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Brake upgrades - start with this

ghetdjc320
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ghetdjc320 Obsessive Comanche Disorder

ghetdjc320

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Per @Pete M’s request, I’m posting this info for anyone who is contemplating upgrading their brakes:

 

i often times read of someone who upgraded some part of their braking system (typically the booster/master and/or rear disks among others) with enormously successful results. The phrase “I can lockup x size tires while doing x speed” is heard far to often. It has been my personal experience though that more often than not, they replaced or coincidentally repaired a fault in their brake system while performing said mod. On the other hand, those with a good overall factory brake system try these “upgrades” only to find that they provide very little if any gain and sometimes even perform worse (eg swap to a larger master cylinder bore with stock brakes). So here is some information I’ve compiled over the years while running a wide variety of upgrades  as well as thoroughly discussing this subject with others far more knowledgeable than myself. 

 

The key to getting the most out of your braking system is a good amount of boost assist to the master cylinder and the correct ratio of master cylinder piston surface area to caliper piston surface area. 
 

Vacuum boosters: first off make sure your engine vacuum is good. 18in+ of vacuum at idle is needed for a vacuum booster to give full power. Vacuum leaks, cam changes and many other factors can contribute to low idle vacuum. This needs to be checked before you consider a booster swap (unless your going with a hydroboost system). Also test your current booster by running your engine for a few seconds with your foot off the brake. Shutoff the engine and wait a minute or so, press on the brake pedal. You should have at least one full vacuum assisted pedal push before the pedal hardens up. If it fails that test then you have a leaky booster/check valve. You can also run an electric vacuum pump for your brakes which can significantly improve the vacuum assist in the event that your engine can not produce enough vacuum.

Hydroboost is my personal favorite but is a costly swap and takes quite some time to setup right. The stopping power can be phenomenal though. I ran a custom unit from Talon hydraulics with a Wilwood MC 

 

Master cylinders: 15/16 is normally the best size for stock front calipers and either drum or disk rears. MC size should only increase when more fluid volume is needed (eg big brake/caliper upgrades). Running a larger MC with stock brakes will result in less fluid pressure and a harder pedal. 
 

Bleeding brakes: Always start by bench bleeding the MC and make sure you are absolutely positive it is air-free. Don’t let the MC run dry at all when bleeding the rest of the system or you’ll have to start over. Vacuum and gravity bleeding have been the most effective in my experience. Speed bleeders also really help if bleeding by yourself. 
 

Brake pads and rotors: Generally speaking, proper pad break in and selection is crucial. When you first get new pads they normally have a coating that embeds into the rotor upon first use. Softer pads wear quicker and create more dust but also generally stop better. Lifetime warranty pads are generally very poor performing since the compound is extremely hard. I recommend black magic brake pads with Centric posi-quiets being a distant second. Regarding rotors, drilled and slotted rotors have less contact area for the pad and therefore require more pressure to have the same braking force. They do offer many other cooling and cleaning benefits though in certain applications. Coated rotors are great to keep the rotors from rusting onto the wheel unit bearings. 
 

Rear disks: Generally they actually offer less braking than drums. Think of tractor trailers, most use drum brakes. Drums also typically have better parking/ebrakes. That being said, disk brakes are so much more convenient and still offer very good braking performance especially when wet or in muddy conditions. They cool much quicker also. Stop and go traffic, windy roads and aggressive driving all greatly benefit from disks. 
 

Prop valves: typically in a rear drum/front disk setup you need to lower the braking fluid pressure to the rear brakes since drums will lock up sooner especially with empty truck beds. Disk front and rear are generally 60/40 or even 50/50 pressure split. In other words, up your rear brake fluid pressure if you switch from drums to disks. 

84-89 Dana 30’s have knuckles that can easily accept various big brake upgrades/kits. There are diy big brake options that use various off the shelf components or bolt on kits from Wilwood among others. 
DIY Big Brake Setup: http://jeepm62superchargerkit.blogspot.com/p/blog-page.html?m=1


Wilwood: https://www.wilwood.com/BrakeKits/BrakeKitSearch?year=1997&make=Jeep&model=Wrangler&option=Req.+conversion+to+87-89+YJ+front+spindles

 

90 and later Dana 30’s have “wings” that hold the pads in place and have significantly fewer options than the earlier style “bolt-on caliper” knuckles. The knuckles can be swapped to the earlier style or one can run black magic pads and good rotors. With a decent MC and booster this combo can easily handle 33’s and perhaps slightly larger tires under regular driving.

Stock brake upgrade parts: https://www.shop.blackmagicbrakes.com/Jeep-XJ-4WD-1990-1998_c48.htm

 

90 and later dana 35’s, Chrysler 8.25’s and TJ Dana 44’s can use the ZJ disks with almost zero mods: https://www.shop.blackmagicbrakes.com/Dana-44-Rear-Disc-Brake-Conversion-Kit-Dana-44-Rear-Disc-Conversion.htm

 

Wilwood also started making a kit for these axles: https://www.wilwood.com/BrakeKits/BrakeKitSearch?year=1997&make=Jeep&model=Wrangler&option=Dana+35+Rear+w%2fo+ABS

 

pre 90 Dana 35s have an early style Dana 44 mounting flange. They can still be upgraded to disks but it’s a bit more work. Stock they have 10” drums and no c clips. I actually like those little axles.

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JMO413 MJ Maniac

JMO413

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After changing out my old master and booster with new ones I completely agree. My master cylinder seemed to have a slight leak and the booster was growing some nasty looking stuff. So I bought a master/booster assembly. This was just factory replacement parts. My brakes are now awesome and all four corners will lock up. I debated on the dual diaphragm swap, but after the results I got I see no need. 

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zomeizter Comanche Addict

zomeizter

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On 8/9/2020 at 6:26 PM, JMO413 said:

After changing out my old master and booster with new ones I completely agree. My master cylinder seemed to have a slight leak and the booster was growing some nasty looking stuff. So I bought a master/booster assembly. This was just factory replacement parts. My brakes are now awesome and all four corners will lock up. I debated on the dual diaphragm swap, but after the results I got I see no need. 

I went through a similar situation as yours JM, except on mine there were no external MC leaks, they were internal. I considered doing the MC/booster upgrade but ended up replacing the MC with one from an '80s F100/150 with slightly larger bore. Night and day difference in stopping power so the stock booster remains...

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ghetdjc320 Obsessive Comanche Disorder

ghetdjc320

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On 9/13/2020 at 10:20 PM, zomeizter said:

I went through a similar situation as yours JM, except on mine there were no external MC leaks, they were internal. I considered doing the MC/booster upgrade but ended up replacing the MC with one from an '80s F100/150 with slightly larger bore. Night and day difference in stopping power so the stock booster remains...


15/16 or 1” bore will be your best stopping power on stock brakes. Increase bore and you increase volume but may decrease pressure without selecting the correct caliper piston sizes, unless you increase boost assist. 

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75sv1 MJ Junkie

75sv1

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On 9/13/2020 at 7:06 AM, Car Enthusiast said:

Does anyone do the WJ knuckle and brake swap?

Do you mean kits? Most I see are not complete. Check out Ironman 4X4 and possibly Stinky Fab. I have done two of them. Also, the cross over steering using Ruffstuff 1-ton Chevy kit. I did mine from scratch, though. 

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75sv1 MJ Junkie

75sv1

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1 hour ago, Car Enthusiast said:

No, not the kits. I just pulled a set out of knuckles and calipers out of a junkyard for my XJ.

This thread should cover your questions. The Link to the NAXJA thread should help too. I'd expect about $1200-$1500 cost in parts. 

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ghetdjc320 Obsessive Comanche Disorder

ghetdjc320

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The 89 and older Dana 30 MJ and XJ knuckles are desirable and worth salvaging. Crown and APTY used to manufacture them and Vanco was using them to build their “kits”. When they stopped producing them (I really wonder why) Vanco switch ti modifying the later style 90+ knuckles to accept bolt on calipers. Vanco now uses their own knuckles and pieces them together with various oem calipers and Ford rotors. I am quite curious what knuckles they are using. I recall reading on a dodge forum the interchangeability or knuckles between some dodge truck and Jeep Dana 30/44’s. The idea was to be able to get a 6 on 5.5 bolt pattern using the dodge unit bearing. I was researching that as a companion to doing a rodeo/passport Dana 44 rear to match lug patterns. If the right knuckle could be found then brakes and wheel patterns could both be easily modified with off the shelf components. To further go down the rabbit hole, JK d30 knuckles have been swapped with WJ knuckles and vice versa. And since we know WJ knuckles will swap onto our d30’s... the possibilities are very intriguing. Reid also used to make an old spindle style D44 knuckle that bolted right on to the d30 inner c and would allow you to run spindles and hubs with almost any bolt pattern. 

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big66440 Comanche Addict

big66440

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On 9/14/2020 at 6:54 AM, Car Enthusiast said:

No, not the kits. I just pulled a set out of knuckles and calipers out of a junkyard for my XJ.

If you're truck is a 2WD you'll also need the stub shafts, and depending on your wheel bolt pattern you might need an adapter/spacer as well as WJ lower ball joints and a wheel alignment when it's all done:L:. I did this upgrade on my MJ and it made a nice difference.

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ghetdjc320 Obsessive Comanche Disorder

ghetdjc320

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21 hours ago, big66440 said:

If you're truck is a 2WD you'll also need the stub shafts, and depending on your wheel bolt pattern you might need an adapter/spacer as well as WJ lower ball joints and a wheel alignment when it's all done:L:. I did this upgrade on my MJ and it made a nice difference.


Why would a 2wd need stub shafts? 

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ghetdjc320 Obsessive Comanche Disorder

ghetdjc320

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8 hours ago, big66440 said:

Aren’t they used to provide preload for the hub when the nut is tightened? 


There is no stub shaft on a 2WD. Not sure what you may be referring to. The stub shaft is the short end of the axle shaft that runs from the u joint to the unit bearing splines. 

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