakes are inherently more powerful and have to be kept in check. [and F-me I just noticed I posted them backwards above, ZJ is the shorter... damn 's no after editing policy!!!!!] However, I could easily have that logic backwards and I can't remember if the reviews by others had the rears as too strong or too weak without the change. I can say that the brake systems on the XJ and ZJ are otherwise pretty similar so Jeep seems to be using a change in the prop valve to compensate for the differences in the brake system power between drums and disks for the relative system gains of the parts in use. Just knowing that means we have a shot at being in the ballpark and meant I definitely want to run the alternate prop valve internals. Even then, it'd be safer to run the whole thing, since subtle changes in hydraulics matter, but that was a great deal of extra work so I went with the wisdom of the internet and did internals only. Looking at it, you might be able to do spring only, but I had the other bits so why not?

The thing is, without knowing which calipers you’re running where (and tracking down specs on the caliper pistons) I can’t tell you if a prop valve change would be good for you or not. It’s not just disks vs. drums either. If you went from Jeep disks to a GM drum (not that you would, but just as a point of argument) and the GM drums happened to use huge wheel cylinders the change in the prop valve could take you in the wrong direction (hence why it’s worth doing some comparison to known vehicles.)

When in doubt if your rears lock up first, try a pad with more bite up front. You could also jump to an adjustable prop valve (biggest downside with those tend to be manners under light braking, you might not care). If the front locks up first, you’re safe but leaving braking power on the table. If you don’t have enough braking power period, then upsizing both ends can be done via added leverage (rotor diameters) or increasing caliper piston sizing (clamping force via hydraulic ratios). Upsizing booster adds power via vacuum assist. Master cylinder changes and pedal leverage changes affect both power and how firm the pedal feels.

That turned WAY WAY longer than I intended but it was a least entertaining to write. Hope it helps.

-Joel

 

[frijolee]

So did everyone's eyes glaze over yesterday? Do you guys not care offroad? I can see how having the available friction constantly changing might mean close is good enough.

Even with folks who are into the go-fast road stuff I'm continually surprised by how many big name brands get this wrong. Probably 90% of the aftermarket big brake kits on the market use pistons that are way too big up front. You end up with grabby front brakes (so I guess they feel sensitive) but suddenly the rears doing way less than they should.

If anyone wants to get into this stuff more. Stoptech is one of the few brands who consistently get it right. A great deal of my thinking on this comes from their technical whitepapers.
http://stoptech.com/technical-support/technical-white-papers

 

[plinkerneil]

I found it interesting. But, as you said, hydraulics are subtle. When you go changing things, the effects can be deceiving, and you're going to have a heck of a time testing the results.

It's best to stick to a system that lots of people use, and are happy with.

 

[dan1977p]

Great info and I really like the idea of tying the soft line into the spring plate. Ultimately I'd like to get new braided lines and weld a retainer tab onto the axle to keep things independent but with stock lines, this works great.
I know you mentioned you didn't want to change the hard lines out unless you had to. One of my biggest factors in spongy brakes was the passenger side hard line. It ended up splitting under the retainer. Not sure if it was just old and ready to die so the added pressure from the upgraded booster killed it but it's something to keep an eye on since you were just messing around in there.
Since you seem to know a bunch about this, do you know of any way to get an inline pressure reading? My brakes work quite well but I'm curious if the rears are doing their fair share.

 

[rockclimber]

So did everyone's eyes glaze over yesterday? Do you guys not care offroad? I can see how having the available friction constantly changing might mean close is good enough.

Even with folks who are into the go-fast road stuff I'm continually surprised by how many big name brands get this wrong. Probably 90% of the aftermarket big brake kits on the market use pistons that are way too big up front. You end up with grabby front brakes (so I guess they feel sensitive) but suddenly the rears doing way less than they should.

If anyone wants to get into this stuff more. Stoptech is one of the few brands who consistently get it right. A great deal of my thinking on this comes from their technical whitepapers.
http://stoptech.com/technical-support/technical-white-papers

I suppose in theory its possible to have pistons that are "too big up front" however, in the real world of offroad and Jeeps, the biggest caliper you can fit into a 17" wheel still isn't too big.

in the Real world panic stop situations I have experienced, both before and after brake upgrades, the jeep OEM braking system has entirely too much work being done in the rear.

a simple change from stock brakes to just a 16" Black Magic kit (12" rotor, 52mm dual piston calipers) in the front made my personal rig extremely predictable and easy to control in hard braking situations.

changing the oem rear drums to explorer discs (same as ZJ) made no discernable change to braking performance. no change to master/booster or prop valve.

 

[frijolee]

Plinkerneil,
Agree, sometimes the further you get off the road well traveled the easier it is to end up lost in the woods. Case in point, I'm a huge fan of LS swaps, but find sometimes certain folks don't like my RX7 because it's not a "unique" swap. Well, drag racing a Yugo would be unique too, don't mean it's a good idea. That philosophy is what lead me to the ZJ brakes in the first place. I copied 90% of what others have done, picking and choosing what approaches I liked best. I then added a couple unique twists with the line routing that I thought I could do better.

Dan,
There are a variety of tools out there. We'd just have to track down something that would work well with XJ's. Case in point: http://www.speedwaymotors.com/SSBC-A1704-Sure-Stop-Brake-Pressure-Gauge-Kit,50352.html. You mentioned an upgraded booster. What are you running?

Rockclimber,
You're the first I've come across who stated that the factory brakes had too much rear bias. You'll definitely have me doing some limit braking tests to see what I can see about what slides first. I'm glad you like your setup and you may be correct that less rear brakes for your setup is more predictable and easiest to control. It wouldn't surprise me if that were a true statement even if you're not seeing the shortest possible stopping distances (rear brakes helping as much as they can IS real world for stopping distances, sorry but I'm sticking by that)... Do you know if the explorers are truly identical to ZJ (diam and piston area are the only two that matter for this conversation) or is that an assumption?


By the way, does anyone here have data they can point to on braking for plowable surfaces? There's a twist in that on-road, you never want to lock up tires for max braking. Offroad I've heard it's argued that's less true since the tires dig into the surface so letting the tires roll on dirt/sand may not be the fastest stop. (Typically what gives ABS fits off-road).

-Joel

PS some really good caliper info here: http://www.pirate4x4.com/forum/jeep-hardcore-tech/851498-info-calipers.html Mostly on the bigger stuff but a great resource never the less.

 

[themauler]

I'll jump in on this with my thought of the rear zj disks brakes with ZJ prop valve.

I did the same exact swap Frijole did. Same parts with middle grade brake pads with the stock XJ prop valve. I noticed no sort of braking upgrade. I remember only two times I had to do an emergency stop at highway speed and I managed to lock the front tires both times.

Later I decided to swap in the ZJ prop valve out of curiosity. Again no real upgrade in braking performance except that I have never been able to lock up any tires since then. I believe the ease of maintenance is a plus. Besides that I have been pretty content with the upgrade. The only thing I think I can do for better braking performance is a WJ brake booster to replace my chitty 92 brake booster.

 

[dan1977p]

Thanks for the link. I can't believe my google-fu is that bad that I couldn't find it myself.
I did the ZJ swap with tests in between.
Spongy stock brakes on 91 non ABS.

• Replaced calipers, rotors, pads, wheel cylinders and shoes. - Little change
• Swapped booster and master. Significant braking increase. Pedal felt about the same
• Swapped in ZJ rear discs and full prop valve. Minor to no change in anything but maintenance will now be easier.
• Found leaking hard line to rear passenger. Minor change to pedal.
• Checked angles on pedal to booster shaft and they are 90*+- a degree. Starting to suspect I should just replace all the hard lines and the two JY soft lines that came with the rear calipers to get a more solid pedal.

Honestly, they work great already so I'm not going to mess with them anymore unless something actually breaks. It's about 4000lbs with heavier than average 33's and I can panic stop straight in a reasonable amount of distance with the tires feeling like they want to break loose but don't. I would just like a little less pedal travel since I'm used to driving VW sport sedans.

 

[dan1977p]

I'll jump in on this with my thought of the rear zj disks brakes with ZJ prop valve.

I did the same exact swap Frijole did. Same parts with middle grade brake pads with the stock XJ prop valve. I noticed no sort of braking upgrade. I remember only two times I had to do an emergency stop at highway speed and I managed to lock the front tires both times.

Later I decided to swap in the ZJ prop valve out of curiosity. Again no real upgrade in braking performance except that I have never been able to lock up any tires since then. I believe the ease of maintenance is a plus. Besides that I have been pretty content with the upgrade. The only thing I think I can do for better braking performance is a WJ brake booster to replace my chitty 92 brake booster.

The booster is easy to do and was the most significant part of the upgrade for me.

 

[frijolee]

Dan,

Which booster did you go with? I'm a '99 and I believe the late model stuff was already supposed to have one of the better XJ boosters, but I can't tell you much about ZJ/WJ boosters. I actually have WJ calipers and knuckles sitting on the shelf, but I think I'm going to live with what I have since it takes so much to swap over (steering, wheels/tires, being the big ones).

I'm expected a decent change but mostly because I was basically running 3 corners of brakes prior. E-brake couldn't stop the rig from rolling on the most gentle hill, etc. It was dumb.

 

[dan1977p]

98 ZJ booster. I think I remember it being the same as then 96+ XJ. I still hate my e-brake because it takes the full throw of the handle to engage it as much as I would like. May be able to adjust the star wheels in one more click but they were rubbing at that point when I set them up initially. I wish there was some sort of 'throw multiplier' that could lengthen the amount of cable pulled.

 

[rockclimber]

iirc yes the ZJ and explorer stuff is identical.

 

[frijolee]

Couple random cleanup topics for this AM.

Finished the POR15 on the middle section of my stiffeners. Same process as I outlined on the floorboard repair.

I really hate rust, so I decided to try to prevent water intrusion and sealed all the longitudinal seams.

I debated the seam sealer for a while actually... I feel like sealing the edges could be a double edged sword. If I do water crossings or otherwise submerge the rails I could trap water that gets past bolt heads and the like, but with general rain driving and the like it'll keep the vast majority of water from getting between the stiffeners and the frame in the first place--the kind of water that's running down the rail from the outside. Since I see rain more than I see water crossings, I went for it and sealed it up. I am keeping the end seams open so that it can weep water out fore/aft if some does get in there (which already happened when I was cleaning up from some brake fluid mess after the prop valve change).

After POR and seam sealing, I went back with some underbody coating. This stuff had great reviews on Amazon so I tried it. Seems to have a nice light texture. It's not smooth (which some reviewers claimed) but does go on pretty evenly compared to some I've used. 60 grit comparable maybe?

Between all my weld through primer, POR, seam sealer, and underbody coating, I think I've pretty much done all that can be done.

Finally, when I was poking around under hood I noticed a heater hose splitting so that got replaced too. There was some decent crap all around the fitting, so I probably need to do a fluid flush and read up on checking for electrolysis.

Time crunch is on now... Taking the girls camping in Johnson Valley next weekend. Pretty much just need to finish the rear bottom frame plating/bump stops. Then rework my mid skid mounting. Check fluids. Nut and bolt check on all the areas I've touched. The front frame stiffeners may need to wait, but we'll see how I do over the next couple days.

Found a sweet shot of Cougar Buttes (not mine but no photographer listed to credit). Good reminder of why we do this stuff.

Happy wrenching,
-Joel

 

[hjeepxj]

That undercoating job rocks. I am going to copy you.

 

[frijolee]

That undercoating job rocks. I am going to copy you.

The more people post cool builds the more we all get inspired to do things better. Forum research if the only way I avoid the line "why didn't you just... blah, blah., blah... that woulda been 10x easier than what you did."


Made a bunch of progress this weekend. Working toward functional rear bump stops. "Trippled" had pointed out that function rear bump stops can cave in the factory frame rails (Thank you sir!). So I needed to plate at least the bottom surface of the rear rails rather than just the sides (HD stiffeners rear sections are side only).

First step: Measurements. Check marks just mean same as opposite.

Getting better using guides with my plasma.

Curve to fit:

Burned in my rosette holes. You guys should be used to all the weld through primer by now.

Oh in the above you can see also where I repaired the muffler heat shield as well. It was tearing through in several locations (probably galvanic corrosion at fault), so I cleaned that all up, oversized the fender washers and gave it a heavy coat of BBQ paint to help keep things isolated.

Since I want the bump and twisting loads to transition both to the underlying rail and to the outerside stiffener, I decide to weld this new one all the way rather than stitching it.

Root pass.

Full pass.

Rosettes... Left access for the rear sway bar mount points just in case. Also planning how to plate the curving shock clearance area (the one part where I'm plating to the inside of the rails).

Turns out if you've been wrenching all day and have dirty fingers it's damn easy to make a template by rubbing paper.

Passenger:

Driver (this one took a bit more forming).

I apparently didn't take a shot burning these in but you get the idea. Stitch welds to the native rail. Full passes w/ root (if needed) from stiffener to stiffener.

More to come.
-Joel

 

[frijolee]

Made standoffs for the bump stops since I didn't feel like digging out the rusted bolts from the interfaces I had before. Decided to put these standoffs on the frame side to save the unsprung weight.

Started with a piece of scrap 3/16" 2x2 tube I cut in half. I'm using multiple engagement points to ensure I have fore/aft adjust-ability.

Cutting an arc to match the frame rails.

Welded nuts on the inside:

Burned them in (more weld through primer).

POR15 (grey because it's all I had left).

Note, one end is boxed to the frame rail the other is open as I didn't want it to be too stiff torsionally least I give my self unintended stress risers.

Since these are only 1" tall (well, maybe 1 1/8" with the stiffener underneath) I'm starting with a 5/8" aluminum spacer I whipped up to ensure the bumps engage in time. I might lessen this down the road.

More underbody coating as well.

Alignment looks pretty good under shock compression. Rear end finally ready to be buttoned up for real.

Started doing the front to rear nut and bolt check and that's where I left it last night.

 

[Redsnake]

Your work is AMAZING!! I love it! BTW... have you weighed or have any idea what the extra weight is on your rig compared to OE after adding all the frame stiffening and armor to your rig? I'm curious because I know our rigs aren't the fastest things on the road but one thing I've always liked about my XJ is that it's a relatively light vehicle which seems to make it somewhat nimble... if that makes sense. Now, I'd add all the stuff to my rig you have if I had the skill and not worry about the weight, but I was curious. Thanks and keep up the great work!

 

[frijolee]

Hi Redsnake...

Here was weight with everything prior to the stiffener effort. I think this was about a 3/4 tank of gas, all my recovery gear in the back, no driver.

The two big aluminum skids net right around 100 lbs. Best guess the stiffeners will total in around 75 lbs. The shipping tag on the 4 front and rear pieces stated 26 lbs. Didn't check the mids but guessing 25 there and another 25 in the extra bits and MIG wire. I still need to do the front section.

If I were doing a desert go-fast effort I'd use a cage for rigidity and run less stiffeners/armor. I'd probably run 33's to keep the D30 and 8.25 healthy and unsprung weight down (that's one area I'm unlikely to change much). I'd at least consider 2WD depending if I played in rocks or not. Tube bumpers and an inside-the-hatch / strap-down tire carrier would be high on the list too.

You got me curious, so I did some looking... A bone stock 99 XJ 4wd checks in at 3153 lbs curb weight (I assume that's dry). That said, you're not doing much wheeling in that without destroying it.

Sounds like I'm pretty middle of the road for an armored rig.
http://www.naxja.org/forum/showthread.php?t=1057883
http://www.naxja.org/forum/showthread.php?t=1043027

In the second thread thread I ran across a guy with a very similar setup, BDS long arm, bumpers, etc...

...then I realized it was me. :dunce:

-Joel