Need Help Diagnosing FZJ80 Brake Issue (1 Viewer)

[Rubiclone]

I have been reading a few other threads but nothing seems to be very definitive so I would like some opinions on whether I am going after the right thing.

Truck:
1993 FZJ80 with a 1HDT swapped, engine and tranny are at 200,000km, everything else is at around 700,000km's. Was daily driven but has been side lined and only drive 1 day a year but mainly sitting outside

Symptoms:
I noticed that it seemed to be getting hard to hit the brakes, I can hit the brakes as hard as I can but I can't lock up the tires on dry pavement (ABS Disabled).
I was pulling 1/2 yard of topsoil and went to hit the brakes but could barely stop.
With the truck running I can stand on the brakes and I feel them slowly moving towards the floor over time.
With the truck running I hit the brakes hard three times, on the third time the brake light comes on.
When driving I can hit the brakes hard once, on the second pump they feel very firm and don't seem as effective.

Maintenance Completed:
Brake pads were replaced a few thousand km's ago
I replaced all the soft lines
Replaced load sensing valve about a year ago
Replaced master cylinder with one from Cruiser Teq (AISIN) thinking this was causing pedal drift.
Brake system was fully bled twice with a power bleeder. Trigger the ABS on a gravel road a few times and cracked the lines while the system was under pressure to vent all the air.

Tests completed:
With the truck off they seem very hard and don't drift.
With the truck off I can pump the brakes until they get hard, holding pressure on the pedal I turn on the engine and the brake pedal drifts down about 3"
Keeping my foot on the brake I shut the truck off and the pedal stays down and does not seem to force the pedal back up after about 1 minute of waiting.
The truck was running and then shut off for about an hour, when I pulled off the vacuum B I could hear a hiss, and then when I removed hose D I heard another hiss.

Using a small vacuum hand pump I found the following
System holds vacuum when drawing 20inhg in locations D, B, C. Let it sit for 3 minutes at each location. No gauge drift.
Check valve C seems to be working, I can draw vacuum but I can't blow back into the system (using my mouth) - SHOULD I TEST THIS ANOTHER WAY?
With hose D connected back to A I can draw vacuum on B and it all holds
Connecting gauge at D and B and then starting the engine shows 28inhg

Opinions needed

I'm thinking my booster might have an internal problem: Thoughts?
My other thought was that I had a leaking caliper or seized caliper but my thoughts are that would simple be a squishy pedal situation.

Please let me know your thoughts, I don't want to just keep throwing parts at it.

Cheers,
Rob

 

[ajax1]

Sounds like booster is bad, or your check valve, if it was me I’d just replace the booster as it comes with the check valve

 

[BILT4ME]

Booster.

You need to drive it more.

 

[SaturnAscends]

You can troubleshoot it in case it’s just a vacuum leak or blocked check valve. Not uncommon for the boosters themselves to go bad though.

I’ve been meaning to replace mine but am just tolerating the 1940s-style pedal action for now. Don’t be like me.

 

[Rubiclone]

You can troubleshoot it in case it’s just a vacuum leak or blocked check valve. Not uncommon for the boosters themselves to go bad though.

I’ve been meaning to replace mine but am just tolerating the 1940s-style pedal action for now. Don’t be like me.

Any specific vacuum check that I could do that I might have missed?

 

[SaturnAscends]

Any specific vacuum check that I could do that I might have missed?

I think the FSM outlines the troubleshooting process, or search for Timmy the toolmans brake booster vid on YT.

 

[Rubiclone]

Ok, still chasing down the problem. Things seem to be air tight compared based on the testing. Does this seem like a slow building vacuum? It seems very slow to me. Engine at high idle (A/C on). I pump the brakes and you can see the gauge drop when releasing the pedal then slowly build back up. Has anyone done a test like this to compare it too?

I'm suspecting a vacuum pump issue, maybe only a single vane since it holds pressure but builds slowly?

Gauge is teed in right before the check valve going into the booster.

 

[Rubiclone]

More testing, bypassed the vacuum can and associated check valve and its still slow to build boost when it goes right into the brake booster. Since the booster passed all tests I could find in the manual and online. I'm suspecting the Vacuum pump. Pulled the pump and everything looks fine except for these little marks on the blades, this side of the blade faces the shaft and is towards the rear cover.

Seems hard to believe that these little wear marks would cause a flow problem with the pump.

Thoughts?

 

[Rubiclone]

This is all really pointing to the booster like others mentioned but with a hefty price tag I want to eliminate everything. I rebuilt the pump and added new hoses directly to from the pump to the booster. No change.

Can anyone confirm that this is in fact a slow building vacuum?

Here is a better video:

 

[Fj80oregon]

@cruiseroutfit has a OEM alternative for 350. I just deleted abs/lspv after fighting brakes and replaced booster and master cylinder. Now I have the best brakes I have ever had. I’m not saying you need to delete anything it just worked for my set up better 2.5” lift 35’s and fully armored I could not get the abs to ever activate or push back on the pedal when heavy braking.

 

[Fj80oregon]

Edit: 327$ and it’s the oem manufacturer!! Also when bleeding the brakes sometimes the old school way will yield better results. I used the motive bleeder but in the end I used a bottle with Fluid in it and above the caliper and pumped out the little bit of air left. Good luck

 

[Pinetop Cruiser]

Same situation for me on both my '91 and '96. Mechanic deleted the ABS on the (without asking) and said it was full of sludge. It's a little better. The '91 was getting rock hard, so I replaced the booster and it's great now. Looking forward to replacing the booster on the '96.

 

[Evil80Forces]

Brake boosters are simple. You don't need to spend 350 dollars on one. Cheap one that fits your application will work just fine. I had the same symptoms around breaking as you, swapped in a cheapo booster and all good from there.

 

[mudgudgeon]

m thinking my booster might have an internal problem: Thoughts?

Pull the check valve, and vacuum test the booster.

 

[Rubiclone]

So finally got around the changing the booster with another japanese one. No change, boost still seems to build at the same rate. I have now rebuilt the vacuum pump, new master, new brake booster and soft lines. Anyone have any other ideas or could put a gauge on their truck to see if the vacuum builds at that same rate?

 

[TurbodreamZ]

Do you hear a hissing sound near the firewall when you press the brake pedal?

 

[1973Guppie]

Brake boosters are simple. You don't need to spend 350 dollars on one. Cheap one that fits your application will work just fine. I had the same symptoms around breaking as you, swapped in a cheapo booster and all good from there.

I disagree. Brakes / steering / Tires don't skimp $ on. Parts store boosters and master cylinders have problems constantly. Use Toyota, Aisin or Seiken for these parts.

 

[Rubiclone]

I disagree. Brakes / steering / Tires don't skimp $ on. Parts store boosters and master cylinders have problems constantly. Use Toyota, Aisin or Seiken for these parts.

That's my theory too. Brake master was aisin and booster is bosch basically the exact same one as OEM which also says Bosch on it

 

[Rubiclone]

Do you hear a hissing sound near the firewall when you press the brake pedal?

I think so, hard to tell when the engine is running. Are you thinking about if I can hear the air rushing in on the pedal side to create the pressure inbalance?

 

[DSRTRDR]

in my case, on the day the booster failed on my LX, I initially had good brakes, but about an hour into wheeling, it was more like 3-times-out-of-4 --- as the day went on, it went to 2-times-good-1-really-hard --- and then alternating, then more bad than good, and finally, the brakes were always hard

needless to say, every time the brake pedal was hard, the truck was harder to stop - luckily, I was wheeling at less than 10 mph, so somewhat manageable --- [what I am intending to say here, it was a gradual process, and often can't just be diagnosed in a driveway]

and although the final failure was down in a creek bed, it wasn't all that much fun noticing what was going on while wheeling on an up-and-down-andup-and-down trail - "rollercoaster", as Kevin coined the trail

since the same thing had happened earlier in the year on my 40 (different trail, farther from home, needing a tow), I knew exactly what was going on from the first moment I had hard brakes