Crappy brakes

[brawndon]

So I have stock brakes on my 89 Comanche with some 33s and the braking is complete garbage. I’m surprised I haven’t rear ended someone yet and I don’t want that day to come. Any upgrade recommendations?

 

 

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[cruiser54]

Convert to a dual diaphragm brake booster and rear discs. 

[brawndon]

Convert to a dual diaphragm brake booster and rear discs. 

Any brand recs


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[Pete M]

the junkyard seems popular.    but honestly I haven't heard of a lot of booster issues so am not sure what to recommend. 

[cruiser54]

Dependson the rearend that's in the Comanche. Dana 35 can use 94 to 98 Grand Cherokee rear disc set-up. Easy.

 

Booster, I prefer the 99 to 2004 Grand Cherokee with master cylinder

[ghetdjc320]

Here is my take after running almost every brake system on my Jeeps. Rear disk do not help improving braking power. Disks have many other advantages though such as better cooling and they are relatively self cleaning. Easy to service also. The key to good braking 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. 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. 
 

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. 
 

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 Tun 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 with black magic brake pads or centric posi-quiet. 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.

 

90 and later dana 35’s can use the ZJ disk with almost zero mods. 
 

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

 

[Pete M]

and you're going to copy/paste that into a DIY thread, yes?     we could definitely use a master brakes thread. 

[ghetdjc320]

36 minutes ago, Pete M said:

and you're going to copy/paste that into a DIY thread, yes?     we could definitely use a master brakes thread. 

Can do! There is a lot more that can be added and I am by no means the brake master. Most of my info is just my personal experience and long conversations with Blaine from Black Magic Brakes and the rest of our Jeep community.

[Pete M]

if you start one, I'm sure other guys will chime in with their thoughts.  

[ghetdjc320]

2 minutes ago, Pete M said:

if you start one, I'm sure other guys will chime in with their thoughts.  

Sounds good

[75sv1]

Don't know if this helps : https://jeepm62superchargerkit.blogspot.com/p/blog-page.html

[ghetdjc320]

3 hours ago, 75sv1 said:

Don't know if this helps : https://jeepm62superchargerkit.blogspot.com/p/blog-page.html

Marty wrote up a bunch of different “big brake” setups for the pre 90 front knuckles. They are good upgrades for sure but before upgrading, go through that list I posted above. People often change or upgrade their system and notice a major improvement because their old parts were defective. This leads them to believe that it was a great upgrade that everyone should do. Others, like myself, have had very little success with some “upgrades” because of some underlying issue that needed to be fixed. 

[75sv1]

16 minutes ago, ghetdjc320 said:

Marty wrote up a bunch of different “big brake” setups for the pre 90 front knuckles. They are good upgrades for sure but before upgrading, go through that list I posted above. People often change or upgrade their system and notice a major improvement because their old parts were defective. This leads them to believe that it was a great upgrade that everyone should do. Others, like myself, have had very little success with some “upgrades” because of some underlying issue that needed to be fixed. 

I would agree, that the OP should look at his present system. I went with the WJ Big Brake. My stock brakes on a '98 didn't handle 31's vert well. Yes, new pads, rotors and calipers. Might have been an issue with some dents in the knuckles. I'd probably try a dual diaphragm brake booster and some upgrades pads first. I'm happy with the WJ setup and the cross over steering to boot. Yes, a bit of $$.  

[silvertwinkiehobo]

Maverick and I just did a brake bleed, so as to change the fluid, and ensure the system didn't have any hydraulic problems. So we did a rear shoe adjustment, almost needed none since the adjustment back in February, which leads me to believe it wasn't doing much back there. Then, from right rear through to left front, we bled the system. After that, we loaded me (380 pounds) and the boys in the back, Mrs. Maveric at the pedal, and Maverick under the truck, to re-bleed the rears, in order to have the prop valve arm held up. By doing that, Maveric found the brakes much more effective with less pedal stiffness, and dynamiting the brakes still caused the rears to slide with no load in the back. So, bleed your hydraulics, make sure your pedal free travel is within spec (likely 1/2-1" travel), and good fresh fluid.

[silvertwinkiehobo]

Just now, silvertwinkiehobo said:

Maverick and I just did a brake bleed, so as to change the fluid, and ensure the system didn't have any hydraulic problems. So we did a rear shoe adjustment, almost needed none since the adjustment back in February, which leads me to believe it wasn't doing much back there. Then, from right rear through to left front, we bled the system. After that, we loaded me (380 pounds) and the boys in the back, Mrs. Maveric at the pedal, and Maverick under the truck, to re-bleed the rears, in order to have the prop valve arm held up. By doing that, Maveric found the brakes much more effective with less pedal stiffness, and dynamiting the brakes still caused the rears to slide with no load in the back. So, adjust the rear shoes, bleed your hydraulics, make sure your pedal free travel is within spec (likely 1/2-1" travel), and good fresh fluid.

 

[ghetdjc320]

On 8/3/2020 at 2:03 PM, Pete M said:

and you're going to copy/paste that into a DIY thread, yes?     we could definitely use a master brakes thread. 

Done!