Brake system failures an MJ commonality ? ? ?

[Comanche County]

Must be a blockage somewhere or perhaps the rear wheel cylinders gave up. Anyway, I just did the WJ swap. Its in the DIY section and my build page.

[87mjdriver]

is there anything that you have to consider with the WJ brake combo that was design for rear disc's and now is pushing to drums?

[Comanche County]

Yes, but I don't know all the differences between prop valves. An early ZJ I saw had the same one as my 89 MJ but had rear discs? I know some models have different pressure ratios, but I'm not an expert. Some of the guys who have eliminated their rear height sensing valve and/or swapped rear discs could probably answer better than I.

[Pete M]

short answer is that results will vary. what I would recommend is do the swap the way you want and if the rears lock up too soon, simply splice in an aftermarket adjustable proportioning valve into the rear line. :thumbsup:

[AMC-MJ]

Ya could prolly just swap over to Disc's at all 4 corners

Ceramic pad's, drilled n slotted rotors oh ya you could really get to stop good :cheers:

 

Mike

[TrailReadyMJ]

is there anything that you have to consider with the WJ brake combo that was design for rear disc's and now is pushing to drums?

Just differences in the proportioning valve, not the Booster/MC itself.

 

I have rear discs and am getting ready to do this swap. So far I have kept the stock prop valve, and just did any adjustments with the stock load sensing valve. I was able to adjust it to where the fronts lock up just before the rears, like it should be. Then I just tied it into a fixed position rather than try to make it functional. I have heard of using the ZJ valve, but so far I haven't had to mess with it.

 

I would be glad to post up if I notice any differences or have to make adjustments after the booster swap, but I kinda doubt there will be.

[AMC-MJ]

I did some goofing around today, I made up some lines and crisscrossed the ports.

So the front line is pushing rear's and shazzam the rear brakes work . . . So for some reason or another the MC's rear brake port isn't pushing fluid under pressure :wall:

 

Master is the issue then ? i am guessing . . .

 

Side note:

Rear disc brakes possible for the D35 & AMC-20 ?

 

Mike

[Comanche County]

Its easy especially for the D35 if you can find a ZJ donor with a 35 and discs. The AMC 20 I'm sure is possible too but I haven't researched that swap.

 

Here's my rear disc swap links FWIW.

 

http://www.iitp.com/techcenter/reardisk ... ersion.htm

http://www.madxj.com/MADXJ/technical/te ... csOnXJ.htm

http://www.jeep-xj.info/HowtoRearDiscs1.htm ( I love Aussies btw)

 

Do a search for Crown Vic rear discs and you'll find more info.

[AMC-MJ]

The reason i asked about those 2 axles is i have the D35 right now, But once i do my AMC V8 power train swap i'll end up with an AMC-20 . . . All that extra go power won't do me much good if i can't stop it ya know :hmm:

 

 

Mike

[Pete M]

the drums on the MJ AMC-20 aren't small. and being that so few vehicles in the world have that particular axle, you aren't likely to find an online writeup.

but with either crown vic parts or explorer parts, you should be able to concoct something. :thumbsup:

[AMC-MJ]

I have no issues with staying rear Drums I just want it to stop :fs1:

 

Apparently my truck is getting tired of engine braking, it used to slow down good by down shifting but the last few days all its dose is rev up tight and continues on rolling :hmm: maybe the ol'2.5er is finally wearing down :rant:

 

Mike

[Eagle]

:cheers: that is just how i tested them cranked it up to 75mph then slammed down as hard as i could on the breaks, the smell was horrendous :ack: The pedal didn't star to fade till shortly after the smoke n stench of hot brakes started pouring into the cab of the truck :dunno:

 

Nothing locked up, way way more smke came out the front then the rear but the rear did some smoldering :yes:

 

I hope i didn't abuse my truck to find out nothing, hopefully this info is helpful to you guys in some way, and YES i did check the rear brakes seem to be right par but tightened them 2 more "clicks" if you will . . .

Sounds like your brakes work.

 

By the time the shoes and pads are smoking, everything is so hot that the brake fluid in the calipers is boiling. That by itself creates brake fade and a soft peddle, because the liquid turns to vapor, and vapor can be compressed and expanded.

[AMC-MJ]

So i just need more stopping power then ?

 

Mike

[Comanche County]

Water in the fluid could be contributing to the boil over. Perhaps bleeding/flushing the lines until all new clear fluid comes out would make a difference,,,,[Edit] in other words: What Eagle said. :D

 

From http://www.aa1car.com/library/bfluid.htm:

"An NHTSA survey found that the brake fluid in 20% of 1,720 vehicles sampled contained 5% or more water!

 

As the concentration of moisture increases, it causes a sharp drop in the fluid's boiling temperature. Brand new DOT 3 brake fluid must have a dry (no moisture) boiling point of at least 401 degrees F, and a wet (moisture-saturated) boiling point of no less than 284 degrees. Most new DOT 3 fluids exceed these requirements and have a dry boiling point that ranges from 460 degrees up to over 500 degrees.

 

Only one percent water in the fluid can lower the boiling point of a typical DOT 3 fluid to 369 degrees. Two percent water can push the boiling point down to around 320 degrees, and three percent will take it all the way down to 293 degrees, which is getting dangerously close to the minimum DOT and OEM requirements.

 

DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!

 

Considering the fact that today's front-wheel drive brake systems with semi-metallic linings run significantly hotter than their rear-wheel drive counterparts, high brake temperatures require fluid that can take the heat. But as we said earlier, the brake fluid in many of today's vehicles cannot because it is old and full of moisture.

 

Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes!"

[AMC-MJ]

my fluid is new DOT-3 Synthetic

:no: Remember my whole braking system is brand new with about 7,500 miles on it :thumbsup:

 

:cheers: Master, booster, caliper's, wheel cylinder's, lines, pads, and shoes all new, drums n rotors where turned :cheers:

 

I'm not dealing with old parts ;)

 

 

Mike

[Eagle]

So i just need more stopping power then ?

 

Mike

No.

 

If you can SMOKE the brakes from 75 MPH, you do NOT need more stopping power.

[AMC-MJ]

:???: Ok then what dose it mean :???:

 

The brake pads & shoes might be biting down hard but the truck takes forever to slow down, I have to routinely be on the brakes hard and down shift to get it to slow down at a decent rate of deceleration . . . Maybe i'm running it to heavy ?

 

85% of my truck is done in the 25-45mph and have to be on the brake fairly hard then down shift for a decent stopping distance . . . this has only become a recent issue normally i could take it out of gear step the brakes and it stops just fine but not as of lately so something is a malfunctioning . . .

 

 

 

Mike

[AMC-MJ]

:cheers: Fixed

 

This is the oddest thing ever, Remember a few weeks back i mentioned an bolt fell out my exhaust and it was leaking causing my MJ to run rough and be rather doggy and sluggish ? . . .

 

Well this Saturday I went in to the Muffler shop, got the bolt replaced sealed the leaking exhaust engine runs great few miles down the road i noticed the brake pedal was way firmer and the truck stopped lots better :hmm:

 

:smart: my thoughts leaking exhaust = rough running = bad vacuum = weak brakes :hmm: Seems crazy to me :dunno:

This is how it played out . . .

 

 

:fs2: Stupid exhaust bolt :fs1:

Mike

[HOrnbrod]

Well, that theory is believable since the brake booster is the biggest MJ vacuum hog. What I don't get is which exhaust bolt are you referring to?

[AMC-MJ]

where the exhaust pipe bolts to the exhaust manifold . . . 1 out of the 2 bolts fell out :wall: All fixed and running great I love my MJ . . . even when it pisses me off :rotf:

 

 

Mike