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brake bleeding question?

cjben

NAXJA Forum User
Location
Illinois
I am putting new rear brake shoes/hardware/wheel cylinders and metal brake lines on my 92. I know I will need to bleed the back brakes when I am done,but I won't need to bleed the fronts because they are two separate systems,right? been awhile since I have done any major brake work,thanks for the refresher!! :)
 
If it's been more than two years since they were last bled, do the front as well anyhow.

Brake fluid is "hygroscopic" - it picks up and absorbs moisture from the air. This depresses the boiling point of the fluid, and can cause internal corrosion of iron/steel parts. Brake fluid should be changed outright every two years - use some variety of suction tool to clear out the master cylinder (and wipe the reservoir out with a clean rag, if you can) and refill. Then, bleed all four wheels until you get clean, clear fluid out at the wheels.
 
I've heard that the XJ's have a nasty habbit of trapping air in the lines even if they are bleed in the right order. I need to replace my master cylinder on my 93 and I'm learry of trapping any air. I have lots of experience with different brake systems (FSJ trucks,and the big 3) but I've never yet had to break open my XJ system. I've done the add fresh until it comes out clear thing when I've had to replace the pads and shoes on this one. Oh yea, it's a non ABS system with a the 9.25 rear axle. If anyone could shead some light on this I would be greatful.
 
snufalufagus said:
I've heard that the XJ's have a nasty habbit of trapping air in the lines even if they are bleed in the right order. I need to replace my master cylinder on my 93 and I'm learry of trapping any air. I have lots of experience with different brake systems (FSJ trucks,and the big 3) but I've never yet had to break open my XJ system. I've done the add fresh until it comes out clear thing when I've had to replace the pads and shoes on this one. Oh yea, it's a non ABS system with a the 9.25 rear axle. If anyone could shead some light on this I would be greatful.

Are you sure it's not the 8.25" rear axle?

And, I've not had trouble with trapped air in the lines - perhaps it's a myth. Of course, I always vacuum bleed (don't own a pressure bleeder. Yet.) so that may have something to do with it as well.
 
I'm going thru the same thing with my '96. A rebuilt and then a new master, new calipers, rotors, pads up front, new drums, shoes, cylinders, springs out back, proper sequence of bleeding (numerous times), vacuum and 'pump the pedal' methods, bench and in the car bled the master, and still the pedal is spongy. As far as I can tell, the booster is fine, and it's not the effort, but the length of travel that I cannot seem to cure. Yeah, the linings need to be broken in, but I don't want do go too far until I fix the length of travel issue. Tonight, I turned out the actuator rod a half a turn, tightened it up a little, but I went down this road 20 years ago, only to end up seizing the brakes. No fun! Any thoughts would be greatly appreciated.....Ray
 
Yes, the calipers are on the correct sides. What concerns me is the flex lines. I assume they're original- I've only owned it since January- but I ran into a problem with the rear rubber lines on my daughter's '93 Sable. The rears were not releasing, and after a few hours on a Taurus site (yuck!), a few guys said that the lines turn into 'check valves' and sure enough, after replacing them, they functioned great. I guess rubber lines are next, but I really just want to pull a big fat air bubble out!...Ray
 
oops! Yes......... It's a 8.25 not a 9.25. dang typos.

? for the team.


I'm the second owner of my xj and when I got it it already had 73K on it and still had decent brakes... if I did my part. I saw on another thread were folks were discussing upgrading the vac booster. I'm thinking I might as well upgrade mine since I 'll be down that far to put on a new master anyway. My ? is: do I have to change the master to a different model to match the new style booster as well or is this just a simple swap.

Snuffy
 
snufalufagus said:
oops! Yes......... It's a 8.25 not a 9.25. dang typos.

? for the team.


I'm the second owner of my xj and when I got it it already had 73K on it and still had decent brakes... if I did my part. I saw on another thread were folks were discussing upgrading the vac booster. I'm thinking I might as well upgrade mine since I 'll be down that far to put on a new master anyway. My ? is: do I have to change the master to a different model to match the new style booster as well or is this just a simple swap.

Snuffy

As far as I know - yes. The dual diaphragm booster uses, I believe, a MOPAR master cylinder with the aluminum body and plastic reservoir, vice the earlier iron Bendix master cylinder.

One of these days, I'd like to look into putting the Bendix M/cyl on the later booster, or find another booster that would fit. While I like the idea of upgrading brakes, I do not like the idea of using plastic for a critical part like that (I know - it's probably just fine. I'm just cranky - cast it out of one piece of iron or one piece of aluminum...)
 
hmmm,mine is a bendix type without plastic tanks. looks like i will need to do more research before I attempt to swap in the new style booster. I'll let ya know what I find out.
 
I'm still trying to figure out where my ZJ is losing fluid. The front brakes are losing about 1/8" of fluid a day under normal driving. I've throughly inspected all the hard lines, rubber lines, ABS system, pulled and checked the calipers too and no sign of a leak. It's the front section of the master, so I don't suspect it's leaking into the booster. Grrr.
 
lawsoncl said:
I'm still trying to figure out where my ZJ is losing fluid. The front brakes are losing about 1/8" of fluid a day under normal driving. I've throughly inspected all the hard lines, rubber lines, ABS system, pulled and checked the calipers too and no sign of a leak. It's the front section of the master, so I don't suspect it's leaking into the booster. Grrr.

Ding Ding Ding..... We have a Winner!!!!! Its probably leaking into the booster. Had the same problem on my 94 ZJ. It was going into the booster. I ended up using my vaccuum bleeder to pull it out of there before removing it.
 
I had a similar problem with the spongy pedal after almost complete brake rebuild.

I had neglected to put new adjuster hardware in. I had replaced the actual springs, but not the cables or adjuster pieces. My cables were stretched out, and the star adjusters weren't working. I must have pumped 3 quarts of brake fluid through the system trying to get the 'air' out.
 
dizzymac said:
Without going out to look (its almost 4 AM)...I thought the front reservoir, closest to the radiator, was for the rear brakes.

That's what I'm accustomed to seeing, but this seems to be backwards on the 93 ZJ. At least the front reservior goes down when I bleed at the front calipers. The back reservior isn't changing. The 93 ZJ is kind of a odd step child anyway with rear drums and front disks.
 
w_howey said:
Ding Ding Ding..... We have a Winner!!!!! Its probably leaking into the booster. Had the same problem on my 94 ZJ. It was going into the booster. I ended up using my vaccuum bleeder to pull it out of there before removing it.

On the 94, which reservior is for the front brakes? On my 93 it's the front, closest to the radiator. If I still can't find the leak I may unbolt the master from the booster and look for a leak there anyway.
 
On both the older and newer XJ systems, the front lines enter the proportioning block, which is where the rear line enters from below. Last summer my '92 broke the hard line to the rear, and the smaller front chamber emptied. The '96 looks to use the same block, only a little closer, mounted right under the M/C. I finally got the system working good on my '96- after installing the THIRD M/C- a new, made in USA unit, from NAPA, which by the way was cheaper than either the Cardone A/1 rebuilt piece from Advance, or the new Chinese unit from Auto Zone. What I noticed is in looking into the front port (Rear brakes, I think) that the piston was already past the point at which the fluid could enter the bore. On the good one in there now, you can see the leading edge of the piston, as it is about only 1/3 of the way under the port, allowing fluid into the bore, to be compressed and sent into the line. It's almost as if the piston doesn't retract far enough. I'm going to disassemble the original to see if maybe there's crud behind the pistons keeping the assembly pushed forward.
 
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