Replaced rear brake line- Can't get pedal pressure after bleed procedure

[phenryiv1]

So here are all of the facts that I can think might be relevant:

• Line over the fuel tank rusted through.  This was th emain line- not the HSV line.
• Fuel tank had a leak.
• Replaced line all the way from the MC to the union/T (I can't remmeber which) at the rear axle.
• Replaced tank and straps.
• Bled brakes- RR, LR, RF, LF
• No pressure.
• Repeat.
• No Pressure.

I am sure that I am getting fresh fluid (I had ATE Blue and switched to Gold) and the pedal only builds pressure after 8-10 pumps.  When I was bleeding each line I got solid fluid and a steady stream.  I tried on 2 different days just to let my brain reset and to be sure I was not rushing through the bleed procedure.

 

Has my MC gone bad?  Any other options to check?

 

If it is the MC I will do the WJ upgrade but after dropping ~$250 on the fuel tank and brake issues I'd sure love to save the money if it is something simple.

 

[kansashogan]

I did the brake upgrade and it would not bleed. I gave up and took the load valve off and it brakes great now.

[Eagle]

If you still have the height-sensing valve and the line feeding it, there's a special procedure to ensure that line also gets bled. It's been posted here several times. Try a search -- or maybe someone has it bookmarked.

[phenryiv1]

If you still have the height-sensing valve and the line feeding it, there's a special procedure to ensure that line also gets bled. It's been posted here several times. Try a search -- or maybe someone has it bookmarked.

Weird...I typically bleed the brackets on this every 12-18 months and I have never done anything special with the HSV in the past. HOWEVER I did add MT springs (in place of 26 year old standard springs) since my last bleed so the HSV may be in a different position from past brake work.

 

I'll try either deleting the HSV (per procedures I found on here) amd re-bleed or try the HSV bleed procedure.

[phenryiv1]

Bleed the BRAKES, that is.

[kansashogan]

I tried the HSV procedure a couple times and it didn't work. Maybe my valve was bad, I don't know. I had to unhook one of the lines but it stops good. If you mash the pedal going fast then the rear end will try to come around some but I grew up without ABS so I am familiar with what to do when it happens.

[HOrnbrod]

If you're not getting good pressure buildup that's holding during the bleed procedure I seriously doubt it's anything to do with the height sensing valve. My HSV works fine and I've never had to do any special bleeding for it. I think the problem is probably your master cylinder. Has your master cylinder gone near-dry during all the brake work you have been doing? If so it may be air-bound. You can "bench bleed" the master on the vehicle by disconnecting the front and rear output lines and using a bench bleed kit with flex hose immersed back into the reservoirs to slowly pump the air bubbles out. If $$ are tight, I'd try that before investing in a new master / booster, although the 95-96 dual diaphragm booster and master is a great brake upgrade that should be done.

[phenryiv1]

The MC has not gone dry but a bench bleed might not be a bad idea.  The cost of the WJ setup (MC and booster) is "only" $80 so I am tempted to just throw the money at it rather than to keep investing time in bleeding and re-bleeding.  If it is a bad MC, no amount of bleedig is going to fix it anf I am just wasting time & brake fluid.  FLuid is cheap but my time is limited.

 

I might give it one more try before I concede that I need a new MC.  Ona positive note, if I do the MC swap the MJ community will have a new source for the 1/4" brackets, as I have a small fabrication business and a surplus of 1/4" Lexan.

[shelbyluvv]

Do the upgrade. The difference in stopping power is worth it alone. The hardest part is making the new lines to the distribution block. Easily solved with NAPA metric lines cut off one end, replace one fitting on each line with the stock 45* fittings, flare lines, bend how you want and bolt them on.

 

How have you been Pat? I haven't seen you around here in a while.

[Incommando]

I have said it several times before and I will say it again: The booster/MC upgrade is worth its weight in gold. 

[phenryiv1]

Do the upgrade. The difference in stopping power is worth it alone. The hardest part is making the new lines to the distribution block. Easily solved with NAPA metric lines cut off one end, replace one fitting on each line with the stock 45* fittings, flare lines, bend how you want and bolt them on.

 

How have you been Pat? I haven't seen you around here in a while.

 

I have been good.  The MJ is in a state of minimal inputs because I just don't drive it often.  I have a long commute, the truck lacks A/C, and I have to pick up 1-2 kids (who need different child safety seats) each day so the MJ is impractical for a daily driver.  I was using it regularly when I saw using it to tow my racecar but I traded the racecar for a different project (which has taken on a life of its own).  The battery was replaced this March after a few no-starts when I needed it this winter and right after that I lost my brakes, which turned into the current fiasco.

 

I considered selling the MJ but I like having a 4wd and the utility of a truck but at the same time my parents live on my street and my father has a truck. 

 

Having just made an investment in the MJ brakes and fuel system it makes sense to ride it out for a while longer.  My daughter wants me to trade it for a YJ so that the whole family can benefit from it but I just don't want to take on another unknown.  I know the devil that is my MJ.  Picking up a YJ would have many unknowns and as I found with my current project a few unknown factors can become a very expensive investment.

 

Here is what I am working on now:

 

http://www.r3vlimited.com/board/showthread.php?t=316880

[phenryiv1]

More info:

 

Tried to re-bleed using Eagle's post about opening a front caliper and putting the vehicle in Accessory.  I got a little air out but not much.

 

The interesting thing is that when the truck is OFF, I feel like I have normal pedal pressure and the calipers clamp tight to the rotors while bleeding.  As soon as I start the vehicle the pedal hits the floor.  In my mind this leads to a bad booster, in which case the WJ Booster/MC conversion is a good idea at this time (as opposed to a new MJ/early-XJ booster.

 

Correct logic?

[HOrnbrod]

Try this:

 

Test Power Brake Booster

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.

[phenryiv1]

Try this:

 

Test Power Brake Booster

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

• With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
• Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

• Run the engine a couple of minutes.
• Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

• Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

• Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

• Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.

In Test 3 where is the check valve? In the booster or the I'm?

[HOrnbrod]

It's plugged into the booster (little black plastic round check valve) and the booster vacuum line connects to it.

 

[phenryiv1]

Okay, the check valve is working properly.

 

As for the tests:

 

Test 1 is moot. The brakes won't hold pressure when the engine is running amd as soon as I start the engine the deal drops dramatically. Much more than 1/4" for sure.

 

Test 2 it does build pressure over consecutive pumps.

 

Test 3 is a failure. It takes 7-8 pumps with the engine running to build any pressure. When the car is off the pressure holds.

 

I checked the check valve and it works as a 1-way valve should. I did not pressure test it.

[phenryiv1]

At my wits' end regarding this brake issue in my '88 MJ.

After dragging my feet for a while I took the opportunity to replace the booster and MC with units from a WJ.  (Writeup here: http://www.naxja.org/forum/showthread.php?t=924285 )

So after bleeding with the engine off I had good pedal pressure and thought that all was well but as soon as I started the truck the pedal went to the floor.  I re-bled with the engine on and still no real braking- it feels exactly the same as when I had the MJ parts installed.

I have searched the lines and cannot find ANY leaking anywhere in the truck- no fluid on the ground after 20-25 presses of the pedal with all bleeders closed, nothing came out of any of the lines while the other 3 were being bled.  I also used the special procedure noted by Eagle regarding bleeding with the HSV stil;l in place.

What am I missing?  Any suggestions on where to try?  I have pumped at least a liter of brand new fluid through the system and still can't get pressure.

[phenryiv1]

 

 

 

 

 

 

 

[ggcnash]

Delete HSV dunno why people insist on keeping it besides the guys that want a factory correct show truck. Not saying that's gonna fix it just saying I would go ahead and eliminate that as a possible issue.

[phenryiv1]

Delete HSV dunno why people insist on keeping it besides the guys that want a factory correct show truck. Not saying that's gonna fix it just saying I would go ahead and eliminate that as a possible issue.

I am fine with doing that but I cannot figure how how/why the system worked until I got the hole in the rear line and somehow NOW the HSV is at fault?  Not likely, but I don't have a problem eliminating it as Eagle (and others) recommend.

 

Other references:

 

http://comancheclub.com/topic/4647-brake-bleeding/?p=42062

 

http://comancheclub.com/topic/4647-brake-bleeding/

 

http://comancheclub.com/topic/21361-load-proportioning-sensor/?p=224383

[phenryiv1]

Well, I ordered the proper fitting for my Motive bleeder and will try this again with the Eagle bleeding procedure (4th, 5th time) but using pressure from a tank versus pedal pressure.

 

Can't hurt and $34 is cheaper than an hour of shop time to pay them to troubleshoot.