1994 FJZ Brake Issues

Joined
Jul 2, 2019
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141
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Indianapolis
I haven't taken a vehicle of mine to a shop in over 10 years, but I'm about out of ideas.....I cannot get a firm pedal in my 80.

Things that have been done:
4 new calipers - These were purchased new from a mix of Rock Auto and Amazon. All fit and match the dimensions of the originals exactly.
New pads/rotors
New lines except for the long line from the MC to the rear proportioning valve. This has been inspected and seems to be in good shape.
ABS/LSPV delete - I followed a couple of online tutorials and believe it's been done correctly.
New Master Cylinder - Followed the advice of folks here and got this one More Information for ADVICS BMT068 - https://www.rockauto.com/en/moreinfo.php?pk=1945126&cc=1276679&pt=1836&jsn=907
Bleeding - I've used a vacuum bleeder, a pressure bleeder, and the 2 person method. I've completely flushed all of the old fluid and the fluid that comes out of every caliper is very very clean.
Booster - From what I can tell it's OEM, but it's certainly functioning because the pedal gets extremely hard when I pull the vacuum line.

Things I've tried:
1. I extended the booster push rod out a lot just to see if that made a difference. It did...the pedal got to a very serviceable point, but after a few miles my brakes locked up and I got treated to the lovely smell of roasted brake pads. Note - this has been adjusted back to within the 0-0.02" spec with a pushrod adjustment tool (the H frame variety"
2. Tapping the lines and calipers - While the pressure bleeder was doing its thing I went around jiggling the lines and hoses and tapping the calipers with a rubber mallet just to see if there was a pocket somewhere.
3. Braking without the booster - That was not fun even at like 4mph.

I'm going out of my mind...at this point it's just a boring old hydraulic braking system and SHOULD be functioning. I checked to make sure I didn't do something stupid like put the calipers on upside down, but it all looks like it should to me. All the bolts are torqued to factory spec, there's fluid at every caliper, it's all clean, there are no visible bubbles, but the pedal still goes nearly to the floor before I feel any actual braking power. I made a similar thread asking whether or not I should delete my ABS, and I generally hate reposting but I'm 100% out of ideas.


Thanks all,
 
Joined
Aug 14, 2019
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53
Location
DFW
I have the exact same issue and have done exactly the same things you have done trying to remedy the situation. My son, who was employed for a while as a Toyota mechanic (now an electrical engineer) feels that I have a vacuum leak on the firewall side of the brake booster diaphragm. I've done a little research and think he may be right, plus it's the last remaining component of the system that has not been replaced. As soon as I get the chance that's where I'm going to look.
 
Joined
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Messages
141
Location
Indianapolis
I have the exact same issue and have done exactly the same things you have done trying to remedy the situation. My son, who was employed for a while as a Toyota mechanic (now an electrical engineer) feels that I have a vacuum leak on the firewall side of the brake booster diaphragm. I've done a little research and think he may be right, plus it's the last remaining component of the system that has not been replaced. As soon as I get the chance that's where I'm going to look.
Internally or that one of the lines is compromised? Also, I was under the impression that as a brake booster goes bad braking will get progressively harder (firmer pedal) until you are left without assistance. Can anyone chime in on how a loss of vacuum would increase the soft/sponginess of a pedal?

I've owned a CJ-5 that had no booster assist at all, and I fought with an overly stiff pedal the entire time I owned it.
 
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I should note that I didn't have a booster gasket, but I did use RTV. There's no way that would have caused the issue, right.?
 
Joined
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Olathe, KS, USA
I should note that I didn't have a booster gasket, but I did use RTV. There's no way that would have caused the issue, right.?
The thickness of the booster gasket affects the adjustment of the booster rod and that will cause the brakes to be either hard pedal or locking the brakes.

The gasket is not really there as anything but a dust seal to help protect the master cylinder seals.
 
Joined
Jul 2, 2019
Messages
141
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Indianapolis
The thickness of the booster gasket affects the adjustment of the booster rod and that will cause the brakes to be either hard pedal or locking the brakes.

The gasket is not really there as anything but a dust seal to help protect the master cylinder seals.
Yeah, I didn't think there was a way that it could have messed up the brakes to such a degree. The only other thing I can think of is that actual pedal needing an adjustment, but with the vehicle off it doesn't have more than a few mm of slop. Even while bleeding, the pedal feels firmish. I may just order a booster on Amazon to see if it fixes the problem and take advantage of their extremely loose return policies if it doesn't immediately.
 
Joined
Jul 2, 2019
Messages
141
Location
Indianapolis
I have the exact same issue and have done exactly the same things you have done trying to remedy the situation. My son, who was employed for a while as a Toyota mechanic (now an electrical engineer) feels that I have a vacuum leak on the firewall side of the brake booster diaphragm. I've done a little research and think he may be right, plus it's the last remaining component of the system that has not been replaced. As soon as I get the chance that's where I'm going to look.
It was the booster. Replaced mine with an amazon special yesterday and the brakes are much much better. I'll probably hunt down an oem replacement now just for piece of mind.
 
Joined
Feb 1, 2006
Messages
194
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Utah County
So your brake pedal was soft not hard? I have a 96 LX450 that has been parked for about 6 months. When parked brakes worked great. Now I start it and the brake pedal is rock hard, and I was super low on brake fluid (was normal when parked last). Think its a booster? You have to stand on the brakes to stop even at 3 MPH.
 
Joined
Jul 2, 2019
Messages
141
Location
Indianapolis
So your brake pedal was soft not hard? I have a 96 LX450 that has been parked for about 6 months. When parked brakes worked great. Now I start it and the brake pedal is rock hard, and I was super low on brake fluid (was normal when parked last). Think its a booster? You have to stand on the brakes to stop even at 3 MPH.
Yeah it was the oddest brake troubleshooting I've ever experienced. FWIW, while pulling out my hair I had exactly what you're describing when I removed the vacuum line to my booster. I won't pretend to know what goes wrong in brake boosters, but if I'm you, I'm checking o make sure the line is pulling a vacuum and then replacing the booster if it is.
 

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