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Brake bleed not working?

Ecomike

Ecomike

NAXJA# 2091
NAXJA Member
Location
MilkyWay Galaxy
I have an 87 (Wagoneer, XJ, 4x4, AW4, 4.0), that I have done extensive brake work on since 2004 (have put 43,000 miles on her since I bought it), and everything was working fine except the vacuum booster last 3-4 months. Needed to get it inspected so had to replace the Vac booster. The new vac booster (rebuilt) I installed is working. I also replaced the master cylinder, with a brand spanking new one (not rebuilt), cast iron Master Cylinder.

Now all I get, even after bleeding twice (using a one man brake bleeder kit I have used several times before with good results), is a mushy peddle (feels like standing on a bag of marsh mellows):smsoap:, down to 80% of stroke, then brakes work and peddle gets firm.

I bleed the MC first. This is about 30th life time I have overhaul of a brake system since 1973, so this is not my first brake job.

Any ideas folks?
 
Have checked to see if any of the wheel cylinders or calipers are sticking??

I had this happen to a car that was sitting for awhile. After tapping the wheel cylinders and go forward and backward while hitting the brakes, they finally started working.

Just a thought..

E
 
Monkey55 said:
Have checked to see if any of the wheel cylinders or calipers are sticking??

I had this happen to a car that was sitting for awhile. After tapping the wheel cylinders and go forward and backward while hitting the brakes, they finally started working.

Just a thought..

E
Click to expand...

Thanks, but the brakes work fine, and worked fine except for being manual (just had no power boost, which is why I replaced the VB) before I replaced the VB and MC. Problem is a 75% soft peddle before anything happens, before they get firm and work. It acts like a bad MC or lots of air in the lines, neither of which makes any sense to me right now..
 
i would say a suborn air pocket in there somewhere. and have you inspected all the soft lines just to be sure that they didnt choose then to crap out? (Murphy's law). if everything checks out within spec, i would start to think faulty components right off the stores shelf.
 
stewie said:
i would say a suborn air pocket in there somewhere. and have you inspected all the soft lines just to be sure that they didnt choose then to crap out? (Murphy's law). if everything checks out within spec, i would start to think faulty components right off the stores shelf.
Click to expand...

The soft lines have had better days, but they are not this problem.
 
Ecomike said:
The soft lines have had better days, but they are not this problem.
Click to expand...

All right. how about the 3/16 tubing back to the soft line/tee-fitting? Had the one on my '92 break, replaced them on the two '96s. Were rather clogged. But, I'll bet you don't get anywhere near the road salt we get up here.
 
heyhar said:
All right. how about the 3/16 tubing back to the soft line/tee-fitting? Had the one on my '92 break, replaced them on the two '96s. Were rather clogged. But, I'll bet you don't get anywhere near the road salt we get up here.
Click to expand...

Rear shoes are adjusted properly. I did nothing to the front or rear brakes. All I did was replace the MC and VBB, and while I had to push hard to stop before (as the VBB had a huge massive vacuum leak) I had a very hard peddle at 15% of stroke, and great brakes before.

I did replace the rear brake T fitting with the rubber line 2 years ago, thinking it was leaking, but it was the rear end axle oil vent line that was leaking.

I am not loosing fluid, so it is not a leaking fitting, hose, cylinder or tube (at least not yet).

What is road salt? Second cousin to road kill?
 
Road salt is the least of our worries. PA a few years ago started spraying a magnesium-sodium mixture on state routes and Interstates up to a day before a plowable snow event. It supposedly keeps the resulting slush from freezing onto the road. You literally can hear your car rusting, the stuff is almost caustic. My '96 went from totally rust-free to Fred Flintstone within two winters. We can do rocker panels blind-folded!
 
I assume you bled the MC on the "bench" before you installed it, then bled the combination valve by cracking all fittings to allow air out, before you started bleeding the rears?
 
xjbubba said:
I assume you bled the MC on the "bench" before you installed it, then bled the combination valve by cracking all fittings to allow air out, before you started bleeding the rears?
Click to expand...

MC bench bleed, yes. Never have needed to bleed the Proportioning valve (combination valve?). I kept the tubing from the P-valve capped after disconnected it from the old MC.

I could not get the fittings loose on the P-valve if I wanted too, with damaging something. Tried that six months ago, for 3 days, using 6 different pen-lubes. If I eveh have problems with the P-valve the entire tubing set will need to go with it, or I will need to bypass it with new tubing.
 
winterbeater said:
Isn't there an adjustable rod in the booster cylinder that must be adjusted to remove the free play between the pedal and the master cyl.?
Click to expand...

I have never had to adjust it before. Always been pre-adjusted. This one looked just like the old, I did a quick a visual check.

If this was an adjustment issue, it would be a huge one!
 
The combination valve (proportioning and metering), can trap air. When you removed the old MC, air gets into the tubes going to the "combo" valve.
I always install the MC fittings loose, then very slowly apply pressure, while I observe for bubbles, tightening the fittings before helper lets up on the pedal.
If you install the lines without bleeding the fittings, it introduces air into the systems. This, in turn, increases the chance that air gets trapped in the combo valve, which has lots of "hidey-holes".
 
Have you had the calipers off the front axle lately? I recently had this same problem, and it turned out that i put the calipers on the wrong side during my axle swap. Make sure the bleeder valves are above the lines.
 
xjbubba said:
The combination valve (proportioning and metering), can trap air. When you removed the old MC, air gets into the tubes going to the "combo" valve.
I always install the MC fittings loose, then very slowly apply pressure, while I observe for bubbles, tightening the fittings before helper lets up on the pedal.
If you install the lines without bleeding the fittings, it introduces air into the systems. This, in turn, increases the chance that air gets trapped in the combo valve, which has lots of "hidey-holes".
Click to expand...

+1, You need to bleed the prop valve. Then the rest of the system.
A pressure bleeder makes this very easy
http://www.amazon.com/Motive-Product...62505&sr= 8-1
 
Make sure you received the right master cylinder too. If the bore diameter of the master cylinder it too small on either the front or the rear, then it will take a lot of extra travel to engage the brakes, even with no air in the lines. Make sure you check the part number again and research the piston diameter for the original and the new ones. Small variances can make a large difference in pedal travel considering the master cylinder bore is about 3/4-1 inch compared to the diameter of the calipers (2+inches, not to mention there is two, plus the wheel cylinders).
 
garr said:
+1, You need to bleed the prop valve. Then the rest of the system.
A pressure bleeder makes this very easy
http://www.amazon.com/Motive-Product...62505&sr= 8-1
Click to expand...

None of the tubing connections will come loose on the prop valve, with out damaging something, Already tried soaking in pen lubes for a week, so I am stuck doing it the hard way. Only question then is what is the best way to get the air out of the prop valve if the MC and brake cylinders are the only workable fittings.


I was always taught to bleed the shortest line first, the drivers side front, but I see a lot of Naxja posts saying to bleed passenger rear first?
 
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